The Nickel Advantage is not limited to the attributes it brings to different materials and processes.

There are the environmental and socio-economic dimensions that go beyond the technical reasons for using or considering using nickel or nickel-containing material.

Nickel is an investment that makes possible many new and emerging products and processes that are important to increase environmental efficiency. Nickel makes many other existing products and processes more energy efficient, durable and tough.

The value of nickel ensures that it is used efficiently and extensively recycled, while the attributes of nickel-containing materials fully support eco-efficiency. It makes significant contributions to sustainability and is responsibly managed through its life cycle by the nickel value chain, starting with the primary nickel industry itself.

The production, use and recycling of nickel is a value-added economic activity that supports communities and governments. The nickel industry embraces its responsibilities to workers, communities, shareholders and the environment.

Overview of nickel-containing stainless steels

Stainless steel is not one single material; there are five families, each of which consists of many grades. Nickel is an important alloying addition in nearly two-thirds of the stainless steel produced today.

Chromium is the key alloying element that makes stainless steels ‘stainless’. More than 10.5 percent needs to be added to steel to allow the protective oxide film to form that provides its corrosion resistance and the bright, silvery appearance. In general, the greater the amount of chromium added, the higher the corrosion resistance. That discovery was made just over a century ago. Some of the early stainless steels also contained nickel, resulting in improved properties, and nickel-containing grades have been in use ever since. Today, even although nickel may be seen as a relatively high-cost alloying addition, around two-thirds of the tonnage of stainless steel produced each year contains nickel. What is the role of nickel and why is it used so extensively?

The primary function of the nickel is to stabilise the austenitic structure of the steel at room temperature and below. This austenitic (i.e. face-centred cubic crystal) structure is particularly tough and ductile. Those, and other properties, are responsible for the versatility of the various grades of stainless steel. Aluminium, copper, and nickel itself are good examples of metals with austenitic structures.

The minimum amount of nickel that can stabilise the austenitic structure at room temperature is around 8 percent, which is why it is the percentage present in the most widely used grade of stainless steel, namely Type 304. Type 304 contains 18 percent chromium and 8 percent nickel and is often referred to as 18/8. That composition was one of the first to be developed in the history of stainless steel, in the early twentieth century. It was used for chemical plants and to clad the iconic Chrysler Building in New York City, which was completed in 1929.

Manganese was first used as an addition to stainless steel in the 1930s. The 200-series of low-nickel, austenitic grades was developed further during the 1950s, when nickel was scarce. More recent improvements in melting practices have allowed the controlled addition of increased amounts of nitrogen, a potent austenite forming agent. While this might suggest that all nickel can be replaced with the structure remaining austenitic, however it is not as simple as that; all the high-manganese austenitic grades commercially available today still have a deliberate additions of nickel. Many also have a reduced chromium content in order to maintain the austenitic structure. However, this approach reduces the corrosion resistance of these alloys compared with the standard 300-series nickel grades.

As the total content of austenite formers is reduced, the structure of the stainless steel changes from 100 percent austenite to a mixture of austenite and ferrite (body-centred cubic crystal); these are the duplex stainless steels. The nickel continues to stabilise the structure of the austenite phase. All the commercially important duplex grades, even the ‘lean duplexes’, contain 1 percent or more nickel as a deliberate addition. Most duplex stainless steels have a higher chromium content than the standard austenitic grades; the greater the mean chromium level, the greater the minimum nickel content must be. This is similar to the case for the 200-series.

The two-phase structure of the duplex grades makes them inherently stronger than common austenitic grades. Their slightly higher chromium content also gives them slightly improved corrosion resistance compared to standard grades. While there are other characteristics to take into consideration, the duplex grades have found some valuable niche applications.

Reducing the nickel content further - even to zero - delivers grades with no austenite at all. These have a completely ferritic structure. Iron and mild steels also have a ferritic structure at ambient temperatures.

Not all the ferritic grades are completely nickel-free. Nickel is known to lower the ductile-to-brittle transition temperature (DBTT), i.e. the temperature below which the alloy becomes brittle. The DBTT is also a function of other factors, such as grain size and other alloying additions. Nevertheless, some of the highly-alloyed super-ferritic grades contain an intentional addition of nickel to improve the DBTT, especially of welds.

Unlike the austenitic grades, the martensitic grades can be hardened by heat treatment. However, some do contain nickel, which not only improves toughness but also enables the steel to have a higher chromium content, which in turn gives increased corrosion resistance. The hardening heat treatment involves heating to a certain temperature and then quenching the material, followed by a tempering operation.

Finally, the precipitation-hardening (PH) grades can also develop high strength through heat treatment. There are various families of PH grades, but all are nickel-containing. Unlike the martensitic family the heat treatment does not involve a quenching step.

  • Formability:

    The characteristics of the austenitic structure give these stainless steels good tensile ductility and good formability, as reflected in comparative forming limit diagrams. The common 18 percent chromium/8 percent nickel grade shows particularly good stretch-forming characteristics but with a somewhat lower limiting drawing ratio than some ferritic grades. Slightly higher nickel contents increase the stability of the austenite further and reduce the work-hardening tendency, thereby increasing suitability to deep drawing. Unlike traditional low-nickel, high-manganese grades, these are not prone to delayed cold cracking. This good formability has led to the widespread use of 300-series austenitic grades for items such as kitchen sinks, pots and pans.

  • Weldability:

    Many pieces of equipment have to be fabricated by welding. In general, the nickel austenitic grades have superior weldability to other grades, and Types 304 and 316 are the most widely-fabricated stainless steels in the world. They are not prone to becoming brittle as a result of high-temperature grain growth and the welds have good bend and impact properties. They are also more weldable in thick sections of, say, above 2 mm.

    The duplex grades are far more weldable than the ferritics for equivalent alloy content, but even the standard and more highly-alloyed super-duplex alloys require greater attention to the details of the welding procedure than the equivalent austenitic grades. The 200-series alloys have welding characteristics similar to the 300 series.

  • Toughness:

    The ability of a material to absorb energy without breaking is essential in many engineering applications. Most stainless steels have good toughness at room temperature; however with decreasing temperature, the ferritic structure becomes progressively more brittle, making ferritic stainless steels unsuitable for use at cryogenic temperatures. In contrast, the common austenitic stainless steels retain good toughness even at liquid helium temperatures; therefore grades such as Type 304 are widely used for cryogenic applications.

  • High-Temperature Properties:

    The addition of nickel gives the austenitic grades significantly better high-temperature strength than other grades, particularly the ability to resist creep. These grades are also much less prone to the formation of deleterious phases as a result of exposure at intermediate and high temperatures. Nickel also promotes the stability of the protective oxide film and reduces spalling during thermal cycling. Consequently, the austenitic grades are favoured for high-temperature applications and where fire resistance is needed.

    It is worth noting that there is a continuum in composition between the austenitic stainless steels and the nickel-based superalloys used for the most demanding high-temperature applications, such as gas turbines.

  • Corrosion Resistance:

    As noted, it is the chromium-rich oxide layer that chiefly accounts for the corrosion resistance of stainless steels. However, this layer is susceptible to damage, particularly in the presence of chlorides, and such damage can lead to the onset of localised corrosion such as pitting and crevice corrosion. Both molybdenum and nitrogen increase resistance to pit initiation in the presence of chlorides. Nickel does not influence the initiation phase but is important in reducing the rate at which both pitting and crevice corrosion propagate (see Figure 9). This is critical in determining how serious corrosion will be.

    Nickel also influences the resistance of stainless steels to another form of localised corrosion, namely chloride stress-corrosion cracking. In such cases, however, there is a minimum resistance at nickel contents of around 8 percent. Stress corrosion-cracking resistance increases markedly at nickel levels both lower and higher than this.

    In general, increasing the nickel content of stainless steels, including ferritic grades, also increases their resistance to reducing acids such as sulphuric acid. Other elements, including molybdenum and particularly copper, also have a strong influence in this regard. However, there are potential drawbacks to using nickel in this way in the ferritic grades. These drawbacks relate to stress corrosion-cracking resistance and the formation of intermetallic phases.

  • Lustre and Finish:

    At first sight, all stainless steel grades look similar. However, side-by-side comparisons of identically polished surface finishes do show differences in colour and lustre. Appearance and aesthetic qualities will always be a matter of taste; the 200-series grades generally appear darker and the ferritic grades cooler-looking, than the nickel austenitic grades. In some architectural applications, a greyer colour might be preferred, but consumers generally prefer a brighter, whiter metal, as witnessed by the popularity of the 300-series. The 200-and 300-series stainless steels are also more scratch-resistant, owing to their inherent work hardening properties.

    Various surface finishes are available on all stainless grades, from mill finishes to mechanically polished (rough to mirror-finished), brushed, bead-blasted, patterned and many more. This emphasises indicates the versatility of the nickel stainless steels in achieving a wide range of aesthetic appearances. One caveat, however, is that a rougher finish will generally have poorer corrosion resistance, particularly in outdoor architectural applications. Marine environments and the presence of de-icing salts require more corrosion-resistant materials, such as Type 316L.

  • Sustainability:

    Taking into account the Brundtland Report’s definition of sustainable development - “development that meets the needs of the present without compromising the ability of future generations to meet their own needs” - it is clear that stainless steels in general, and the nickel-containing ones in particular, can play a major role in the areas of environmental protection, economic growth, and social equality. Some examples are given below.

    To appreciate the contribution a material makes toward sustainability, it is important to examine that material’s whole life cycle, from extraction to recycling or disposal at the end of the product’s life.

    Most nickel-containing materials are fully recyclable at the end of a product’s useful life; in fact the high value of nickel encourages this. Recycling lessens the environmental impact by reducing both the need for virgin raw materials and the use of energy for production. For example, the amount of stainless steel scrap being used today reduces the energy required for the manufacture of stainless steel to about one-third less than would be required if 100 percent virgin materials were to be used (Yale ). Nearly half of that reduction comes from end-of-life scrap (using IISF data ). Only a lack of availability of more scrap, owing to the extended useful life and considerable growth in the use of stainless steel products, prevents a greater reduction.

    The key contributions of nickel-containing stainless steels are that, when properly applied, they maintain and improve the quality of life of citizens and allow businesses and other institutions to deliver sustainable solutions. These sustainable solutions rely on the attributes and services provided by nickel: corrosion protection, durability, ease of cleaning, temperature resistance and recyclability.

    The most visible examples of the durability of stainless steels are in buildings. The restorations of St Paul’s Cathedral and the Savoy Hotel canopy in London, U.K. (1925 and 1929, respectively), the Chrysler Building in New York City (1930), the Progreso Pier in Mexico’s Yucatan state (c. 1940), the Thyssen Building in Düsseldorf, Germany (1960) and the Gateway Arch in St Louis, U.S.A. (1965) are all testament to the long life delivered by nickel-containing stainless steel.

  • Ease of production:

    This aspect is not something that is immediately apparent to the final user. However, the long experience of manufacturing the common austenitic grades, their widespread use, their versatility and the scale of their production mean that they have become commodity grades of a high quality. These grades are economically available in all forms and in all parts of the world.

  • Stainless steel in use:

    The picture that emerges is of the common nickel-containing austenitic grades being good all-round performers. They are widely available, well-understood, versatile and easy to use. They also demonstrate high performance and are extensively recyclable. All of which means they often provide the most practical, lowest-risk solution.

    As they have been in use for so long, the 300 series grades are often already approved for use in situations that involve contact with food or drinking water. In addition, all product forms needed are usually readily available.

Chapter 1: Physical and Mechanical Properties

Physical properties - The physical properties of the stainless steels can be categorized broadly in terms of the families to which they belong, as shown in Table 1.

There is relatively little difference in density or specific heat between the families. However, the differences in thermal conductivity and expansion are significant and of practical importance (see Table 2 below). The lower thermal conductivity of the austenitic grades may be advantageous in reducing the speed with which fire spreads through a building. Lower thermal conductivity might be a disadvantage where high heat transfer is desirable, which is why stainless steel pans often have a copper or aluminum base. However, effects at the surface, such as films and scale, may have a far greater impact on overall heat transfer than conduction through the wall (see the heat exchanger example in the table). If higher mechanical strength allows thinner-walled components to be used, this may more than offset the lower thermal conductivity.

The thermal expansion coefficients of austenitic stainless steels are 60-70 percent higher than those of the other grades. However, this can be allowed for at the design stage in cases where thermal cycling is expected - for example, with roofing, cryogenic equipment or equipment intended to operate at high temperatures. Distortion during welding is a particular problem and is discussed in more detail in the section on fabrication. The general approach is to minimise the heat input.

It is worth noting that the thermal expansion coefficient of austenitic stainless steel is still less than that of other common metals such as aluminium and copper.

The austenitic grades are generally non-ferromagnetic at room temperature, unlike other grades. This property enables the grades to be used in cases where ferromagnetic materials must be avoided, such as near the powerful magnets used in MRI (Magnetic Resonance Imaging) scanners or concrete reinforcing bar at docks where naval ships are demagnetised. Some austenitic grades can develop small amounts of ferromagnetism as a result of martensite formed by cold work (see Figure 1). Increasing the nickel content reduces the effect, so that whilst the effect can be quite pronounced in Type 301, Type 310 remains non-magnetic after extensive cold work.

Austenitic stainless steels are one of the world's most recycled materials

The lack of ferromagnetism in the austenitic grades makes it easy to separate them from other stainless steel grades and from carbon steel when scrap is being sorted for recycling.

Figure 2 compares tensile properties, showing that there are significant differences in how the different grades behave. All stainless steels have a room temperature elastic modulus of around 200 GPa, similar to other steels. However, this is where the similarity of room-temperature mechanical properties ends. As Figure 2 shows, the austenitic stainless steels have a high work-hardening rate and high ductility in the annealed condition. These are attributable to their face-centred cubic crystal structure. Thus, while the yield strength may be similar to that of the ferritic grades, the tensile strength and ductility are much greater. There are two consequences of this; first, austenitic grades can be cold-worked to have high proof and tensile strengths with, at the same time, good ductility and toughness; second, a lot of energy is required to deform them so that they can absorb energy as part of a vehicle design to mitigate the effects of a crash. This toughness is retained even at high deformation rates (again, an important factor in crashworthiness).

The austenitic grades cannot be strengthened by heat treatment. They can, however, be strengthened by cold working to very high levels.

Enhanced proof strength levels from 350 to 1300 MPa and tensile strength levels from 700 to 1500 MPa are listed in EN 10088-2. ASTM A666 lists the strength properties for various tempers for the 200 and 300 series stainless steels. For any particular temper (strength, e.g. 1/4 hard), the properties vary slightly with the grade.

Manganese is particularly effective in enhancing the cold work strengthening effect in, for example, Type 201. See Figure 3, which also shows that for similar austenitic grades, the lower the nickel content, the more pronounced the effect of cold work.

Nitrogen is also a very significant contributor to higher tensile properties as shown by the grades 201LN, 6 percent Mo, 4565S and 7 percent Mo, as shown in Table 3.

The duplex grades have inherently higher strength at room temperature than the basic austenitic grades. This is due to their duplex structure, as shown in Table 4 below.

This is a result of the inherent high strength of the ferrite phase coupled with controlled nitrogen additions. Recent trends in the development of duplex grades have been toward both leaner and more highly alloyed grades.

Even higher strengths can be obtained in the precipitation-hardening grades. Tensile strengths up to 1793 MPa can be achieved, exceeding the strength of martensitic grades. This strength is achieved with good ductility and corrosion resistance and requires heat treatment at relatively modest temperatures of up to 620 °C.

Nickel (and other elements) in solid solution increase the proof stress of ferritic grades. However, because of the lower work-hardening rate of the ferritic structure, the tensile strengths are less than in similar austenitic grades.

Low-temperature mechanical properties:
Proof and tensile strengths of the austenitic grades also increase at low temperatures, as shown in Figure 4.

Figures 4 and 5 also show that (in contrast to some other families of stainless steel) both ductility and toughness of the austenitic grades are maintained to low temperatures. This is also true of cold-worked material. Therefore, the austenitic grades are suitable for service even at liquid helium temperatures.

The useful toughness of the duplex grades does extend to around minus 100 °C, lower than that of the ferritic grades.

Higher levels of nitrogen in the austenitic grades do stabilise the austenitic structure at low temperatures and so thus the low magnetic permeability of those grades in the annealed condition, as shown in Table 5.

High-temperature mechanical properties:
Two particularly important factors to consider here are hot strength and thermal stability, which will be discussed in detail in Chapter 5.

Structural Properties:
Both austenitic and duplex stainless steels are used structurally in many applications where corrosion resistance or fire and explosion resistance are advantageous. The Steel Construction Institute ( has produced a reference publication titled 'A Design Manual For Structural Stainless Steel'. This is available from the Nickel Institute website ( Another reference is the ANSI/ASCE-8-90 Specification for the Design of Cold-Formed Stainless Steel Structural Members.

Cast stainless steels:
This document focuses on wrought stainless steels. Most wrought austenitic and duplex stainless steels have a cast-equivalent grade, which will have a different designation. Cast grades generally have slightly modified compositions to improve fluidity and to prevent hot cracking, which can have some impact on their corrosion resistance in certain media. Residual element content may also vary considerably. Grain size may vary between wrought products, resulting in slightly different mechanical properties. See NI publication 11022 for more details.

Chapter 2: Corrosion Resistance

The corrosion of materials is a complex process. The capacity of an acid to corrode can vary considerably based on temperature, the percentage of acid, the degree of aeration, the presence of impurities (which can have inhibiting or accelerating effects), flow rate and so on. In addition, equipment design, welding and fabrication, heat treatment, surface condition and cleaning chemicals all influence how long a piece of equipment will last.

Stainless steels are most often specified over carbon or low alloy steels because of their increased corrosion resistance. However, as with many generalisations, there are always exceptions. For example, there are cases where some stainless steels may fail sooner than carbon steels. Similarly, while Type 316L is, in most cases, more corrosion-resistant than Type 304L, there are circumstances when the latter is more resistant than the former, for example in highly oxidizing acids such as nitric or chromic acid.

The role of nickel in corrosion resistance of stainless steels is often quite subtle. Not only does it have an effect purely as a bulk alloying element, it affects the passive oxide layer and the micro-structure (for example, by reducing the formation of detrimental phases). Selecting the proper alloy means finding one that will last the required length of time without contaminating the product it contains.

General corrosion:
Table 6 shows data extracted from Schwind, et al 1. Along with other alloys, Types 304, 201 and 430 were tested according to an MTI procedure, where for a given acid concentration the maximum temperature is given where the corrosion rate is less than 0.13mm/a (5 mils/yr). The higher the number, the greater the corrosion resistance of the alloy.

There was one environment where all three alloys performed similarly, yet in all the environments reported, Type 304 either had equivalent or higher corrosion resistance. There were environments where Type 201 was superior to Type 430, as well as environments where Type 430 was better than Type 201. When dealing with general corrosion, it is therefore important not to focus on the role of any single element but on the combination of those elements.

Increasing the nickel content of an alloy used in a reducing solution such as sulphuric acid is one way to improve corrosion resistance. Normally one does not use an alloy when it has a high corrosion rate, but those conditions may occur during ‘upset’ or abnormal operating conditions. Figure 6 shows the effect of increasing nickel content in reducing the corrosion rate in a 15 percent sulphuric acid solution at 80° C. As previously mentioned, the corrosion resistance of any stainless grade results from the combination of the alloying elements, not from any single element alone.

Another way of looking at corrosion resistance is from the perspective of electrochemical behaviour. This is illustrated in the schematic of the effect of alloying elements in stainless steels on the anodic polarisation curve in Figure 7.


Nickel reduces the current density of Epp (the primary passivation potential) and pushes that potential in a more noble direction. It also reduces the passivation current density, resulting in a lower corrosion rate in the passive condition, while increasing the potential (Ep) at which the material goes into the trans-passive range.

Figure 8 shows how this works in practice, by comparing Types 304, 201 and 430 for 5 percent sulphuric acid solution.

This shows that nickel has positive effects on reducing corrosion rates both when active corrosion is occurring and when a stainless steel is in the passive state. Normally, an alloy is chosen that will have an acceptable corrosion rate in the passive state. However, small changes in process conditions, such as a temporary increase in temperature, may cause an alloy to ‘go active’. It is important, therefore, to have an alloy that does not have an unreasonably high active corrosion rate and will re-passivate rapidly when process conditions return to normal.

Chloride pitting resistance:
The relative resistance of an alloy to initiation of pitting corrosion is given by the Pitting Resistance Equivalent Number (PREN). The most commonly used formula is PREN = percent Cr + 3.3(percent Mo) + 16(percent N), although there are many different formulae that have attempted to correlate the behaviour observed in tests to the alloying composition. Some, for example, include a positive figure for tungsten while others apply a negative factor for manganese. Sedriks attributes a small but positive effect from nickel. The bulk alloying content is important, but it only describes one factor in determining the practical pitting resistance of an alloy. The presence of intermetallic phases (sigma, chi, etc.) owing to poor heat treatment and the presence of inclusions (particularly manganese sulphides) are a major factor in reducing pitting resistance. In the case of high chromium- and molybdenum-alloyed stainless steels, intermetallic phases may form during normal welding, with the ferritic stainless steels being most sensitive (see chapter 5 on joining). The most significant contribution of nickel to pitting resistance is that it changes the structure of the material, allowing ease of production of the stainless material of the appropriate thickness along with ease of welding and fabrication without forming detrimental intermetallic phases, particularly of the higher alloyed grades.

Crevice Corrosion:
Nickel is known to decrease the active corrosion rate in crevice corrosion, as shown in Figure 9. This is analogous to the decrease in corrosion resistance with increasing nickel content shown in Figure 6. In both cases, the metal is corroding in an active state.

Stress Corrosion Cracking:
There are many different types of stress corrosion cracking (SCC). Austenitic stainless steels have excellent stress corrosion-cracking resistance in hydrogen sulphide environments, such as those found in the natural gas sector. Austenitic stainless steels, and more recently duplex stainless steels, have shown excellent long-term performance; guidelines for their use can be found in standards such as NACE MR0175/ISO 15156.

Chloride stress-corrosion cracking has been studied for years; many people are familiar with the ‘Copson Curve’, derived from testing in aggressive boiling magnesium chloride. This has shown that the ferritic stainless steels without a nickel addition are superior to the standard stainless steels with 6-12 percent nickel. Alloys with more than 45 percent nickel were found to be virtually immune to cracking in magnesium chloride. In practice, most other chloride solutions are far less aggressive than the magnesium chloride. While grades such as Types 304 and 316L are generally avoided, the stainless alloys with 6 percent molybdenum have sufficient resistance in most cases, as do the duplex stainless steels.

Offshore platforms rely on nickel-containing stainless steels for processing equipment and piping, as well as to present seawater corrosion.

Austenitic stainless steels are very useful in hydrogen sulphide environments

Chapter 3: High Temperature

For elevated, as well as for lower, temperatures, a material is selected based on its properties and usually there are compromises. At elevated temperatures, properties of interest to the designer include mechanical ones, such as yield and tensile strength, creep strength or creep rupture, ductility, thermal fatigue, and thermal shock resistance. Physical properties of possible interest include thermal expansion, thermal conductivity and electrical conductivity. Properties that show environmental resistance include oxidation, carburisation, sulphidation and nitriding. Fabrication properties include weldability and formability. Other properties, such as wear, galling and reflectivity may also need to be considered.

These properties are of interest for the full range of temperatures to which the material is subjected, and it is particularly important to look at potential changes to properties during service life. The structural stability of austenitic stainless steels is a major reason for their widespread use at high temperatures.

Structural stability is a major reason for their widespread use at high temperatures

In general, austenitic stainless steels remain strong at elevated temperatures, at least compared with other materials. Figure 11 compares the short-time, high-temperature yield and tensile strengths of some austenitic and ferritic stainless steels at various temperatures. At temperatures below about 540° C (1,000° F), the differences are not that great. At higher temperatures, the strength levels drop off rapidly on the ferritic grades. Some special ferritic stainless steels can be alloyed for increased high-temperature strength.

Ferritic stainless steels with 13 percent or more chromium will embrittle in the temperature range of 400-550° C (750-1020° F) in shorter time periods and as low as 270° C with longer times in the higher-alloyed (chromium/molybdenum) grades. The temperature of the shortest time to becoming brittle, called the ‘nose of the curve’, is around 475° C (885° F), and this phenomenon is thus called ‘475° C embrittlement’ (or ‘885°F embrittlement’). The embrittlement phenomenon shown in Figure 12 as the lower ‘nose’, also affects the ferrite phase in duplex stainless steels, which is one reason most duplex alloys have a maximum temperature for long-time exposure of around 270° C (520° F) or slightly lower. Although austenite is immune to this embrittlement, the ferrite in austenitic stainless welds and castings will embrittle, though usually there is a small enough amount that it does not have a significant detrimental effect on properties except at cryogenic temperatures. Ferritic stainless steels with less than 13 percent chromium, such as 409 or 410S, may be immune to this embrittlement or else the embrittlement may occur only with long time exposure, depending on the actual chromium content. Nevertheless, their low chromium content and low strength limit their usefulness to around 650° C (1,200° F). The low-alloyed ferritic stainless steels do find widespread application in automotive exhaustive systems.

Another microstructural change that needs to be considered is the formation of deleterious hard and brittle intermetallic phases such as sigma. For the sake of simplicity, we will call all these intermetallic phases ‘sigma’ phases. These can occur in both austenitic and ferritic stainless steels, including duplex alloys. The upper ‘nose’ of Figure 12 is this embrittlement in a high-alloyed ferritic stainless steel. Figure 13 shows the intermetallic formation for a 5 percent molybdenum stainless steel. The temperature range for formation varies depending on the composition of the alloy, but is generally in the range of 565-980° C (1,050-1,800° F), albeit with prolonged times. The ‘nose’ of the curve is generally in the upper end of the temperature range.

In addition to temperature, the time required to form sigma phase varies considerably depending on composition and processing (for example the amount of cold work). Chromium, silicon, molybdenum, niobium, aluminium and titanium promote the sigma phase, whereas nickel, carbon and nitrogen retard its formation. With a sufficiently high level of nickel, sigma phase formation can be completely suppressed. If a material is to be used in the sigma phase formation range, it is important to evaluate how much embrittlement is likely to occur over the service life of the component and what effect this will have on the component’s performance. The embrittlement is normally not a problem when the material is at operating temperature (except when thermal fatigue is involved) but can become a serious issue at ambient temperatures.

Grain size can be an important factor when using materials for high-temperature service. In austenitic stainless steel, a fine grain size is generally not desirable as it is associated with inferior creep strength. A medium-to-fine grain size gives the best combination of properties, although in certain cases where high creep and rupture strength is important, a coarse grain size in an austenitic alloy may be preferred. The downside of a coarse grain size is twofold: inferior thermal fatigue and thermal shock properties. In purely ferritic stainless steels, grain growth can happen rapidly above 1100° C (2010° F). This can occur during welding and may result in a coarse and low-ductility heat-affected zone (HAZ). Coarsening of the grains occurs much more quickly in ferritic stainless steels than in austenitic alloys.

Carbon in austenitic stainless steels is generally beneficial for high-temperature service, giving increased creep strength throughout the temperature range. If carbides form, they may result in some corrosion problems when corrosives are present (normally at lower temperatures during shutdown conditions). In most design codes for elevated temperature pressure vessels, there are austenitic grades with minimum carbon contents as well as a maximum that have higher design strengths than for the low-carbon grades or where there is no minimum carbon content. For example, Type 304H has a minimum carbon content of 0.04 percent.

When using any material at high temperatures, thermal expansion must be considered in the design of the equipment; otherwise failure will result. The thermal expansion coefficient of the ferritic stainless steels is lower than that of austenitic grades but must always be allowed for during design. The higher-nickel stainless grades, such as Type 310 and alloy 330, have a lower thermal expansion rate than the standard Type 304 and stabilised variations. The nickel alloys (Alloy 600, for example) have even lower rates of expansion.

Many factors affect the thermal conductivity of a component in practice. The austenitic stainless steels have a lower thermal conductivity than either ferritic stainless steels or carbon steel; in others words, they have lower heat transfer through the metal. Surface oxide layers also act as barriers to heat transfer.

Oxidation resistance of an alloy is important and relatively easy to measure, although problems can arise in real-life applications. Ideally, an oxide layer would form on the stainless steel and the growth rate would slow, in time, at very low levels. The oxide would also have the same expansion coefficient as the stainless steel. In reality, when the oxide layer thickens above a certain level and the temperature fluctuates, the oxide layer partially spalls off and new oxide growth begins. Maximum temperatures for continuous and intermittent conditions are usually quoted.

...thermal expansion...must always be allowed for...

Chromium content is important for the formation of a protective oxide layer at increasingly elevated temperatures and is sometimes aided by smaller additions of silicon, aluminium and cerium. The oxide layer is never perfect, and with both thermal expansion/contraction and mechanical stresses, many cracks and other defects will form. Thicker oxide films may spall off with a new oxide film forming underneath, resulting in a loss of metal thickness. The generally higher thermal expansion rate of austenitic stainless steels, compared with ferritic alloys, causes austenitic grades to have a higher rating in continuous service than in intermittent service in standardised tests. The opposite is true in the case of ferritic stainless grades. This is illustrated in Table 7, which gives the approximate scaling temperature and suggested maximum service temperature in air in continuous and intermittent service for some stainless alloys. There are a number of special stainless steels with optimised oxidation properties available. Manganese has a detrimental effect on oxidation resistance, and therefore the 200 series has only limited use at high temperatures.

The resistance of a stainless steel to carburisation is a function of the nature of the protective oxide scale and the nickel content. Reducing environments at high temperature that contain either carbon monoxide or a hydrocarbon can cause carbon to diffuse into the metal, making the surface layer hard and brittle. The solubility of carbon in a stainless steel decreases as the nickel content increases. As a result, the alloys used in carburising environments are either stainless steels with high nickel content or nickel alloys.

Preventing metal dusting requires the use of special nickel alloys

Silicon is beneficial in enhancing the protective oxide layer, so the selected alloy will often have an elevated silicon content. Alloy 330 with 19 percent chromium, 35 percent nickel and 1.25 percent silicon is commonly used. Nickel-free stainless steels have poor carburisation resistance. Preventing metal dusting, also called ‘catastrophic carburisation’, a special form of carburisation, requires the use of special nickel alloys. Sulphur in hot gases, on the other hand, may be detrimental to the high-nickel alloys, particularly if the environment is reducing in nature. Generally, one will choose a lower-nickel austenitic stainless steel, or in severe cases, a high-chromium ferritic grade. In such a situation, a compromise in properties has to be made, irrespective of which grade is selected.

Chapter 4: Forming

Hot Forming

The hot-forming characteristics of the 200 and 300 series of austenitic stainless steels are considered excellent in terms of operations such as hot rolling, forging and extrusion. The temperature range for these operations typically starts somewhat below the annealing temperature. Table 8 shows typical hot-forming temperatures for some common austenitic stainless steel grades and a few duplex grades, along with their solution annealing temperatures. These are general ranges; often more restrictive practices are needed for specific operations and grades.

It is important to have a uniform temperature for the piece, as hotter areas will deform more easily than cooler ones. Most often, hot-formed components will receive a full solution anneal to ensure maximum corrosion resistance. Special care must be taken in hot forming the high alloy austenitic grades such as the 6 percent Mo stainless steels. They are subject to hot cracking during forging and will need an adequate soak during subsequent annealing to remove intermetallic phases formed during hot forming. The duplex grades, while having higher strength at lower temperatures, are generally quite weak at the hot forming and annealing temperatures; care must be taken to ensure dimensional stability during these operations. Specific data should be consulted for each grade and tests should be made after hot operations to ensure that the material has the expected corrosion properties.

Warm Forming

It is not unusual to warm an austenitic stainless steel piece to facilitate forming. Unlike the ferritic or duplex grades, austenitic stainless steels are not at risk for the 475°C embrittlement mentioned in Chapter 3. The low carbon and stabilised austenitic stainless steels can withstand short periods of time at temperatures of up to 600° C (1,100° F) without any significant detrimental effects to their corrosion resistance. For duplex stainless steels, it is best to avoid warm forming above 300° C (575° F).

Austenitic stainless steels can be formed by a wide variety of processes

Cold Forming

Austenitic stainless steels have outstanding ductility. A common acceptance criterion is that they can be cold-bent 180° with a radius of one-half the material thickness, without regard to rolling direction. However, when forming temper-rolled austenitic stainless steel, rolling direction is important and tight bends should be oriented to the transverse rolling direction. The minimum bending radius needs to be increased as the initial temper (strength) of the material is increased. For example, hard Type 304 sheet with minimum yield strength of 760 MPa (110 ksi) should be able to be bent 180° over a mandrel with a radius equal to the sheet thickness. In general, the duplex stainless steels are not as ductile as the austenitic grades but still have good ductility in the annealed condition. The duplex grades are not commonly used in the temper-rolled condition, except as cold-drawn wire.

Most of the duplex grades and any of the higher-strength 200 or 300 series stainless steels can be harder to form, owing to their higher yield strengths. Equipment that may be near its limit with annealed 300 series stainless steels may have great difficulty with the higher strength materials of the same thickness. Given the work hardening, springback is a concern with all austenitic and duplex stainless grades. Generally speaking, the higher the initial strength and the greater the degree of cold working, the greater the amount of springback. Figure 14 compares the springback characteristic for bending of annealed Type 316L and the duplex 2205 grade. In this case, the duplex requires greater overbending than the austenitic grade. To achieve a 90° angle, the Type 316L must be bent to 100° whereas the higher strength duplex requires bending to 115°.

Roll forming is a highly efficient and practical way to produce long lengths of shapes such as angles or channels in all the austenitic and duplex grades.

The forming of standard Type 304 and its variants would be considered extraordinary except that it has been common practice for many years

Drawing and Stretching

Both the austenitic and ferritic stainless steels are commonly formed by both drawing and stretching. The combination of high ductility and high work hardenability that are characteristic of austenitic stainless steels leads to outstanding formability of sheet.

Drawing or deep drawing entails forming a sheet without clamping of the blank. The metal flows in the plane of the sheet with minimal thinning. In general, an austenitic material with a lower work-hardening rate (e.g. Type 304) is preferred for pure drawing operations. Stretch forming is the forming of the sheet through a die with hard clamping of the edge of the blank. All deformation is accomplished by stretching, with a corresponding thinning of the sheet. Here, a high work-hardening rate typical of Type 301 may be advantageous as it enables larger punch depths. The technology of sheet forming is complex, and in most practical operations, the actual forming is a combination of these two types. Surface finish, forming sequence and lubrication are critical to ensuring the smooth, high-quality appearance associated with austenitic stainless steel. The formability of standard Type 304 and its variants would be considered extraordinary except that it has been common practice for many years. Even with the high ductility of austenitic stainless steel, in extreme forming applications, one or more intermediate annealing steps may be necessary to restore ductility and enable further forming.


  • metal flows freely into die
  • deformation of large circle into narrow cylinder must come from width rather than thickness (= high anisotrophy "r")



  • metal held by the blankholder
  • considerable thickness reduction
  • high elongation (A%) and hardening (n) required

Duplex stainless steels are not often significantly formed by drawing or stretching. Where this has been achieved successfully, the equipment and dies have been modified to take into account the lower ductility and higher strength.


Spin forming (also known as lathe spinning) is a method of extensively forming sheet or plate to make rotationally symmetric parts. The method is well-suited to forming conical parts, something that is relatively difficulty by other methods. The deformation of the sheet may be large and a low work-hardening rate grade, such as Type 305, can be advantageous. Type 305 has a slightly higher nickel content and a slightly lower chromium content, both of which serve to reduce the work-hardening rate. The duplex stainless steel grades can also be spin formed, although they require more powerful equipment and potentially more intermediate annealing steps.

Cold Heading

For bar products, it is common to form heads for screws, bolts and other fasteners by axial stamping operations within a die. The material needs to have good ductility, while a small amount of work hardening is an advantage. Type 305 or an 18/8 type with copper (sometimes called Type 302HQ) are often used. There are 200 series stainless steels with low work-hardening properties that can also be easily cold headed. Cold heading has been done on some of the duplex stainless steels.

Chapter 5: Joining


Nickel plays a major role in the weldability of all types and families of stainless steel. The austenitic grades have a forgiving nature, which means good and reproducible results can be obtained even under difficult circumstances. When welding any grade of stainless steel, there are certain steps needed to ensure good quality, including cleanliness and post-weld cleaning. Stainless steels are often used in demanding applications, such as those where corrosion resistance or high temperature properties are needed, so it is necessary to ensure that the weld metal is not the weakest link in the chain. Generally, the more highly-alloyed a grade is, the greater care and precautions need to be taken.

Austenitic stainless steels

One important property of austenitic stainless steels is that they are not hardenable by heat treatment or by the heat from welding. As they are not susceptible to hydrogen embrittlement, austenitic stainless steels normally do not require any pre-heating or post-weld heating. Materials ranging in thickness from thin to heavy can be easily welded. Cleanliness (freedom from oil, grease, water, scale, etc.) is very important.

Austenitic stainless steels can be welded using most commercial processes with the exception of oxy-acetylene welding, which cannot be used on any stainless steel. The most common processes include SMAW (shielded metal arc), GMAW (gas metal arc), GTAW (gas tungsten arc), SAW (submerged arc), FCAW (flux-cored arc), spot or resistance, laser and electron beam. Many, but not all, austenitic stainless steels can be welded without filler metal and without any further heat treatment. Most of the super-austenitic alloys require the use of filler metal to obtain proper corrosion resistance of the weld. Normally, the weld metal is able to meet the minimum yield and tensile strength requirements of the annealed base material. The ductility of the welds is generally lower than base metal, but they are still very ductile. Low carbon grades (L-grades) of filler metals are normally used for corrosion-resistant service. For high-temperature service, the higher carbon filler metals may offer superior high-temperature strength.

The austenitic grades have a forgiving nature

The compositions of many of the 300 series filler metals are adjusted so that they solidify with a certain amount of ferrite, to prevent hot cracking during solidification. This allows for higher heat inputs and thus higher welding speeds. The presence of a certain amount of ferrite means that welds are slightly ferromagnetic. Those alloys that solidify fully, or nearly fully, austenitic must be welded with lower heat inputs. For certain applications, a low ferrite weld metal is desirable and there are specific filler metals produced for that purpose. For most 300 series stainless steels, a nominally matching filler metal is the most commonly used. Some of the exceptions to that rule are as follows:

  • When welding titanium-stabilised grades, niobium-stabilised filler metals are most-often used, since titanium oxidises in the arc. For example, Type 321 is welded with Type 347 filler metal.

  • Stainless steels with 6 percent or more molybdenum are welded with nickel alloy filler metals of the Ni-Cr-Mo type (for example, Alloy 625 or ‘C’ type). There are some cases where grades with a molybdenum content as low as 3 percent are welded with a filler metal over-alloyed in molybdenum.

  • The 200 series are most often welded with 300 series filler metals of appropriate strength because of their wider availability and, to some extent, better weldability. The high-nitrogen 200 series grades can lose some nitrogen during welding. For a few applications, a 200 series filler metal is the correct choice to achieve certain properties (although usually at a higher cost). The standard filler metals for the Types 304L and 316L grades are, by far, the most commonly available.

  • The free-machining austenitic stainless steels such as Type 303 contain high levels of sulphur and are generally considered unweldable. Where it is absolutely necessary, small welds are made with Type 312 filler metal, even although there may be many small cracks that won’t withstand much stress. Generally, it is best not to weld this grade.

The austenitic base metals generally have excellent cryogenic properties. For example, the ASME Boiler and Pressure Vessel Code does not require the low-temperature impact testing of wrought austenitic grades such as Types 304, 304L and 316L for service as low as minus 254° C (minus 450° F). However, castings and weld metal do need to be tested since they contain some ferrite, which does become brittle at low temperatures. Certain welding processes and/or certain filler metals may need to be used to meet the low-temperature impact requirements.

When welding dissimilar austenitic grades, such as Types 304L and 316L, an austenitic filler metal is used. The grade selection depends on the required properties of the weld metal, most often corrosion resistance. For welding carbon steel or a ferritic, martensitic or precipitation-hardenable stainless steel to an austenitic stainless steel, again, an austenitic filler metal is mostly commonly used. Also, the required properties of the weld metal, such as strength and corrosion resistance, must be carefully evaluated before choosing the filler metal. Filler metals such as Types 309L, 309MoL and 312 are produced for such purposes and all have compositions that result in a ferrite content higher than that of the standard grades. This makes them more forgiving to certain impurities and differences in thermal expansion.

Duplex stainless steels

The base metal of most duplex stainless steels has a controlled composition and receives a controlled heat treatment to give a range of ferrite of 40-55 percent, with the balance being austenite. When making welds, the heating and cooling rates are less tightly controlled, which gives a wider range of possible ferrite. It is important to avoid welding conditions where more than 65-70 percent ferrite results in either the weld metal or HAZ (heat-affected zone), as this may have serious adverse effects on corrosion resistance and potentially mechanical properties.

For similar reasons, most specifications will also specify a minimum ferrite level of either 25 percent or 30 percent, although the consequences are not quite so severe. To avoid high ferrite, most duplex filler metals contain 2-3 percent more nickel than the base metal. In general, welding without filler metal should be avoided. In the case of one lean duplex stainless with about 1.5 percent nickel, the filler metal has about 6-7 percent more nickel to ensure suitable properties in the weld. Proper annealing of duplex welds can often reduce unacceptably high levels of ferrite content; as a result, castings and welded pipe and fittings can be welded by filler metals without the elevated nickel content, or even without filler metal at all.

Most duplex filler metals contain 2-3% more nickel than the base metal

Welding of duplex stainless steels is normally done without pre-heating or post-weld heat treatment. Welding of duplex to austenitic grades is done using either a duplex filler metal or an austenitic one. The latter weld may be weaker than the duplex base metal, but will be stronger than the austenitic base metal. Welding duplex to carbon steel is normally done with one of the higher ferrite-content austenitic filler metals (309L or 309MoL) or a duplex filler metal. Dissimilar welding to some higher-strength (hardness) carbon or low-alloy steels may require pre-heat and post-weld heat on the non-stainless metal, which may have an effect on the duplex stainless steel. Metallurgical advice should be sought.

Duplex stainless steels, and particularly the higher-alloyed ones, used for severe environments, require extra steps to ensure a weldment that meets the expected corrosion and mechanical properties.

Ferritic Stainless Steels

For the 10.5-12 percent chromium ferritic stainless steels, which should be non-hardenable by heat treatment, welding is most often undertaken either without filler metal or with a matching filler metal, although often stabilised. Austenitic filler metals such as Type 308L are sometimes used. Some of the weldable ferritic base metals (e.g. UNS S41003) have an intentional nickel addition to control grain size both during manufacture of particularly thick sections and during welding. These are not true ferritic stainless steels and are better called “ferritic-martensitic alloys”. They are usually welded with a 309L or occasionally another austenitic filler metal.

The 16-18 percent chromium ferritic grades that are molybdenum-free are most often welded with an austenitic filler metal, though matching filler metals may exist. These too are often stabilised.

The higher-alloyed ferritic stainless steels present special challenges in welding, discussion of which is outside the scope of this publication. In practice, austenitic filler metals are often used for welding these alloys. Always consult the alloy producer’s datasheet for welding information. As most of these alloys are not available in heavier wall thicknesses, there are often dissimilar metal welds - for example, a thin-gauge ferritic tube to an austenitic tubesheet. These welds are always made using austenitic filler metals.

Martensitic and Precipitation-Hardenable (PH) Stainless Steels

These materials also present special challenges when it comes to welding. If the weld metal needs to be as strong (and hard) as the base metal, then a filler metal that responds to the same hardening treatment as the base metal should be used. This is frequently not the case, and either austenitic stainless steel or nickel alloy filler metals are used. The resulting welds will be weaker than the base material yet quite ductile. For martensitic grades, pre-heat and post-weld heat treatments are usually required, whereas for the PH grades, these may only be necessary for heavier thicknesses.

Post-weld Cleaning

Since all stainless steels rely on a protective oxide layer for corrosion resistance, it is important to perform an appropriate post-cleaning operation suitable to the end use.

Other Joining Methods

Other joining methods used for stainless steels include brazing and soldering as well as mechanical joining methods, all of which are discussed below.


Austenitic stainless steels are regularly joined by brazing. Silver braze alloys are probably the most common brazing metal, even though they are quite expensive. They are easy to use at a fairly low braze temperature and have good corrosion resistance. Nickel braze filler metals, some with chromium, have greater corrosion resistance but require higher braze temperatures. For special applications, copper braze and gold braze filler metals are used. Before a braze metal is chosen, each application needs to be evaluated with regard to strength, corrosion resistance, the effect of braze temperature on the base metal and the possibility of detrimental interaction of the braze metal with the base metal.

Austenitic stainless steels are regularly joined by brazing


All stainless steels are fairly easily soldered, though titanium-stabilised grades can be problematic. Normally a lead-tin or a tin-silver solder is used. It is important that the protective oxide layer be removed by the flux. All solders have greatly inferior corrosion resistance and strength to the base metal.

Mechanical Joining Methods

Joining methods such as bolting, screwing, riveting, clinching, lock seaming and gluing are all used with stainless steels. Generally, all these joints will have a lower strength than welded joints. Corrosion may occur in the crevices that are formed. Potable water piping inside buildings is often cost-effectively and securely joined by mechanical systems. Consideration should also be given to galvanic corrosion, where different metals, and even significantly different stainless alloys, are used. For example, aluminium and galvanised carbon steel fasteners are less noble than stainless steel and may start to corrode quickly, particularly given their small area in relation to the stainless steel.

Cross Reference for Filler Metals mentioned in this chapter
AWS (A5.4) EN (1600)
308L 19 9 L
309L 23 12 L
309MoL 23 12 2 L
312 29 9
316L 19 12 2 L

Chapter 6: Sustainable Nickel

Previous chapters have dealt with metallurgical aspects relating to design and performance requirements. This chapter sets out some of the broader implications of those attributes, focusing on their sustainability aspects.

Individuals and societies invest in products and systems to meet their needs. In our complex world, the needs are many and increasing and there are usually different approaches for meeting them. The cost of the resources needed, including the consequences of sourcing those resources, is testing the planet’s capacity to deliver. Reducing the intensity of material use is increasingly important; here nickel contributes.

The efficient use of materials is essential. The luxury of meeting needs in a crude, blunt fashion - throwing a lot of material and energy at a problem - is no longer sustainable. Employing small amounts of nickel in stainless steels often allows a decrease in material and energy used, allowing more efficient and more elegant solutions for society’s needs. The presence or absence of nickel is, in many ways, a measure of eco-efficiency where it is the nickel that delivers the positive difference.

Just a few examples are offered here; they are, however, representative of many more.

If something can deliver the same function with less material, it is an advance

Building Lasting Infrastructure


If a piece of infrastructure or a piece of equipment can deliver the same function using less material, this is an advance. Because of their strength, combined with corrosion resistance, nickel-containing rebar can be of a lighter gauge and yet bear the same loads. As the weight of steel in a structure is reduced, the amount of concrete needed for pillars can be proportionally decreased. In this example, the presence of a small amount of nickel allows a significant reduction in the amount of iron, cement and aggregate needed while delivering the same function and utility.

Enhanced corrosion resistance

In climatic and geographic regions where salt or heavy industrialisation is found, the addition of a small amount of nickel will allow substantial reductions in resource use over the life cycle of structure or product. In many cases, it will increase the lifespan of the product (and the uninterrupted availability of its function) by several multiples. It also can - depending on the product or function - completely remove the need for repeated maintenance and rehabilitation; no paint, no expensive repair of spalling concrete because of rusting rebar and no delays (with waste of fuel) and/or diversions (with increase in fuel use). In addition, the ‘cover’ (the depth of the concrete and asphalt) needed to protect the rebar from corrosion attack is reduced. Less concrete and asphalt means less weight to be borne and the possibility of slimmer pillars and support beams, again resulting in less material used and lower weight. The use of nickel-containing stainless steels fuels this virtuous cycle.


Indicative analyses show that the material intensity of a bridge or overpass over its full life cycle can be cut by 50 percent by using nickel-containing stainless steels. Elements for this estimate take account of the energy associated with the production, use and final disposal of materials, from paint to asphalt, as well as the higher percentage of material recovered and recycled at end-of-life. Nickel-containing stainless steels will have unimpaired quality and value and are comprehensively recyled. This makes material (and financial resources and labour) available for other societal needs at the same time as the environmental impact of the structure is reduced.

Improving Energy Efficiency


Retaining heat during the cold months of the year and keeping heat out of buildings during the hot months is a challenge. Typically, this has been managed by using energy; energy to heat, energy to cool, all with significant climate change implications. Intelligent design offers a better approach. Durable stainless steel roofing materials with appropriate surface finishes and roof slopes allows a better heat balance. The result is less material intensive - the roof lasts the life of the building before being recycled at rates approaching 100 percent - and less energy intensive.

The use of durable stainless steel roofing material allows a better heat balance

Enhanced corrosion resistance

The obvious contributions for curtain walls and roofs have already been dealt with. There are, however, many other contributions that use only small amounts of material, are hidden from sight, but which contribute significantly to efficiencies. One example is condensing gas boilers. These are the most energy-efficient boilers available, with efficiencies approaching 90 percent, a performance made possible because of nickel-containing stainless steel heat exchange surfaces. In this condensing heat exchange section, the combustion gases are cooled to a point where the water vapour condenses, thus releasing additional heat into the building.

Recycling at End-of-Life

Almost any material can be recycled. The differences revolve around the amount of effort - including energy - needed to recycle and the quality of the recycled material. Metals in general perform very well in this regard, and nickel-containing stainless steels are excellent for recycling. Nickel-containing scrap has significant economic value, sustains a large collection and scrap preparation industry, and allows the continuous and expanding production of 'new' stainless steel with a global average of 60% recycled content, with no loss of quality.

This 60 percent recycled content in the commodity grades of stainless steel is not a metallurgical limit; it is simply a constraint caused by the limited availability of supply. The expansion of demand for stainless steels, combined with the longevity of those products that contain it, creates a lag in scrap becoming available. There are no metallurgical reasons why the recycled content of nickel-containing stainless steels could not approach 100%.

Recycling does more than conserve physical resources, although it does that very well. It also currently reduces energy demand by 33% and CO2 production by 32% per tonne. As the ratio of scrap to virgin materials in stainless steel production increasingly favours scrap, the savings rise to a potential 67% for energy and 70% for CO2. (Yale: Johnson, J. et al, The energy benefit of stainless steel recycling, Energy Policy. Vol.36, Issue 1, Jan. 2008, p181ff)

Nickel stocks and flows for the year 2000, in thousands of metric tonnes

Source: Yale University, 2008

Much of today's nickel stock is in use, bound in durable structures, engines, or piping that is still serving out its useful life in the products's life cycle.

Responsible production and use

The industry that produces the nickel and the value chain that directly supports the eco-efficient use of materials and energy is global. The primary nickel industry is present and active in every climatic and geographic area of the world and contributes to the economies of countries at every stage of economic development.

The management of the primary nickel industry is committed to responsible behaviour in all its operations. That alone may does not make the nickel industry stand out, but it goes further. It actively engages with the nickel value chain to transfer technology and techniques, maximise efficiencies, improve occupational health standards and performances, increase recycling and support basic scientific research on the impact on human and environmental health.

In summary, there are many reasons to use the nickel advantage for technical solutions to engineering and architectural challenges. At the same time, nickel's contributions to sustainability and climate change reduction are being maximised. Furthermore, nickel itself is being responsibly managed through its life cycle by the nickel value chain, starting with the primary nickel industry itself.

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