Stainless Steel

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Stainless steel is by far the largest user of nickel. It takes approximately 60% of the annual world production of primary nickel. It also is the largest user of nickel-containing scrap. Approximately 50% of the nickel in new stainless steel comes from nickel-containing scrap.

Production

Wrought stainless steels are almost entirely produced in large meltshops -- typically by a two-stage process. Raw materials (including recycle material) are melted together in an electric arc furnace and then transferred to a refining vessel (most commonly an argon-oxygen decarburisation vessel -- "AOD") which reduces the impurities (especially the carbon content) to the low levels required for high quality product.

Recycled stainless steel scrap is a convenient raw material feed for the electric arc furnace, where it melts down quickly to produce a melt that is close to the required composition.

While most raw materials are added to the arc furnace, some are added in the refining vessel to act as process coolant and to allow the composition to be adjusted to the final alloy specification. As the addition of raw material to the refining vessel is a complex operation requiring some form of automatic feeding, only special forms of prepared scrap (e.g., chopped wire) can be used at this stage.

This combination of a large, rapid melting furnace with a separate refining vessel gives the typical stainless steel manufacturer a high degree of flexibility to utilise raw materials (including scrap) of widely differing qualities.

With the exception of the units added right at the end of the process ("finishing units"), raw materials do not have to be high quality, refined virgin metals. Steelmakers use this flexibility to optimise their use of low-cost raw materials ("least cost mix" operation). As long as nickel units are available from scrap at lower net cost than primary nickel units, the steelmaker will usually adjust the melting practice to maximise secondary nickel use.

"Unit" is an expression of mass used for the materials that go into a melting furnace. As you are seeing, the stainless steel industry will take nickel in many forms. In the end, however, the inputs have to match a certain recipe. For a common type of stainless steel there should be 18 units of chromium and 10 units of nickel for every 72 units of iron. When material is being prepared for the furnace, they are of interest only for what they contain (nickel units, for instance), not for what they were (a car exhaust manifold, a saucepan, a fork, a piece of nickel cathode).

The molten steel from the refining vessel is then usually cast using a continuous caster. This continuous process minimizes the amount of scrap generated during casting. The continuously cast steel is then cut into slabs, blooms and billets and rolled to produce stainless steel plates, coils, sheets, bars and wires. The rolling processes are again carefully controlled in order to minimize the generation of scrap.

Internal scrap

Internal scrap is generated within the steelworks at each stage of this production process.

Usually the scrap arises as massive pieces of stainless steel, which are charged (fed) back into the arc furnace for remelting. In the arc furnace and refining vessel, nickel-containing material is collected as ladle skulls (residue left after raw steel has been poured from the ladle) and as alloy trapped in slags. These can either be put back into the arc furnace for further treatment or they can be separately treated to separate the metal from non-metal contents before the metal fraction is returned to the arc furnace.

Most large stainless steel melt shops have a slag processing plant on-site or nearby which undertakes this separation process -- producing a nickel containing metal fraction for remelting and a granulated slag product for resale -- e.g., as road-making ballast. In the casting and rolling plants, scrap units occur as end pieces or as product that is rejected because of poor chemistry or surface defects. These units are suitable for direct return to the arc furnace.

Nickel units are also produced as dust during melting and grinding operations. This is captured in flue filters as bag house dust. The dust is usually remelted to form a massive product before being returned back to the arc furnace. This remelting can be done on site or at a specialist melting facility off site.

Acid tanks are often used to clean the surface of stainless steel when high quality surface finish is required ("pickling"). Residues from pickle tanks have historically tended to go to landfill, although much effort is now going into developing economic processes for recycling these and the small quantities of nickel contained in them.

Internal scrap is usually collected and recycled (i.e., remelted) within a few weeks of being generated. All the internal nickel scrap units can be considered as recycled except the amount contained in the steelplant's emissions to air and water and the amount contained in the slag product of the slag processing plant. Losses are small. The overall efficiency of nickel use is in excess of 99%

Industrial Scrap

Fabricators and specialist service centres buy stainless steel products from the steel mills and make the steel into finished products for use. Industrial scrap is generated during these fabrication processes, usually as sheet cuttings and turnings, but also as reject (faulty or flawed)
fabrications. The amount of scrap generated varies with the complexity of the fabrication process being used but historical estimates are that about 10-15% of the stainless steel input into the fabrication process is collected and recycled as industrial scrap. (This percentage is likely to decrease in future as computerised cutting facilities improve yield.)

Fabrication usually takes place away from the immediate vicinity of the original stainless melt shop -- often in a different country, sometimes on a different continent. Fabricators usually collect the scrap and resell it to merchants; only exceptionally is it sold directly back to the original steel melter.

Industrial scrap is usually collected, sold back to a steel melter and remelted within 3 to 6 months of its original melting.

The exact timing of the recycling will depend upon detailed commercial considerations (nickel price trend, need of the fabricator for cash) as well as logistics (arising and collection time). It is not unknown for both fabricators and merchants to speculate on price trends by holding scrap back from the market in order to benefit from a possible future rise in nickel price.

Speculation effects apart, it is safe to assume that all the nickel scrap generated at the fabrication stage, including grinding products, will be collected and remelted, with the exception of the direct emissions of the fabrication plant as a result of such processes as welding, cutting and polishing. The overall efficiency of nickel use in fabrication is in excess of 99%.

Reclaimed Scrap

Reclaimed Scrap is the scrap collected by merchants from many different sources usually at end of product life. This is discussed in the following section but some comments are appropriate here.

Most stainless steel products are designed for a long life -- typically several decades. End-of-life can be caused by product failure (e.g., due to eventual corrosion), by technological redundancy (e.g., product replaced by a more efficient technology) or by fashion change (the product still functions well but the design is out-dated, e.g., shops, restaurants.) The global shift in manufacturing can sometimes result in the closing of excess capacity in one country (providing new scrap) at the same time as new capacity is being constructed elsewhere (creating demand for more scrap).

Only 85-90% of stainless steel will ever become end-of-life scrap: 10-15% will already have been recycled (see industrial scrap). Not all of the end-of-life scrap will become available at the same time, however.

While the best estimates are that the average service life of stainless steel is between 15 and 20 years, some scrap will become available earlier (exhausted catalysts, battery 'cans', automobile scrap), and some much, much later. The stainless steel of the Chrysler Building in New York, for example, has been in place for 70 years and there are no plans for its replacement.

Blended Scrap

Blended scrap uses nickel units from a variety of materials and scraps. A physical mixture (blend) is produced which, when melted in the electric arc furnace of a stainless steel plant, will result in a melt of chemical composition close to that of standard grade stainless steel. The scrap merchant providing the blend essentially guarantees the composition that the steel maker will get on melting. The steel maker gets access to more secondary units at an attractive input price.

This business is possible because of the increased sophistication of scrap merchants using complex analytical techniques to characterize batches of scrap accurately and the ability of the stainless steel making process (especially electric arc/AOD) to produce a quality product from heterogeneous raw material.

Blending started to become a significant source of secondary stainless steel units in the mid 1980's and has since grown steadily. Availability of relatively cheap units for blending will vary with economic circumstances of other nickel-using industries -- units for blending are basically the units which, at the time, other nickel-using industries do not value as much as the stainless steel industry. Availability can also be impacted by aberrations in the market.

Aberrations

Aberrations arise from special economic and political changes that temporarily distort the normal "trend" pattern of secondary nickel availability. By far the most significant for the nickel and stainless steel industries have been the dramatic changes in the former Soviet Union and its satellite states since 1989.

The USSR was and remains the largest primary nickel producer in the world. Gross inefficiencies in the Soviet system, over-engineering, emphasis on armaments, and lack of economic discipline led to large scale and inefficient use of primary nickel. There were few incentives to recycle. In addition, the nature of stainless steel meant that it did not decompose or deteriorate over time but rather accumulated in Soviet society in over-built manufacturing infrastructure and large amounts of mixed scrap and slag.

Since 1990, hundreds of thousands of tonnes of nickel units in these materials have been exported, mostly to Western Europe. The ability of the stainless steel melting process means that almost all of this material has been used by that industry.

Recorded stainless steel scrap exports from Russia and it former territories (Ukraine, Kazakhstan, etc.) exceeded 400,000 tonnes in 1998 alone. If scrap nickel exports used for producing blended scrap are added, total secondary nickel units exported in 1998 were in excess of 40,000 tonnes of nickel.

In this way the world is absorbing the accumulated scrap reserve of the former Soviet Union. This "destocking" is continuing (2000 saw another surge in scrap exports) but eventually a combination of depleting stocks of scrap and increasing domestic Russian consumption of scrap for internal use should see a reassertion of the trend in the apparent nickel recycling rate in Western Europe