Recycling of Stainless Steel

Stainless steel is up to 100 % reusable and thereby one of the most recycled materials in our daily life. A lot of advantages are therefore derived from using stainless steel for scrap.

Stainless steel is a highly functional group of alloys with a broad field of applications. I.e., stainless steel is used in dairies, butcheries, breweries and pharmaceutical plants. We also see it within catering as well as in our private kitchens.  Stainless steel is the universal favourite for ”critical applications”, and it also used for decorative art and in building architecture due to the durability and esthetic appearance.

What is used for scrap?

Beyond recycling elements from the household the industry also sources stainless steel scrap from e.g. the following elements:

• Discarded production equipment (e.g. tanks and pipe systems)
• Production residues (from cutting, punching, etc.)
• Chips from turning and other types of machining
• Pieces of filler metal (welding)
• Bent and twisted sheets and tube sections

Recycling Tradition 

Stainless steel is recyclable in all shapes and sizes. Recycling is a natural part of the steel manufacturers’ sorting of various residues. Today, that applies both for paper/cardboard, plastic, and various metals. As to recycling of plastic, improvements and recycling possibilities are constantly being developed/considered. Within stainless steel, however, a long tradition prevails in Europe for collecting stainless steel scrap and transporting it to the steel mills where the scrap is included in the production on equal terms with the raw materials needed for producing stainless steel. 

One of the strengths in recycling of stainless steel set against other materials is that all grades of stainless steel are precisely standardized. That means that they are fully ”compatible” with each other in the smelt.  During the melting process, the stainless steel is also automatically cleaned for even small impurities, as all organic matter burns up in the 1500°C hot molten steel. 

The Recycling Process 

The process is quite straightforward: The steel manufacturer collects all chips, cutting residues, and other variations of stainless steel scrap in a container. When that container is full, a scrap dealer can be called for to pick it all up. Here it is important to keep the stainless steel scrap separated from for instance mild steel and in particular brass. Brass is a copper-zinc alloy and normally contains 30+ % zinc (Zn) and free machining brass even 3-4 % lead (Pb). Both may damage the mechanical and chemical properties of the stainless steel.

Hereafter, a rough sorting is carried out between magnetic and non-magnetic steel, respectively. Then, a PMI analyser is used as a very useful tool for sorting the steel grades on a factual basis. With this tool, the material is analysed within only a few seconds and the content of the most important alloy elements is shown. That makes the PMI analyser a great help in this first rough sorting, and at the same time gives the basis for a more precise price fixation of the scrap. 

The content of Nickel (Ni) also has a great impact on the steel being magnetic (austenites) or not (martensites/ferrites), and the scrap value is in general higher for the non-magnetic, nickel-containing steel than for the other qualities. This due to the high Ni value. However, the rough sorting is not only made out of consideration of the price fixation, but it is also of importance for the following process at the mill.

At the mill, the stainless streel scrap is melted, cast and used in the production of new stainless steel. The rough sorting in austenites and martensites/ferrites ensures that the scrap always fits the intented steel composition fairly well. But never completely. The composition of the molten usually requires some adjustment by adding the necessary elements: Cr, Ni, Mo, Ti, etc. and by removing the unwanted elements (S, P, C, etc.). The upgrade is usually done by adding the elements as ”pre-alloys”, rather than pure elements. Chromium is normally added as a Cr-Fe alloy with 50-80 % Cr. Mn, Ni, and Mo are also added as Mn-Fe, Ni-Fe, and Mo-Fe, respectively.  However, Ugitech in Franch has succeeded in producing stainless steel based on 100% recycling, but only based on a high degree of scrap precision and an extra smelting process.

The increased recycling of stainless scrap has led to a gradually higher concentration of the elements Cobber (Cu) and Molybdenum (Mo). Some steel grades  (e.g. 4501, 4507, 4542 og 4567), contain 1-4 % cubber according to the standard. When scrap from these grades is mixed with other stainless steel scrap, more grades will contain 0.2-0.4 % Cu. The increased amount of Cu in the material is therefore a sign that the mill has been recycling the steel. 

In addition to that, copper strengthens the corrosion resistance in reducing acids (e.g. sulphuric acid), while there are no negative side effects. Mo is good against all types of corrosion, even in small amounts, as neither Cu nor Mo appears in the standards for the 4301 class.

Recycling of stainless steel scrap is a great advantage for the entire value chain. The mills reduce their costs significantly by using scrap instead of ores. Further, the production eats less into the world’s reserves, just like the final product - the stainless steel - will be less dependend on the pries for the individual raw materials, wher especially nickel (Ni) and molybdenum (Mo) are quite expensive.

Extend and C0₂

According to some of the major mills in Europe, Ugitech (Fr), Aperam (Fr) and Acerinox (Esp), respectively, the degree of recirculation is around 80-90 %.
This makes stainless steel produced in Europe one of the most recycled materials.

There is a distinct difference between stainless steel from Europe and Asia, respectively. In Asia the use of stainless steel scrap in the production is far more limited. In addition to that the long shipping transport should also be considered. All-in-all, stainless steel from The Far East leaves a significantly higher C0₂ foootprint than materials produced in Europe.

Advantages by Recycling Stainless Steel 

Roughly spoken, there are only advantages by recycling stainless steel. Some of the most obvious reasons are the following: 

• Reduction of CO₂. When using 80 % scrap, approx. 1.1 tons CO₂ is created to produce 1 tons stainless steel. If using only 10 % scrap, approx. 4 tons CO₂ is created to produce 1 tons stainless steel. (Source: CRONIMET Envirotec GmbH)
• We protect the world’s reserves. The need for extracting ores and minerals is significantly reduced
• Less polution of e.g. drinking water. By cutting down on the mining industry, we protect the nature and water agains lots of heavy metals and other kinds of unwanted chemicals, such as SO2, CO₂, dust, oil, etc. 
• We save substantial amounts of energy by not needing to extract the metals from the
  ore (e.g. oxides and sulphides)

Why not only use scrap for the production of of stainless steel?

The answer is divided into two:

Firstly, we have to do with two different melting processes

Secondly it takes in average 40-50 years before the steel sold today returns to the melt.
As China alone produces more than 50 % of the stainless steel in the world, the use of scrap in China will make a huge difference for the world’s CO₂

It will take further 20-30 years, before China and the other Asian countries have enough scrap to really make a difference in the CO₂ emission from stainless steel production. The reason quite simply is tht the industrialisaiton in Asia started later than in e.g. Europe, and that’s why the availability of scrap also is long in coming.