The first materials able to withstand the aggressive action of the acids were discovered in 1821, thanks to the mixing and the merger of oxides of iron and chromium.
A little bit of history
Initially, this alloy contained a percentage of chromium of around 1.5 and high carbon values. Only at the end of the 19th century, with the introduction of the Bessemer’s, the Martin’s and the Martin-Siemens’s ovens, an industrial-level production of carbon-chromium steel became possible.
In the early 20th century, instead
- Martensitics stainless steels: around 13% of chromium;
- Ferritics stainless steels: around 17% of chromium (with a level of carbon from 0,12% to 1%);
- Austenitics stainless steels: with alloys of iron-chromium-nickel.
From Mineral to Stainless Steel: How Does the Process Work?
Production from Iron Ore
- Pig iron containing approximately 4–6% carbon is produced in a blast furnace using iron ore and coke.
- The molten pig iron is then transferred to a converter, where the contents of phosphorus, sulphur, carbon, silicon, and other unwanted elements are reduced through refining processes.
- Ferrochromium is added to the molten metal in order to introduce chromium, the main alloying element required for stainless steel production. At this stage, the chemical composition becomes close to that of the final stainless steel grade.
- The molten steel is then processed using AOD (Argon Oxygen Decarburization) or VOD (Vacuum Oxygen Decarburization) systems. These processes reduce the carbon content while preserving the chromium concentration required for stainless steel.
- Finally, the chemical composition is adjusted by adding alloying elements such as chromium (Cr), nickel (Ni), molybdenum (Mo), titanium (Ti), and copper (Cu), until the desired final composition is achieved.
Production from Scrap – A Brief Look at Production Before 1960
Before the introduction of modern decarburization systems, stainless steel production from scrap required long processing times and high electricity consumption.
- Scrap steel was melted in an electric arc furnace, after which ferroalloys such as ferrochromium were added in order to increase the chromium content to approximately 12%.
- The electric furnace operated through three graphite electrodes, generating the extremely high temperatures required for melting and refining.
- The following refining stage involved secondary metallurgy processes carried out outside the furnace, allowing further temperature control and chemical adjustment of the molten steel.
Only after 1960 did the introduction of the AOD and VOD processes significantly improve production efficiency and stainless steel quality.
- AOD: Argon Oxygen Decarburization
- VOD: Vacuum Oxygen Decarburization
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