Effect of Vacuum Heat Treatment on Chromium in Stainless Steel

Stainless Steel (Stainless Steel) is defined in GB/T20878-2007 as a steel with stainless steel and corrosion resistance as its main characteristics, with a chromium content of at least 10.5% and a carbon content of no more than 1.2%. It is widely used in construction, household appliances, kitchen utensils and other fields.

The main alloying element in stainless steel is Cr (chromium). Only when the Cr content reaches a certain value, the steel has corrosion resistance. Therefore, stainless steel generally has a Cr (chromium) content of at least 10.5%. When the amount of chromium atoms in the steel is not less than 12.5%, the electrode potential of the steel can be abruptly changed from negative potential to positive electrode potential. Prevent electrochemical corrosion.

According to reports, heat treatment of stainless steel in a vacuum furnace, such as heating to above 1000 ℃, will cause the dissipation of chromium on the surface of stainless steel, and chromium is the most critical anti-corrosion element of stainless steel, so it will cause the corrosion resistance of stainless steel to decline. However, if the stainless steel is heated to 400~700℃, it will increase the chromium content on the surface.

According to reports, when the temperature is in the range of 400~700℃, the amount of chromium element will reach the minimum level. At the same time, because it is heated in a vacuum furnace, the loss of chromium element caused by oxidation can be reduced. In this way, due to the diffusion of chromium elements from the inside of the stainless steel base to the outside, a large amount of chromium elements are enriched on the surface as a result. According to Italian experiments, 409 stainless steel (equivalent to Cr13 or 2Cr13 heat-resistant stainless steel in my country) with a chromium content of 11% is heated to 500~600℃ in a vacuum and kept for 48 hours. The chromium content on the surface exceeds the chromium content inside the matrix. 6 times the amount, the depth of the chromium-enriched layer is about 1 μm. It can be seen that, if the low-chromium stainless steel is heat treated by low temperature vacuum, it can completely replace the traditional high-chromium stainless steel, which will save a lot of expensive metal chromium.

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