Chromium is a factor of non-corrosion in such materials. In the past, it was found that the chromium content must be above 12% to form a dense surface oxide film to achieve corrosion protection. Therefore, the heat treatment of any stainless steel must take into account the chromium content Has it caused any changes?
(1) Matian loose iron stainless steel:
This type of stainless steel has a body-centered cubic structure (BCC) that can be attracted by magnets. It is made from the rapid cooling of Osten temperature. This has the best corrosion resistance, but the material is hard but brittle, and then tempered to increase Ductility, but corrosion resistance will be reduced, especially the tempering between 450°C and 650°C, will cause the carbon atoms in the crystal lattice gap to diffuse and precipitate chromium carbides that form a network with chromium, causing chromium elements in the adjacent area Consumption reduces the chromium content, prevents the formation of a protective film, and loses corrosion resistance, so special attention is required. The following is the heat treatment temperature of various Matian loose iron stainless steel materials.
(a) The temperature of 403, 410, 416se is 650-750℃.
(b) The temperature of 414 is 650-730℃.
(c) The temperature of 431 is 6.
(d) The temperature of 440-A, 440-B, 440-C, 420 is 680-750℃.
(2) Ferrous iron stainless steel:
This kind of stainless steel has a body-centered cubic structure (BCC) that can be attracted by magnets and is usually used in the automobile industry or the chemical industry. The strength will not be changed by heat treatment, but it can be cold-worked to increase the strength.
(3) Ostian iron stainless steel:
This type of stainless steel has a face-centered cubic structure (FCC) and does not work on magnets. As mentioned above, this type of material is easy to process, so after processing, different heat treatments can be applied to eliminate the residual stress of the material.
(4) Precipitation hardening stainless steel:
This kind of stainless steel is quenched at a high temperature and then heat treated at a low temperature. The aluminum or copper contained in the material precipitates along the slip surface or grain boundaries of the differential to form inter-metallic compounds, which can increase its strength or hardness. The commonly used precipitation hardening stainless steel is 17-4 PH, and there are 17-7 PH, PH15-7MO, AM-350, AM-355, etc.
(5) Heat treatment after welding of various stainless steels:
The chromium element contained in stainless steel, after welding, will often diffuse and precipitate and combine with carbon to form chromium carbide in the high-temperature area (heat-affected zone), resulting in partial reduction of the chromium component and failure to form a protective film. Corrosion conditions such as perforation are often It occurs in these heat-affected zones. In order to remedy this situation, the industry often heat-treats the object after welding. The function is to diffuse the chromium element in other areas to this chromium-deficient area to achieve a protective effect.