Only martensite has strong magnetic properties in the process of microstructure transformation of austenitic stainless steel. Usually, austenitic stainless steel produces martensite during quenching, but austenite can also produce martensite due to processing effects in unstable cases, but austenite can also produce martensite due to processing effects in unstable cases Martensite.
Factors affecting the stability of austenite The stability of austenitic stainless steel is determined by its composition:
1) The more austenite-forming elements such as Ni, C, and Mn, the more stable the austenite;
2) Cr is iron The ferrite forming element has a diffusion effect in the solid solution. Therefore, when a large amount of Cr is dissolved in austenite, it can prevent the austenite from transforming into martensite and stabilize the austenite;
3) Mo is formed by ferrite. Elements, and can increase the passivation of stainless steel, improve corrosion resistance, especially the tendency to prevent pitting corrosion.
2. The transformation path of austenite The path of austenitic stainless steel to martensite transformation is as follows:
1) When the temperature of austenitic stainless steel is lowered to the Ms point (the starting temperature of martensite transformation), its structure will be transformed into martensite. body.
2) Martensite can also be produced by plastic working at a temperature higher than the Ms point, but the upper limit of the γ→α transformation temperature of martensite is called the Md point, that is, the maximum temperature of martensite transformation caused by processing is Md. . If Md is higher than normal temperature, part of austenite will be transformed into martensite by cold working at normal temperature. The Md point of stainless steel is roughly at about 320 ℃ above the Ms point. Therefore, after the head is formed by strong cold spinning such as drum pressing and flanging at room temperature, the stability of austenite is reduced due to the effect of lattice deformation, causing maladies. Tensite transformation.
