In the process of 316L stainless steel plate production and processing, heat treatment is the most prone to some defects. In the heat treatment process, it most easily lead to austenite grain coarsening, so that the mechanical properties of parts decline. Let's look at some defects.
1. Decarbonization and oxidation: When 316L stainless steel plate is heated, the surface carbon reacts with oxygen, hydrogen, carbon dioxide and water vapor in the medium, which reduces the surface carbon concentration and called decarbonization.
When heated, the iron and alloy on the surface of 316L stainless steel plate react with oxygen, carbon dioxide and water vapor in the medium to form oxide film, which is called oxidation. The dimension accuracy and surface brightness of high temperature workpiece deteriorate after oxidation, and the hardenability of steel with poor oxide film is easy to appear quenching soft spots.
2. Fracture inheritance: After reheating and quenching, the 316L stainless steel plate with superheated structure can refine the austenite grain, but sometimes it still appears coarse granular fracture. The theory of fracture inheritance is controversial. It is generally believed that MnS and other impurities were dissolved into austenite and enriched in the crystal interface because of the high heating temperature. When cooled, these inclusions would precipitate along the grain interface and fracture along the coarse austenite grain boundary would occur easily.
3. Inheritance of coarse structure: When 316L stainless steel plate parts with coarse martensite, bainite and widmanstatten are re-austenitized, the austenite grains are still coarse when they are slowly heated to conventional quenching temperature, or even lower. This phenomenon is called structural inheritance. To eliminate the heredity of coarse tissues, intermediate annealing or repeated high temperature tempering can be used.
4. General overheating: 316L stainless steel plate heating temperature is too high or at high temperature holding time is too long, causing austenite grain coarsening called overheating. Coarse austenite grains will reduce the strength and toughness of 316L stainless steel plate, increase the brittle transition temperature and increase the tendency of deformation and cracking during quenching. The reason for overheating is that the temperature and the instrument are out of control or mixed. After annealing, normalizing or multiple high temperature tempering, the superheated microstructure can be re-austenitized to refine the grain under normal conditions.
5. Over-firing phenomenon: Excessive heating temperature, not only cause austenite grain coarsening, but also local oxidation or melting of grain boundary, resulting in grain boundary weakening, known as overfiring. The performance of the 316L stainless steel plate is seriously deteriorated after overburning and cracking occurs during quenching. 316L stainless steel plate can not be recovered after overburning, but can only be scrapped. Therefore, we should avoid overburning in our work.
6. Hydrogen embrittlement: The phenomenon that the plasticity and toughness of high strength steel decrease when heated in hydrogen-rich atmosphere is called hydrogen embrittlement. Hydrogen embrittlement can also be eliminated by hydrogen removal treatment (such as tempering, aging, etc.). Hydrogen embrittlement can be avoided by heating in vacuum, low hydrogen atmosphere or inert atmosphere.
So in the follow-up process of 316L stainless steel plate, if there are too many defects, we have to do a better study from more levels, better solve the common defects.
Just like you, 70% customers choose long-term cooperation with BBN steel not only for our good product and service quality, good reputation in the international market, but also for our experienced one-stop raw material supply and further steel processing!
