Determination of CCT curve and microstructure of a hot stamping steel

Taking a hot stamping steel 22MnB5 as the test material, the critical transformation point of the steel was measured on the quenching phase change instrument by combining the expansion method with the metallographic method and the hardness method, and the continuous cooling transformation curve of the material was obtained. The results show that when the cooling rate was 0.1 ℃/s, the microstructure was coarse ferrite and pearlite. When the cooling rate was 0.5—5 ℃/s, the microstructure was mainly bainite, with a small amount of pearlite and ferrite. When the cooling rate was greater than 7.5 ℃/s, the microstructure was martensite and bainite. When the cooling rate was greater than 20 ℃/s, the bainite transformation basically ended and all transformed into martensite. Vickers hardness increased with the increase of cooling rate.