Effect of cryogenic treatment on tempering transformation of AHP T15M powder metallurgy high speed steel

Magnetization measuring in synchronism with cryogenic treatment and tempering of AHP T15 M powder metallurgy high speed steel(PM HSS) at different states was carried out by vibration sample magnetometer(VSM). Effect of cryogenic treatment on tempering transformation of AHP T15 M PM HSS was studied. The results show that ferrite content in annealed PM HSS is 71.5%(volume fraction); Martensitic volume fraction value in quenched steel is approximately 45.2%. Martensitic volume fraction values in the first, second and third time tempered steel are approximately 68.5%, 71.0% and 71.3%, respectively. With addition of cryogenic treatment, martensitic volume fraction values in cryogenic treated and the first, second and third time tempered steel are approximately 59.8%, 69.9%, 70.9% and 71.3%, respectively. Cryogenic treatment moves up martensite transformation from retained austenite, suppresses carbide precipitation in retained austenite, and especially promotes a larger number(about 2.3%) of fine carbides precipitation in martensite. With cryogenic treatment, the hardness of steel increases by 52 HV0.1.