Cryogenic Treatment Of Powder Metallurgy High Speed

Powder high speed steel is one of the dominant materials for manufacturing complex tools.To improve the tool industry technology,it is necessary to improve the quality of the powder of high speed steel and research new technology and new methods.Currently,the research on cryogenic treatment(CT)is still in an early stage at home.There is no report about the effects of CT on the powder high speed steel.This paper analyses the effects of CT on the mechanical properties and the microstructure,and explores the best CT process parameters and reasonable process route.The magnetic was tested by PPMS-VSM.Magnetic method was used to research phase transformation of high speed steel,which can provide the theoretical basis for the CT process parameters and reasonable process route.The Influence of CT process on the mechanical properties of S390 powder high speed steel was analysed by hardness,flexural and mpact testing.The effects of CT on the microstructure was analysed by SEM and TEM.The martensitic transformation of CT process was analyzed.With the CT temperaturereducing,retained austenite was gradually transformed into martensite,some fine carbides were precipitated from martensite in this process,martensite finishing point is about 123K(-150℃).Mechanical test results show that CT after quenching can increase thehardness about 2.6HRC.Adding CT based on tempering can advance the hardness about 2.0HRC.After CT,some finer needles-like martensite was observed through electron microscope,and fine carbides precipitated in the martensitic matrix,the presence of these carbides can begreatly improving the hardness and toughness of steel.Through comprehensive comparative analysis,the suitable cryogenic treatment process(especially demaning high hardness)as follows:quenching+(-130-150℃)cryogenic treatment+tempering twice;The cryogenic treatment holding time is long enough to make the steel cold through.