Effect Of Cryogenic Treatment On Microstructure And Properties Of Bainitic Steel

Effect of cryogenic treatment on the microstructure and properties of Mn-series bainitic steel was investigated in the present work.Based on the study of microstructure characterization and mechanical properties,the influence trends and mechanism of cryogenic treatment were analyzed and discussed.The experimental results showed that cryogenic treatment process can improve the general properties to a certain degree,especially for austempering-tempering treatment(AT).Compared with traditional AT process,the strength,hardness and corresponding wear-resistance properties were enhanced obviously after austempering-cryogenic-tempering treatment(ACT),while the toughness and plasticity were kept at the same level.These results are related to transformation of retained austenite and the precipitation of carbides.When cryogenic temperature decreased from-80 ℃ to-196℃,the retained austenite fraction in employed steel can be reduced,and the strength and hardness were improved obviously.When the cryogenic holding time is from 12 h to 24 h,relatively better general properties can be achieved.The tempering parameters in cryogenic treatment also have certain effect on final performance.Based on the present results,cryogenic treatment has an important effect on retained austenite in bainitic steel.This treatment can eliminate parts of the blocky retained austenite,resulting in more stability of retained austenite.The tempering following cryogenic treatment contributes to carbide precipitation and there are quantities of fine carbides in martensite/austenite islands.The present work provides an effective treatment process to control the microstructure of Mn-series bainitic steels,optimizing the general mechanical and wear-resistant properties,especially for those bainitic parts with large sizes.