Effect Of Carbon And Nitrogen Content On Microstructure And Properties Of High Nitrogen Martensitic Stainless Bearing Steel

7Cr14Mo V high carbon martensitic stainless steel（MSS）with high hardness,high strength,high wear resistance has been widely used in industrial production.It is easy to form large eutectic carbides with high contents of carbon and other alloying elements in the steel.Nitrogen is substituted for carbon in this experiment.In the case of a certain total contents of carbon and nitrogen,large carbides are eliminated by icreasing nitrogen content and reducing carbon content.The effects of carbon and nitrogen content on precipitates,mechanical properties and corrosion properties in heat treatment test steel were studied,and the effects of cryogenic treatment on microstructure and properties were analyzed,which provided a theoretical basis for its practical application in engineering,and then promoted the application of high nitrogen martensitic stainless steel in the field of bearing steel.In this paper,the total carbon and nitrogen content was controlled between 0.65%and0.70%.The results show that when the tempering temperature is 160℃～560℃,the amount of M₂₃C₆MSS is less,and the amount of VN and Cr₂N is more in 0.21N MSS compared with0.11N MSS,.The hardness and tensile strength of the two MSSs decrease with the increasing tempering temperature,while the impact toughness and elongation increase with the increasing tempering temperature.After tempering at 560℃,the hardness and strength are1365MPa,HRC43.6 in 0.11N MSS and 1520MPa,HRC48.3 in 0.21N MSS,respectively.The decline of hardness and tensile strength in 0.21N MSS are lower than that of 0.11 MSS,and the tempering stability of 0.21N MSS is higher.At different tempering temperatures,the pitting resistance of 0.21N MSS is better than that of 0.11N MSS.The hardness of the 0.21N MSS increases and the residual austenite is obviously eliminated when it is kept at-80℃for 2h after quenching.Compared with the samples without cryogenic treatment,the amount of M₂₃C₆in the cryogenic treatment samples after tempering at 160℃is less and the tensile strength is higher,but the elongation and impact toughness are poorer.Under high temperature tempering,there are more M₂₃C₆after cryogenic treatment,and the hardness and strength of cryogenic treatment samples are lower than those of the samples without cryogenic treatment.At different tempering temperatures,the amount of fine nitrogen precipitated phases is more,and the pitting resistance is worsein cryogenic treatment samples compared with the samples without cryogenic treatment.