30Cr15Mo1N is a kind of strength martensitic stainless steel with nitrogen mass fraction of 0.4％,the important problem in its application is the matching of high hardness and high corrosion resistance.The microstruc-ture and corrosion resistance of 30Cr15Mo1N steel after tempering with different temperatures were studied by SEM,TEM,chemical precipitates analysis and salt spray test.The results show that the microstructure after quenching,cryogenic treatment and tempering with temperature below 500℃ is distributed of micrometer undis-solved precipitates and nanometer newly precipitated precipitates on the lath martensite matrix.With the increase of tempering temperature,the types of precipitates remain unchanged,which are M23C6 and Cr2(C,N)types,and the number and size of precipitates increase gradually.In particular,when tempering at 475℃,the precipitated phase mass fraction suddenly increases,the martensite gradually dissolves and the tempering sorbite occurs when temper-ing temperature is higher than 500℃.At 500℃,the peak hardness of secondary hardening is 60.7HRC.With the increase of tempering temperature,the strengthening effects of martensite and solid solution gradually decrease,and the secondary hardening effect mainly comes from the strengthening effect of a large amount of precipitated phases.The salt spray test results show that small pitting corrosion is the main feature when the tempering temperature below 400℃,and visible corrosion occurs after tempering at 450℃.When the tempering temperature is no less than 450℃,granular and lamellar corrosion products are deposited on the specimen surface.The samples tempered at 475-500℃ have the most serious corrosion,and the corrosion resistance deteriorates as the tempering temperature increases.During the tempering process,the precipitation of Cr containing precipitates leads to Cr-depletion zone in the surrounding matrix,which leads to the decline of corrosion resistance.When the tempering temperature reaches 600℃,the distance between the Cr depletion on the edge of the precipitates increases,and the corrosion resistance is slightly improved.Therefore,if high hardness and high corrosion resistance coexist,meet the hardness require-ments of bearings no less than 58HRC,tempering temperature should not be higher than 400℃.
martensitic stainless steeltemperingprecipitate phaseneutral salt spray testCr-depletion zone
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