Microstructure and mechanical properties of SCM435 steel quenched at 870℃and tempered at 350-650 ℃ were studied by means of SEM,TEM and tensile test.The results show that when tempering temperature is 350 ℃,the structure is martensite lath and a small amount of carbide.With the increase of tempering temperature,the lath morphology of martensite gradually disappears,and carbides precipitate and grow along the direction of lath.The microstructure tempered at 525 ℃ still has obvious martensite lath morphology and short rod cementite is dispersed.By controlling the mechanical properties of the SCM435 steel within the studied tempering temperature range,it can meet the mechanical performance requirements of 8.8-12.9 level fasteners.The fatigue properties of the steel quenched at 870℃and tempered at 525 ℃ is experimentally verified,with a median fatigue limit of 425 MPa,indicating good fatigue properties.
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