Optimization Of Heat Treatment Technology For 35CrMo Pick Materials

The effects of different heat treatment technologies on the microstructure and properties of the 35Cr Mo cutting pick steel were researched through heat treatment optimization experiments,mechanical properties and microstructure analysis,and the morphology observation on the impact specimen fraction through the Scanning Electron Microscopy?SEM?.The results show that the Ac1 and Ac3 phase-transition temperature of the 35CrMo steel measured by the hardness method are 750? and 800? respectively.With the increase of the quenching temperature,the strength and hardness of the experimental materials show a downward trend after the high-temperature tempering.The optimum quenching temperature is 800?.After quenching and high-temperature tempering for the 35CrMo cutting pick steel below 800?,the microstructure of the experimental materials are mainly composed of sorbite and a small amount of fine massive ferrite,after quenching and high-temperature tempering beyond 800?,the microstructure of the experimental material is composed of sorbite.When the quenching temperature at 800? and holding different time,the peak of the impact toughness appears when holding 40min,the optimum heating and quenching technology of the experimental material is 800?×40min.When quenching at 800?,the tendency of organization coarsening of the experimental materials in different holding time is not obvious.After tempering in high temperature,all the impact fractures of the experimental materials are toughness fracture morphology,and a small amount of sulfide and oxide inclusions exist on the impact fractures.When quenching at 800?and holding 40min,and tempering in different temperatures,the hardness and the tensile strength of the experimental materials show a decreasing trend with the increase of tempering temperature.The tempering brittleness appears when tempering temperature reaches 300?.When tempering at 500?,the hardness and strength of the experimental material tend to decrease with the increase of the holding time,however,the extend of the decrease is not significant.The optimum tempering process is 500?×2h,and the mechanical properties are Rm1254MPa,A14%,Z58.5%,A_KU58.5J,and HRC42.9 respectively,which could satisfy the property requirements of the cutting pick industry.When the experimental material quenching at 800?and holding 40min,the hardness of experimental material is highest when cooled in water,followed by commercial quenching liquid cooling and oil-cooling,air-cooling has the lowest hardness.After high-temperature tempering,the microstructure of experimental materials after water-cooling,oil-cooling and which could satisfy the property requirements of the cutting pick industry.When the experimental material quenching at 800?and holding 40min,the hardness of experimental material is highest when cooled in water,followed by commercial quenching liquid cooling and oil-cooling,air-cooling has the lowest hardness.After high-temperature tempering,the microstructure of experimental materials after water-cooling,oil-cooling and commercial quenching liquid cooling are mainly sorbite and a small amount of ferrite,the microstructure of experimental materials after air-cooling and isothermal quenching are sorbite and ferrite and the experimental material has the highest impact toughness when cooled in commercial quenching liquid,and it has the highest comprehensive mechanical property.The microstructure of five kinds of composite heat treatment materials are mainly tempered sorbite retaining the morphology of quenched martensite.The optimized composite heat treatment technology of experimental material is high-temperature tempering+quenching and tempering heat treatment.