Austempering process of the 68CrNiMo steel hacksaw chain cutters was studied by using metal material simulation software JmatPro.The phase transformation temperatures of the 68CrNiMo steel are obtained through JmatPro simulation,and the critical austenite transformation temperature Ac1 and Ac3 in equilibrium state are 726.5 ℃ and 746.9℃,respectively.The austempering process of 68CrNiMo steel is proposed as follows:heating at 840 ℃ for 40 min,then directly falling into the isothermal salt tank from the discharge port for isothermal treatment,holding at 285-300 ℃ for 35 min,air cooling followed by 180 ℃ × 60 min tempering.The results show that,after the proposed austempering+tempering,the microstructure of the 68CrNiMo steel is composed of lower bainite,tempered martensite and retained austenite,the hardness is in the range of 54-56 HRC and relatively uniform,and there is no fracture when the cutter is bended for 90°,where the microstructure and properties meet the requirements of hacksaw chain.
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