热处理工艺对纳米贝氏体渗碳轴承钢表层组织和性能的影响

Effect of Heat Treatment on Surface Microstructure and Properties of Nano Bainitic Carburized Bearing Steel

目前渗碳纳米贝氏体轴承钢表层高碳成分组织与性能的演变规律还不是很清楚。设计一种高碳钢模拟G23Cr2Ni2Si1Mo纳米贝氏体渗碳轴承钢表层高碳成分,利用SEM、TEM、硬度和冲击等研究微观组织与力学性能随相变时间的演变规律。结果表明,试样在200℃贝氏体等温相变需要总时间为48 h。随着等温时间从0 h延长到48 h,组织中的马氏体含量逐渐降低、贝氏体铁素体含量逐渐升高、残余奥氏体含量先升高后降低,在等温12 h时含量最高38.5%。等温48 h后,组织中贝氏体板条平均厚度为48 nm。随等温时间的延长,试验钢的硬度先降低后升高,在等温12 h有最小值58.1 HRC;冲击韧性值逐渐增大,在等温48 h达到最大值96.0 J/cm^(2);抗压强度逐渐降低,断裂应变逐渐增大。该研究结果更清晰地展示了纳米贝氏体渗碳轴承钢表层组织与性能的变化规律,为其工艺优化提供了理论支撑。

At present,the evolution of the structure and properties of high carbon components on the surface of carburized nano-bainitic bearing steel is not clear.A kind of high carbon steel is designed to simulate the high carbon surface layer of G23 Cr2 Ni2 Si1 Mo nano-bainitic carburized bearing steel.The evolution of microstructure and mechanical properties with increasing austempering time at 200℃are studied by using SEM and TEM characterization,hardness and impact tests.Results shows that the total time required for the isothermal transformation of bainite at 200℃is 48 h.With increasing holding time from 0 h to 48 h,the content of martensite is gradually decreased,and the content of bainitic ferrite is gradually increased.The content of retained austenitic is increased firstly and then decreased gradually,with a peak value of 38.5%being obtained at 12 h.The average plate thickness of bainitic ferrites in 48 h specimen is 48 nm.Moreover,with increasing the holding time at 200℃,the hardness of steel is decreased firstly and then increased,with a minimum value of 58.1 HRC being obtained at 12 h specimen.However,the impact toughness of steel is gradually increased,with a maximum value of 96.0 J/cm^(2) being obtained at 48 h specimen.The compressive strength is decreased gradually and the fracture strain is increased gradually.The studied results clearly show the evolution of microstructure and the related mechanical properties of the surface layer of nano-bainitic carburized bearing steel,providing a theoretical support for the process optimization of this kind of bearing steel.