低温贝氏体转变对渗碳纳米贝氏体轴承钢表层组织与性能的影响

Effects of low temperature bainite transition on surface structure and properties of carburized nano-bainite bearing steel

本文设计了一种高碳钢,用于模拟轴承用渗碳纳米贝氏体钢表层的高碳层,并研究了随等温时间延长,其组织演变和力学性能变化规律。结果表明,当试验钢在200℃等温淬火时,贝氏体转变结束时间为48 h。随着等温时间的延长,马氏体含量降低,贝氏体铁素体含量升高,残余奥氏体含量先升高后降低,并在8 h时达到最高值,约为34.5%。贝氏体板条平均厚度约为69 nm。随等温时间的延长,试验钢的硬度先降低后升高,冲击韧性先升高后降低,且均在8 h等温时间条件下获得极值,硬度为最低值58.4HRC,冲击韧性为最高值101 J/cm^2。由于采用无缺口冲击试样,显著削弱了块状残余奥氏体对冲击韧性的消极影响,导致本文中冲击韧性与残余奥氏体含量呈现完全正相关的规律。

In this paper,a high-carbon steel was designed to simulate the high-carbon layer on the surface of the carburized nanobainite steel for bearings.The evolution kinetics of the microstructure and mechanical properties of the high-carbon steel was studied as austempering time increases.Results indicated that the bainite transformation was nearly finished when the steel was austempered at 200℃for 48 h.With austempering time,the volume fraction of martensite decreased,while it increased for bainite ferrite.Yet,the volume fraction of retained austenite increased first and then decreased,with the maximum value of about 34.5%being obtained at 8 h.The mean thickness of bainite plates was about 69 nm.With austempering time,the hardness decreased first and then increased,while the impact toughness changed inversely.Both the hardness and impact toughness of the steel austempered for 8 h reached the extreme values,with the hardness of about 58.4 HRC and the impact toughness of about 101 J/cm^2.Due to the use of non-notched impact specimen,the negative impact of blocky retained austenite on impact toughness was weakened significantly,resulting in a completely positive correlation between the impact toughness and the volume fraction of retained austenite.