高碳铬轴承钢中最大夹杂物尺寸对其疲劳寿命有重要影响.冶金工艺进步推动钢质洁净度不断提高,采用常规轧材夹杂物检验方法已不能满足轴承钢质量进一步提高的要求.研究并提出了一种轴承钢中夹杂物尺寸的分析方法——极值分析法,在金相试样尺寸及数量、夹杂物观察及尺寸计算、Gumbel分布函数的参数估计等多个方面进行了改进调整,使之实用化.在此基础上,采用该方法推测轴承钢轧材中的最大夹杂物尺寸,并用能谱仪分析了大尺寸夹杂物的元素成分.结果表明:基于Gumbel分布函数的极值分析法可以作为估计轴承钢中最大夹杂物尺寸的一种方法;控制B类粗系和DS类球形夹杂物,降低钢中的钛含量是进一步提高轴承钢产品质量的努力方向.

The reason of surface crack of low alloy carburizing steel 20CrMnTi die forging eccentric wheel was analyzed by means of SEM and metallurgical microscope.It was found that surface crack was caused by flowing of metal.Ferrite and martensite co-existed in crack parts,it was α+γ two-phase-region deformation.The differences of plasticity of hard ferrite and soft austenitic led to cracking.The die forging temperature lower than Ar3 was the main reason of cracking.

Through metallographic organization analysis,it is found that after forging,the large size round steels 20CrMnTi tend to have inhomogeneous surface tissue which are mainly mixed crystal.Repeated heat treatment test proves that repeated normalizing can eliminate mixed grain,and refine grains;isothermal heat treatment can also eliminate mixed crystal,but with obvious segregation.Comparatively speaking,repeated normalizing can eliminate mixed crystal with grain refinement,which is a superior technique.

The normalizing and fully annealing tests were performed on the two samples of carburized bearing steel G20CrNi2MoA,which has two kinds of original structures;the isothermal annealing test has been done on the sample with normal structure,it was observed and shown that band structure can be eliminated by normalizing,while fully annealing makes the band structure worse,and the higher the isothermal annealing temperature is,the worse the banded structure is,which happens more obviously when the temperature is above 650 ℃.