连铸与模铸高铁车轴钢的高周疲劳破坏行为

连铸车轴钢能否达到模铸车轴钢的性能水平是其能否应用的一个关键。对此,采用旋转弯曲疲劳试验及疲劳裂纹扩展速率试验对比研究了连铸与模铸工艺生产的高铁车轴钢的高周疲劳破坏行为。结果表明,工业试制的连铸车轴钢的强度和疲劳极限均低于模铸车轴钢,且前者的疲劳裂纹扩展速率略高于后者。疲劳断口分析表明,疲劳断裂大部分起源于试样表面基体。微观组织分析表明,尽管两者的微观组织均为高温回火马氏体,但连铸车轴钢中原奥氏体晶粒尺寸及碳化物均略大于模铸车轴钢。金相评级法及夹杂物极值统计法的结果均表明,连铸车轴钢中的夹杂物尺寸明显大于模铸车轴钢。因此,为了以连铸工艺取代模铸工艺,还需要进一步优化连铸车轴钢的成分、冶金生产和热处理等工艺,以获得优良的冶金质量和组织性能。

Comparison of high-cycle fatigue properties of continuous casting and mould casting axle steels

It is a challenge to ensure that the mechanical properties of continuous casting axle steel are comparable to those of mould casting axle steel. Thus, the high-cycle fatigue fracture behavior of high-speed railway axle steels manufactured by continuous casting and mould casting was studied by using rotating-bending fatigue test and fatigue crack growth (FCG) test. The results showed that both the tensile strength and fatigue strength of the trial continuous cast steel was lower than those of the mould cast steel, while the fatigue crack growth rate of the former was slightly higher than that of the latter. SEM analysis of all the fatigue fractured specimens revealed that most of them initiated from specimen surface matrix. Both the average prior austenite grain size and cementite size of the continuous cast steel were slightly larger than those of the mould cast steel, although both of the microstructures were high-temperature tempered martensite. Further analyses of both metallographic rating and the statistics of extremes methods of non-metallic inclusions showed that the inclusion size of the continuous cast steel was notably larger than that of the mould cast steel. Therefore, in order to replace the mould cast process with the continuous casting process, it is necessary to further optimize the chemical composition, continuous casting process and heat treatment parameters to obtain excellent metallurgical quality and structural properties.