自回火对重轨钢疲劳裂纹扩展行为的影响

Effect of Self-tempering on Fatigue Crack Growth of Heavy Rail Steel

针对重轨钢在线淬火后自回火造成的抗疲劳裂纹扩展能力降低的问题,在淬火冷速分别为3℃/s、5℃/s、8℃/s,终冷温度为450℃条件下,研究了自回火对重轨钢疲劳裂纹扩展行为的影响,测算了疲劳裂纹扩展速率的Paris公式,采用扫描电镜及硬度计分别对自回火后钢轨的疲劳断口进行观察及硬度测试。结果表明:经过自回火后,钢轨的疲劳裂纹扩展速率增快、硬度降低,且自回火之前钢轨的淬火冷速越大,自回火后其硬度降低越显著,硬度的降低增加了裂纹扩展的可能性;自回火后钢轨在Ⅰ区的疲劳裂纹扩展速率远大于直接淬火试样,使钢轨疲劳裂纹扩展的整体进程缩短,这是疲劳裂纹扩展速率增快的重要原因。不同淬火冷速后的自回火试样在应力强度因子范围ΔK(ΔK=K_(max)-K_(min))为10 MPa·m^(1/2)时,断口的疲劳辉纹、解理面和二次裂纹较少,河流花样数量较多、面积小、沟壑浅,而在ΔK=13.5 MPa·m^(1/2)时,断口的疲劳辉纹间距增大,解理面和二次裂纹较多,河流花样数量增多、面积增大,疲劳裂纹扩展速率da/dN较快。

The influence of self-tempering on the fatigue crack growth behavior of hypereutectoid rail was studied under the condition of quenching speed of 3℃/s,5℃/s,8℃/s and final cooling temperature of 450℃,Paris formula of fatigue crack growth rate was calculated,and the self-tempering was carried out by SEM and hardness tester the fatigue fracture of post hypereutectoid rail was observed and its hardness was tes-ted.The results show that after self-tempering,the fatigue crack growth rate of rail is accelerated,and hardness reduction,and the greater the quenching cooling rate before self-tempering,the more obvious the reduction of the anti-fatigue crack growth ability the and hardness after self-tempering,which the decrease of hardness increases the possibility of crack growth;there is no obvious threshold area after self-tempering,which will shorten the overall process of rail fatigue crack growth and accelerate the fatigue crack growth rate of quenched rail;different WhenΔK=10 MPa·m^(1/2),the number of fatigue striations,cleavage surfaces and secondary cracks is less,the number of river patterns is more,the area is small,and the gullies are shallow.WhenΔK=13.5 MPa·m^(1/2),the distance between fatigue striations increases,the cleavage surfaces and secondary cracks are more,the number and area of river patterns increase,and the fatigue crack growth rate is faster.