钢轨表面宽带激光淬火工艺及其疲劳磨损性能

Laser Wide-band Hardening of Steel Rails and Corresponding Fatigue Wear Property

针对目前钢轨强化采用的欠速淬火方法存在强化层硬度偏低、耐磨性难以满足重载线路使用要求的问题,使用3种不同光斑宽度的激光,研究了U71Mn材质钢轨的激光淬火强化工艺,获得了不同扫描速度下的临界功率和淬火层深,并测试了淬火层在滚动接触条件下的磨损与接触疲劳性能。结果表明:在临界熔化的激光能量密度下,光斑宽度由6mm增加到20mm时,淬火层深度提高了38%,或在获得相同的淬火层深度情况下,处理效率提高6.8倍;淬火层组织为针状马氏体,硬度从原来的300HV提高到800HV以上;20万周次的磨损试验后,激光淬火试样的磨损量只有未处理试样磨损量的25%,未处理试样以表面接触疲劳剥落和塑性变形为主,激光淬火试样仅有轻微的疲劳磨损,耐磨性和抗接触疲劳性能优异。

Nowadays,online slack quenching technique was widely used for the hardening of steel rails,but the hardness of hardened layers was relatively low and was insufficient to meet the wear resistance demands of heavy-haul railways.Laser hardening process was carried out on U71 Mn rail surfaces by utilizing rectangle laser beam size with three different widths.The critical laser powers and hardened layer depths at different scanning velocities were obtained for the three different laser beam sizes.Furthermore,the wear and rolling contact fatigue property of laser-hardened layers were also investigated.Results show that under the same critical laser powers,the increase of laser beam widths from 6mm to 20 mm results in a significant increase in hardened depths(about 38%)or productivity(about 6.8times);the microstructures of the laser-hardened layers are composed of acicular martensite and have a much higher microhardness of 800 HV in comparison with that of the original steel rails(about 300HV);the weight losses of laser-hardened specimens are only 25%of the untreated ones after200 thousand cycle RCF tests;the damaged surfaces display severe contact fatigue spalling and plastic deformations for the untreated specimens but only slight fatigue wear for the laser-hardened specimens,which indicate the outstanding wear and RCF resistances for the laser-hardened rails.