U71Mn钢轨表面激光熔覆Fe基合金组织与性能研究

Research on the Microstructure and Properties of Laser Cladding Fe-base Alloy on U 71 Mn Rail Surface

研究目的:随着列车运行速度的大幅提高,对钢轨的耐磨性能及滚动接触疲劳性能提出了更高的要求。为提高钢轨的耐用性,本文利用激光宽带熔覆技术对U71Mn钢轨表面进行强化,采用同步送粉方式进行自熔性Fe基粉末的激光熔覆,目的是获得厚度1mm左右无裂纹、气孔等缺陷,且与钢轨冶金结合的高性能激光熔覆层。研究结论:通过测试分析和试验结果表明,在CO2激光功率4200W、扫描速度为300mm/min、送粉速率18g/min等工艺条件下,可获得厚度1mm的优质涂层,其显微硬度平均值可达HV780,高于熔合区及基体的硬度,在过渡区处存在硬度拐点,但经静载抗压实验看出,涂层在453kN静载荷下无开裂现象。激光熔覆涂层的组织主要由γ-Fe、Cr0.19Fe0.7Ni0.11、NiCrFe、FeCr等物相组成,但是在熔合区靠近基体处有马氏体组织形成,是由于激光快速加热及快速冷却造成的。

Research purposes：With much increase of train running speed,the higher properties of wear-resistance and rolling contact fatigue-resistance are required to the rail.For increasing service life of the rail,the surface of U71Mn rail was strengthened by wide-band laser cladding technique.In order to obtain high-performance about 1mm thick coating free of cracks and pores that metallurgically bonded with the rail matrix,the cladding process was conducted by CO2 laser with direct injection of the Fe-based powder into the molten pool.Research conclusions：The results of experiments and analysis showed that high quality cladding coating with the thickness of about 1 mm can be obtained under the conditions of laser power being 4 200 watts,scanning speed being 300 mm/min and powder feeding velocity being 18 g/min etc.The coating had a higher hardness value of HV780 than that of the substrate material,but there existed a hardness knee point between the coating and the substrate.The laser cladding coating did not appear cracks under the static load of 453 kN.The organs of the Fe-based coating were mainly composed of γ-Fe,Cr0.19Fe0.7Ni0.11,NiCrFe and FeCr etc.The martensite structure was formed in the fusion area adjacent to the substrate because of the rapid heating and rapid cooling.