铁路车轮轮辋疲劳裂纹和踏面剥离掉块的微观伤损因素分析

摘要

以某型铁道车辆装用的3组(20个为1组)车轮(其中,1组车轮的轮辋出现疲劳裂纹,1组车轮的踏面存在剥离掉块,1组车轮运行30万km未出现伤损)为研究对象,采用ASPEX自动扫描电镜系统研究3组车轮轮辋中非金属夹杂物的组成、性质及定量关系,并采用扫描电子显微镜和金相显微镜,研究轮辋疲劳裂纹、踏面剥离的伤损形貌和特征,分析导致轮辋疲劳裂纹和踏面剥离的微观伤损因素.结果表明:辋裂车轮中的非金属夹杂物以脆性夹杂物为主,约占非金属夹杂物总数的85％,并且断口中存在的毫米级脆性氧化物类夹杂物属于冶炼或浇注过程中混入的耐材或熔渣等外来物,这是轮辋疲劳裂纹形成的主要原因;在踏面剥离掉块车轮和未损伤车轮中,塑性非金属夹杂物占绝对多数,分别约占非金属夹杂物总数的84％和93％,踏面剥离掉块车轮的踏面塑性变形层平均厚度约为1mm,为未伤损车轮踏面塑性变形层的10倍,说明踏面塑性变形层的相对变形量较大是导致车轮踏面剥离掉块的主要原因.%There are three different sets,and twenty standard wheels which are with shattered rim and with tread shelling and noncondemnable damage wheel of average kilometrage of 300 000 in revenue service designated as a set of the same types of cars.They have been selected to systematically investigate the component and quantitative relationship of different types of non-metallic inclusions using ASPEX automatic scanning electron microscope system,which can scan a large range of metallographic specimen.The morphology and characteristics of shattered rim and tread shelling wheels have been observed and measured by scanning electron microscope and optical microscope to study the mechanism of shattered rim and tread shelling.Results indicate that an absolute majority of the non-metallic inclusions from wheels with shattered rim are brittle inclusions which are accounted for 85％ of the total inclusions,and the visible millimeter brittle oxide inclusions which belong to refractory materials or slag in smelting or pouring process existing in the crack initiation zone are the main reason to shattered rim.Moreover,the non-metallic inclusions are almost plastic inclusions which are accounted for 84％ and 93％ of the total inclusions respectively distinguished from tread shelling wheels and noncondemnable damage wheels.The failure reason of tread shelling wheels is a significant amount of plastic deformation layer thickness of which the average is about 1 mm and is approximately ten times than that of noncondemnable damage wheels.