钢轨横截面出现斑痕的原因分析

REASON ANALYSIS FOR THE OCCURRENCE OF SPOTS ON THE CROSS SECTION OF RAILS

焊接前的钢轨横截面在打磨过程中出现斑痕。经手提式硬度计检测,钢轨横截面硬度异常,疑是局部偏析或夹杂物等缺陷所致。通过取样检验,钢轨横截面试样正反两面的低倍组织,一面有斑痕,另一面无斑痕;经硬度测定和金相检验,认为钢轨横截面出现的斑痕是因打磨量控制不当,造成钢轨打磨面局部表层温度急剧升高,因钢轨母材仍处于常温状态,使打磨面表层快速冷却产生了马氏体组织转变,致使该面出现斑痕。

Some spots were found on the cross section of rails when the rails were being grinded before welding. The spots were supposed to be defects such as local segregations or inclusions because the hardness values measured with portable hardometer were irregular and abnormal. However, the mirostructure in low magnification on both sides of the cross section of rail head showed that the spots occurs only on one side, and hardness measurement and microstructure examination found that the spots are not local segregations or inclusions but martensite microstructure. It is concluded that the spots result from the unsuitable control of the amount of grinding, which results in the dramatic rise of temperature on local surface of the rail. When the local temperature exceeds the phase transformation temperature, the rapid cooling rate caused by the matrix of the rail at ambient temperature can result in martensite transformation at certain depth from the rail surface.