车轮钢形变断裂过程的原位研究及氢影响

在扫描电镜下对CL60车轮钢单边缺口薄试样(厚度≤0.5mm)进行了原位拉伸实验,并研究了氢的影响.在金相显微镜下观察了带预裂纹的厚度为30mm的楔形张开加载试样开裂过程.结果表明,对薄试样拉伸变形时,不论是否有氢,先共析铁素体优先发生塑性变形,微裂纹沿先共析铁素体与珠光体团的边界形核、扩展;在有氢的情况下,微裂纹更容易通过夹杂物的剥落或夹杂物与基体界面的分离而萌生;薄试样拉伸主要是韧窝断口;对厚试样,裂纹主要通过珠光体中渗碳体片层开裂而扩展,断口也因此主要呈解理特征.

In situ study of deformation and fracture process in wheel steel and effect of hydrogen

In situ tensile tests in scanning electron microscope (SEM) were carried out using single-edge notched specimens of no larger than 0.5?mm in thickness made of CL60 wheel steel with or without hydrogen charging. Observations under optical microscope (OM) were also done to a wedge opening-loading (WOL) specimen with a thickness of 30?mm which was precracked. The result shows that, for the thinner specimen, plastic deformation occurs firstly in proeutectoid ferrite and then grows along the prior austenite grain boundary, and then, a microcrack initiates and propagates preferentially at the interface of proeutectoid ferrite and pearlite colony. The process of deformation and fracture is almost same each other for both specimens with and without hydrogen, except that the microcrack initiates more frequently by way of inclusion separating and shelling from matrix for the specimen with hydrogen. The fracture surface fractograph of the thinner specimen is ductile fracture. However, for the thicker specimen (WOL), plastic deformation and cracking mainly occurs in the pearlite colony, which results in cleavage fracture.