CAJ | 학술논문

在扫描电镜下原位观察了两种钢的拉伸变形过程，两种钢分别为以铁素体为主、含少量珠光体的纯净高强钢和以珠光体为主、含少量先共析铁素体的车轮钢。纯净钢拉伸时，不论试样厚度满足平面应变与否，均以铁素体的滑移变形为主，并最终导致韧性开裂，裂纹连续扩展，少量的珠光体对整个变形断裂过程几乎没有影响；断口呈现韧窝状。对于车轮钢，当试样厚度很薄不满足平面应变条件时，尽管先共析铁素体很少，拉伸时，仍以先共析铁素体的变形为先导过程，并在先共析铁素体与珠光体的界面处优先开裂，成为不连续微裂纹，断口呈现韧窝和准解理两种混合特征；当试样厚度满足平面应变条件时，则以珠光体中渗碳体片层的脆性开裂为主，断口呈现准解理特征。
재소묘전경하원위관찰료량충강적랍신변형과정，량충강분별위이철소체위주、함소량주광체적순정고강강화이주광체위주、함소량선공석철소체적차륜강。순정강랍신시，불론시양후도만족평면응변여부，균이철소체적활이변형위주，병최종도치인성개렬，렬문련속확전，소량적주광체대정개변형단렬과정궤호몰유영향；단구정현인와상。대우차륜강，당시양후도흔박불만족평면응변조건시，진관선공석철소체흔소，랍신시，잉이선공석철소체적변형위선도과정，병재선공석철소체여주광체적계면처우선개렬，성위불련속미렬문，단구정현인와화준해리량충혼합특정；당시양후도만족평면응변조건시，칙이주광체중삼탄체편층적취성개렬위주，단구정현준해리특정。
In situ tensile tests in a scanning electron microscope ( SEM) were carried out using single-edge notched specimens for two types of steels:a pure high-strength steel ( HSS) composed mainly of ferrite and a small amount of pearlite, and a wheel steel composed mainly of pearlite and a small amount of proeutectoid ferrite. Regardless of the specimen thickness meeting the plane strain condition or not, the process of deformation and cracking for the pure HSS starts at ferrite slip, then continuously propagates and finally results in ductile fracture;the small amount of pearlite has nearly no impact on the overall deformation process;and the fracture surface is composed of dimples. However, for the wheel steel, when the specimen thickness is thin, which means that it does not meet the plane strain condition, plastic deformation occurs firstly in proeutectoid ferrite, even though its amount is very small, and then microc-racks initiate and grow along the interface of proeutectoid ferrite and the pearlite colony, and finally evolves into discontinuous microc-racks. The fracture surface fractograph presents both dimple and quasi-cleavage characteristics. For a wheel steel specimen with the thickness meeting plane strain condition, plastic deformation and cracking mainly occurs in the pearlite colony, which results in cleav-age fracture.