A low-alloy medium-carbon bainitic steel was isothermally tempered at 300 °C for up to 24 hours which led to a significant hardness decrease. In order to explain the decreasing hardness, extensive microstructural characterization using scanning and transmission electron microscopy, X-ray diffraction, and atom probe tomography was conducted. The experimental work was further supplemented by thermodynamic and kinetic simulations. It is found that the main underlying reason for the hardness reduction during tempering is related to dislocation annihilation, possibly also with corresponding changes in Cottrell atmospheres. On the other hand, cementite precipitate size, effective grain size of the bainite, and retained austenite fraction appear unchanged over the whole tempering cycle.

低合金中碳贝氏体钢在300°C下等温回火长达24小时，导致硬度显着下降。为了解释硬度的降低，使用扫描和透射电子显微镜，X射线衍射和原子探针层析成像技术进行了广泛的微观结构表征。热力学和动力学模拟进一步补充了实验工作。发现回火过程中硬度降低的主要原因可能与位错location没有关，也可能与Cottrell气氛的相应​​变化有关。另一方面，渗碳体沉淀物的尺寸，贝氏体的有效晶粒度和残留的奥氏体分数在整个回火循环中都没有变化。