In-situ high-energy X-ray diffraction experiments with high temporal resolution during rapid cooling (280 °C s⁻¹) and isothermal heat treatments (at 450 °C, 500 °C, and 550 °C for 30 minutes) were performed to study austenite decomposition in two commercial high-strength low-alloy steels. The rapid phase transformations occurring in these types of steels are investigated for the first time in-situ, aiding a detailed analysis of the austenite decomposition kinetics. For the low hardenability steel with main composition Fe-0.08C-1.7Mn-0.403Si-0.303Cr in weight percent, austenite decomposition to polygonal ferrite and bainite occurs already during the initial cooling. However, for the high hardenability steel with main composition Fe-0.08C-1.79Mn-0.182Si-0.757Cr-0.094Mo in weight percent, the austenite decomposition kinetics is retarded, chiefly by the Mo addition, and therefore mainly bainitic transformation occurs during isothermal holding; the bainitic transformation rate at the isothermal holding is clearly enhanced by lowered temperature from 550 °C to 500 °C and 450 °C. During prolonged isothermal holding, carbide formation leads to decreased austenite carbon content and promotes continued bainitic ferrite formation. Moreover, at prolonged isothermal holding at higher temperatures some degenerate pearlite form.

在快速冷却（280°C s ^-1）和等温热处理（在450°C，500°C和550°C下进行30分钟）期间进行具有高时间分辨率的原位高能X射线衍射实验研究两种市售高强度低合金钢中的奥氏体分解。首次现场研究了在这些类型的钢中发生的快速相变。，有助于对奥氏体分解动力学进行详细分析。对于主要成分为重量百分比Fe-0.08C-1.7Mn-0.403Si-0.303Cr的低淬透性钢，在初次冷却过程中已经发生了奥氏体分解为多边形铁素体和贝氏体的现象。但是，对于主要成分为Fe-0.08C-1.79Mn-0.182Si-0.757Cr-0.094Mo（重量百分比）的高淬透性钢，奥氏体的分解动力学主要是由于添加了Mo，因此受阻，因此在此过程中主要发生贝氏体相变。等温保温 将温度从550°C降低到500°C和450°C，可以明显提高等温保温时的贝氏体转化率。在长时间等温保持期间，碳化物的形成导致奥氏体碳含量降低，并促进持续的贝氏体铁素体形成。而且，