The current investigation encompasses the development of a microstructure-based 3D finite element model (FEM) of water quenching process of large-size, high-strength steel forgings with accurate predictions of the volume fraction of phases. The approach is based on modified TTT/CCT curves that consider a lower martensite start temperature value. An experimental procedure consisting in the validation of the FEM simulations was conducted using high-resolution dilatometry, optical and scanning electron microscopy, and instrumentation of a large-size steel block with several thermocouples at different locations. Results showed a very good agreement between the temperature predictions of the 3D FEM model and those obtained from direct measurement of instrumented forged block with an average error of about 1 pct in the quarter region. The volume fraction of phases and hardness distribution across the block were also predicted by the proposed 3D FEM model. The numerical results revealed bainitic volume fractions of about 74 pct at the center of the block and about 91 pct in the quarter region. These predictions were also confirmed by dilatometry test and metallographic examination of the microstructure. Micro hardness measurements were conducted on dilatometry samples that simulate the heat treatment cycle of different thicknesses of the forged block were compared with those predicted by the FEM, and very good agreements were obtained, further confirming the validity of the simulations. The proposed procedure in this research improves the quality of predictions by increasing the reliability of material parameters such as TTT optimization and accurate determination of thermo-physical parameters.

当前的研究包括大型，高强度钢锻件水淬过程的基于微观结构的3D有限元模型（FEM）的开发，该模型具有对相体积分数的准确预测。该方法基于修改后的TTT / CCT曲线，该曲线考虑了较低的马氏体起始温度值。使用高分辨率膨胀计，光学和扫描电子显微镜，以及在不同位置带有数个热电偶的大型钢块的仪器，进行了包含FEM模拟验证的实验程序。结果表明，在3D FEM模型的温度预测与直接测量仪器化的锻造块获得的温度预测之间有很好的一致性，在四分之一区域的平均误差约为1 pct。提出的3D FEM模型还预测了相的体积分数和整个块体的硬度分布。数值结果表明，在块的中心的贝氏体体积分数约为74 pct，在四分之一区域的贝氏体体积分数约为91 pct。这些预测也通过膨胀试验和金相组织检查得到证实。在膨胀计样品上进行了微硬度测量，这些样品模拟了不同厚度的锻造块的热处理周期，并与FEM预测的值进行了比较，并获得了很好的一致性，进一步证实了模拟的有效性。