以通用有限元软件ABAQUS为计算平台，采用Fortran语言编程，分别单独基于单个Q345钢模拟焊接热影响区连续冷却组织转变曲线(SH-CCT，峰值温度分别为900、1100和1300℃，简记为SH-CCT₉₀₀、SH-CCT₁₁₀₀和SH-CCT₁₃₀₀)和同时基于3个不同温度下的SH-CCT图建立了4种组织与硬度计算模型，利用所建立的模型对Q345钢TIG重熔焊接接头的温度场、组织分布和硬度分布进行了计算，通过模拟结果与实验结果的比较，研究了采用不同的计算模型对焊接接头组织与硬度预测的适用性与准确性。采用单个SH-CCT图的组织计算结果仅在热影响区(HAZ)局部区域与实验结果吻合良好，其他区域有较大偏差。采用单个SH-CCT₉₀₀图时，计算所得的部分相变区铁素体体积分数与实验结果的相对误差为7.7%；采用单个SH-CCT₁₁₀₀图时，计算所得的细晶区铁素体、贝氏体和马氏体体积分数与实验结果的相对误差分别为11.3%、17.3%和15.5%；采用单个SH-CCT₁₃₀₀图时，计算所得的粗晶区马氏体体积分数与实验结果的相对误差为29.6%。同时采用3个SH-CCT图时，组织计算结果在整个HAZ上与实验结果吻合良好。采用单个SH-CCT图的硬度计算结果仅在HAZ局部较窄区域与实验结果较为接近，而同时采用3个SH-CCT图的硬度计算结果在整个HAZ上都与实验结果较为吻合，其硬度绝对差值范围为0~14 HV。采用上述4种计算模型所得到的焊缝区组织与硬度计算结果都与实验结果有较大偏差，需进一步获取精确的焊缝区SH-CCT图。在实际焊接过程中，若只考虑热影响某一区域(如粗晶区)的相变情况，也可以仅采用对应的单一SH-CCT图来进行数值预测。

Q345 steel is a low-alloy high-strength steel that is widely used in production. As the solid-state phase transition of Q345 steel is very sensitive to temperature, the microstructure and hardness of joints fabricated with this steel are difficult to predict. Therefore, studying the welding metallurgy, residual welding stress, and welding deformation of Q345 steel joints is essential for improving the safety and service life of Q345 welding structures. In this study, the microstructure and distribution of hardness of a Q345-steel tungsten-inert-gas welded and re-melted joint were calculated using four models encoded in the general finite element software, ABAQUS, and FORTRAN language. Three models were based on only one of three welding continuous-cooling transformation curves of the simulated heat-affected zone (SH-CCT) of Q345 steel, with peak temperatures of 1300, 1100, and 900^oC (hereafter denoted as SH-CCT₁₃₀₀, SH-CCT₁₁₀₀, and SH-CCT₉₀₀, respectively). The final model was based on the associated diagram consisting of these curves SH-CCT diagram above. Comparing the simulation and experimental results, the capabilities and accuracies of the prediction methods based on the different models were investigated. The microstructural calculations of the single SH-CCT diagram agreed with the experimental results only in the local heat-affected zone (HAZ) and largely deviated in the other areas. In the model based on SH-CCT₉₀₀, the relative error of the ferrite volume fraction in the inter-critically HAZ (ICHAZ) was 7.7%. In the model based on SH-CCT₁₁₀₀, the relative errors of the ferrite, bainite, and martensite volume fractions in the fine-grained HAZ (FGHAZ) were 11.3%, 17.3%, and 15.5%, respectively. In the model based on SH-CCT₁₃₀₀, the relative error of the martensite volume fraction in the coarse-grained HAZ (CGHAZ) was 29.6%. In contrast, the microstructural calculations of the associated SH-CCT diagram agreed with the experimental results over the whole HAZ. The results showed that models based on the single SH-CCT diagrams met the tested hardness only in several narrow areas of the HAZ, but the hardness computed by the model, based on the associated diagram, was consistent with the tested hardness, with absolute differences ranging from 0 to 14 HV. The calculated microstructure and hardness in the fusion zone (FZ) greatly deviated from the test results in all the four models, indicating that predictions in the FZ require an accurate SH-CCT diagram of the FZ. In practical welding processes, the corresponding single SH-CCT diagram can adequately predict the microstructure and hardness during the phase transition of one HAZ area (such as the CGHAZ).