Grain refinement by plastic deformation during conventional TIG welding can help to compensate for the loss of mechanical properties of welded joints. The thermomechanical welding (TMW) tests were performed on S700MC steel with different combinations of TIG arc energy and high frequency hammering over three target cooling times (t_8/5 = 5s, 15s, and 25s). Additionally, the effect of initial microstructures on the weld joint quality was analysed by testing three materials conditions: hot-rolled (as-received) and cold-rolled with 10% and 30% thickness reductions, respectively. The effects of plastic deformation and the mechanical vibration on the grain refinement were studied separately. Optical microscopy, electron backscattered diffraction, and Vickers hardness were used to characterise the weld microstructure heterogeneity. The weld width and depth and the mean grain size were correlated as the function of cooling time t_8/5. The results show that the weld dimensions increase with increasing the t_8/5. The weld microstructures transformed from the mixed martensite and bainite into mixed ferrite and bainite with increasing the t_8/5 time, and the related mean grain size increased gradually. The TMW welds exhibit smaller grains compared to TIG welds due to the coupled effects of mechanical vibration and plastic deformation. The mechanical vibration contributes to weld metal homogenisation, accelerating TiN precipitation in the fusion zone. The proposed TMW process can refine the weld microstructure of S700MC steel, enhancing its mechanical properties.

传统 TIG 焊接过程中通过塑性变形细化晶粒有助于补偿焊接接头机械性能的损失。在三个目标冷却时间（t _8/5  = 5s、15s 和 25s）内，采用 TIG 电弧能量和高频锤击的不同组合对 S700MC 钢进行热机械焊接 (TMW) 测试。此外，通过测试三种材料条件来分析初始微观结构对焊接接头质量的影响：热轧（按收到状态）和冷轧，厚度分别减少 10% 和 30%。分别研究了塑性变形和机械振动对晶粒细化的影响。使用光学显微镜、电子背散射衍射和维氏硬度来表征焊缝微观结构的不均匀性。焊缝宽度和深度以及平均晶粒尺寸作为冷却时间t _8/5的函数相关。结果表明，焊缝尺寸随着t _{8/5 的}增加而增加。随着t _8/5时间的增加，焊缝组织由马氏体和贝氏体混合组织转变为铁素体和贝氏体混合组织，且平均晶粒尺寸逐渐增大。由于机械振动和塑性变形的耦合效应，与 TIG 焊接相比，TMW 焊接呈现出更小的晶粒。机械振动有助于焊缝金属均匀化，加速熔化区 TiN 的析出。所提出的TMW工艺可以细化S700MC钢的焊缝显微组织，从而提高其机械性能。