To investigate the effect of alloying elements on the microstructure and mechanical properties of medium-carbon steel weldments, 0.4% carbon steels with different chromium and titanium contents were fabricated by melting and hot-rolling for friction stir welding (FSW). The microstructures in the stir zones of friction stir welded (FSWed) medium-carbon steels without chromium, with 1% chromium and 4% chromium are ferrite and pearlite, bainite, and fully lath martensite, respectively. The prior austenite grain size was refined by the addition of titanium. High densities of ultrafine-twins are observed in the martensite of FSWed 0.4%C–4%Cr and 0.4%C–4%Cr-0.2%Ti steels, while dense auto-tempered iron carbides with less ultrafine-twins are observed in the lath martensite of FSWed 0.4%C–4%Cr-0.4%Ti steel. The strength of FSWed 0.4%C–4%Cr steels is improved by the martensitic structure, while the ductility of 0.4%C–4%Cr steels decreases significantly compared to that of 0.4%C steels with low chromium content. A small amount of 0.4% titanium addition significantly increases the ductility of 0.4%C–4%Cr-0.4Ti steel, leading to a good combination of high strength of 2270 MPa and high elongation of 18.3%. The substructure changes of the lath martensitic structure caused by the addition of titanium contribute to the brittle to ductile transition of FSWed medium-carbon steel with 4% chromium.

为了研究合金元素对中碳钢焊件的组织和力学性能的影响，通过熔融和热轧制备了0.4％含铬和钛含量不同的碳钢，用于搅拌摩擦焊（FSW）。含铬1％和含铬4％的无铬摩擦搅拌焊接（FSWed）中碳钢的搅拌区的显微组织分别为铁素体和珠光体，贝氏体和全板条马氏体。通过添加钛来细化先前的奥氏体晶粒尺寸。在FSWed 0.4％C–4％Cr和0.4％C–4％Cr-0.2％Ti钢的马氏体中观察到高密度的超细双相钢，而在FSWed 0.4％C–4％Cr和0.4％C–4％Cr-0.2％Ti的马氏体中观察到高密度的超细双相钢。 FSWed 0.4％C–4％Cr-0.4％Ti钢的板条马氏体。FSWed的强度为0。马氏体组织改善了4％C–4％Cr钢，而0.4％C–4％Cr钢的延展性与低铬含量的0.4％C钢相比显着降低。少量添加0.4％的钛可显着提高0.4％C–4％Cr-0.4Ti钢的延展性，从而实现了2270 MPa的高强度和18.3％的高延伸率的良好组合。由添加钛引起的板条马氏体组织的亚结构变化有助于含4％铬的FSWed中碳钢的脆性至延性转变。导致2270 MPa的高强度和18.3％的高伸长率的良好组合。由添加钛引起的板条马氏体组织的亚结构变化有助于含4％铬的FSWed中碳钢的脆性至延性转变。导致2270 MPa的高强度和18.3％的高伸长率的良好组合。由添加钛引起的板条马氏体组织的亚结构变化有助于含4％铬的FSWed中碳钢的脆性至延性转变。