以抗拉强度700 MPa级Nb-Ti微合金化C-Mn钢为研究对象,采用高功率光纤激光器对4.6 mm厚钢板进行了拼焊实验,研究了热输入(162、175、187、226 J/mm2)对全熔透焊接接头显微组织、显微硬度、拉伸性能及冲击韧性的影响。研究表明,4种热输入条件下,焊缝区和粗晶区组织均以板条马氏体为主,存在不同含量的贝氏体和铁素体;随着热输入的增加,粗晶区原始奥氏体晶粒尺寸逐渐增大;热输入对细晶区和混晶区的组织影响不明显。焊缝区和热影响区平均硬度均高于母材;随着热输入的提高,焊缝区硬度和焊接接头的峰值硬度逐渐降低,主要原因是热输入增大形成贝氏体和铁素体。4种热输入条件下焊接接头的抗拉强度高于母材。4种热输入条件下焊接接头冲击吸收功均高于母材,且均为韧性断裂,研究范围内的热输入对焊接接头冲击性能影响不明显。 A Nb-Ti microalloyed C-Mn steel with a tensile strength of 700 MPa was used as the research object. A high-power fiber laser was used to weld the 4.6 mm thick steel plate. The effects of heat input (162,175,187,226 J / mm2) on the full penetration of the welded joint microstructure, microhardness, tensile properties and impact toughness. The results show that under the four heat input conditions, the martensite and martensite in the weld zone and the coarse grain zone are mainly composed of bainite and ferrite with different contents. With the increase of heat input, the coarse grain zone The grain size of the original austenite gradually increased; heat input had no obvious effect on the microstructure of the mixed zone. The average hardness of the weld zone and the heat affected zone are higher than the base metal; with the increase of heat input, the hardness of the weld zone and the peak hardness of the welded joints gradually decrease, mainly due to the increase of heat input to form bainite and ferrite . Tensile strength of welded joints under four heat input conditions is higher than that of base metal. The impact energy absorbed by the welded joints under the four heat input conditions is higher than that of the base metal, and all of them are ductile fracture. The heat input within the study range has no obvious effect on the impact properties of the welded joints.