Abstract: In order to study the latest designed large heat input welding material of marine engineering extrathick plate, EH36 steel was joined by using twin-wire submerged arc welding with heat inputs of 85, 100 and 115 kJ/cm separately. Meanwhile, the microstructure and mechanical properties were evaluated to explore the toughening mechanism of weld metal. Results show that a lot of active inclusions are obtained in the weld metal due to the design idea of low carbon and oxide metallurgy, which contributes to the generation of numerous fine and interlocking acicular ferrite. The acicular ferrite volume ratio of weld metal exceeds 60%. Moreover, the impact energy at −40 ◦C surpasses 115 J and the crack tip opening displacement value at −10 ◦C is more than 0.2 mm under three heat inputs owing to the role of acicular ferrite, of which 85 kJ/cm is the best. The martensiteaustenite constituents are minor in size and the microstructure of the weld metal in reheated zone is dominated by small massive equiaxed ferrite, without impairing the toughness. As the heat input increases, the content of acicular ferrite drops and then rises; the impact toughness and fracture toughness first worsen consequently and then stabilize on account of the dramatic expansion of the proeutectoid ferrite size.

Key words: large heat input, extra-thick plate, weld metal, acicular ferrite, toughness

摘要： 为研究最新开发的海工特厚板大热输入用焊接材料，对EH36海工钢进行热输入为85、100和115 kJ/cm的双丝埋弧焊接试验，对焊缝金属的显微组织和力学性能进行分析以探究焊缝金属的韧化机理。结果表明：由于焊材采用低碳及氧化物冶金的设计思路，焊缝金属中获得大量夹杂物作为异质形核点，针状铁素体含量超过60%；焊缝金属中出现的马氏体-奥氏体组元尺寸细小且均匀分布，焊缝再热区主要是细小的等轴块状铁素体；焊缝金属低温韧性优异，−40 ℃冲击吸收功超过115 J，−10 ℃裂纹尖端张开位移值超过0.2 mm；随着热输入的增加，焊缝中针状铁素体含量先下降后上升，低温冲击韧性和断裂韧性先下降后趋于稳定。

关键词: 大热输入，特厚板，焊缝金属，针状铁素体，韧性