采用COD 试验方法测定了15MnVN 钢多道焊四种热输入量焊接热影响区的断裂韧性。详细观察并测定了其微观组织、晶粒尺寸和不同组织的比例。结果表明,热输入量大,增大了热影响区粗晶区的晶粒尺寸,而由后续焊遭热循环作用产生的细晶区面积则减少,从而提高了转变温度。本文分析了多道焊热影响区脆化的原因和热输入量对脆化程度的影响,提出了板厚56mm 的这种合金钢的合适的焊接热输入量。 The fracture toughness of four heat input welding HAZs of 15MnVN steel was measured by COD test method. The microstructure, grain size and the proportion of different tissues were observed and measured in detail. The results show that the heat input is large, increasing the grain size in the heat affected zone, while the area of ​​the fine crystalline zone resulting from the subsequent heat cycle is reduced, thus increasing the transition temperature. In this paper, the reason of the embrittlement in the HAZ and the effect of heat input on the degree of embrittlement are analyzed. The suitable welding heat input of this alloy steel with a thickness of 56mm is proposed.