微量元素对超大线能量EH36船板热影响区粗晶区组织和性能的影响

The effect of trace elements on the microstructure and properties of coarse grain heat affected zone of EH36 ship steel with super large heat input

通过焊接热模拟研究了在超大线能量下焊接时Al元素、Mg元素和Ti元素含量对EH36高强船板钢热影响区粗晶区组织、性能的影响规律,采用Thermo-Calc热力学计算与SEM,EDS测试相结合的方法揭示了Al元素、Mg元素和Ti元素含量与母材中氧化物类型、尺寸、数量及粗晶区相变的关系.结果表明,Al_(2)O_(3)无法诱导针状铁素体相变,当Al元素质量分数低于0.005%时,钢中可形成Mg元素、Ti元素或其复合氧化物,可促进粗晶区针状铁素体相变.Mg元素和Ti元素联合添加时,当Mg元素质量分数由0.0042%降低为0.0013%,氧化物类型由MgO转变为Mg_(2)TiO_(4),经统计20个视场内的氧化物数量由408个提高到503个,平均直径由1.37μm减小到1.10μm,显著提高了非均匀形核的比表面积,抑制了晶界铁素体的形成,使t8/5=300 s时粗晶区热模拟试样-20℃冲击吸收能量由43 J提升到127 J.

The influence of Al,Mg,and Ti element content on the microstructure and properties of the coarse grain zone in the heat affected zone of EH36 high-strength ship steel during large heat input welding was studied through welding thermal simulation.The relationship between Al,Mg,and Ti element content and oxide type,size,quantity,and coarse grain zone phase transformation in the base material was revealed using Thermo-Calc thermodynamic calculation combined with SEM and EDS testing.The results showed that Al_(2)O_(3) couldn`t induce the transformation of acicular ferrite.When the mass percent of Al element was below 0.005%,Ti,Mg or their composite oxides could be formed in the steel,which could promote the transformation of acicular ferrite in the coarse grain area.When Ti and Mg were added together,and the mass percent of Mg element decreased from 0.0042%to 0.0013%,the oxide type changed from MgO to Mg_(2)TiO_(4),the number of oxides in 20 fields of view increased from 408 to 503,the average diameter of the oxide reduced from1.37μm to 1.10μm.The specific surface area of non-uniform nucleation was significantly increased,the formation of grain boundary ferrite was suppressed,and the impact energy of the thermal simulation sample at−20℃ in the coarse grain zone was increased from 43 J to 127 J at t8/5=300 s.