研究了一种Fe-Cr-Ni-Mo高强钢经不同峰值温度(T_p) (760、830、1020和1320 ℃)焊接热循环后的显微组织与冲击韧性。结果表明,随着T_p的升高,特征热影响区的平均冲击功先增大后减小。粗晶区(CGHAZ,T_p=1320 ℃)和细晶区(FGHAZ,T_p=1020 ℃)的显微组织为淬火马氏体。由于晶粒粗大,造成CGHAZ冲击韧性较差,低于晶粒细小的FGHAZ冲击韧性。部分相变区(ICHAZ,T_p=760 ℃和T_p=830 ℃)的显微组织为淬火马氏体和回火马氏体组成的混合组织,由于冲击试样V型缺口处的混合组织界面所占比例具有随机性,造成ICHAZ冲击功波动较大。ICHAZ (T_p=830 ℃)中均匀的细晶组织对冲击裂纹具有止裂作用,使得该微区具有最佳的冲击性能。尽管ICHAZ (T_p=760 ℃)晶粒细小,但存在的极细晶组织(尺寸为1~2 μm)在遭受冲击载荷时易形成密集分布的次生微孔,基体中未溶的M₂C及MC析出相促使微孔连接形成裂纹,导致该微区冲击韧性最差,成为热影响区的薄弱区域。

Marine engineering steel is the key material for the construction of major marine infrastructure projects. Due to the harsh environment in the deep sea, the mechanical properties such as strength, low temperature toughness and so on of the marine steel are required to be higher. In this work, the weldability of a Fe-Cr-Ni-Mo high-strength steel was studied, and the microstructure and impact toughness of the steel after welding thermal cycling at different peak temperatures were analyzed. The results show that the average impact toughness of characteristic heat affected zone under different temperatures increases first and then decreases with the increase of peak temperature (T_p). The microstructures of coarse grain heat-affected zone (CGHAZ, T_p=1320 ℃) and fine grain heat-affected zone (FGHAZ, T_p=1020 ℃) are quenched martensite. Because of the coarse grain size, the impact toughness of CGHAZ is poor, which is lower than that of FGHAZ. The microstructure of inter-critical heat-affected zone (ICHAZ, T_p=830 ℃ and T_p=760 ℃) is composed of quenched martensite and tempered martensite. Due to the randomness of the proportion of the interfaces between the mixed microstructures near the V-notch, the impact energy values of ICHAZ fluctuates greatly. The homogeneous fine grain structure in ICHAZ (T_p=830 ℃) has a crack arrest effect during the impact deformation, which makes the characteristic zone have the best impact toughness. Although the grain size in ICHAZ (T_p=760 ℃) is also fine, the existence of the ultra-fine grain zones (the grain size in which is only 1~2 μm) benefits the formation of secondary voids under the impact load. The undissolved M₂C and MC precipitations in matrix promote the connecting of secondary voids and then form the secondary cracks. As a result, the impact toughness of the characteristic zone is poor, and becomes the weak region of HAZ.