Mo添加对低屈强比460 MPa级焊接结构钢组织性能的影响

Effect of Mo addition on microstructure and mechanical properties of low yield ratio 460 MPa grade welded structural steel

利用光学显微镜、扫描电镜、电子探针、透射电镜等研究了少量Mo添加对460 MPa级焊接结构钢组织性能的影响。结果表明:采用相同轧制与冷却工艺时,添加0.18 mass%的Mo后试验钢的强度提升、屈强比下降、塑韧性小幅降低;Mo在钢中未发生明显偏聚,通过固溶强化提高试验钢的淬透性,有利于在控轧控冷工艺条件下使试验钢获得高比例的针状铁素体组织,组织内部具有较高的位错密度,而未添加Mo的试验钢组织以多边形铁素体为主,位错线分布稀疏;Mo添加后造成试验钢组织中大角度晶界比例由38%降至22%,受载时更易发生裂纹扩展,小幅降低试验钢的冲击韧性;Mo部分进入含Nb析出相中,并改变其团簇状分布形态,使析出物颗粒更加弥散,平均尺寸由212 nm降至62 nm,析出强化增量达到无Mo钢的1.5倍以上。

Effect of a small amount of Mo addition on microstructure and properties of 460 MPa grade welded structural steel was studied by means of optical microscope,scanning electron microscopy,electron probe micro-analysis and transmission electron microscopy.The results show that the strength of the experimental steel prepared with the same rolling and cooling process increases,the yield strength ratio decreases,and the plasticity and toughness decrease slightly after 0.18 mass% Mo addition.No obvious segregation of Mo is observed in the experimental steel,and the hardenability of the steel is improved by solution strengthening of Mo,which is beneficial to obtain a high fraction of acicular ferrite structure under the condition of controlled rolling and controlled cooling,with high dislocation density in the microstructure,while the microstructure of the steel without Mo addition is polygonal ferrite,with sparse distribution of dislocation lines.The addition of Mo results in the decrease of the proportion of large angle grain boundary from 38% to 22% in the microstructure of the experimental steel,which will make crack propagation easier and slightly reduces the impact toughness of the experimental steel.Part of Mo diffuses into the Nb containing precipitates and changes its cluster distribution,which makes the precipitates more dispersed,the average size of precipitates decreases from 212 nm to 62 nm,and the precipitation strengthening increment is more than 1.5 times that of Mo free steel.