冷却速率对高强钢焊接粗晶热影响区组织和性能的影响

Effect of Cooling Rate on Microstructure and Properties of Welded Coarse Grain Heat Affected Zone of High Strength Steel

利用热模拟机、金相显微镜、扫描电子显微镜、电子背散射衍射仪,以及维氏硬度测试与夏比V型冲击试验分析了冷却速率对高强钢粗晶热影响区组织和性能的影响。结果说明:当冷却速率处于0.5~4℃/s时,粗晶区组织主要为粒状贝氏体;当冷却速率处于6~20℃/s时,粗晶区组织主要为板条贝氏体;当冷却速率处于30~60℃/s时,粗晶区组织为马氏体,马氏体转变起始温度Ms的测定值为437℃。当冷却速率为1℃/s时,对应粗晶区的室温冲击功为4.9 J,大角度晶界的占比为28.6%,断裂类型为准解理断裂;当冷却速率为10、60℃/s时,对应粗晶区的室温冲击功分别为20.2、18.9 J,大角度晶界的占比分别为41.4%、31.4%,断裂类型均为韧性断裂。总之,粗晶区组织为粒状贝氏体时韧性最差,粗晶区组织为板条贝氏体时韧性最佳。

The effect of cooling rate on the microstructure and properties of coarse grain heat affected zone(CGHAZ) of high strength steel were analysed by thermal simulator,optical microscope(OM),scanning electron microscope(SEM),electron backscatter diffraction(EBSD),Vickers hardness test and Charpy V-notch impact test.The results show that when the cooling rate is 0.5-4 ℃/s,the microstructure of the CGHAZ is mainly granular bainite.When the cooling rate is 6-20 ℃/s,the microstructure of the CGHAZ is mainly lath bainite.When the cooling rate is 30-60 ℃/s,the microstructure of the CGHAZ is martensite.The measured value of the martensite transformation initiation temperature Msis 437 ℃.When the cooling rate is 1℃/s,the impact energy at room temperature corresponding to the CGHAZ is 4.9 J,and the proportion of high angle grain boundaries(HAGBs) is 28.6%,and the fracture type is quasi-cleavage fracture.When the cooling rate is 10,60 ℃/s,the impact energy at room temperature corresponding to the CGHAZ is 20.2,18.9 J respectively,and the proportion of HAGBs is 41.4%,31.4% respectively,the fracture type is ductile fracture.In summary,the toughness is the worst when the microstructure of the CGHAZ is granular bainite,and the toughness is the best when it is lath bainite.