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800 MPa级光伏支架用钢冲击韧性影响规律及焊接性分析

Impact toughness influence law and weldability analysis of 800 MPa grade steel for photovoltaic brackets

  • 摘要: 通过焊接热模拟试验,模拟不同冷却速度下800 MPa级光伏支架用钢粗晶热影响区(coarse grain heat affected zone, CGHAZ)的焊接热循环过程,在光学显微镜( optical microscope,OM)下观察热模拟试样的显微组织,分析冷却速度对CGHAZ显微组织的影响规律;并且,通过对热模拟试样进行冲击试验,结合扫描电镜(scanning electron microscope,SEM),分析冷却速度对CGHAZ韧性的影响规律. 结果表明,随着冷却速度的增大,CGHAZ显微组织由粒状贝氏体(granular bainite,GB) + 晶界处存在的先共析铁素体(proeutectoid ferrite,PF),逐渐转变为GB + 少量板条贝氏体( lamellar bainite,LB),最后转变为全部LB. 并且,随着冷却速度的提高,冲击韧性逐渐改善,断后伸长率均值从14.33 J逐渐提高到58 J,冲击断口从典型的脆性断裂形貌逐渐转变为韧性 + 解理混合断裂,最后转变为明显的韧性断裂特征. 此外,考虑到800 MPa级光伏支架用钢强度较高,通过碳当量法和Graville图法间接评价焊接性,并通过冷裂纹敏感性指数评估了其冷裂纹倾向,分析结果表明,焊接性良好,焊接冷裂纹倾向较小.

     

    Abstract: Through welding thermal simulation experiments, simulate the welding thermal cycle process of the coarse grain heat affected zone (CGHAZ) of 800 MPa grade steel for photovoltaic brackets under different cooling rates. Observe the microstructure of the thermal simulation sample under an optical microscope(OM) and analyze the influence of cooling rate on the microstructure of CGHAZ; The influence of cooling rate on the toughness of CGHAZ was analyzed by impact test of thermal simulation sample and scanning electron microscope(SEM). The results showed that with the increase of cooling rate, the microstructure of CGHAZ gradually changed from granular bainite(GB) and proeutectoid ferrite(PF) existing at grain boundary to GB and a small amount of lamellar bainite(LB), and finally to all LB. Moreover, with the increase of cooling rate, the impact toughness gradually improves, and the average impact energy gradually increases from 14.33 J to 58 J. The impact fracture morphology gradually changes from a typical brittle fracture morphology to a toughness and cleavage mixed fracture, and finally becomes a clear ductile fracture feature. In addition, considering the high strength of 800 MPa grade steel for photovoltaic brackets, its weldability is indirectly evaluated by the carbon equivalent and the Granville diagram, and its cold crack tendency is evaluated by the cold crack sensitivity index. The analysis results show that its weldability is good, and the welding cold crack tendency is small.

     

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