组织对贝氏体钢焊缝粗粒热影响区冲击韧性和疲劳性能的影响,Journal of Materials Engineering and Performance

通过微观结构表征和有限元建模研究了在多个焊接热循环下贝氏体钢焊缝粗晶热影响区 (CGHAZ) 的微观组织形成。进一步研究了 CGHAZ 的冲击韧性和抗疲劳裂纹扩展性，阐明了微观结构和力学性能之间的相关性。焊根处的 CGHAZ (CGHAZ-R) 经历了三个焊接热循环，峰值温度分别为 1198、892 和 603 °C。CGHAZ-R处的组织在第一层焊接后演变为细板条贝氏体，然后在第二层焊接后转变为细小的多边形铁素体和粒状贝氏体，并带有细化的马氏体-奥氏体（MA）岛。最后，在第三层焊接过程中对 MA 岛进行回火处理。对于焊趾处的 CGHAZ (CGHAZ-T)，三个热循环的峰值温度分别为 525、1022 和 1250 °C。由于最后一个热循环中的中间冷却速率，其最终的显微组织由板条贝氏体和粒状贝氏体组成。电子背散射衍射结果表明，CGHAZ-R处的高角晶界（HAGB）密度高于CGHAZ-T处。与 CGHAZ-T 相比，CGHAZ-R 具有优异的冲击韧性和较低的疲劳裂纹扩展速率。CGHAZ-R 较高的冲击韧性是由于多边形铁素体较高的塑性变形能力和回火的细 MA 岛。

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Microstructure formation in coarse-grained heat-affected zones (CGHAZs) of bainitic steel welds under multiple welding thermal cycles was investigated by microstructure characterization and finite element modeling. The impact toughness and fatigue crack growth resistance for the CGHAZs were further examined, and the correlation between microstructure and mechanical properties was clarified. The CGHAZ at weld root (CGHAZ-R) experienced three welding thermal cycles with peak temperatures of 1198, 892 and 603 °C, respectively. The microstructure at the CGHAZ-R evolved into fine lath bainite after the first-layer welding, and then transformed into fine polygonal ferrite and granular bainite with refined martensite–austenite (M-A) islands after the second-layer welding. Finally, the M-A islands were tempered during the third-layer welding. For the CGHAZ at the weld toe (CGHAZ-T), the peak temperatures of three thermal cycles were 525, 1022 and 1250 °C, respectively. Its resultant microstructure was composed of lath bainite and granular bainite due to the intermediate cooling rate in the last thermal cycle. Electron backscatter diffraction results show that the density of high angle grain boundary (HAGB) at the CGHAZ-R was higher than that at the CGHAZ-T. Compared to the CGHAZ-T, the CGHAZ-R presented superior impact toughness and a lower fatigue crack growth rate. The higher impact toughness of CGHAZ-R was because of the higher plastic deformation capacity of polygonal ferrite and the tempered fine M-A islands. The retarded fatigue crack growth of CGHAZ-R was due to the numerous crack deflections induced by the high-density HAGB and the high plastic deformability of the polygonal ferrite.