Low carbon bainitic steel (LCBS) with excellent combined properties is the first choice for materials of pipeline transiting geological disaster. However, welding will worsen its toughness. In this paper, three kinds of welding heat input were designed to study the relationship between the toughness and microstructure in the coarse grain zone of welding heat affect zone (CGHAZ) of LCBS. The evolution characteristics of the microstructure of LCBS and the CGHAZ, and impact fracture were investigated by optical microscopy (OM), scanning electron microscopy (SEM). The results indicated that microstructure of LCBS consists mainly of bainite ferrite (BF) and granular bainite (GB). Heat input for 22 kJ/cm, the original austenite grains become coarsening, the microstructure is a small amount of quasi polygonal ferrite (QF) and polygonal ferrite (PF), which exhibits low Charpy impact toughness. However, for heat input of 19 kJ/cm, the degree of grain coarsening is small and distribution of martensite-austenite (M-A) constituents is the chain. The statistics of image software show that with the increase of heat input (16–22 kJ/cm), the average grain size of original austenite is basically the same (25 um), which is mainly due to Nb solute drag restraint the growth of austenite grain.

中文翻译：

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不同焊接能量对低碳贝氏体钢热影响区组织和韧性的影响

综合性能优良的低碳贝氏体钢（LCBS）是管道穿越地质灾害的首选材料。但是，焊接会使它的韧性变差。本文设计了3种焊接热输入，研究了LCBS焊接热影响区（CGHAZ）粗晶区韧性与显微组织的关系。通过光学显微镜（OM）、扫描电子显微镜（SEM）研究了LCBS和CGHAZ的显微组织演变特征和冲击断裂。结果表明，LCBS的显微组织主要由贝氏体铁素体（BF）和粒状贝氏体（GB）组成。热输入为22 kJ/cm，原奥氏体晶粒变粗化，显微组织为少量准多边形铁素体（QF）和多边形铁素体（PF），其表现出低夏比冲击韧性。然而，对于 19 kJ/cm 的热输入，晶粒粗化程度较小，马氏体-奥氏体 (MA) 成分的分布呈链状。图像软件统计显示，随着热输入的增加（16～22 kJ/cm），原始奥氏体的平均晶粒尺寸基本相同（25 um），这主要是由于Nb溶质阻力抑制了奥氏体的生长。奥氏体晶粒。