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万家寨水利枢纽的 1～ 3号机组 ,其发电机转子支持为圆盘式焊接结构。在焊接后曾多次出现裂纹 ,而裂纹均出现在 2 0SiMn钢的近缝区 ,属于冷裂纹性质。经分析 ,2 0SiMn钢材中有一定量的非受控元素 ,如 :Cr、Ni、Mo、Cn ;而受控制元素的含量也均在标准量的上限 ,致使碳当量Cog和裂纹敏感系数Pcm均偏高。可以判定这是产生冷裂纹的主要原因。经过实践认为 ,对 2 0SiMo钢的大件焊接结构 ,当裂纹敏感系数偏大时 ,则焊接的预热温度宜选择在 1 0 0～ 1 2 0℃范围内 ,这样既可防止焊接中产生裂纹 ,而又不致于产生变形。
Unit 1 ~ 3 of Wanjiazhai Water Control Project, whose generator rotor support is disc welded structure. Cracks appeared many times after welding, and the cracks appeared in the near-seam area of 20SiMn steel, which belongs to the cold crack property. According to the analysis, a certain amount of uncontrolled elements such as Cr, Ni, Mo, Cn are present in 20SiMn steel, and the content of controlled elements is also the upper limit of the standard amount, resulting in a carbon equivalent Cog and a crack susceptibility Pcm both high. It can be judged that this is the main reason for cold cracking. After practice, the large welded structure of 20SiMo steel, when the crack sensitivity coefficient is too large, then the welding preheating temperature should be selected in the range of 100 ~ 120 ℃, so as to prevent cracks in the welding , But not to produce deformation.