大规格5CrNiMo钢锻件白点成因及预防措施

Causes and Preventive Measures of White Spots on Large-sized 5CrNiMo Steel Forgings

低合金5CrNiMo模具钢形成白点的倾向比较大。白点显著降低钢材的力学性能,破坏钢材基体的连续性,往往是疲劳裂纹的发源地。一般H含量过高和内应力的存在增大了白点的形成几率,围绕H含量和内应力的控制进行了研究。结果表明,使用干燥的原材料、合理的VD真空脱气工艺,使H含量降至2.0×10^(-6)以下,配合正火和去氢退火的热处理工艺模式,控制冷却速度,有效减少组织转变过程中的内应力,实现了大规格锻件无白点缺陷的合格生产。

Low alloy 5CrNiMo die steel has a relatively large tendency to form white spots.White spots significantly reduce the mechanical properties of steel,destroy the continuity of the steel substrate,and are often the origin of fatigue cracks.Generally,too high H content and the existence of internal stress increase the probability of white spot formation.The control of H content and internal stress has been studied.The results show that the use of dry raw materials and reasonable VD vacuum degassing process can reduce the H content to less than 2.0×10^(-6),and cooperate with the heat treatment process mode of normalizing and dehydrogenation annealing,and control the cooling rate and effectively reduce the internal stress during microstructure transformation,and the qualified production of large-scale forgings without white spot defects has been realized.