核电用SA516Gr.70钢板冷弯断裂原因浅析

Brief Analysis on the Cold Bending Fracture Causes of SA516Gr.70 Steel Plate for Nuclear Power

以120 mm厚度正火返红交货态SA516Gr.70核电用钢板为研究对象,借助冷弯试验机、实验室电阻炉、金相显微镜、扫描电镜等设备,对冷弯断裂部位进行金相组织观察、非金属夹杂物和断口分析;对交货态性能检验后的余料进行正火+空冷热处理试验,观察金相组织,发现钢板表面异常增碳,在正火后的冷弯试验中仍然断裂。综合分析认为:SA516Gr.70核电用钢板交货态冷弯性能不合格的原因为钢板表面马氏体层比较厚、强度过高,在冷弯过程中塑性变形能力差,造成表面开裂。核实钢板取样位置后,在远离冒口处重新取样进行冷弯试验,冷弯性能合格。

Taking the 120 mm thickness SA516Gr.70 steel plate for nuclear power in the delivery condition of re-tempering after normalizing as the research object,metallographic structure observation,non-metallic inclusion analysis and fracture analysis are performed on cold bending rupture portion by means of cold bending testing machine,lab electric resisfance furnace,metallographic microscope,scanning electron microscope and other equipments.Heat treatment test of normalizing and air cooling is carried out on the remaining sample after the mechanical properties test in delivery condition,the metallographic structure observation reveals abnormal carburization,the sample still ruptures in cold bending test even after normalizing.The comprehensive analysis concludes that the surface rupture due to the thick martensite layer at the plate surface,excessive higher strength,poor plastic deformation ability during cold bending is the cause of cold bending disqualification of SA516Gr.70 steel plate for nuclear power in delivery condition.After verifying the sampling position,cold bending test is carried out by taking new cold bending sample at the position away from the riser,the cold bending properties are quaified.