SCM420合金冷镦钢拉拔断裂原因分析

ANALYSIS OF FRACTURE CAUSES OF COLD HEADING STEEL OF SCM420 ALLOY

SCM420合金冷镦钢在镦制前的第一道拉拔工序发生断裂,拉拔断口为杯锥状,裂纹源位于试样横向1/4直径处;取断口处纵向未腐蚀金相试样,显微镜下观察到在横向直径1/4处有亮白色偏析带,亮白色偏析带上分布有密集的拉拔变形孔洞;腐蚀后,白色偏析带为淡黄色金相组织,经金相检测、显微硬度比对,确定淡黄色组织为块状贝氏体组织,是造成材料拉拔断裂的主要原因。针对此问题,结合生产工艺及客户使用情况,提出避免材料拉拔断裂的相关措施。

The cold heading steel of SCM420 alloy cracked in the first drawing process. The drawing fracture was in theshape of cup cone and the source of the crack was located at diameter of the transverse direction of the specimen. When theuncorroded metallographic from the longitudinal crack was test under the microscope, there was a bright white segregationzone at 1 / 4 of the transverse diameter and drawn deformed holes were densely distributed on the bright white segregationzone. After the corrosion, the white segregation zone became yellowish microstructure, which was determined as massivebainite and the main cause of the material drawing fracture after detected by metallography and micro-hardness comparison.In response to this problem , the production process and the condition of customer usage, related measures to avoid the material drawing fracture were proposed.