T9A碳素弹簧钢丝脆断原因分析

Cause analysis on brittle fracture of T9A carbon spring steel wire

直径1.7 mm的T9A碳素弹簧钢丝在制簧过程中发生脆断。用扫描电镜对断口形貌进行分析,用金相显微镜观察断口附近横向、纵向及裂纹处金相组织,对断口处非金属夹杂物进行能谱分析,结果表明,钢丝异常组织降低了索氏体基体的塑性。加入钢中的稀土元素具有强烈易氧化的性质,与钢中的氧、硫等元素反应生成稀土夹杂物。钢中氧化物夹杂经轧制破碎及大总压缩率拉拔后,在其周围形成长度0.2μm的微裂纹。制簧过程中,裂纹发生扩展,最终使弹簧脆断。

Brittle fracture occurred when spring was coiled by diameter 1.7mm T9A carbon spring steel wire.Fracture morphology was analyzed by adopting SEM.Microstructure of traverse,longitudinal and crack near fracture was observed.Non-metallic inclusion near fracture was analyzed by using energy spectrum.Results showed that steel wire abnormal structure decreased plastic properties of sorbite matrix.Rare earth element added in steel had the properties of strong oxidizability,the reaction with element of oxygen and sulfur in steel produced rare earth inclusion.Microcrack of length 0.2μm occurred near oxidizing inclusion in steel after it was rolled broken and large total compression ratio drawn.The crack extended in the process of spring production,spring brittle fractured at last.