The cracks of spanners made of hot-rolled round steel 45 were analysed by metallographic examination. The result showed that these cracks arise from stress concentration.

• 摘要45号圆钢加工制成扳手后印痕处发现裂纹。笔者对45号钢扳手进行了金相检验及分析。结果表明：扳手印痕处的裂纹是应力集中造成的。