23CrNi3Mo钢钎具断裂失效分析

Fracture failure analysis of 23CrNi3Mo steel drill

采用扫描电镜和光学显微镜观察了不同类型23CrNi3Mo钢钎具疲劳破坏缺陷试样断裂形貌及显微组织,分析讨论了缺陷试样失效的原因。结果表明,高疲劳寿命的阿特拉斯钎尾缺陷试样在疲劳源裂纹萌生、扩展过程中,塑性变形特征明显,表明其具有良好的抵抗疲劳裂纹扩展能力,而国内潜孔钻头试样脆性断裂特征明显。两种缺陷试样表面均为高硬度渗碳马氏体层,但阿特拉斯钎尾缺陷试样渗碳层与基体组织的下贝氏体过渡区域较宽,基体以贝氏体组织为主,硬度梯度过渡平缓,具有良好的强度与韧性匹配;而国内潜孔钻头试样的过渡区域较窄,基体是马氏体组织。可见合理的硬度梯度分布对钎具钢强韧性匹配和疲劳寿命影响很大。

Fracture morphology and microstructure of different defect samples of 23CrNi3Mo steel drill tools were observed by optical microscope and scanning electron microscope ( SEM ) .Failure reason of drill tools was discussed .The results show that the Atlas defect sample with high fatigue life has obvious plastic deformation features during fatigue cracks initiating and propagating , and it is benefit to resist fatigue crack propagation .The failed down-the-hole drill sample appears brittle fracture features .Surface of the drill samples both have carburized layer with high hardness .Atlas drill has well matching in the strength of carburized layer and bainite matrix , for the wide transitive zone of low bainite between carburized layer and matrix .So, Atlas drill has well hardness gradient .The down-the-hole drill has narrow transitive zone and martensite matrix .Thus the reasonable hardness gradient affects the matching of strength and toughness and the drill fatigue life greatly .