将两种碳素结构钢(15,45)和Cr25Ni20不锈钢的试样在扫描电镜中进行拉伸试验,并对它们的延性断裂的微观过程进行了动态观察。结果表明,裂纹总是优先在夹杂物与金属基体的界面上,孪晶与基体之间的界面上以及σ相与基体之间的界面上成核。前二者的裂纹沿界面传播、钝化并沿拉伸方向变宽;对于后者来说,裂纹成核后,在σ相内解理扩展。最后,裂纹沿切变方向彼此连接并导致断裂。
The microprocess of failure by ductile fracture under tensile stress in speci-mens of two carbon steels containing 0.15% and 0.45% C respectively and of a25Cr20Ni type stainless-steel has been examined in-situ in SEM. Cracking wasnucleated preferentially in three different ways, e.g., at the inclusion/matrix, atthe twin/matrix boundary and at the σ-phase/matrix interface. In both the firstand second cases, the cracks were formed at the inter-faces and widened in thesteel matrix along the direction of applied stress. In the third case the crackswere nucleated at the σ-phase/matrix interface and grown into σ-phase particle.As the applied stress became greater and greater, other oracks nearby appear tocoalescence along the shear direction of the steel with the result of total failure.
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