低碳贝氏体钢低温CTOD试验断口分离分析

Fracture separation in low temperature CTOD of low-carbon bainite steels

通过对低碳贝氏体钢在-20℃CTOD试验中出现的分离断口进行微观分析,研究了断口分离和失稳断裂的原因。结果表明,断口分离面均为脆性断裂,至主断面为韧性扩展,分离裂纹产生的主要因素不是夹杂物,而是材料内部的带状组织和成带状的硬相组织受三维应力作用的结果。拉伸材料的分离裂纹是在达到一定抗拉强度之后开始萌生和扩展,不影响材料的使用性能。在断裂韧度试验中,一方面分离裂纹能降低材料裂纹尖端的三维应力约束,提高材料的韧性;另一方面较大程度的分离裂纹,减小了裂纹形核功和扩展功,诱发主裂纹的失稳扩展。

The separation fracture and instability fracture in-20 ℃ CTOD test of low-carbon bainite steel is investigated by means of micrograph analysis.It is found that the separation fracture is macro-brittleness,and its main crack section is toughness growth,inclusions are not main factors which cause separation.Separation crack is caused by the effect of 3D stress on band microstructure and hard phase microstructure within the material.It is showed that the separation crack of tensile materials begin to form after achieving fixed tensile strength and then grow up,and it has no effects on applied properties of materials.On the one hand,the separation crack in the fracture toughness testing can reduce 3D stress of constraint and improve material toughness.On the other hand,bigger separation crack reduces the work of crack initiation and growth,and cause instable propagation of the main crack.