钢中脆硬粒子裂纹形成机理

钢中的脆硬粒子对钢的解理脆断有直接的影响，解理断裂源大都发生在脆硬粒子上.根据微裂纹形成的热力学模型，利用钢中脆硬粒子开裂时所释放的弹性应变能、位错塞积弹性能，所产生的表面能，对脆硬粒子裂纹形成机理进行分析.模型计算表明，正应力和位错塞积力都是脆硬粒子开裂的必要条件，这与实验事实相符；同时给出脆硬粒子开裂的临界条件计算方法，计算发现，脆硬粒子临界开裂应力不仅取决于脆硬粒子尺寸及表面能，而且与晶粒直径有一定的相关关系，当晶粒直径较小时，这种关系与实验测定的材料解理断裂应力与晶粒尺寸的关系一致，说明整体失稳解 关键词： 解理断裂 裂纹形核 脆硬粒子

Mechanism of crack formation at hard brittle particles in steels

Hard brittle particles can have an important influence on cleavage fracture in steels, and can act as cleavage initiators. Considering the strain elastic energy and the dislocation pile-up elastic energy to be released, and surface energy to be produced, during the hard brittle particle cracking, the mechanism of crack formation at hard brittle particles in steels was studied by a thermal dynamic model. It has been demonstrated theoretically that both normal stress and dislocation pile-up at the hard brittle particles are necessary for its cracking. Furthermore, a criterion for hard particle cracking has been derived, by which the critical cracking stress for the hard brittle particle was predicted not only to depend on its size and surface energy, but also to have correlations with the grain size. Their correlations are the same as the relationship between the fracture stress determined experimentally and the grain size in the case of finer grain constituents. It can be indicated that in such a situation the hard brittle particle cracking is responsible for the ultimate cleavage fracture of the material. In the case of coarser grain constituents, the critical cracking stress for the hard brittle particle is smaller than the fracture stress determined experimentally. This indicated that propagating a particle-size crack into the surrounding ferrite matrix is the critical event for the ultimate failure of the material.