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 ,说明整体失稳解理断裂的控制环节为脆硬粒子开裂 ;当晶粒直径较大时 ,脆硬粒子临界开裂应力就小于材料解理断裂应力 ,说明脆硬粒子尺寸的微裂纹向晶粒中扩展成为材料整体失稳解理断裂的控制环节 The brittle and hard particles in steel have a direct influence on the cleavage and brittle fracture of steel, most of the cleavage fracture sources occur on the brittle and hard particles. According to the thermodynamic model formed by the micro-cracks, the elasticity Strain energy, the performance of dislocation plug elasticity, and the generated surface energy, the crack formation mechanism of brittle and hard particles is analyzed.The model calculations show that both normal stress and dislocation plugging force are necessary for brittle hard particle cracking, The calculation of the critical condition of the brittle-hard particle cracking is also given. The calculation results show that the critical cracking stress of the brittle-hard particle depends not only on the size and surface energy of the brittle-hard particle but also on the grain diameter. When the particle diameter is small, the relationship is consistent with the experimentally determined cleavage fracture stress and the grain size, which shows that the control part of the overall instability cleavage fracture is brittle and hard particle cracking. When the grain diameter is large, The critical cracking stress of hard particles is less than the cleavage stress of the material, which indicates that the micro-cracks of brittle hard particles expand into the grains and become the control link of the overall instable cleavage of the material