大型锻件内部脆性夹杂物边界裂纹是影响大型锻件疲劳寿命与冲击性能的主要缺陷。热锻变形过程中，脆性夹杂物周围区域的应力场是影响边界裂纹闭合的主要因素之一。为研究应力场的影响，给出平均相对球应力的定义及其数学表达式，并借助数值模拟研究不同应力场的平均相对球应力对脆性夹杂物边界裂纹的影响。结果表明，只有当脆性夹杂物周围区域的应力场的平均相对球应力代数值小于其临界值，并产生一定大小的变形量，才能使脆性夹杂物边界处的原生裂纹锻合。利用专门设计的试件和型砧，在Gleeble-3180热模拟试验机上进行热压缩变形试验，扫描电镜上观察压缩后试件内部脆性夹杂物边界裂纹的情况。试验结果支持数值模拟结果。

Cracks between the inclusion and the matrix metal are major defects affecting the forgings’ fatigue life and impact properties. In hot forging processes, the stress field around a brittle inclusion is one of the most important factors for crack coalescence. In order to study the stress field’s influence on crack initiation, the definition of average relative spherical stress(ARSS) and its mathematical expression are given. Influences of ARSSes of various stress fields on matrix metal-brittle inclusion crack growth are investigated by way of numerical simulation. Results show that existing matrix metal-brittle inclusion cracks can coalesce only when the algebraic value of the ARSS of the stress field around the inclusion is smaller than its critical value and there exists a certain amount of deformation. Hot compression test are done using dedicated specimens and anvils on a Gleeble-3180 thermo-mechanical simulator. Cracks before and after compression tests in the specimens are observed with a scanning electron microscope. Experimental results agree well with the numerical ones.