CAJ | 학술논문

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。
대형단건내부취성협잡물변계렬문시영향대형단건피로수명여충격성능적주요결함。열단변형과정중，취성협잡물주위구역적응력장시영향변계렬문폐합적주요인소지일。위연구응력장적영향，급출평균상대구응력적정의급기수학표체식，병차조수치모의연구불동응력장적평균상대구응력대취성협잡물변계렬문적영향。결과표명，지유당취성협잡물주위구역적응력장적평균상대구응력대수치소우기림계치，병산생일정대소적변형량，재능사취성협잡물변계처적원생렬문단합。이용전문설계적시건화형침，재Gleeble-3180열모의시험궤상진행열압축변형시험，소묘전경상관찰압축후시건내부취성협잡물변계렬문적정황。시험결과지지수치모의결과。
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.