Wang Zhenhua, Wang Yong
School of Mechanical Engineering, Yanshan University, Qinhuangdao 066004, China.
State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, China.
Materials (Basel). 2019 Apr 10;12(7):1175. doi: 10.3390/ma12071175.
Superheavy forgings are increasingly used in the nuclear industry. The strain rate is extremely low during hot forging due to the huge size of the superheavy forging; in fact, the surface temperature of the forging decreases obviously during each deformation step. Hot-deformation behavior differs from that of isothermal deformation. In this study, 18Mn18Cr0.6N steel was selected as a model material. Hot-compression tests were conducted using a Gleeble 3800 simulator at a strain rate of 10 s and continuous cooling rates of 0.0125 Ks and 0.025 Ks. The microstructure was observed using electron backscatter diffraction analysis and transmission electron microscopy. The flow stress increased with increasing strain: the higher the cooling rate, the higher was the hardening rate. Continuous cooling inhibited dynamic recrystallization by delaying its nucleation. The subgrain/cell size increased linearly with increasing final temperature of deformation in the temperature range 1273 to 1448 K. An intense <001> texture formed in 0.8-strained specimens and the matrix exhibited a low Taylor factor orientation. Most dislocations were separately distributed in subgrains and did not entangle with each other or with the subgrain boundary. Dislocation arrays transferred easily through boundaries and dislocation accumulation at boundaries was weak. This study contributes to understanding the hot-forging process of superheavy forgings.
超重型锻件在核工业中的应用越来越广泛。由于超重型锻件尺寸巨大，热锻过程中的应变速率极低；实际上，在每个变形步骤中，锻件的表面温度都会明显下降。热变形行为与等温变形不同。在本研究中，选择18Mn18Cr0.6N钢作为模型材料。使用Gleeble 3800模拟器以10 s的应变速率以及0.0125 K/s和0.025 K/s的连续冷却速率进行热压缩试验。使用电子背散射衍射分析和透射电子显微镜观察微观结构。流变应力随应变增加而增大：冷却速率越高，硬化速率越高。连续冷却通过延迟动态再结晶的形核来抑制动态再结晶。在1273至1448 K的温度范围内，亚晶粒/胞尺寸随变形终温的升高呈线性增加。在应变0.8的试样中形成了强烈的<001>织构，基体表现出低泰勒因子取向。大多数位错分别分布在亚晶粒中，彼此之间以及与亚晶粒边界不缠结。位错阵列很容易穿过边界，边界处的位错堆积较弱。本研究有助于理解超重型锻件的热锻过程。
