Simulation Research on Solidification Defects and Microstructure of Mn18Cr18N Hollow Ingots
Author of the article:ZHU Hua;ZHANG Bo;TIAN Jihong;LIU Jiachen;CHEN Huiqin
Author's Workplace：School of Materials Science and Engineering,Taiyuan University of Science and Technology,Taiyuan 030024,China;Aotu Personalized Education,Wuhan 430000,China
Key Words：hollow ingots pouring with bottom gating system porosity defects columnar grains equiaxed grains
Abstract：
The solidification process of 4.2 t Mn18 Cr18 N hollow ingot with conventional bottom gating system was simulated, and the influence of pouring and cooling parameters on solidification defects and microstructure evolution was analyzed. The results show that cooling conditions of the inner and outer walls has intensive effect on solidification sequence and microstructure. As the heat transfer coefficient of the inner and outer walls decreases, the solidification position finally moves to the side with low heat transfer coefficient, and the transformation(CET) of columnar crystals is advanced, and the length of columnar crystals decreases. Under the condition of low temperature of 1 415 C and low pouring velocity of 25 kg/s, when the heat transfer coefficient ratio of inner and outer walls is 2 ∶5, the ingot gradually solidifies radially from the lateral wall thickness of inner and outer walls. The final solidification position is at the 1/4~1/3 wall thickness near the inner wall, where there is a certain degree of loose defects, and the solidification structure is equiaxed grains. The columnar crystal structure is found on the inner and outer wall, and the proportion of the two structures is similar on the wall thickness section. In nucleation parameters, shape nucleation density is the main parameter that affects CET and grain size, while surface nucleation density can control the primary dendrite spacing of columnar grains.
