Control mechanism of compound sulfides in steel for automotive control arms containing Ca
LU Jin-long1,2, QIU Wen-sheng1, CHENG Guo-guang2, LONG Hu1, LI Yao2
1. Technology and Research Center, Guangdong Shaogang Songshan Co., Ltd., Shaoguan 512123, Guangdong, China;
2. State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Beijing 100083, China
Abstract：There is a large cutting workload during automotive control arm manufacturing processes because of its complex shape. In order to increase the cutting performance of parts, a small amount of Ca element is further added into steel with 0.03% sulfur, so that common slender strip MnS would be transformed into spindle (Ca, Mn)S. However, when the sulfur mass fraction is 0.03%, the solubility of Ca element in molten steel is very low, and the generation of pure (Ca, Mn)S during cooling and solidification processes is quite small. Therefore, controlling mechanism of sulfide morphology is proposed to induce (Ca, Mn)S to nucleate and grow on oxides containing CaO formed in molten steel, promoting generation of a large number of duplex compound sulfides. In order to obtain the formation mechanism of optimal duplex compound sulfides, 3 commercial steels with different smelting processes were selected. Morphologies and component characteristics of typical compound sulfide were investigated with scanning electron microscope and energy spectrum analysis (SEM-EDS), size characteristics were manually measured, and evolution behaviors of inclusions during cooling and solidification were calculated by thermodynamic software FactSage. The results show that inside oxides of compound sulfides are mainly Al2O3 or magnesium aluminum spinel with low MgO ratio, wrapped sulfides are pure MnS with long strip shape after rolling in the steel without Ca treatment. After Ca treatment, there are two different compound sulfides.One is typical D or Ds type inclusions, with high CaO ratio inside oxides and high CaS ratio wrapped (Ca, Mn)S, basically no deformation. The other is spindle-shaped, with low CaO ratio inside oxides and low CaS ratio wrapped (Ca, Mn)S. Controlling the proper proportion of CaO in liquid oxides of Ca-treated steel is the key to obtain a large amount of spindle-shaped sulfides in steel, owing to high sulfide nucleation ability of core oxides and proper CaS proportion in peripheral (Ca, Mn)S. When the Ca/S ratio in steel is about 0.07, the optimal Ca content in peripheral sulfide is about 2%-5%.
鲁金龙, 丘文生, 成国光, 龙鹄, 李尧. 含Ca汽车控制臂用钢中复合硫化物控制机理[J]. 钢铁, 2022, 57(5): 118-128.
LU Jin-long, QIU Wen-sheng, CHENG Guo-guang, LONG Hu, LI Yao. Control mechanism of compound sulfides in steel for automotive control arms containing Ca[J]. Iron and Steel, 2022, 57(5): 118-128.
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