Evolution behavior of oxide inclusions in spring steel deoxidized by silicon during hot rolling
LI Yong-chao1,2, YANG Yu-dan1, LU Cai-ling1, LI Cai-qing1, WANG Wei1,2
1. Technology Center, Henan Jiyuan Iron and Steel Group Co., Ltd., Jiyuan 459000, Henan, China; 2. Henan Special Steel Material Research Institute Co., Ltd., Jiyuan 459000, Henan, China
Abstract：Large non-deformable oxide inclusion is the main cause of spring fatigue failure. The negative effect of inclusion can be alleviated by reducing the size of oxide inclusion after hot rolling by obtaining low melting point plastic inclusion with good deforming properties. In order to study the evolution behavior of oxide inclusion in industrially produced silicon deoxidized spring steel during rolling process, The morphology, composition, size and density of oxide inclusions in continuous casting bloom, rolled billet and wire rod were analyzed by SEM+EDS. The results show that SiO2-Al2O3 and SiO2-Al2O3-CaO were spherical inclusions in the continuous casting bloom, which were basically in the low melting point region. SiO2-Al2O3 and SiO2-Al2O3-CaO inclusions in the rolled billet were long strip shape, and the tadpole-like SiO2 inclusions were also found. There were five kinds of inclusions in the wire rod, four of which were long strip shape inclusions, in addition to SiO2-Al2O3 and SiO2-Al2O3-CaO inclusions,also include SiO2-CaO-MgO and SiO2-Al2O3-CaO-MgO inclusions with high content of CaO and MgO. From the bloom to the rolled billet, the width less than 3 μm inclusions density increased from 1.1 /mm2 to 3.2 /mm2, and the proportion increased from 50% to 80%. In the wire rod the width less than 3 μm inclusions almost reached 100%. The width less than 3 μm inclusions in each stage were mainly composed of SiO2-Al2O3、SiO2-Al2O3-CaO、SiO2. During the rolling process, the aspect ratio of SiO2-Al2O3 and SiO2-Al2O3-CaO inclusions increased continuously, and their deformation index was higher than other types of inclusions. Meanwhile, due to the compression ratio, the deformation index of all inclusions in the rolled billet was higher than those in the wire rod. According to the morphology and composition evolution of the inclusions, combined with the crystallization behavior of the inclusions during heating, it is reasonable to speculate that the crystalline phase precipitated in the continuous casting bloom inclusions during high temperature heating, and the crystalline phase was separated in the subsequent rolling process, forming SiO2 inclusions and high CaO and MgO content composite inclusions.
李永超, 杨玉丹, 卢彩玲, 黎才庆, 王维. 硅脱氧弹簧钢中夹杂物在轧制过程中的演变行为[J]. 钢铁, 2023, 58(2): 83-89.
LI Yong-chao, YANG Yu-dan, LU Cai-ling, LI Cai-qing, WANG Wei. Evolution behavior of oxide inclusions in spring steel deoxidized by silicon during hot rolling[J]. Iron and Steel, 2023, 58(2): 83-89.
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2023, Vol. 58 
