摘要
针对高碳铬轴承钢棒材碳化物带控制要求,研究了大方坯凝固结构中点状偏析在轧材组织中的遗传性及连铸工艺参数对铸态点状偏析的影响。采用低倍侵蚀、枝晶侵蚀、电子探针元素扫描、统计分析等手段,分析了点状偏析的形貌特征及分布,对比研究了不同工艺条件下铸坯中点状偏析在尺寸、数量及成分上的差异性及其与后续轧材碳化物带宽度的关联性。结果表明,高碳铬轴承钢铸坯中心等轴晶区存在大小不一的点状偏析,其中均存在较突出的C、Cr元素正偏析。通过调控浇注过热度、结晶器电磁搅拌(M-EMS)、浸入式水口使用工艺,可以有效控制大方坯凝固结构中的等轴晶区,进而改善点状偏析形貌和后续棒材碳化物带宽度。其中,在较高过热度、关闭结晶器电磁搅拌和采用4孔水口旋转45°的安装工况下,大方坯铸态中心等轴晶率较原工艺降低26.80个百分点,点状偏析最大尺寸由3.94 mm降低为1.45 mm,等效直径100μm以上的点状偏析数量也由314个降为54个。2种改进连铸工艺条件下的大方坯棒材中碳化物带最大平均带宽由原工艺的105.75μm分别降低为57.25μm和75.75μm,产品碳化物带评级合格率得到显著提升。
To control the extremely harmful carbide bandings segregation in as-rolled bearing steel,the effect of casting process parameters on the spot-segregation in the initial solidification structure had been studied.It is realized that the semi-macrosegregation in the as-cast steel equiaxed crystal zone are the source of the band defects in the following rolled products.Accordingly,the spot segregation in bearing steel bloom casting and banded segregation defects in the rolled bar were experimentally studied to reveal the differences in size,quantity,and composition under different casting processes.The morphology and distribution of the spot-segregation in the experimental bloom castings were studied using hot-acid etching,dendritic etching,electron-probe micro-analysis(EMPA),and statistical calculations.It is found that there is different size of spot-segregation in the equiaxed crystal zone of the high-carbon chromium bearing steel bloom,in which severe positive segregation of C and Cr elements is observed.By a set of improved continuous casting processes with higher superheat,turned-off M-EMS and nozzle installation in 45°direction,the equiaxed crystal rate is reduced by 26.80 percent point compared with the original process.The maximum size of spot-segregation in equiaxed crystal zone is reduced from 3.94 mm to 1.45 mm in the control group,and the number of spot-segregation is reduced from 314 to 54.The maximum average bandwidths of the carbide bandings in process 1 and 2 are reduced from 105.75μm to 57.25μm and 75.75μm,respectively.As a result,the qualified rate based on product carbide bandings evaluation is significantly improved.
作者
沈腾飞
张壮
牛帅
江野
王德炯
张家泉
SHEN Tengfei;ZHANG Zhuang;NIU Shuai;JIANG Ye;WANG Dejiong;ZHANG Jiaquan(School of Metallurgical and Ecological Engineering,University of Science and Technology Beijing,Beijing 100083,China;Special Steel Department,Nanjing Iron and Steel Co.,Ltd.,Nanjing 210035,Jiangsu,China)
出处
《中国冶金》
CAS
CSCD
北大核心
2023年第6期54-64,80,共12页
China Metallurgy
关键词
轴承钢
大方坯
凝固组织
点状偏析
碳化物带
bearing steel
bloom casting
solidification structure
spot-segregation
carbide bandings
作者简介
沈腾飞(1997-),男,硕士生,E-mail:1148595590@qq.com;通信作者:张家泉(1963-),男,博士,教授,E-mail:jqzhang@metall.ustb.edu.cn。
