Formation mechanism and improvement of detected defects in large forged Cr5 back-up roll
ZHANG Wei-feng1,2, SHI Ru-xing2, ZHANG Yan-ling1, WANG Guan-bo1, CHENG Guo-guang1, WANG Peng-fei2
1. State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Beijing 100083, China; 2. Research Institute of Casting and Forging, Luoyang CITIC HIC Casting and Forging Co., Ltd., Luoyang 471039, Henan, China
Abstract:Based on ultrasonic flaw detection on the large forged Cr5 back-up roll during manufacturing process, the flaw detection was analyzed by anatomical sampling, IF→LF→VD→VC smelting process of forged roll was traced and sampled, defects type on the forged roll and source of the whole smelting process was determined by scanning electron microscope (SEM) and energy dispersive x-ray spectroscopy (EDS). Combined with FactSgae 8.1 software, the formation mechanism and control of flaws leading to the ultrasonic flaw detection were calculated theoretically. The research results show that the defects leading to the incompatibility of flaw detection are linearly aggregated SiO2-MnO-Al2O3 large-size inclusions, the size of single particle can reach 200 μm, the compositions of inclusion of flaws are consistent with the inclusions before pouring of vacuum casting(VC). A large amount of SiO2-MnO-Al2O3 inclusions are found before the tapping of IF and still a few remained at the end of LF process, while large SiO2-MnO-Al2O3 inclusions are entrapped to the roll melt during VD process under large stirring conditions. SiO2-MnO-Al2O3 inclusions with a low contact angle can be well wetted by the liquid steel, it is difficult to float and remove from the liquid steel during the LF refining process. The inclusions are aggregated and remained during the solidification process to form the area of large inclusions and lead to ultrasonic flaw detection after forging eventually. Thermodynamic calculations show that SiO2-MnO-Al2O3 liquid inclusions will be stable with the steel composition containing mass fraction of Al below 0.003% and O above 0.015%, and SiO2-MnO-Al2O3 liquid inclusions are stable with a higher O content with increasing of Al content in liquid steel.SiO2-MnO-Al2O3 phase stable field will disappear with Al increasing to 0.023% in the liquid steel. Before the tapping of IF and in the subsequent processes, controlling the Al mass fraction in the liquid steel above 0.023% can effectively modify the SiO2-MnO-Al2O3 liquid inclusions into Al2O3 or Al2O3-rich inclusions with a good removability. Practical results show that the unqualified rate of ultrasonic flaw detection of Cr5 back-up roll forgings is reduced.
张威风, 石如星, 张延玲, 王冠博, 成国光, 王鹏飞. Cr5大型锻钢轧辊探伤缺陷的形成机理及控制[J]. 钢铁, 2022, 57(6): 91-99.
ZHANG Wei-feng, SHI Ru-xing, ZHANG Yan-ling, WANG Guan-bo, CHENG Guo-guang, WANG Peng-fei. Formation mechanism and improvement of detected defects in large forged Cr5 back-up roll[J]. Iron and Steel, 2022, 57(6): 91-99.
[1] 陈国浩. 轧辊锻件用钢的现状和发展[J]. 钢铁, 1996,31(3):75. (CHEN Guo-hao. Status and trend of steel for roll mills roll forgings[J]. Iron and Steel, 1996, 31(3): 75.) [2] 贾蓉, 李旭东, 李俊琛, 等. 我国Cr5系钢轧辊工艺研究进展[J]. 热加工工艺,2013,42(9):62.(JIA Rong, LI Xu-dong, LI Jun-chen, et al. Present research situation on Cr5 series large back-up roll process in China[J]. Hot Working Technology, 2013, 42(9):62.) [3] 薛永栋, 张威风, 辛雪倩, 等. 50Cr5MoV轧辊用钢氧和夹杂物控制实践[J]. 炼钢,2020, 36(1):67.(XUE Yong-dong, ZHANG Wei-feng, XIN Xue-qian, et al. Practise on control of oxygen and inclusions for 50Cr5MoV backup roll[J]. Steelmaking, 2020,36(1):67.) [4] 薛永栋, 庞庆海. Cr5锻钢轧辊夹杂性缺陷分析[J]. 热加工工艺, 2018, 47(13):253.(XUE Yong-dong, PANG Qing-hai. Inclusion defects analysis of Cr5 forged backup roll[J]. Hot Working Technology,2018,47(13):253.) [5] 赵欣, 门正兴, 甘红胜,等. 特大型轧辊超声检测缺陷分析与工艺优化[J]. 大型铸锻件, 2015(2):17.(ZHAO Xin, MEN Zheng-xing, GAN Hong-sheng. et al. Defect analysis in ultrasonic test and process optimization for super large backup roll[J]. Heavy Casting and Forging, 2015(2):17.) [6] 董文斐, 张广威, 李春辉,等. 轧辊辊身表面缺陷分析[J]. 重型机械, 2014(3):76.(DONG Wen-fei, ZHANG Guang-wei, LI Chun-Hui. et al. Analysis on surface defects of backup roll[J]. Heavy Machinery, 2014 (3):76.) [7] 叶明峰, 吴光亮. 50Cr5MoV锻钢轧辊表面点状缺陷分析及探讨[J].物理测试,2017,35(4):36.(YE Ming-feng, WU Guang-liang. Analysis and discussion of the spot defects on the surface of 50Cr5MoV forged steel roll[J].Physics Examination and Testing, 2017, 35(4):36.) [8] 陈伟,王永,韩剑. 工作辊在冷轧过程中辊身剥落原因分析[J]. 金属热处理,2020,45(6):232.(CHEN Wei, WANG Yong, HAN Jian. Cause analysis on spalling of working roll during cold rolling[J]. Heat Treatment of Metal, 2020,45(6):232.) [9] 董宝龙. 支承辊外露夹杂原因分析及炼钢工艺优化[J].大型铸锻件,2019(2):46.(DONG Bao-Long. Cause analysis on exposed inclusions and steel melting process optimization of backup roll[J]. Heavy Casting and Forging, 2019(2):46.) [10] 邓志银,周业连,朱苗勇. 铝镇静钢中夹杂物形态对其去除的影响[J].钢铁,2018,53(1):34.(DENG Zhi-yin,ZHOU Ye-lian,ZHU Miao-yong. Effect of state of inclusions on removal in Al-killed liquid steel[J]. Iron and Steel,2018,53(1):34.) [11] 邓志银,戈文英,胡博文,等.合金化对铝镇静钢中夹杂物的影响[J].钢铁,2019,54(10):30.(DENG Zhi-yin,GE Wen-ying,HU Bo-wen, et al. Effect of alloying on inclusion in aluminum killed steel by a ferrochromium alloy[J]. Iron and Steel,2019,54(10):30.) [12] 焦魁明. 镁处理对40Cr铝镇静钢中夹杂物的影响[J].钢铁,2020, 55(12):39. (JIAO Kui-ming. Effect of magnesium treatment on inclusions in 40Cr Al-killed steel[J]. Iron and Steel, 2020, 55(12):39.) [13] WANG Qi-ming, CHENG Guo-guang, LI Jing-yu, et al. Formation mechanism of large inclusions in 80t 20Cr-8 Ni stainless steel casting for nuclear power[J].Steel Research International,2019,90(12):1. [14] Vasundhara Singh, Rashul khan, Bharath Bandi, et al. Effect of non-metallic inclusions (NMI) on crack formation in forged steel[J]. Materials Today: Proceedings,2021,41(5):1096. [15] 王新华,姜敏,于慧香,等.超低氧特殊钢中非金属夹杂物研究[J].炼钢,2015, 31(6):1.(WANG Xin-hua,JIANG Min,YU Hui-xiang, et al. Investigation on non-metallic inclusions in ultra-low oxygen special steels[J]. Steelmaking, 2015,31(6):1.) [16] Hidekazu Todoroki, Fumiaki kirihara, Yuichi kanbe, et al. Effect of compositions of non-metallic inclusions on CC nozzle clogging of a Fe-Cr-Ni-Mo system stainless steel[J].Tetsu-to-Hagané, 2014, 100(4):539. [17] LI Xiao-ao, WANG Nan, CHEN Min, et-al. Tracking large-size inclusions in Al deoxidated tinplate steel in industrial practice[J]. ISIJ International. 2021,61(7):2074. [18] Gavin Parry, Oleg Ostrovski. Wetting of solid iron, nickel and platinum by liquid MnO-SiO2 and CaO-Al2O3-SiO2[J]. ISIJ International, 2009, 49(6):788. [19] 周业连,邓志银,朱苗勇. 固/液态夹杂物穿过钢渣界面的分离机理[J].过程工程学报,2018, 18(1):96. (ZHOU Ye-lian, DENG Zhi-yin, ZHU Miao-yong. Separation mechanism of solid/liquid inclusions transfer at steel-slag interface[J]. The Chinese Journal of Process Engineering, 2018, 18 (1):96.) [20] Hirotada Arai, Naomi Lida, Katsudishi Matasumoto, et al. Effect of particle contact angle on characteristics of adhesion and removal of suspended particles in liquid by bubble[J]. Tetsu to Hagane,2007,93(1):1. [21] Hirotada Arai, Katsutoshi Matsumoto, Shin-ichi Shimasaki, et al. Model experiment on Inclusion removal by bubble flotation accompanied by particle coagulation in turbulent flow[J]. ISIJ International, 2009,49(7):965. [22] Strandh J, Nakajima K, Eriksson R. A mathematical model to study liquid inclusion behavior at the steel-slag interface[J]. ISIJ International, 2005,45(12): 1838.