Abstract：Surface crack,which generates in the process of hot charging,restricts the application of hot charging,and surface quenching technology can effectively improve this problem. This paper takes a 180 mm×180 mm cross-section billet caster as the object,and selects 40Cr steel as quenching experiment steel to carry out off-line quenching experiment research,combined with analysis of microstructure and heat transfer of quenching and self-tempering process by means of optical microscope and numerical simulation technique,the influence of quenching on the surface microstructure evolution of the billet was studied. The results showed that surface quenching can effectively eliminate the film-like ferrite,and form a certain hardening depth. In the quenching time range of 40-100 s,a tempered sorbite layer with the depth of 2-10 mm can form at the surface layer,and film-like ferrite begins to form at the depth of 19-38 mm from the surface. At the same time,with the extension of quenching time,the quenching depth increases significantly. Based on the purpose of quenching,it is proposed to use the depth at which film-like ferrite begins to form as the basis for judging the quenching depth of casting billet after quenching. Combined with heat transfer analysis and types and characteristics of the microstructure after quenching,two online quenching process schemes were proposed. The expected surface microstructure after quenching is refined ferrite with pearlite(weak cooling scheme) and tempered sorbite(strong cooling scheme) respectively. For the weak cooling scheme,the expected hardening depth is 7-13 mm,for the strong cooling scheme,the expected hardening depth can reach 2-10 mm(taking tempered sorbite as the criterion for determining the hardening depth) or 19-38 mm (taking film-like ferrite as the criterion for determining the hardening depth). Based on the off-line quenching experiment combined with heat transfer analysis in this paper,the determined on-line quenching process schemes can make a certain theoretical foundation for the implementation of surface quenching technology at the plant.
[1] 罗刚,梁祥祥,张剑桥,等.中断淬火的温度对淬火-配分低铬铁素体不锈钢组织和性能的影响[J].上海金属,2021,43(5):45.(LUO Gang,LIANG Xiang-xiang,ZHANG Jian-qiao,et al. Effect of temperatures at the time of quenching interruption on microstructure and properties of a low-chromium ferritic stainless steel quenched and partitioned[J].Shanghai Metals,2021,43(5):45.) [2] 兰伟,余驰斌,鲍思前,等. 直装加热过程连铸坯应力场分析[J]. 钢铁研究,2011,39(5):11.(LAN Wei,YU Chi-bin,BAO Si-qian,et al. Analysis of stress filed of billet during its heating in the CC-DHCR process[J]. Research on Iron and Steel,2011,39(5):11.) [3] 罗志文. 50钢铸坯冷却过程断裂分析[J]. 中国冶金,2017,27(3):40.(LUO Zhi-wen. Fracture analysis in cooling process of 50 steel slab[J]. China Metallurgy,2017,27(3):40.) [4] 刘思雨,朱玉员,付建勋,等. 直接热装轧制的X60微合金钢连铸坯红送裂纹形成机制的研究[J]. 上海金属,2018,40(4):85.(LIU Si-yu,ZHU Yu-yuan,FU Jian-xun,et al. Formation mechanism of hot charging cracks in continuously cast billet of X60 micro-alloy steel during direct hot rolling[J].Shanghai Metals,2018,40(4):85.) [5] 张新文,江宏亮,轩康乐,等. 热轧圆钢Q345E表面裂纹的研究与控制[J]. 中国冶金,2021,31(4):44.(ZHANG Xin-wen,JIANG Hong-liang,XUAN Kang-le,et al. Research and control of surface crack of hot rolled round steel Q345E[J]. China Metallurgy,2021,31(4):44.) [6] 王宏明,李桂荣. 热送热装工艺中板坯出连铸机温度的影响因素分析[J]. 上海金属,2003(2):24.(WANG Hong-ming,LI Gui-rong. Analysis of the factors affecting the temperature of slab out of CCM during hot delivery and charging process[J].Shanghai Metals,2003(2):24.) [7] 王新东,常金宝,李杰. 棒材高效低碳生产技术与集成化应用[J]. 钢铁,2021,56(8):26.(WANG Xin-dong,CHANG Jin-bao,LI Jie. High efficiency and low carbon production technology and integrated application of bar[J]. Iron and Steel,2021,56(8):26.) [8] 张开发,王明林,张慧,等. 热送热装工艺的数值模拟[J]. 连铸,2021,46(1):26.(ZHANG Kai-fa,WANG Ming-lin,ZHANG Hui,et al. Numerical simulation of heat transfer and heat charging process[J]. Continuous Casting,2021,46(1):26.) [9] 王新东,常金宝,李杰. 小方坯连铸-轧钢“界面”技术的发展与应用[J]. 钢铁,2020,55(9):125.(WANG Xin-dong,CHANG Jin-bao,LI Jie. Development and application of "Interface" technology of billet continuous casting-rolling[J]. Iron and Steel,2020,55(9):125.) [10] Kato T,Ito Y,Kawamoto M,et al. Prevention of slab surface transverse cracking by microstructure control[J]. ISIJ International,2003,43(11):1742. [11] Hurtado-Delgado E,Morales R D. Hot ductility and fracture mechanisms of a C-Mn-Nb-Al steel[J]. Metallurgical and Materials Transactions B,2001,32(5):919. [12] 乔晓燕,赖承班,陈卓,等.奥氏体化工艺对30Cr13钢淬火后的组织和硬度的影响[J].上海金属,2021,43(5):33.(QIAO Xiao-yan,LAI Cheng-ban,CHEN Zhuo,et al. Effect of austenitizing process on microstructure and hardness of 30Cr13 steel after quenching[J].Shanghai Metals,2021,43(5):33.) [13] 邓杰,宋新莉,孙新军,等.含钛中锰钢淬火-配分组织及力学性能[J]. 钢铁,2021,56(6):103.(DENG Jie,SONG Xin-li,SUN Xin-jun,et al.Quenching and partitioning microstructure and mechanical properties of medium manganese steel bearing titanium[J].Iron and Steel,2021,56(6):103.) [14] 鲁永剑. 低合金钢中厚板连铸坯热送裂纹形成及预防机理研究[D]. 重庆:重庆大学,2013.(LU Yong-jian. The Formation and Prevention Mechanism of Surface Cracks for Low Alloyed Steel Slabs During Hot Charge Process[D]. Chongqing:Chongqing University,2013.) [15] Carboni A,Ruzza D W,Feldbauer S L. Quenching for improved direct hot charging quality[J]. Iron and Steelmaker,1999,26(8):39. [16] 王建钢,王皓,李人杰,等. 热送裂纹产生机制及生产工艺控制研究[J]. 连铸,2017(2):22.(WANG Jian-gang,WANG Hao,LI Ren-jie,et al. The mechanism and control measures research of hot charging crack[J]. Continuous Casting,2017(2):22.) [17] 蔡兆镇,刘志远,王重君,等. 微合金钢高温板坯全连续淬火新技术开发及应用[C]//第十二届中国钢铁年会. 北京:中国金属学会,2019:569.(CAI Zhao-zhen,LIU Zhi-yuan,WANG Chong-jun,et al. Development and application of new continuously quenching technology for high temperature micro-alloyed steel slab[C]//The 12th CSM Steel Congress. Beijing:The Chinese Society for Metals,2019:569.) [18] 李永超,李宝秀,郭明仪. 铸坯表面淬火技术的发展与应用[J]. 河北冶金,2016(3):44.(LI Yong-chao,LI Bao-xiu,GUO Ming-yi. Development and application of casting blank surface quenching technology[J]. Hebei Metallurgy,2016(3):44.) [19] 龙木军,陈登福,李宏亮,等. 方坯通用仿真软件的研究及其在二冷中的应用[J]. 材料与冶金学报,2008,7(1):15.(LONG Mu-jun,CHEN Deng-fu,LI Hong-liang,et al. Development of all-purpose simulation software for billet continuous casting and its application to secondary cooling[J]. Journal Materials and Metallurgy,2008,7(1):15.) [20] 王伟佳. 多种常用钢在不同淬火介质中换热系数的测算[D]. 大连:大连理工大学,2007.(WANG Wei-jia. Calculation on Heat Transfer Coefficient of Several Typical Steels in Different Quenchants[D]. Dalian:Dalian University of Technology,2007.) [21] 谢建斌. 金属及合金在不同介质中淬火时的数值模拟和应用研究[D]. 昆明:昆明理工大学,2003.(XIE Jian-bin. Studies on the Numerical Simulation for Metals and Alloys During Different Medium Quenching and Its Application[D]. Kunming:Kunming University of Science and Technology,2003.) [22] 朱学仪. 钢材热处理手册[M]. 北京:中国标准出版社,2007.(ZHU Xue-yi. Handbook of Steel Heat Treatment[M]. Beijing:China Standards Press,2007.)
2022, Vol. 57 
