立式连铸P91钢大圆坯表面纵裂缺陷及其控制  

Surface longitudinal crack defect and its control for vertical continuous casting round blooms of steel P91

作　　者：宗健 董延楠 涂高岭 程晃 潘禹博 张家泉[1] ZONG Jian;DI ONG Yannan;TU Gaoling;CHENG Huang;PAN Yubo;ZHANG Jiaquan(School of Metallurgical and Ecological Engineering,University of Science and Technology Beijing,Beijing 100083,China;High Purity Steel Company,Henan Zhongyuan Special Steel Equipment Manufacturing Co.,Ltd.,Jiyuan 459008,Henan,China)

机构地区：[1]北京科技大学冶金与生态工程学院,北京100083 [2]河南中原特钢装备制造有限公司高洁净钢公司,河南济源459008

出　　处：《中国冶金》2024年第5期65-73,共9页China Metallurgy

摘　　要：P91钢为微合金化改良型9Cr-1Mo马氏体耐热钢,具有良好的高温强度、高温抗氧化性和抗腐蚀性,是当前先进的电站用大口径高温高压蒸汽管道制备材料。针对国内外以坯代锭、开发圆坯连铸高合金钢高效制备工艺的需要,研究分析了P91钢连铸圆坯常见的表面纵裂问题及其影响因素。基于低倍观察、OM、SEM与EDS分析,揭示了这类表面裂纹的形貌、组织与成分特征;利用相变热力学计算揭示了其高温初凝的相变特点。研究表明,P91高合金钢具有亚包晶钢的凝固特点,其在结晶器弯月面附近可能发生的强烈δ→γ相变收缩是连铸坯壳凹陷与纵裂倾向大的内在诱因,浇注工艺不良所导致的初凝坯壳与气隙不均是造成裂纹发生的重要外部因素;P91钢圆坯纵裂起源于连铸结晶器内。生产试验表明,通过合理选择水口、控制钢水注流对初凝坯壳的冲刷,选用合适黏度与熔点的保护渣、增加液渣层厚度及其对坯壳气隙的充填能力等措施,均能从连铸工艺上不同程度地控制P91连铸圆坯的表面纵裂率;进一步优化设计结晶器铜管冷却结构,适当弱化一冷强度、提高结晶器周向冷却的均匀性,可以更有效地控制其连铸表面纵裂缺陷的发生率。研究结果可为P91等高合金钢圆坯连铸生产中表面纵裂的控制提供参考。Steel P91 is one of micro-alloyed enhanced 9Cr-1Mo martensitic heat-resistant steels,which shows ad-vanced service properties such as excellent high-temperature strength,high-temperature oxidation resistance and corrosion resistance.Steel P91 has been widely adopted now for the manufacture of important high-temperature pressure resistant steam pipe in power plants equipment.In order to develop big round bloom continuous casting in-stead of traditional ingot casting for efficient manufacture of the high alloy steel,the continuous casting round bloom surface longitudinal crack frequently occurred in P91 semi-products was studied.The crack appearance,macro-mor-phology and inclusions had been studied by the aid of OM,SEM and EDS analysis,and the steel phase transforma-tion characteristic at initial solidification was calculated in terms of commercial thermodynamic software.The re-search shows that steel P91 solidifies initially very similar to hypo-peritectic steels with inherent surface depression and/or longitudinal crack sensitive,whose main inner reason is strong shrinkage of→near the mold meniscus,but the uneven shell thickness and gap due to poor casting practices should be the important extra reasons to induce the cracks.And it is believed that the longitudinal crack in P91 continuous casting round bloom should initiate from the mold region.Then,it has been observed by casting tests that the crack frequency drops obviously through an improved operation like as changing the bifurcated SEN port direction to avoid the outlet liquid flow impinging di-rectly upon the shell,or adopting a new mold powder for thicker melt flux layer by lower melting point and larger viscosity.However,it is found additionally that the crack frequency can be remarkably reduced by the application of a new mold with denser internal cooling water channels, which shows a weaker mold cooling intensity but more evenheat flux distribution at circumference direction. The research results can provide reference for the control of surfacelongitu

关 键 词：P91钢 大圆坯 连铸 表面纵裂 生产与控制 

分 类 号：TF777[冶金工程—钢铁冶金]