热轧结构钢棒材内裂纹原因分析及工艺改进  

Cause analysis and process improvement of internal cracks in hot rolled structural steel bars

作　　者：谢常胜 许宝玉 代鑫 任振海 恽伟达 XIE Changsheng;XU Baoyu;DAI Xin;REN Zhenhai;YUN Weida(Technology Center,Zenith Steel Group(Nantong)Co.,Ltd.,Nantong 226156,China;Technology Center,Zenith Steel Group Co.,Ltd.,Changzhou 213011,China;College of Metallurgy and Energy,North China University of Science and Technology,Tangshan 063210,China)

机构地区：[1]中天钢铁集团(南通)有限公司技术中心,江苏南通226156 [2]中天钢铁集团有限公司技术中心,江苏常州213011 [3]华北理工大学冶金与能源学院,河北唐山063210

出　　处：《轧钢》2024年第4期149-154,共6页Steel Rolling

基　　金：江苏省双创博士资助项目(JSSCBS20222482)。

摘　　要：针对某钢厂生产的低碳低合金结构钢棒材内部存在长约0.1~0.3 mm显微裂纹的问题,通过低倍组织检查、光学显微镜和扫描电镜观察等方法对低碳低合金棒材内部微裂纹进行了分析和研究,并提出了工艺改进措施。结果表明:低碳低合金钢棒材热轧后内部出现多个彼此不相连、无方向性、长度约0.1~0.3 mm的微裂纹,周围没有异常夹杂物等冶金缺陷,微裂纹沿带状组织的珠光体条带扩展,且珠光体条带周围分布着贝氏体、马氏体混合组织;成分偏析导致低碳低合金钢棒材中出现级别较高的带状组织,且带状组织周围存在贝氏体和马氏体混合组织,在发生较大塑性变形时更容易产生微裂纹;连铸时将过热度控制在20~30℃,电磁搅拌参数设置为200 A、2.0 Hz,二冷区比水量降低至0.41 L/kg,拉坯速度控制在1.2 m/min时,可从连铸坯的源头减轻带状组织;适当延长连铸坯在(1180±10)℃高温段保温时间至250~305 min,可改善成分偏析;热轧棒材入坑缓冷可以避免贝氏体、马氏体组织的产生。工艺改进后对热轧低碳低合金钢棒材进行无损探伤未再发现内裂纹缺陷,改善效果明显。Aiming at the problem of micro-cracks about 0.1-0.3 mm in length inside the low-carbon and low-alloy structural steel bars produced by a steel plant,the micro-cracks inside the steel bars were analyzed and studied through low power structure inspection,optical microscope and scanning electron microscope observation,and process improvement measures were proposed.The results show that after hot rolling,multiple micro-cracks with a length of about 0.1-0.3 mm,which were not connected to each other and no directionality,appear inside the steel bars.There were no metallurgical defects such as abnormal inclusions around the micro-cracks.The micro cracks propagated along the pearlite strip with a banded structure,and a mixed structure of bainite and martensite was distributed around the pearlite strip.Compositional segregation resulted in the formation of high-grade banded structures in steel bars,and mixed structures of bainite and martensite existed around the banded structures,which were more likely to produce micro cracks when large plastic deformation occurred.During continuous casting,the superheat was controlled at 20-30℃,the electromagnetic stirring parameters were set at 200 A and 2.0 Hz,the specific water content in the secondary cooling zone was reduced to 0.41 L/kg,and the casting speed was controlled at 1.2 m/min,which could reduce the banded structure from the source of the continuous casting billet.The composition segregation could be improved by appropriately prolonging the holding time of billet at high temperature of(1180±10)℃to 250-305 min.The slow cooling of the hot rolled steel bars into the pit could avoid the generation of bainite and martensite structures.After the process improvement,no internal crack defects were found in the non-destructive testing of hot rolled low-carbon low alloy steel bars,and the improvement effect was significant.

关 键 词：低碳低合金 热轧棒材 内裂纹 成分偏析 带状组织 连铸工艺优化 

分 类 号：TG335.11[金属学及工艺—金属压力加工]