帘线钢中氮含量对TiN析出的影响

Effects of Nitrogen Content on Precipitation of Ti-N Inclusions in Tire Cord Steel

研究了攀钢新钢钒公司生产帘线钢72A过程中钢中氮含量变化对钢中TiN夹杂析出的影响。研究发现,随着钢中氮含量的升高,钢中析出的TiN夹杂数量变多,尺寸变大。热力学研究表明,在帘线钢中TiN一般只能在固相区形成,考虑元素偏析对凝固前沿元素富集的影响,凝固过程中TiN能在固液两相区析出。在帘线钢生产过程中,为了控制钢中TiN的析出,除了控制钛含量,控制钢中氮含量及氮偏析更加重要。理论计算结果表明,当钢中钛的质量分数控制在0.000 3%～0.000 5%区间时,将钢中氮的质量分数控制在0.001 7%～0.002 9%区间内能显著降低乃至杜绝帘线钢中TiN的析出。攀钢将帘线钢中钛、氮的质量分数分别控制在0.000 5%以下和0.002%以下,显著减少了钢中TiN的析出,个别炉次中没有发现尺寸大于2μm的TiN夹杂。

Effects of N content in steel on precipitation of TiN inclusions during the production of 72A tire cord steel was investigated in Panzhihua New Steel Vanadium Co. Ltd. It is found that number of TiN precipitated in steel in creases along with the increase of N content in steel, and TiN size becomes bigger. The results of thermodynamics study show that TiN inclusions can only form in solid phase area in tire cord steel without considering elements segregation. However, TiN inclusions can precipitate in solid liquid two phase area during solidification process with regarding effects of element segregation on element enrichment in solidification front. In order to restrain precipitati on of TiN during production process of tire cord steel, controlling N content as well as N segregation is more important than control of Ti content. Theoretical calculation and test results indicate that controlling N content in the range of 0. 0017% to 0. 002% as wellas controlling Ti content in the range of 0. 0003% to 0. 0005% can observably reduce or even eliminate precipitation of TiN in tire cord steel. Ti and N content in tire cord steel is controlled under 0. 000 5% and 0. 002% respectively in Pangang plant, which dramaticlly reduces the precipitation of TiN in steel and resulted in none of TiN inclusion bigger than 2μm in some heats.