关于钢洁净度指数的讨论

Discussion on the index of steel cleanliness

首先从高品质钢的洁净化、精准化、均质化和细晶化四个方面引申出了钢中非金属夹杂物的问题,阐述了"非金属夹杂物不是钢的所有问题,但所有钢都有非金属夹杂物的问题"、"非金属夹杂物是钢的天然成分,可以通过研究非金属夹杂物的生成机理来确定其控制方略,进而改善钢的质量"等重要观点。讨论了总氧含量(T.O)作为钢洁净度指数的不足之处,进而提出了钢的洁净度指数(I_c=xT.O+y(Al_2O_3)),即对于铝脱氧钢,式中y为零,夹杂物的控制主要强调钢中T.O含量要低;对于硅锰脱氧钢,式中x为零,夹杂物的控制主要强调夹杂物中的Al_2O_3含量要低。基于此洁净度指数,总结了多种钢的洁净度和非金属夹杂物的控制目标。文中还讨论了稳态浇铸与非稳态浇铸对钢洁净度的影响,提出了钢水洁净度水平最好的情况是非稳态持续时间短,且钢中非金属夹杂物控制水平好。最后讨论了钢中非金属夹杂物数量和个数表征的几个经典问题,包括如何计算夹杂物的平均含量和平均尺寸、夹杂物尺寸组的大小和数量的关系、如何把二维的夹杂物尺寸分布结果转化为三维的结果。

In the current paper,four aspects of high quality steels—purification,accurate control,composition homogenization and grain refinement—were discussed,and then the issue of non-metallic inclusions in steel was put forward.The current paper claimed many new concepts of steel cleanliness.The problem of inclusions is not all the problems of high quality steels,however,all steels have the problem of inclusions.Non-metallic inclusions are the natural component of a steel,and the scheme to control inclusions in steel should be obtained from their generation mechanisms.The total oxygen of the steel(T.O)was used as the index steel cleanliness by many reported literatures,which is a serious problem since it is hardly impossible to find enough amount of inclusions with a certain size in steel samples for the analysis of total oxygen.In the current paper,a new index of steel cleanliness was proposed,Ic=xT.O+y(Al2O3),namely.For Al-killed steels,y is zero and the T.O content of the steel should be lowered as possible as it can;for SiMn-killed steel,the main task is to control the content of Al2O3 in inclusions.The control scheme of many kinds of steels was discussed in the current paper.The effect of steady state casting and unsteady state casting on steel cleanliness was also discussions,and it was concluded that the best steel cleanliness control is a proper control of inclusions and with a short unsteady state duration.Three classical issues for the characterization of inclusions in steel were discussed,including how to calculate the average amount and the mean size of inclusions,the effect of a bin size on the size distribution of inclusions,and how to convert the two-dimensional size distribution of inclusions into a three-dimensional one.