Development of a New Method for Evaluating Effects of Tramp Elements on Surface Hot Shortness in Steels

研究了一种新的评价钢对废钢中铜和锡引起的表面热脆性敏感性的方法的可行性。所用钢为含0.1-0.2%Cu和少量Sn的IF钢和0.1%C-0.4%Cu钢。控制IF钢的化学成分，目的是使其尽可能与新日铁公司在实际轧制过程中通过目视方法检查其磁化率的钢的化学成分相似。在空气或Ar气中加热试样后，在1100 ℃下进行拉伸试验。总伸长率和最大载荷由载荷-伸长率曲线测量。通过将在空气和Ar气中获得的总伸长率或最大载荷之间的差除以Ar气中的总伸长率或最大载荷，计算参数Ee或Ep。通过考虑由于氧化而导致的试样直径的减小，计算了Ep校正值Ep '。的Ee、Ep和Ep' ...更多信息 IF钢对应于在实际轧制过程中观察到的表面裂纹的穿透程度。当钢-鳞界面富铜相数量较少时，表面裂纹在变形初期即停止沿着深度方向扩展。使用具有人造圆形裂纹的试样进行的拉伸试验表明，Ee和Ep'随着裂纹深度的增加而增加，相反，Ep'略有增加，Ee随着裂纹数量的增加而减少。参数Ee和Ep'在约3 × 10 - 4 s-1的应变速率下显示出最大值<-2><-1>，并且在该应变速率附近，钢中它们的值的差异最大。因此，尽管该应变速率比热加工的应变速率慢得多，但在该应变速率附近，可以灵敏地知道合金元素或杂质元素等任何因素对表面热脆性的影响。采用新的表面热脆敏感性评价方法，考察了某些元素对表面热脆的影响，获得了许多有益的结果。少

The feasibility of a new method for evaluating the susceptibility of steels to surface hot shortness due to Cu and Sn derived from iron scrap was examined. Steels used are IF steels containing 0.1-0.2%Cu and a small amount of Sn and 0.1%C-0.4%Cu steels. Chemical compositions of the IF steels were controlled with the purpose of being as similar as possible to those of steels of which the susceptibility was previously examined by a visual method in a practical rolling process at Nippon Steel Corporation. Tensile tests were carried out at 1100ﾟC after heating a specimen in air or Ar gas. The total elongation and maximum load were measured from a load-elongation curve. By dividing the difference between the total elongations or maximum loads obtained in air and Ar gas by the total elongation or maximum load in Ar gas, the parameters Ee or Ep were calculated. By considering the reduction in specimen diameter due to oxidation, the Ep corrected, Ep', was calculated. The Ee, Ep and Ep' of the … More IF steels corresponded to the degree of the penetration of surface cracks observed in the practical rolling process. Surface cracks stop growing along the depth direction at the earlier stage of deformation when the amount of Cu-enriched phase is the smaller at steel-scale interface. Tensile tests using specimens having artificial round cracks clarified that the Ee and Ep' increased with an increase in the crack depth and that, in contrast, the Ep' increased slightly and the Ee decreased with an increase in the number of cracks. The parameter Ee and Ep' showed a maximum value at a strain rate of around 3X10^<-2>s^<-1>, and the difference in their values among the steels is largest around this strain rate. Therefore it is possible to know sensitively the effects of any factors like alloying or impurity elements on surface hot shortness at around this strain rate although this strain rate is much slower than those of hot workings. Using the new method of evaluating susceptibility to surface hot shortness, effects of some elements on the shortness were examined and many fruitful results were obtained. Less