Yunoshin Imai and TeturIshizaki
To be Continued to 3rd report, the present investigation has been carried out to ascertain the effect of nitrogen on the blue brittleness in steels containing lower nitrogen and to examin the effect of aluminium or titanium as the denitrogenizer on the blue-brittleness in steels. By adding the aluminium or titanium in steels containing 0.4%C and 0.7%Mn,as shown in Table 1, the blue-brittleness almost disappeared as are shown in Fig. 1∼Fig. 6. On the remelting electrolytic iron, three different types of denitrogening treatment were used; the first method is to cast the steel under such conditions that nitrogen should not be absorbed in steels from air as well as possible after 0.2 or 0.5% aluminium addition. For there charges, the tensile properties are plotted in Fig. 9 and Fig. 10. The 2nd type of treatment is to make the steel under such conditions as the small quantity of nitrogen is absorbed in steel from air after 0.3 or 0.4% aluminium addition as usually used in steel making.
The results of these charges are shown in Fig. 7 and Fig. 8. The third method is the steel making under such condition that nitrogen should be reabsorbed in steels from air after aluminium or Titanium addition. Tne results of these charges are plotted in Fig. 11∼Fig. 14. From the present investigation authors concluded the effect of the nitrogen on the blue brittleness in steels is as follows:
(1) By adding aluminium or titanium, the blue brittleness almost disappears.
(2) Adding alminium in the molten electrolitic iron the blue brittleness on the change of tensile strength vanishes completely, but the more alminium content in steels, the more blue brittleness is reduced.
(3) The blue brittleness on the change of elongation is decreased by adding alminium up to about 0.2% and with more alminium content, the blue brittleness in reincreased.
(4) Titanium is a strong denitrogenizer than Al. Those effects of alminium or titanium on the blue brittleness of steels mean that the blue brittleness is due chiefly to nitrogen in steels.
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