Mn-Si系高張力鋼の熔接ビード下割れに及ぼすAlの影響について

Abstract

The effects of aluminum content upon the properties of Mn-Si high tensile steel containing C 0.20%, Si 0.30%, Mn 1.40% as shown in Table 1 and 2 were studied. Mainly the effect of aluminum upon the underbead weld crack sensitivity was studied by CTS test and Battelle one.By the result of CTS test, the use of small or medium amount of aluminum (about 0.01% as acid soluble alumininum) was found to increase the underbead weld crack and the crack seemed to be reduced by either omitting aluminum or by using large additions as shown in Table 3 and 4.By the result of Battelle test, the crack fo the forged and normalized steels decreased as the aluminum content increased. The crack of the steels as casting seemed not to be much effected by the alumininum content and was much more sensitive for the crack than the forged and normalized steels as shown in Fig. 3.The addition of aluminum gave no change to the tensile properties of the forged and normalized steels except yield strength and decreased the elongation and area reduction of the steels as casting as shown in Fig. 4. The effect of aluminum upon the casting structure and non-metalic inclusion as casting was shown in Fig. 5 and 6.As stated above for Table 3 and 4, the effect of aluminum upon the underbead weld crack of Mn-Si high tensile steel seems to be complicated. This phenomenon has beed also indicated by C.E. Sims and others (literature No.4).The mechanism of the phenomenon that the crack is reduced by using large addition of aluminum is explained as the effect of aluminum carbide in steel. But the mechanism of the phenomenon that the crack is reduced by omitting aluminum or using very small additions does not seem to be explained. I studied about the possibility that the aluminium nitride would be effective to reduce the weldability of the steel containing both nitrogen and aluminum.