Abstract
Effects of Ti and Al in steels on the notch toughness of the synthetic weld heat affected zone have been investigated using 41 kgf/mm2 grade steels containing various quantities of N. The results obtained are as follows: (1) Synthetic HAZ toughness of the steel containing 13 ppm of N is the most superior to the other all steels. Charpy transition temperature (vTrs) is droped about 15°C per the decreasing of 10 ppm of N. When N in steels is less than 20 ppm, additions of Ti and/or Al deteriorate the notch toughness. (2) Notch toughness is improved by Ti addition, especially, when Ti is added about 3.4 times of N content, the notch toughness becomes the best, because of the decreasing of free N content and the refining of microstructures on each N content of 20 to 60 ppm. (3) Even if the ratio of Ti and N contents, Ti/N, is 3.4, the notch toughness is improved with the decrease in N content of steels. However, when 0.06 wt% of Al is added in steels containing more than 0.015 wt% Ti and more than 50 ppm N the notch toughness is further improved. (4) Optimum Ti content neccesary to improve the notch toughness is 0 wt% in steels containing 10 ppm N, and about 3.4 times of N content in more than 20 ppm N. (5) vTrs of synthetic HAZ of steels containing optimum content of Ti is very low comparing to steel without Ti and this tendency becomes remarkably as N content increases. While the additions of Al are effective in steels with nitrogen above 35 ppm.
