18%Ni 마르에이징강의 시효처리 최적화에 관한 연구

Abstract

This study aims to optimize the aging condition process in order to improve mechanical characteristics of ultra high strength 18%Ni maraging steel which is being highlighted in the fields of the aerospace, nuclear energy and vehicles. The results of this study are as follows.

1. The solution-treated specimen's hardness was reduced by about 3 percent more than the basic material, but the 1-hour aging-treated specimen's hardness increased by nearly 60 percent and then, showed almost similar values after that.

2. It showed the highest tensile strength value of around 1,800MPa for five to eight hours which was about two times bigger than the basic material's. On the other hand, it showed the highest elongation at a low temperature and for less time, and it was similar to the basic material's.

3. The more the aging temperature and aging time increased, the more its fatigue life increased. On the other hand, when applying the aging treatment for eight hours at a temperature of 510℃, the specimen's fatigue life was most favorable.

4. When applying the aging treatment for eight hours at a temperature of 482℃, the specimen which satisfied 250 grade, was created, and it showed the most excellent mechanical characteristics.

5. When analyzing the effects of the aging temperature and aging time on response values, and evaluating the significance, significant factors were derived from each response values. Then, the main effects and interaction's impact were analyzed.

6. When analyzing a correlation between factors, the possibility of its application was verified, by extracting a proper regression equation through regression analysis and response surface analysis regarding reaction variables of the aging temperature and aging time and then, a regression equation and the optimum reaction were achieved, by establishing a correlation between factors. When applying the optimum reaction, it was found that it is the most appropriate condition to apply the aging treatment for 6.5 hours at a temperature of 482℃.