| 摘要 |
PROBLEM TO BE SOLVED: To improve the fracture toughness of a welded joint part by subjecting the part near the welded joint of a welded structure consisting of maraging steel to a heat treatment to heat the part to a specific high temp. then to cool the part, then subjecting this part to an aging treatment. SOLUTION: The part near the welded joint part 2 of the welded structure 1 consisting of the 18% Ni type maraging steel is irradiated with a high-density energy beam 3 from an electron gun 4 and is subjected to the heat treatment to locally heat up and hold this part to and at a temp. range from an austenitization temp. of 500 to 800 deg.C to a m. p. of 1500 deg.C, by which the elements, such as Mo and Ti, solidified and segregated at the grain boundaries of weld zones are diffused and the segregation thereof is prevented. Next, the part near the welded joint part is subjected to an aging heat treatment of once cooling this part then holding the part for one to two hours at 400 to 600 deg.C and to a soln. heat treatment in a temp. range of the austenitization temp. to 900 deg.C. The fracture toughness of the welded joint part 3 is improved and the reliability of the welded structure formed by using the maraging steel is improved. |
