STRUCTURAL MEMBER AND PROCESS FOR PRODUCING THE SAME

摘要

A structural member which is composed of, on the weight basis, at most 0.07 % of carbon, at most 1 % of silicon, at most 1 % of manganese, 2.5-5 % of copper, 3-3.5 % of nickel, 14-17.5 % of chromium, at most 0.5 % of molybdenum, 0.15-0.45 % of niobium, and the balance substantially consisting of iron, and wherein an (epsilon) phase is deposited in a matrix composed of 6-30 % by volume of an austenitic phase and the rest substantially consisting of a martensitic phase. A process for producing a structural member by subjecting a stainless steel having the above composition to the first solution heat treatment at 1010 to 1050 C and then to aging at 520 to 630 C, wherein the second solution heat treatment is conducted at 730 to 840 C before aging is conducted at 520 to 630 C, or welding is conducted to give an arbitrary shape to a structural member before the second solution heat treatment is conducted. Another process for producing a structural member comprises subjecting a stainless steel having the above composition to the first solution heat treatment at 1010 to 1050 C and then to aging at 520 to 630 C, conducting welding to give an arbitrary shape to a structural member, raising the temperature at a rate of 100 C/h or below, conducting the second solution heat treatment at 1010 to 1050 C, lowering the furnace temperature to room temperature at a cooling rate of 100 C/h or below, conducting aging at 520 to 630 C, and lowering the furnace temperature to room temperature at a cooling rate of 100 C/h or below.