NI-BASE HEAT-RESISTANT ALLOY AND WELD JOINT THEREOF

摘要

A Ni-base heat-resistant alloy which has a chemical composition: C: 0.1 % or less, Si: 2 % or less, Mn: 2 % or less, P: 0.025 % or less, S: 0.005 % or less, N: 0.04 % or less, Cr: 10 to 30 %, Al: 2.1 or more and less than 4.5 % , Mo: 2.5 to 15 % or W: 2.5 to 9 % or the sum of Mo and W: 2.5 to 15 %, and balance: substantially Ni, with the proviso that the above respective conten ts satisfy the following formula (1): (104Si + 1980P + 1980S + 9Al + 15Ti + 11N b + 1.8W + 11600B) = {1.1(240 20000S 1900P 30Al 10Ti 9W + 17000B (1); and a weld joint which has a base metal and a weld metal both comprising an alloy having the above composition and in which the ST value of the weld metal calculated by the following formula (2) or (3): when Ti <= 4C, ST <= M o + 1.5W + 100Ti --- (2) when Ti > 4C, ST = Mo + 1.5W + 400C --- (3) is greater th an that of the base material and the difference between those values is 3 or more. The Ni-base heat-resistant alloy is excellent in weldability and strength at a high temperature, and thus is suitable for use in a cracking furnace and a reforming furnace for a ethylene plant.