Ferritic heat-resistant steel and heat-resistant structure with excellent creep properties of the weld heat affected zone

摘要

PROBLEM TO BE SOLVED: To provide a heat-resistant structure which inhibits a type-IV damage from occurring at a weld heat-affected zone of a heat-resistant ferritic steel material.;SOLUTION: The heat-resistant ferritic steel material includes, by mass%, 0.01-0.20% C, 0.02-0.50% Si, 0.05-1.0% Mn, 0.02% or less P, 0.01% or less S, 0.4 to 12.0% Cr, 0.002-0.15% N, one or more elements of 0.05-2.0% Mo, 0.05-3.0% W, and 0.05-2.0% Re, and the balance Fe with unavoidable impurities, and has a Cr equivalent value of 0.4 to 20 at the weld heat-affected zone; and has such potential characteristics that (z1) a low temperature transformation structure having former austenite grains with average particle sizes of 10 μm or larger is produced, (z) in the weld heat-affected zone of the steel material to be heated to the Ac₁ transformation temperature to (the Ac₁ transformation temperature + 300°C), and that (z2) grain boundary lengths of M₂₃C₆ type carbides occupy 30% or more in boundaries between large inclined grains of the zone, in heat treatment after having been welded at 300°C to the Ac₁ transformation temperature.;COPYRIGHT: (C)2009,JPO&INPIT