AUSTENITIC HEAT-RESISTANT ALLOY AND WELDED STRUCTURE

1 . An austenitic heat-resistant alloy having a chemical composition of, in mass %:

0.04 to 0.14% C;

0.05 to 1% Si;

0.5 to 2.5% Mn;

up to 0.03% P;

less than 0.001% S;

23 to 32% Ni;

20 to 25% Cr;

1 to 5% W;

0.1 to 0.6% Nb;

0.1 to 0.6% V;

0.1 to 0.3% N;

0.0005 to 0.01% B;

0.001 to 0.02% Sn;

up to 0.03% Al;

up to 0.02% O;

0 to 0.5% T;

0 to 2% Co;

0 to 4% Cu;

0 to 4% Mo;

0 to 0.02% Ca;

0 to 0.02% Mg;

0 to 0.2% REM; and

the balance being Fe and impurities,

the alloy having a microstructure with a grain size represented by a grain size number in accordance with ASTM E112 of 2.0 or more and less than 7.0.

2 . The austenitic heat-resistant alloy according to claim 1 , wherein the chemical composition contains one or more elements selected from one of the first to third groups provided below, in mass %:

first group: 0.01 to 0.5% Ti;

second group: 0.01 to 2% Co, 0.01 to 4% Cu, and 0.01 to 4% Mo; and

third group: 0.0005 to 0.02% Ca; 0.0005 to 0.02% Mg; and 0.0005 to 0.2% REM.

3 . A welded structure including the austenitic heat-resistant alloy according to claim 1 .

4 . A welded structure including the austenitic heat-resistant alloy according to claim 2 .