Austenitic heat-resistant steel

Abstract

An austenitic heat-resistant steel containing, by mass, 0.05-0.16% of C, 0.1-1% of Si, 0.1-2.5% of Mn, 0.01-0.05% of P, less than 0.005% of S, 7-12% of Ni, 16-20% of Cr, 2-4% of Cu, 0.1-0.8% of Mo, 0.1-0.6% of Nb, 0.1-0.6% of Ti, 0.0005-0.005% of B, 0.001-0.15% of N, and 0.005% or less of Mg and/or 0.005% or less of Ca, the amounts of Nb and Ti being 0.3% or above in total, with the remainder being made up by Fe and unavoidable impurities. The cumulative number density of a precipitate has a particle diameter of over 0 nm to 100 urn being 0.1-2.0/μm 2 , the precipitate particle diameter corresponding to half of the cumulative number density in the distribution of the cumulative number density and the precipitate particle diameter is 70 nm or less, the average hardness is 160 Hv or less, and the grain size number is 7.5 or above.

1 . An austenitic heat-resistant steel, comprising:
 C: 0.05 to 0.16% by mass;   Si: 0.1 to 1% by mass;   Mn: 0.1 to 2.5% by mass;   P: 0.01 to 0.05% by mass;   S: 0.005% by mass or less (not including 0% by mass),   Ni: 7 to 12% by mass;   Cr: 16 to 20% by mass;   Cu: 2 to 4% by mass;   Mo: 0.1 to 0.8% by mass;   Nb: 0.1 to 0.6% by mass;   Ti: 0.1 to 0.6% by mass;   B: 0.0005 to 0.005% by mass;   N: 0.001 to 0.15% by mass; and   at least one of Mg: 0.005% by mass or less (not including 0% by mass) and Ca: 0.005% by mass or less (not including 0% by mass), with the remainder being Fe and unavoidable impurities,   wherein a total of a content of Nb and a content of Ti is 0.3% by mass or more,   a cumulative number density of a precipitate whose particle diameter falls within a range of more than 0 nm up to 100 nm is 0.1 to 2.0 Number/μm 2 ,   a precipitate particle diameter corresponding to a half of the cumulative number density in a distribution of the cumulative number density and the precipitate particle diameter is 70 nm or less,   an average hardness is 160 Hv or less, and   a grain size number is 7.5 or more.   
     
     
         2 . The austenitic heat-resistant steel according to  claim 1 , further comprising at least one of Zr: 0.3% by mass or less (not including 0% by mass), a rare earth element: 0.15% by mass or less (not including 0% by mass) and W: 3% by mass or less (not including 0% by mass).