Ni-Based Heat Resistant Alloy and Method for Producing the Same

Abstract

A Ni-based heat resistant alloy of the present invention contains predetermined amounts of C, Si, Mn, P, S, N, O, Ni, Co, Cr, Mo, W, B, Al, Ti, Nb, REM, Mg, Ca, and the balance of Fe and impurities, wherein [0.1≤Mo+W≤12.0], [1.0≤4×Al+2×Ti+Nb≤12.0], and [P+0.2×Cr×B<0.035] are satisfied, a shortest distance from a center portion to an outer surface portion of a cross section of an alloy member is 40 mm or more, the cross section being perpendicular to a longitudinal direction of the alloy member, an austenite grain size number at the outer surface portion is −2.0 to 4.0, a total content of Al, Ti and Nb which are present as precipitates obtained by extraction residue analysis satisfies [(Al+Ti+Nb)PB/(Al+Ti+Nb)PS≤10.0], and [YSS/YSB≤1.5] and [TSS/TSB≤1.2] are satisfied at a normal temperature.

1 . A Ni-based heat resistant alloy having a chemical composition consisting of, in mass %:
 C: 0.005 to 0.15%;   Si: 2.0% or less;   Mn: 3.0% or less;   P: 0.030% or less;   S: 0.010% or less;   N: 0.030% or less;   O: 0.030% or less;   Ni: 40.0 to 60.0%;   Co: 0.01 to 25.0%;   Cr: 15.0% or more to less than 28.0%;   Mo: 12.0% or less;   W: less than 4.0%;   B: 0.0005 to 0.006%;   Al: 0 to 3.0%;   Ti: 0 to 3.0%;   Nb: 0 to 3.0%;   REM: 0 to 0.1%;   Mg: 0 to 0.02%;   Ca: 0 to 0.02%; and   the balance: Fe and impurities, wherein   following formulas (i) to (iii) are satisfied,   a shortest distance from a center portion to an outer surface portion of a cross section of the alloy is 40 mm or more, the cross section being perpendicular to a longitudinal direction of the alloy,   an austenite grain size number at the outer surface portion is −2.0 to 4.0,   a total content of Al, Ti and Nb which are present as precipitates obtained by extraction residue analysis satisfies a following formula (iv), and   mechanical properties at a normal temperature satisfy a following formula (v) and a following formula (vi):
   0.1≤Mo+W≤12.0   (i)
 
   1.0≤4×Al+2 ×Ti+Nb≤12.0   (ii)
 
   P+0.2×Cr×B<0.035   (iii)
 
   (Al+Ti+Nb) PB /(Al+Ti+Nb) PS ≤10.0   (iv)
 
   YS S /YS B 31.5   (v)
 
   TS S /TS B ≤1.2   (vi)
 
   wherein, symbol of an element in the formulas (i) to (iii) refers to content (mass %) of each element, and meaning of each symbol in the formulas (iv) to (vi) is as follows:   (Al+Ti+Nb) PB : total content of Al, Ti and Nb which are present at center portion as precipitates obtained by extraction residue analysis   (Al+Ti+Nb) PS : total content of Al, Ti and Nb which are present at outer surface portion as precipitates obtained by extraction residue analysis   YS B : 0.2% proof stress at center portion   YS S : 0.2% proof stress at outer surface portion   TS B : tensile strength at center portion   TS S : tensile strength at outer surface portion.   
     
     
         2 . The Ni-based heat resistant alloy according to  claim 1 , wherein
 the chemical composition comprises one or two elements selected from a group consisting of, in mass %:   Mg: 0.0001 to 0.02%; and   Ca: 0.0001 to 0.02%.   
     
     
         3 . The Ni-based heat resistant alloy according to  claim 1 , wherein
 10,000-hour creep rupture strength at 700° C. in the longitudinal direction at the center portion is 150 MPa or more.   
     
     
         4 . A method for producing a Ni-based heat resistant alloy, the method comprising the steps of:
 performing hot working on an ingot or a cast piece having the chemical composition according to  claim 1 ; and   thereafter performing heat treatment where the ingot or the cast piece is heated to a heat-treatment temperature T (° C.) ranging from 1070 to 1220° C., is held for 1150 D/T to 1500 D/T (min), and is cooled with water,   wherein symbol “D” denotes a maximum value (mm) of a linear distance between an arbitrary point on an outer edge of a cross section of the alloy and another arbitrary point on the outer edge, the cross section being perpendicular to a longitudinal direction of the alloy.   
     
     
         5 . The method for producing a Ni-based heat resistant alloy according to  claim 4 , wherein
 in the step of performing the hot working, the hot working is performed one or more times in a direction substantially perpendicular to a longitudinal direction in the hot working.   
     
     
         6 . The Ni-based heat resistant alloy according to  claim 2 , wherein
 10,000-hour creep rupture strength at 700° C. in the longitudinal direction at the center portion is 150 MPa or more.   
     
     
         7 . A method for producing a Ni-based heat resistant alloy, the method comprising the steps of:
 performing hot working on an ingot or a cast piece having the chemical composition according to  claim 2 ; and   thereafter performing heat treatment where the ingot or the cast piece is heated to a heat-treatment temperature T (° C.) ranging from 1070 to 1220° C., is held for 1150 D/T to 1500 D/T (min), and is cooled with water,   wherein symbol “D” denotes a maximum value (mm) of a linear distance between an arbitrary point on an outer edge of a cross section of the alloy and another arbitrary point on the outer edge, the cross section being perpendicular to a longitudinal direction of the alloy.   
     
     
         8 . The method for producing a Ni-based heat resistant alloy according to  claim 7 , wherein in the step of performing the hot working, the hot working is performed one or more times in a direction substantially perpendicular to a longitudinal direction in the hot working.