High-strength, heat-resistant alloy for exhaust valves with improved overaging-resistance

Abstract

Disclosed is a heat resistant alloy for exhaust valves, in which Ni-content is constrained to at maximum 62% due to the material cost, while the strength is maintained equal or better to those of conventional alloys and the strength is kept even after use at high temperature for a long period of time. The alloy has the composition essentially consisting of, by weight %, C: 0.01-0.2%, Si: up to 1.0%, Mn: up to 1.0%, P: up to 0.02%, S: up to 0.01%, Ni: 30-62%, Cr: 13-20%, W: 0.01-3.00%, Mo: up to 2.0%, provided that Mo+0.5 W: 1.0-2.5%, Al: 0.7% or higher and less than 1.6%, Ti: 1.5-3.0%, Nb: 0.5-1.5%, B: 0.001-0.010%, provided that [% Ti]/[% Al]: 1.6 or more to less than 2.0, and the balance of Fe and inevitable impurities. Optional components are I) at least one of Mg: 0.001-0.030%, Ca: 0.001-0.030% and Zr: 0.001-0.100%, II) Cu: up to 2.0%, and III) V: 0.005-1.00%.

We claim:  
     
         1 . A high strength, heat resistant alloy for exhaust valves with good overaging-resistance, which has an alloy composition essentially consisting of, by weight %, C: 0.01-0.2%, Si: up to 1.0%, Mn: up to 1.0%, P: up to 0.02%, S: up to 0.01%, Ni: 30-62%, Cr: 13-20%, W: 0.01-3.00%, Mo: up to 2.0%, provided that MO+W: 1.0-2.5%, Al: 0.7% or higher and less than 1.6%, Ti: 1.5-3.0%, Nb: 0.5-1.5%, B: 0.001-0.010%, provided that [% Ti]/[% Al]; 1.6 or more to less than 2.0, and the balance of Fe and inevitable impurities.  
     
     
         2 . The heat resistant alloy for exhaust valves according to  claim 1 , wherein the alloy further contains at least one of the group consisting of Mg: 0.001-0.030%, Ca: 0.001-0.030% and Zr: 0.001-0.100%.  
     
     
         3 . The heat resistant alloy for exhaust valves according to  claim 1 , wherein the alloy further contains Cu: up to 2.0%.  
     
     
         4 . The heat resistant alloy for exhaust valves according to  claim 1 , wherein the alloy further contains V: 0.05-1.00%.  
     
     
         5 . The heat resistant alloy for exhaust valves according to  claim 1 , wherein the alloy further contains Cu: up to 2.0% and V: 0.05-1.00%.  
     
     
         6 . The heat resistant alloy for exhaust valves according to  claim 2 , wherein the alloy further contains Cu: up to 2.0%.  
     
     
         7 . The heat resistant alloy for exhaust valves according to  claim 2 , wherein the alloy further contains V: 0.05-1.00.  
     
     
         8 . The heat resistant alloy for exhaust valves according to  claim 2 , wherein the alloy further contains Cu: up to 2.0% and V; 0.05-1.00.  
     
     
         9 . The heat resistant alloy for exhaust valves according to one of  claims 1  to  8 , wherein the alloy has a composition in which a portion of Ni is replaced with Co in an amount of up to 5% of the alloy.  
     
     
         10 . The heat resistant alloy for exhaust valves according to one of  claims 1  to  8 , wherein the alloy has a composition in which whole or a portion of Nb is replaced with Ta.  
     
     
         11 . The heat resistant alloy for exhaust valves according to one of  claims 1  to  8 , wherein the alloy has a composition in which a portion of Ni is replaced with Co in an amount of up to 5% of the alloy and whole or a portion of Nb is replaced with Ta.