Precipitation hardened martensitic stainless steel, manufacturing method therefor, and turbine moving blade and steam turbine using the same

Abstract

The precipitation hardened martensitic stainless steel is characterized by containing, in percent by weight, 12.25 to 14.25% Cr, 7.5 to 8.5% Ni, 1.0 to 2.5% Mo, 0.05% or less C, 0.2% or less Si, 0.4% or less Mn, 0.03% or less P, 0.005% or less S, 0.008% or less N, 0.90 to 2.25% Al, the balance substantially being Fe, and the total content of Cr and Mo being 14.25 to 16.75%. A turbine moving blade and a steam turbine are manufactured by using this martensitic stainless steel.

1 . A precipitation hardened martensitic stainless steel containing, in percent by weight, 12.25 to 14.25% Cr, 7.5 to 8.5% Ni, 1.0 to 2.5% Mo, 0.05% or less C, 0.2% or less Si, 0.4% or less Mn, 0.03% or less P, 0.005% or less S, 0.008% or less N, 0.90 to 2.25% Al, the balance substantially being Fe, and the total content of Cr and Mo being 14.25 to 16.75%.  
     
     
         2 . The precipitation hardened martensitic stainless steel according to  claim 1 , wherein  
         Cr equivalent=[Cr]+2[Si]+1.5[Mo]+5.5[Al]+1.75[Nb]+1.5[Ti] Ni equivalent=[Ni]+30[C]+0.5[Mn]+25[N]+0.3[Cu],  
       and the Cr equivalent is less than 28.0, and the Ni equivalent is less than 10.5.  
     
     
         3 . The precipitation hardened martensitic stainless steel according to  claim 1 , wherein the total content of Cr and Mo is 15.5 to 16.75%.  
     
     
         4 . The precipitation hardened martensitic stainless steel according to  claim 1 , wherein the Al content is higher than 1.35% and not lower than 2.25%.  
     
     
         5 . A manufacturing method for a precipitation hardened martensitic stainless steel, characterized in that a steel billet, which has a chemical composition, in percent by weight, of 12.25 to 14.25% Cr, 7.5 to 8.5% Ni, 1.0 to 2.5% Mo, 0.05% or less C, 0.2% or less Si, 0.4% or less Mn, 0.03% or less P, 0.005% or less S, 0.008% or less N, 0.90 to 2.25% Al, the balance substantially being Fe, and the total content of Cr and Mo being 14.25 to 16.75%, is subjected to aging treatment at 510 to 550° C. after being subjected to solution heat treatment at 910 to 940° C.  
     
     
         6 . A manufacturing method for a precipitation hardened martensitic stainless steel, characterized in that a steel billet, which has a chemical composition, in percent by weight, of 12.25 to 14.25% Cr, 7.5 to 8.5% Ni, 1.0 to 2.5% Mo, 0.05% or less C, 0.2% or less Si, 0.4% or less Mn, 0.03% or less P, 0.005% or less S, 0.008% or less N, 1.35 to 2.25% Al, the balance substantially being Fe, and the total content of Cr and Mo being 14.25 to 16.75%, is subjected to aging treatment at 550 to 600° C. after being subjected to solution heat treatment at 910 to 940° C.  
     
     
         7 . The manufacturing method for a precipitation hardened martensitic stainless steel according to  claim 5 , wherein in the precipitation hardened martensitic stainless steel,  
         Cr equivalent=[Cr]+2[Si]+1.5[Mo]+5.5[Al]+1.75[Nb]+1.5[Ti] Ni equivalent=[Ni]+30[C]+0.5[Mn]+25[N]+0.3[Cu],  
       and the Cr equivalent is less than 28.0, and the Ni equivalent is less than 10.5.  
     
     
         8 . The manufacturing method for a precipitation hardened martensitic stainless steel according to  claim 5 , wherein in the precipitation hardened martensitic stainless steel, the total content of Cr and Mo is 15.5 to 16.75%.  
     
     
         9 . A turbine moving blade using the precipitation hardened martensitic stainless steel according to  claim 1 .  
     
     
         10 . A steam turbine provided with a turbine moving blade using the precipitation hardened martensitic stainless steel according to  claim 1  and a rotor in which a 9 to 12 Cr steel is used for at least a long blade implanting portion.  
     
     
         11 . The precipitation hardened martensitic stainless steel according to  claim 2 , wherein the total content of Cr and Mo is 15.5 to 16.75%.  
     
     
         12 . The precipitation hardened martensitic stainless steel according to  claim 2 , wherein the Al content is higher than 1.35% and not lower than 2.25%.  
     
     
         13 . The manufacturing method for a precipitation hardened martensitic stainless steel according to  claim 6 , wherein in the precipitation hardened martensitic stainless steel,  
         Cr equivalent=[Cr]+2[Si]+1.5[Mo]+5.5[Al]+1.75[Nb]+1.5[Ti] Ni equivalent=[Ni]+30[C]+0.5[Mn]+25[N]+0.3[Cu],  
       and the Cr equivalent is less than 28.0, and the Ni equivalent is less than 10.5.  
     
     
         14 . The manufacturing method for a precipitation hardened martensitic stainless steel according to  claim 6 , wherein in the precipitation hardened martensitic stainless steel, the total content of Cr and Mo is 15.5 to 16.75%.  
     
     
         15 . A turbine moving blade using the precipitation hardened martensitic stainless steel according to  claim 2 .  
     
     
         16 . A steam turbine provided with a turbine moving blade using the precipitation hardened martensitic stainless steel according to  claim 2  and a rotor in which a 9 to 12 Cr steel is used for at least a long blade implanting portion.