High-strength martensite heat resisting cast steel, method of producing the steel, and applications of the steel

Abstract

A high-strength martensite heat resisting steel which has long-time creep rupture strength required for steam temperature condition of 600-630° C. and toughness at room temperature, and which is suitable for use as a material of a steam turbine rotor shaft and as large-sized forged steel with an improvement of hot forgeability. A method of producing the steel and applications of the steel are also provided. The high-strength martensite heat resisting steel contains 0.05-0.20% by mass of C, 0.1% or less of Si, 0.05-0.6% of Mn, 0.1-0.6% of Ni, 9.0-12.0% of Cr, 0.20-0.65% of Mo, 2.0-3.0% of W, 0.1-0.3% of V, 2.0% or less of Co, 0.02-0.20% of Nb, 0.015% or less of B, 0.01-0.10% of N, and 0.015% or less of Al, (W/Mo) being 4.0-10.0.

1 . A high-strength martensite heat resisting steel containing 0.07-0.20% by mass of C, 0.1% or less of Si, 0.15-0.7% of Mn, 0.15-7% of Ni, 9.5-12.0% of Cr, 0.20-0.65% of Mo, 1.8-3.0% of W, 0.1-0.3% of V, 0.03-0.15% of Nb, 0.01-0.10% of N, 0.5-2.0% of Co, and 0.008-0.015% of B, wherein a ratio of W/Mo is 4.0-10.0, thereby causing the high-strength martensite heat resisting steel to have a minimum creep rupture strength and toughness, and wherein the balance of the high-strength martensite heat resisting steel is Fe and unavoidable impurities. 
   
   
       2 . A high-strength martensite heat resisting steel containing 0.07-0.20% by mass of C, 0.1% or less of Si, 0.15-0.7% of Mn, 0.15-0.7% of Ni, 9.5-12.0% of Cr, 0.20-0.65% of Mo, 1.8-3.0% of W, 0.5-2.0% of Co, 0.1-0.3% of V, 0.03-0.15% of Nb, and 0.01-0.10% of N, wherein a ratio of W/Mo is 4.0-10.0, thereby causing the high-strength martensite heat resisting steel to have a minimum creep rupture strength and toughness, and wherein the balance of the high-strength martensite heat resisting steel is Fe and unavoidable impurities. 
   
   
       3 . A high-strength martensite heat resisting steel containing 0.09-0.16% by mass of C, 0.03-0.08% of Si, 0.3-0.55% of Mn, 0.2-0.7% of Ni, 10-11% of Cr, 0.3-0.55% of Mo, 2.0-2.5% of W, 0.1-0.3% of V, 0.04-0.10% of Nb, and 0.01-0.07% of N, 0.5-2.0% of Co, and 0.008-0.015% of B, wherein the ratio of W/Mo is 4.0-8.07, thereby causing the high-strength martensite heat resisting steel to have a minimum creep rupture strength and toughness, and wherein the balance of the high-strength martensite heat resisting steel is Fe and unavoidable impurities. 
   
   
       4 . A high-strength martensite heat resisting steel containing 0.09-0.16% by mass of C, 0.03-0.08% of Si, 0.3-0.55% of Mn, 0.2-0.7% of Ni, 10-11% of Cr, 0.3-0.55% of Mo, 2.0-2.5% of W, 0.1-0.3% of V, 0.04-0.10% of Nb, 0.01-0.07% of N, and 0.5-2.0% of Co, wherein a ratio of (W/Mo) is 4.0-8.0, thereby causing the high-strength martensite heat resisting steel to have a minimum creep rupture strength and toughness, and wherein the balance of the high-strength martensite heat resisting steel is Fe and unavoidable impurities. 
   
   
       5 . (canceled) 
   
   
       6 . A method of producing a high-strength martensite heat resisting steel containing 0.07-0.20% by mass of C, 0.1% or less of Si, 0.15-0.7% of Mn, 0.15-0.7% of Ni, 9.5-12.0% of Cr, 0.20-0.65% of Mo, 1.8-3.0% of W, 0.1-0.3% of V, 0.03-0.15% of Nb, 0.01-0.10% of N, 0.5-2.0% of Co, and 0.008-0.015% of B, wherein the ratio of W/Mo is 4.0-10.0, thereby causing the high-strength martensite heat resisting steel to have a minimum creep rupture strength and toughness, wherein the balance of the high-strength martensite heat resisting steel is Fe and unavoidable impurities, and wherein the method includes a series of steps of hot plastic working, quenching, primary tempering, and secondary tempering at higher temperature than that in the primary tempering. 
   
   
       7 . A method of producing a high-strength martensite heat resisting steel containing 0.07-0.20% by mass of C, 0.1% or less of Si, 0.15-0.7% of Mn, 0.15-0.7% of Ni, 9.5-12.0% of Cr, 0.20-0.65% of Mo, 1.8-3.0% of W, 0.5-2.0% of Co, 0.1-0.3% of V, 0.03-0.15% of Nb, and 0.01-0.10% of N, wherein the ratio of W/Mo is 4.0-10.0, thereby causing the high-strength martensite heat resisting steel to have a minimum creep rupture strength and toughness, wherein the balance of the high-strength martensite heat resisting steel is Fe and unavoidable impurities, and wherein the method includes a series of steps of hot plastic working, quenching, primary tempering, and secondary tempering at higher temperature than that in the primary tempering. 
   
   
       8 . The method of producing the high-strength martensite heat resisting steel containing 0.09-0.16% by mass of C, 0.03-0.08% of Si, 0.3-0.55% of Mn, 0.2-0.7% of Ni, 10-11% of Cr, 0.3-0.55% of Mo, 2.0-2.5% of W, 0.1-0.3% of V, 0.04-0.10% of Nb, 0.01-0.07% of N, 0.5-2.0% of Co, and 0.008-0.015% of B, wherein a ratio of (W/Mo) is 4.0-8.0 thereby causing the high-strength martensite heat resisting steel to have a minimum creep rupture strength and toughness, wherein the balance of the high-strength martensite heat resisting steel is Fe and unavoidable impurities, and wherein the method includes a series of steps of hot plastic working, quenching, primary tempering, and secondary tempering at a higher temperature than that in the primary tempering. 
   
   
       9 . A method of producing the high-strength martensite heat resisting steel containing 0.09-0.16% by mass of C, 0.03-0.08% of Si, 0.3-0.55% of Mn, 0.2-0.7% of Ni, 10-11% of Cr, 0.3-0.55% of Mo, 2.0-2.5% of W, 0.1-0.3% of V, 0.04-0.10% of Nb, 0.01-0.07% of N, and 0.5-2.0% of Co, wherein a ratio of (W/Mo) is 4.0-8.0, thereby causing the high-strength martensite heat resisting steel to have a minimum creep rupture strength and toughness, wherein the balance of the high-strength martensite heat resisting steel is Fe and unavoidable impurities, and wherein the method includes a series of steps of hot plastic working, quenching, primary tempering, and secondary tempering at a higher temperature than that in the primary tempering. 
   
   
       10 . (canceled) 
   
   
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