Mo-V-Ni high temperature steels, articles made therefrom and method of making

Abstract

Low carbon carburizing (surface hardening) and higher carbon through hardening steels primarily containing molybdenum, vanadium and nickel and, to a lesser amount, chromium used for rolling contact bearings, gears and other similar applications where high hardness at elevated temperatures is required. The alloy steel includes, in % by weight: 0.05% to 1.25% C; up to 1.25% Cr; 0.40% to 4% Mn; up to 4.0% Mo; up to 2.0% V; 1.0% to 3.0% Ni; 4% to 8% (Mo+V+Ni+Cr); less than 0.20% Si; and balance Fe plus incidental additions and impurities. The method for providing a steel having improved hardness at elevated temperatures includes the steps of: (a) providing an alloy including, in % by weight: less than 1.25% Cr, 0.4% to 4% Mn, up to 4% Mo, up to 2% V, 1 to 3% Ni, 4% to 8% (Mo+V+Ni+Cr), less than 0.2% Si, a C content selected from one of 0.05% to 0.40% C defining a carburizing steel or greater than 0.40% to 1.25% C defining a through hardening steel, and the balance Fe plus incidental additions and impurities; (b) performing a step selected from the group consisting of (i) subjecting the carburizing steel to carburizing and quenching to provide a quenched carburized steel, or (ii) subjecting the high carbon steel to hot working to provide a wrought high carbon steel; (c) preheating the quenched carburized steel or wrought high carbon steel and then austenitizing said steel to provide an austenitized steel; (d)quenching the austenitized steel to provide quenched austenitized steel; and (e) tempering the quenched austenitized steel followed by air cooling.

1 . An alloy steel comprising in % by weight:
 0.05% to 1.25% C;   up to 1.25% Cr;   0.40% to 4% Mn;   up to 4.0% Mo;   up to 2.0% V;   1.0% to 3.0% Ni;   4% to 8% (Mo+V+Ni+Cr);   less than 0.20% Si; and   balance Fe plus incidental additions and impurities.   
     
     
         2 . The steel of  claim 1  containing 0.05% to 0.40% C, suitable for carburization. 
     
     
         3 . The steel of  claim 1  containing 0.80% to 1.00% C, suitable for through hardening. 
     
     
         4 . An alloy steel suitable for carburizing and exhibiting high hardness at elevated temperatures, comprising in% by weight:
 0.05% to 0.40% C;   up to 1.25% Cr;   0.40% to 4% Mn;   up to 4.0% Mo;   up to 2.0% V;   1.0% to 3.0% Ni;   4% to 8% (Mo+V+Ni+Cr);   less than 0.20% Si; and   balance Fe plus incidental additions and impurities.   
     
     
         5 . An alloy steel suitable for through hardening, comprising in % by weight:
 0.80 to 1.25% C;   up to 1.25% Cr;   0.40% to 4% Mn;   up to 4.0% Mo;   up to 2.0% V;   1.0% to 3.0% Ni;   4% to 8% (Mo+V+Ni+Cr);   less than 0.20% Si; and   balance Fe plus incidental additions and impurities.   
     
     
         6 . The alloy steel of  claim 5  containing 0.80 to 1.00% C. 
     
     
         7 . An article of manufacture suitable for use as a rotating element having high hardness at elevated temperatures, said article made from an alloy steel comprising in% by weight:
 0.05% to 1.25% C;   up to 1.25% Cr;   0.40% to 4% Mn;   up to 4.0% Mo;   up to 2.0% V;   1.0% to 3.0% Ni;   4% to 8% (Mo+V+Ni+Cr);   less than 0.20% Si; and   balance Fe plus incidental additions and impurities.   
     
     
         8 . The article of  claim 7  in the form of a rolling contact/bearing element. 
     
     
         9 . The article of  claim 7  in the form of a gear. 
     
     
         10 . The article of  claim 7  wherein the alloy steel contains 0.05% to 0.40% C and the article is in a carburized, heat treated and tempered condition and possesses a surface hardness of at least 60 HRC at room temperature and a surface hardness of at least 58 HRC at temperatures up to 540° C. 
     
     
         11 . The article of  claim 7  wherein the alloy steel contains 0.80% to 1.00% C and the article is through hardened and possesses a surface hardness of at least 60 HRC at room temperature and a surface hardness of at least 58 HRC at temperatures up to 540° C. 
     
     
         12 . An Mo—V—Ni containing steel suitable for one of carburizing or through hardening and exhibiting high hardness at elevated temperatures, said steel consisting essentially of in% by weight:
 0.05% to 1.25% C;   0.8% to 1.2% Cr;   0.4% to 4% Mn;   up to 4% Mo;   up to 2% V;   1% to 3% Ni;   4% to 8% (Mo+V+Ni+Cr);   less than 0.20% Si;   one or more elements selected from the group consisting of N, Nb and Ti in an amount of up to 0.05% each; and   balance Fe plus incidental additions and impurities.   
     
     
         13 . The steel of  claim 12  containing 0.05% to 0.40% C, suitable for carburization. 
     
     
         14 . The steel of  claim 12  containing 0.80% to 1.00% C, suitable for through hardening. 
     
     
         15 . The alloy of  claim 12  containing 0% to no more than an impurity level of W. 
     
     
         16 . A method of making an alloy steel having improved hardness at elevated temperatures comprising the steps of:
 (a) providing an alloy including, in % by weight: less than 1.25% Cr, 0.4% to 4% Mn, up to 4% Mo, up to 2% V, 1 to 3% Ni, 4% to 8% (Mo+V+Ni+Cr), less than 0.2% Si, a C content selected from one of 0.05% to 0.40% C defining a carburizing steel or greater than 0.40% to 1.25% C defining a through hardening steel, and the balance Fe plus incidental additions and impurities;   (b) performing a step selected from the group consisting of (i) subjecting the carburizing steel to carburizing and quenching to provide a quenched carburized steel, or (ii) subjecting the high carbon steel to hot working to provide a wrought high carbon steel;   (c) preheating the quenched carburized steel or wrought high carbon steel and then austenitizing said steel to provide an austenitized steel;   (d) quenching the austenitized steel to provide quenched austenitized steel; and   (e) tempering the quenched austenitized steel followed by air cooling.   
     
     
         17 . The method of  claim 16 , wherein the alloy provided in step (a) contains 0.05% to 0.40% C and wherein the carburizing and quenching steps of (b)(i) are performed. 
     
     
         18 . The method of  claim 16 , wherein the alloy provided in step (b) contains greater than 0.40% to 1.25% C and wherein the hot working step of (b)(ii) is performed. 
     
     
         19 . The method of  claim 16 , wherein the preheating and austenitizing of step (c) are conducted at a temperature of up to 870° C. for preheating and at a temperature of 1125° C. to 1225° C. for austenitizing. 
     
     
         20 . The method of  claim 16  wherein the steel possesses a surface hardness of at least 60 HRC at room temperature and a surface hardness of at least 58 HRC at temperatures up to 540° C. 
     
     
         21 . A bearing element or gear made according to the method of  claim 20 . 
     
     
         22 . The method of  claim 16 , wherein the tempering step (e) is conducted at a temperature up to 550° C. followed by air cooling. 
     
     
         23 . The method of  claim 22 , wherein the tempering step (e) is conducted twice. 
     
     
         24 . A method of making an alloy steel having improved hardness at elevated temperatures comprising the steps of:
 (a) providing a steel alloy including, in % by weight: less than 1.25% Cr, 0.4% to 4% Mn, up to 4% Mo, up to 2% V, 1 to 3% Ni, 4% to 8% (Mo+V+Ni+Cr), less than 0.2% Si, 0.05% to 0.40% C, and the balance Fe plus incidental additions and impurities;   (b) carburizing and quenching the steel;   (c) preheating the steel and then austenitizing said steel to provide an austenitized steel;   (d) quenching the austenitized steel to provide a quenched austenitized steel; and   (e) tempering the quenched austenitized steel followed by air cooling.   
     
     
         25 . The method of  claim 24 , wherein the carburizing step (b) is conducted at 960° C. 
     
     
         26 . The method of  claim 24 , wherein the preheating and austenitizing of step (c) are conducted at a temperature of up to 870° C. for the preheating and at 1125° C. to 1225° C. for the austenitizing. 
     
     
         27 . The method of  claim 24 , wherein the tempering step (e) is conducted at a temperature of up to 550° C. followed by air cooling and is conducted twice. 
     
     
         28 . The method of  claim 24 , wherein the steel possesses a surface hardness of at least 60 HRC at room temperature and a surface hardness of at least 58 HRC at temperatures up to 540° C. 
     
     
         29 . A bearing element or gear made according to the method of  claim 28 . 
     
     
         30 . A method of making an alloy steel having improved hardness at elevated temperatures comprising the steps of:
 (a) providing an alloy including, in % by weight: less than 1.25% Cr, 0.4% to 4% Mn, up to 4% Mo, up to 2% V, 1 to 3% Ni, 4% to 8% (Mo+V+Ni+Cr), less than 0.2% Si, greater than 0.40% to 1.25% C, and the balance Fe plus incidental additions and impurities;   (b) hot working the steel to provide a wrought steel;   (c) preheating the wrought steel and then austenitizing said steel to provide an austenitized steel;   (d) quenching the austenitized steel to provide quenched austenitized steel; and   (e) tempering the quenched austenitized steel followed by air cooling.   
     
     
         31 . The method of  claim 30 , wherein the alloy provided in step (a) contains 0.80% to 1.00% C. 
     
     
         32 . The method of  claim 30 , wherein the preheating and austenitizing of step (c) are conducted at a temperature of up to 870° C. for the preheating and at 1125° C. to 1225° C. for the austenitizing. 
     
     
         33 . The method of  claim 30 , wherein the tempering step (e) is conducted at a temperature of up to 550° C. followed by air cooling and is conducted twice. 
     
     
         34 . The method of  claim 30 , wherein the steel possesses a surface hardness of at least 60 HRC at room temperature and a surface hardness of at least 58 HRC at temperatures up to 540° C. 
     
     
         35 . A bearing element or gear made according to the method of  claim 34 .