Press hardening steel with high oxidation resistance

Abstract

A steel composition is provided. The steel composition includes 0.1-0.45 wt. % carbon (C), greater than 0-4.5 wt. % manganese (Mn), 0.5-5 wt. % chromium (Cr), 0.5-2.5 wt. % silicon (Si), greater than 0-2 wt. % copper (Cu), and a balance of iron (Fe). The combined concentration of the Mn, Cr, and Cu is greater than about 2 wt. %. The steel composition is configured to form a surface oxide layer comprising oxides of Cr, Si, and Cu after being subjected to press hardening. Press-hardened steel fabricated from the steel composition and a method of fabricating a press-hardened steel component from the steel composition are also provided.

What is claimed is: 
     
         1 . A steel composition comprising:
 carbon (C) at a concentration of greater than or equal to about 0.1 wt. % to less than or equal to about 0.45 wt. %;   manganese (Mn) at a concentration of greater than 0 wt. % to less than or equal to about 4.5 wt. %;   chromium (Cr) at a concentration of greater than or equal to about 0.5 wt. % to less than or equal to about 5 wt. %;   silicon (Si) at a concentration of greater than or equal to about 0.5 wt. % to less than or equal to about 2.5 wt. %;   copper (Cu) at a concentration of greater than 0 wt. % to less than or equal to about 2 wt. %; and   a balance of iron (Fe),   wherein the combined concentration of the Mn, Cr, and Cu is greater than or equal to about 2 wt. %, and   wherein the steel composition is configured to form a surface oxide layer comprising oxides of Cr, Si, and Cu after being subjected to press hardening.   
     
     
         2 . The steel composition according to  claim 1 , further comprising:
 nickel (Ni) at a concentration of greater than 0 wt. % to less than or equal to about 5 wt. %,   wherein the combined concentration of the Mn, Cr, Cu, and Ni is greater than or equal to about 2 wt. %, and   wherein the steel composition is configured to form a surface oxide layer comprising oxides of Cr, Si, Cu, and Ni after being subjected to press hardening.   
     
     
         3 . The steel composition according to  claim 2 , wherein the steel composition is free of coatings. 
     
     
         4 . The steel composition according to  claim 1 , further comprising an additional element selected from the group consisting of:
 molybdenum (Mo) at a concentration of greater than 0 wt. % to less than or equal to about 1 wt. %;   vanadium (V) at a concentration of greater than 0 wt. % to less than or equal to about 1 wt. %;   niobium (Nb) at a concentration of greater than 0 wt. % to less than or equal to about 0.5 wt. %;   boron (B) at a concentration of greater than 0 wt. % to less than or equal to about 0.01 wt. %;   titanium (Ti) at a concentration of greater than 0 wt. % to less than or equal to about 0.1 wt. %;   aluminum (Al) at a concentration of greater than 0 wt. % to less than or equal to about 0.5 wt. %; and   combinations thereof.   
     
     
         5 . The steel composition according to  claim 1 , wherein the steel composition is in the form a coiled sheet. 
     
     
         6 . A press-hardened steel comprising:
 an alloy matrix comprising:
 carbon (C) at a concentration of greater than or equal to about 0.1 wt. % to less than or equal to about 0.45 wt. %; 
 manganese (Mn) at a concentration of greater than 0 wt. % to less than or equal to about 4.5 wt. %; 
 chromium (Cr) at a concentration of greater than or equal to about 0.5 wt. % to less than or equal to about 5 wt. %; 
 silicon (Si) at a concentration of greater than or equal to about 0.5 wt. % to less than or equal to about 2.5 wt. %; 
 copper (Cu) at a concentration of greater than 0 wt. % to less than or equal to about 2 wt. %; and 
 a balance of iron (Fe); and 
   an oxide layer formed on a surface of the alloy matrix during hot forming of the press-hardened steel, the oxide layer comprising oxides of the Cr, Si, and Cu, wherein the oxide layer protects the alloy matrix from oxidation.   
     
     
         7 . The press-hardened steel according to  claim 6 , wherein the combined concentration of the Mn, Cr, and Cu is greater than or equal to about 2 wt. %. 
     
     
         8 . The press-hardened steel according to  claim 6 , wherein the matrix further comprises:
 nickel (Ni) at a concentration of greater than 0 wt. % to less than or equal to about 5 wt. %, and   wherein the oxide layer further comprises oxides of the Ni.   
     
     
         9 . The press-hardened steel according to  claim 8 , wherein the oxide layer is uniform and continuous. 
     
     
         10 . The press-hardened steel according to  claim 6 , wherein the oxide layer has a thickness of greater than or equal to about  1  nm to less than or equal to about 10 μm. 
     
     
         11 . The press-hardened steel according to  claim 6 , wherein the matrix has a microstructure comprising greater than or equal to about 90 vol. % martensite, and a balance comprising retained austenite and optionally ferrite, wherein when the balance comprises ferrite, the ferrite has a concentration of greater than 0 vol. % to less than or equal to about 5 vol. %. 
     
     
         12 . The press-hardened steel according to  claim 6 , wherein the matrix further comprises an additional element selected from the group consisting of:
 molybdenum (Mo) at a concentration of greater than 0 wt. % to less than or equal to about 1 wt. %;   vanadium (V) at a concentration of greater than 0 wt. % to less than or equal to about 1 wt. %;   niobium (Nb) at a concentration of greater than 0 wt. % to less than or equal to about 0.5 wt. %;   boron (B) at a concentration of greater than 0 wt. % to less than or equal to about 0.01 wt. %;   titanium (Ti) at a concentration of greater than 0 wt. % to less than or equal to about 0.1 wt. %;   aluminum (Al) at a concentration of greater than 0 wt. % to less than or equal to about 0.5 wt. %; and   combinations thereof.   
     
     
         13 . An automobile part comprising the press-hardened steel according to  claim 6 . 
     
     
         14 . A method of fabricating a press-hardened steel component, the method comprising:
 heating a blank to a temperature of greater than or equal to about 880° C. to less than or equal to about 950° C. to form a heated blank, the blank comprising a steel composition comprising:
 carbon (C) at a concentration of greater than or equal to about 0.1 wt. % to less than or equal to about 0.45 wt. %; 
 manganese (Mn) at a concentration of greater than 0 wt. % to less than or equal to about 4.5 wt. %; 
 chromium (Cr) at a concentration of greater than or equal to about 0.5 wt. % to less than or equal to about 5 wt. %; 
 silicon (Si) at a concentration of greater than or equal to about 0.5 wt. % to less than or equal to about 2.5 wt. %; 
 copper (Cu) at a concentration of greater than 0 wt. % to less than or equal to about 2 wt. %; and 
 a balance of iron (Fe), 
   pressing the heated blank in a die to form a structure having a predetermined shape from the heated blank; and   quenching the structure to a temperature less than or equal to about a martensite finish (M f ) temperature of the steel composition and greater than or equal to about room temperature to form the press-hardened steel component,   wherein the press-hardened steel component comprises:
 an alloy matrix comprising the C, Mn, Cr, Si, Cu, and Fe, 
 an oxide layer formed on a surface of the alloy matrix, the oxide layer being continuous and uniform, comprising oxides of the Cr, Si, and Cu, and being configured to resist oxidation, and 
 a microstructure comprises greater than or equal to about 90 vol. % martensite, and 
   wherein the press-hardened steel component is formed without descaling and is free of a coating.   
     
     
         15 . The method according to  claim 14 , wherein the blank and the matrix further comprise:
 nickel (Ni) at a concentration of greater than 0 wt. % to less than or equal to about 5 wt. %, and   wherein the oxide layer further comprises oxides of the Ni.   
     
     
         16 . The method according to  claim 15 , wherein the press-hardened steel component comprises about 0.2 wt. % C, about 1.5 wt. % Mn, about 1.5 wt. % Cr, about 1.5 wt. % Si, about 0.8 wt. % Ni, about 0.3 wt. % Cu, and about 0.03 wt. % Nb. 
     
     
         17 . The method according to  claim 15 , wherein the combined concentration of the Mn, Cr, Cu, and Ni in the blank and in the matrix is greater than or equal to about 2 wt. %. 
     
     
         18 . The method according to  claim 14 , wherein the microstructure of the press-hardened steel component further comprises greater than about 0 vol. % to less than or equal to about  10  vol. % retained austenite, and greater than or equal to about  0  vol. % to less than or equal to about 5 vol. % ferrite. 
     
     
         19 . The method according to  claim 14 , wherein the method is free of a secondary heat treatment after the quenching. 
     
     
         20 . The method according to  claim 14 , wherein the press-hardened steel component is an automobile part selected from the group consisting of a wheel, a pillar, a bracket, a bumper, a roof rail, a rocker rail, a rocker, a control arm, a beam, a tunnel, a step, a subframe member, a pan, a panel, and a reinforcement panel.