Steel for hot stamping with enhanced oxidation resistance

Abstract

An alloy composition is provided. The alloy composition includes chromium (Cr) at a concentration of greater than or equal to about 0.5 wt. % to less than or equal to about 9 wt. %, carbon (C) at a concentration of greater than or equal to about 0.15 wt. % to less than or equal to about 0.5 wt. %, manganese (Mn) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 3 wt. %, silicon (Si) at a concentration of greater than or equal to about 0.5 wt. % to less than or equal to about 2 wt. %, and a balance of the alloy composition being iron. Methods of making shaped steel objects from the alloy composition are also provided.

What is claimed is: 
     
         1 . An alloy composition comprising:
 chromium (Cr) at a concentration of greater than or equal to about 0.5 wt. % to less than or equal to about 9 wt. %;   carbon (C) at a concentration of greater than or equal to about 0.15 wt. % to less than or equal to about 0.5 wt. %;   manganese (Mn) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 3 wt. %;   silicon (Si) at a concentration of greater than or equal to about 0.5 wt. % to less than or equal to about 2 wt. %; and   a balance of the alloy composition being iron.   
     
     
         2 . The alloy composition according to  claim 1 , wherein the alloy composition comprises Si at a concentration of greater than or equal to about 0.6 wt. % to less than or equal to about 1.5 wt. %. 
     
     
         3 . The alloy composition according to  claim 1 , wherein the alloy composition comprises Cr at a concentration of greater than or equal to about 2 wt. % to less than or equal to about 3 wt. %. 
     
     
         4 . The alloy composition according to  claim 1 , wherein the alloy composition further comprises:
 aluminum (Al) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 5 wt. %.   
     
     
         5 . The alloy composition according to  claim 1 , wherein the alloy composition further comprises:
 nitrogen (N) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 0.01 wt. %.   
     
     
         6 . The alloy composition according to  claim 1 , wherein the alloy composition further comprises at least one of:
 molybdenum (Mo) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 1 wt. %;   nickel (Ni) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 1 wt. %;   boron (B) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 0.01 wt. %;   niobium (Nb) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 0.5 wt. %; and   vanadium (V) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 0.5 wt. %.   
     
     
         7 . The alloy composition according to  claim 1 , wherein the alloy composition is in the form of an alloy coil. 
     
     
         8 . The alloy composition according to  claim 7 , wherein the alloy coil comprises ferrite, martensite and retained austenite (RA). 
     
     
         9 . The alloy composition according to  claim 7 , wherein the alloy composition has been subjected to a quench and partitioning process. 
     
     
         10 . A hot stamping method of forming a shaped steel object, the hot stamping method comprising:
 austenitizing a blank comprising an alloy composition according to  claim 1 ;   stamping the austenitized blank to form a shaped object; and   quenching the shaped object to form the shaped steel object.   
     
     
         11 . A cold stamping method of forming a shaped steel object, the cold stamping method comprising:
 cutting a blank from a coil comprising an alloy composition according to  claim 1 , wherein the alloy composition has been subjected to a quench and partitioning process; and   stamping the blank into a predetermined shape at ambient temperature to form the shaped steel object.   
     
     
         12 . A method of forming a shaped steel object; the method comprising:
 cutting a blank from a coil of an alloy composition comprising:
 chromium (Cr) at a concentration of greater than or equal to about 0.5 wt. % to less than or equal to about 9 wt. %, 
 carbon (C) at a concentration of greater than or equal to about 0.15 wt. % to less than or equal to about 0.5 wt. %, 
 manganese (Mn) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 3 wt. %, 
 silicon (Si) at a concentration of greater than or equal to about 0.5 wt. % to less than or equal to about 2 wt. %, and 
 a balance of the alloy composition being iron; 
   heating the blank to a temperature above an upper critical temperature (Ac3) of the alloy composition to form a heated blank comprising austenite;   stamping the heated blank into a predetermined shape to form a stamped object; and   quenching the stamped object to form the shaped steel object, wherein the shaped steel object comprises martensite.   
     
     
         13 . The method according to  claim 12 , wherein the quenching comprises decreasing the temperature of the stamped object at a rate of greater than or equal to about 15° C./s until the stamped object reaches a temperature below a martensite finish (Mf) temperature of the alloy composition. 
     
     
         14 . The method according to  claim 12 , wherein the method is free from pre-oxidizing the alloy composition, coating the shaped steel object, and shot blasting. 
     
     
         15 . The method according to  claim 12 , wherein the quenching comprises a quench and partitioning process, wherein the quench and partitioning process comprises:
 decreasing the temperature of the stamped object until the stamped object has a temperature between a martensite start (Ms) temperature of the alloy composition and a martensite finish (Mf) temperature of the alloy composition;   incubating the stamped object at a partitioning temperature wherein carbon (C) is partitioned from martensite into austenite; and   decreasing an austenite Mf temperature below room temperature.   
     
     
         16 . The method according to  claim 15 , wherein the quench and partitioning process forms the shaped steel object, wherein the shaped steel object comprises ferrite, martensite and retained austenite (RA). 
     
     
         17 . The method according to  claim 16 , wherein the shaped steel object is substantially free of cementite. 
     
     
         18 . A method of forming a shaped steel object; the method comprising:
 cutting a blank from a coil of an advanced high strength steel (AHSS); and   stamping the blank into a predetermined shape at ambient temperature to form the shaped steel object,   wherein the AHSS is made by subjecting an alloy composition to a quench and partitioning process, the alloy composition comprising:
 chromium (Cr) at a concentration of greater than or equal to about 0.5 wt. % to less than or equal to about 9 wt. %, 
 carbon (C) at a concentration of greater than or equal to about 0.15 wt. % to less than or equal to about 0.5 wt. %, 
 manganese (Mn) at a concentration of greater than or equal to about 0 wt. % to less than or equal to about 3 wt. %, 
 silicon (Si) at a concentration of greater than or equal to about 0.5 wt. % to less than or equal to about 2 wt. %, and 
 a balance of the alloy composition being iron. 
   
     
     
         19 . The method according to  claim 18 , wherein the AHSS is substantially free of an oxide layer. 
     
     
         20 . The method according to  claim 18 , wherein the shaped steel object is bare or zinc (Zn coated).