Hot formed parts with coating-free press hardening steels and method thereof

Abstract

An alloy composition comprises that carbon at a concentration of from greater than or equal to about 0.15% by weight to less than or equal to about 0.5% by weight of the alloy composition, manganese at a concentration of from greater than or equal to about 0.1% by weight to less than or equal to about 3% by weight of the alloy composition; silicon at a concentration of from greater than or equal to about 0.1% by weight to less than or equal to about 0.5% by weight of the alloy composition; either: chromium at a concentration of from greater than or equal to about 2% by weight to less than or equal to about 10% by weight of the alloy composition and aluminum at a concentration of from greater than or equal to about 0% by weight to less than or equal to about 5% by weight of the alloy composition, or aluminum at a concentration of from greater than or equal to about 2% by weight to less than or equal to about 10% by weight of the alloy composition and chromium at a concentration of from greater than or equal to about 0% by weight to less than or equal to about 5% by weight of the alloy composition; and a balance of the alloy composition being iron. Also discloses an alloy composition and a method of producing a press hardening steel object.

What is claimed is: 
     
         1 . An alloy composition comprising:
 carbon at a concentration of from greater than or equal to about 0.15% by weight to less than or equal to about 0.5% by weight of the alloy composition;   manganese at a concentration of from greater than or equal to about 0.1% by weight to less than or equal to about 3% by weight of the alloy composition;   silicon at a concentration of from greater than or equal to about 0.1% by weight to less than or equal to about 0.5% by weight of the alloy composition;   either:
 chromium at a concentration of from greater than or equal to about 2% by weight to less than or equal to about 10% by weight of the alloy composition and aluminum at a concentration of from greater than or equal to about 0% by weight to less than or equal to about 5% by weight of the alloy composition, or 
 aluminum at a concentration of from greater than or equal to about 2% by weight to less than or equal to about 10% by weight of the alloy composition and chromium at a concentration of from greater than or equal to about 0% by weight to less than or equal to about 5% by weight of the alloy composition; and 
   a balance of the alloy composition being iron.   
     
     
         2 . The alloy composition according to  claim 1 , comprising chromium at a concentration of from greater than or equal to about 2.25% by weight to less than or equal to about 5% by weight of the alloy composition. 
     
     
         3 . The alloy composition according to  claim 2 , comprising aluminum at a concentration of from greater than or equal to about 0.02% by weight to less than or equal to about 0.05% by weight of the alloy composition. 
     
     
         4 . The alloy composition according to  claim 2 , wherein the alloy composition has been oxidized at a temperature of from greater than or equal to about 400° C. to less than or equal to about 700° C. for a time of from about greater than or equal to about 1 minute to less than or equal to about 60 minutes and then cooled. 
     
     
         5 . The alloy composition according to  claim 2 , wherein the alloy composition is configured to be hardened into a press hardening steel by subjecting the alloy composition to a temperature of from greater than or equal to about 850° C. to less than or equal to about 1050° C. form a time of from about greater than or equal to about 1 minute to less than or equal to about 15 minutes and then cooled. 
     
     
         6 . The alloy composition according to  claim 5 , wherein the press hardening steel does not require shot blasting after being used for hot forming. 
     
     
         7 . The alloy composition according to  claim 2 , wherein the alloy composition is in the form of a sheet and at least one surface of the sheet comprises a layer of Cr-enriched oxide. 
     
     
         8 . The alloy composition according to  claim 7 , wherein the layer of Cr-enriched oxide has a thickness of from greater than or equal to about 1 μm to less than or equal to about 40 μm. 
     
     
         9 . The alloy composition according to  claim 1 , comprising aluminum at a concentration of from greater than or equal to about 2% by weight to less than or equal to about 6% by weight of the alloy composition. 
     
     
         10 . The alloy composition according to  claim 9 , comprising chromium at a concentration of from greater than or equal to about 0.05% by weight to less than or equal to about 0.3% by weight of the alloy composition. 
     
     
         11 . The alloy composition according to  claim 10 , wherein the aluminum has a concentration of about 4% by weight of the alloy composition. 
     
     
         12 . The alloy composition according to  claim 9 , wherein the alloy composition has a density that is 5% less than a second alloy composition having the same components, but with an aluminum concentration of less than or equal to about 0.05% by weight of the second alloy composition. 
     
     
         13 . The alloy composition according to  claim 9 , wherein the alloy composition is configured to be hardened into a press hardening steel by subjecting the alloy composition to a temperature of from greater than or equal to about 850° C. to less than or equal to about 1050° C. form a time of from about greater than or equal to about 1 minute to less than or equal to about 15 minutes and then cooled. 
     
     
         14 . The alloy composition according to  claim 13 , wherein the press hardening steel has a predetermined shape and at least one surface of the predetermined shape comprises a layer of Al-enriched oxide. 
     
     
         15 . The alloy composition according to  claim 14 , wherein the press hardening steel does not require shot blasting after being used for hot forming. 
     
     
         16 . An alloy composition comprising:
 carbon at a concentration of from greater than or equal to about 0.2% by weight to less than or equal to about 0.3% by weight of the alloy composition;   boron at a concentration of from greater than or equal to about 0.001% by weight to less than or equal to about 0.005% by weight of the alloy composition;   manganese at a concentration of from greater than or equal to about 0.5% by weight to less than or equal to about 3% by weight of the alloy composition;   silicon at a concentration of from greater than or equal to about 0.1% by weight to less than or equal to about 0.5% by weight of the alloy composition;   either:
 chromium at a concentration of from greater than or equal to about 2.25% by weight to less than or equal to about 5% by weight of the alloy composition and aluminum at a concentration of from greater than or equal to about 0% by weight to less than or equal to about 5% by weight of the alloy composition, or 
 aluminum at a concentration of from greater than or equal to about 2% by weight to less than or equal to about 5% by weight of the alloy composition and chromium at a concentration of from greater than or equal to about 0% by weight to less than or equal to about 5% by weight of the alloy composition; and 
   a balance of the alloy composition being iron.   
     
     
         17 . A method of producing a press hardening steel object, the method comprising:
 heating an alloy blank to a temperature of from greater than or equal to about 850° C. to less than or equal to about 1050° C. for a time of from about greater than or equal to about 1 minute to less than or equal to about 15 minutes to generated a heated alloy blank, wherein the alloy blank is composed of an alloy composition comprising:
 carbon at a concentration of from greater than or equal to about 0.15% by weight to less than or equal to about 0.5% by weight of the alloy composition, 
 manganese at a concentration of from greater than or equal to about 0.1% by weight to less than or equal to about 3% by weight of the alloy composition, 
 silicon at a concentration of from greater than or equal to about 0.1% by weight to less than or equal to about 0.5% by weight of the alloy composition, either: 
 chromium at a concentration of from greater than or equal to about 2% by weight to less than or equal to about 10% by weight of the alloy composition and aluminum at a concentration of from greater than or equal to about 0% by weight to less than or equal to about 5% by weight of the alloy composition, or 
 aluminum at a concentration of from greater than or equal to about 2% by weight to less than or equal to about 10% by weight of the alloy composition and chromium at a concentration of from greater than or equal to about 0% by weight to less than or equal to about 5% by weight of the alloy composition, and 
 a balance of the alloy composition being iron; 
   transferring the heated alloy blank to a die to form the heated alloy blank into an object with a predetermined shape; and   quenching the object with a predetermined shape to generate an object composed of press hardening steel,   wherein the press hardening steel object has at least one surface comprising an oxide layer and wherein the method does not require shot blasting.   
     
     
         18 . The method according to  claim 17 , wherein the quenching the object comprises cooling the object at a rate of greater than or equal to about 15° C./s. 
     
     
         19 . The method according to  claim 17 , wherein the alloy composition comprises chromium at a concentration of from greater than or equal to about 2.25% by weight to less than or equal to about 5% by weight of the alloy composition, and the method further comprises, prior to the heating:
 pre-oxidizing the alloy composition by heating the alloy composition to a temperature of from greater than or equal to about 400° C. to less than or equal to about 700° C. for a time of from about greater than or equal to about 1 minute to less than or equal to about 60 minutes and then cooling the alloy composition.   
     
     
         20 . The method according to  claim 17 , wherein the alloy composition comprises aluminum at a concentration of from greater than or equal to about 2% by weight to less than or equal to about 10% by weight of the alloy composition, and the method further comprises, prior to the quenching:
 soaking the heated alloy blank at a temperature of from greater than or equal to about 850° C. to less than or equal to about 1050° C. in the presence of niobium and vanadium.