Tailored Properties By Post Hot Forming Processing

Abstract

A method of forming a product from an initial blank comprises subjecting the initial blank to a hot forming and press hardening operation to form the product with substantially a uniform first tensile strength. Subsequently, the product is subjected to post hot-forming processing in which a first region of the product is heated selectively to above a known temperature, using one of conduction heating, resistance heating, and induction heating. The first region is then cooled, such that the first region attains a second tensile strength that is substantially less than the first tensile strength.

1 . A method of forming a product from an initial blank, comprising:
 subjecting the initial blank to a hot forming and press hardening operation to form the product with substantially a uniform first tensile strength; and subsequently,   subjecting the product to post hot-forming processing, comprising selectively heating a first region of the product to above a known temperature, while simultaneously maintaining below the known temperature a second region of the product that is adjacent to the first region, and then cooling the first region such that the first region attains a second tensile strength that is substantially less than the first tensile strength.   
     
     
         2 . A method according to  claim 1 , wherein the post hot-forming processing comprises using conduction heating to heat the first region of the product to above the known temperature. 
     
     
         3 . A method according to  claim 2 , wherein the conduction heating is performed using a heated die including at least one of an upper heated die half and a lower heated die half. 
     
     
         4 . A method according to  claim 2 , wherein the conduction heating is performed using at least one heated plate. 
     
     
         5 . A method according to  claim 2 , wherein the conduction heating is performed using a heated fluid. 
     
     
         6 . A method according to  claim 2 , wherein the conduction heating is performed using a heated fluid and a contacting medium. 
     
     
         7 . A method according to  claim 6 , wherein the contacting medium is selected from the group consisting of sand, salt and ceramic. 
     
     
         8 . A method according to  claim 1 , wherein the post hot-forming processing comprises using resistance heating to heat the first region of the product to above the known temperature. 
     
     
         9 . A method according to  claim 1 , wherein the post hot-forming processing comprises using induction heating to heat the first region of the product to above the known temperature. 
     
     
         10 . A method according to  claim 9 , wherein the induction heating is performed using a pair of induction coils disposed one each along opposite sides of the first region. 
     
     
         11 . A method according to  claim 9 , wherein the induction heating is performed using a single induction coil. 
     
     
         12 . A method according to  claim 9 , wherein the induction heating is performed using a pair of induction plates disposed one each along opposite sides of the first region. 
     
     
         13 . A method according to  claim 1 , wherein the initial blank is heated to an austenitization temperature during the hot forming and press hardening operation, and wherein the known temperature is substantially lower than the austenitization temperature. 
     
     
         14 . A method according to  claim 1 , comprising protecting the second region from being heated to substantially the known temperature. 
     
     
         15 . A method according to  claim 1 , wherein the known temperature is between approximately 370° C. and approximately 800° C. 
     
     
         16 . A method according to  claim 1 , wherein the known temperature is between approximately 400° C. and approximately 700° C. 
     
     
         17 . A method according to  claim 1 , wherein the initial blank is fabricated from a press hardenable steel alloy material. 
     
     
         18 . A method of forming a product from an initial blank, comprising:
 heating the initial blank to an austenitizing temperature;   hot-shaping the initial blank in a cooled pair of dies to form the product;   cooling the product during a first period of time, using a rate of cooling that is sufficiently rapid to support formation of a martensitic structure within substantially the entire product;   subjecting a first portion of the product to post hot-forming processing, comprising selectively heating the first portion of the product to a known temperature that is less than the austenitizing temperature, while simultaneously maintaining below the known temperature a second portion of the product that is adjacent to the first portion; and,   cooling the product such that tempered martensite is formed within the first portion of the product while at the same time the second portion of the product remains substantially free of tempered martensite.   
     
     
         19 . A method of forming a product from an initial blank, comprising:
 providing the initial blank;   heating the initial blank to the austenite state;   hot-stamping the initial blank in a cooled pair of dies to form the product;   hardening substantially the entire product while it is still inside the pair of dies by cooling the product using a rate of cooling that is sufficiently fast to form a martensitic structure;   using conduction heating, heating a first portion of the product to at least a predetermined first temperature, while at the same time maintaining a second portion of the product below a predetermined second temperature that is lower than the first temperature; and,   cooling the product such that tempered martensite is formed within the first portion of the product while at the same time the second portion of the product remains substantially free of tempered martensite,   wherein subsequent to cooling, a tensile strength of the first portion of the product is less than a tensile strength of the second portion of the product.   
     
     
         20 . A method of forming a product from an initial blank, comprising:
 providing the initial blank;   heating the initial blank to the austenite state;   hot-stamping the initial blank in a cooled pair of dies to form the product;   hardening substantially the entire product while it is still inside the pair of dies by cooling the product using a rate of cooling that is sufficiently fast to form a martensitic structure;   using resistance heating, heating a first portion of the product to at least a predetermined first temperature, while at the same time maintaining a second portion of the product below a predetermined second temperature that is lower than the first temperature; and,   cooling the product such that tempered martensite is formed within the first portion of the product while at the same time the second portion of the product remains substantially free of tempered martensite,   wherein subsequent to cooling, a tensile strength of the first portion of the product is less than a tensile strength of the second portion of the product.   
     
     
         21 . A method of forming a product from an initial blank, comprising:
 providing the initial blank;   heating the initial blank to the austenite state;   hot-stamping the initial blank in a cooled pair of dies to form the product;   hardening substantially the entire product while it is still inside the pair of dies by cooling the product using a rate of cooling that is sufficiently fast to form a martensitic structure;   using induction heating, heating a first portion of the product to at least a predetermined first temperature, while at the same time maintaining a second portion of the product below a predetermined second temperature that is lower than the first temperature; and,   cooling the product such that tempered martensite is formed within the first portion of the product while at the same time the second portion of the product remains substantially free of tempered martensite,   wherein subsequent to cooling, a tensile strength of the first portion of the product is less than a tensile strength of the second portion of the product.