Methods to avoid over-developed aluminized coatings during hot stamping line stoppages

Abstract

A method of treating a blank is provided. The method includes moving a blank through a first section of a furnace at an inter-critical temperature and through a second section of the furnace at a critical temperature greater than the inter-critical temperature before hot stamping the blank. Movement of the blank from the first section to the second section of the furnace is delayed during a hot stamping line stoppage. The blank is in the first section of the furnace for a first time period and in the second section of the furnace a second time period less than the first time period. Also, the first section of the furnace may have a first length and in the second section of the furnace may have a second length that is less than the first length.

What is claimed is: 
     
         1 . A method of treating a blank comprising:
 moving a blank through a first section of a furnace at an inter-critical temperature and through a second section of the furnace at a critical temperature greater than the inter-critical temperature; and   hot stamping the blank, wherein movement of the blank from the first section to the second section of the furnace is delayed during a hot stamping line stoppage.   
     
     
         2 . The method according to  claim 1 , wherein the blank is in the first section of the furnace for a first time period and in the second section of the furnace a second time period less than the first time period. 
     
     
         3 . The method according to  claim 2 , wherein the first time period is at least 1.2 times greater than the second time period. 
     
     
         4 . The method according to  claim 1 , wherein the first section of the furnace has a first length and the second section of the furnace has a second length less than the first length. 
     
     
         5 . The method according to  claim 1 , wherein the first length is at least 1.2 times greater than and the second length. 
     
     
         6 . The method according to  claim 1 , wherein the blank is formed from coated press hardenable steel. 
     
     
         7 . The method according to  claim 1 , wherein the blank is formed from aluminized press hardenable steel, the inter-critical temperature is between 725° C. and 825° C., and the critical temperature is above 910° C. 
     
     
         8 . The method according to  claim 1 , wherein the blank is formed from aluminized press hardenable steel, the inter-critical temperature is between 750° C. and 800° C., and the critical temperature is above 920° C. 
     
     
         9 . The method according to  claim 8 , wherein the blank is positioned in the first section of the furnace at the inter-critical temperature for a time period up to 1200 seconds before moving to the second section of the furnace and being hot stamped. 
     
     
         10 . The method according to  claim 9 , wherein the hot stamped blank comprises an inter-diffusion layer with a thickness less than 16 μm. 
     
     
         11 . The method according to  claim 8 , wherein the blank is positioned in the first section of the furnace at the inter-critical temperature for a time period up to 1800 seconds before moving to the second section of the furnace and being hot stamped, and the hot stamped blank comprises an inter-diffusion layer with a thickness less than 16 μm. 
     
     
         12 . The method according to  claim 8 , wherein the blank is positioned in the first section of the furnace at the inter-critical temperature for a time period up to 2400 seconds before moving to the second section of the furnace and being hot stamped, and the hot stamped blank comprises an inter-diffusion layer with a thickness less than 16 μm. 
     
     
         13 . The method according to  claim 1 , wherein:
 the blank is formed from aluminized press hardenable steel;   the blank is in the first section of the furnace during the hot stamping line stoppage for a time period up to 1800 seconds;   the blank moves from the first section to the second section and is hot stamped after the hot stamping line stoppage is over; and   the hot stamped blank comprises an inter-diffusion layer with a thickness less than 16 μm.   
     
     
         14 . The method according to  claim 13 , wherein the inter-critical temperature is between 725° C. and 825° C., and the critical temperature is between 910° C. and 950° C. 
     
     
         15 . The method according to  claim 1 , wherein:
 the blank is formed from aluminized press hardenable steel;   the inter-critical temperature is between 750° C. and 800° C., and the critical temperature is between 920° C. and 940° C.   the blank is in the first section of the furnace during the hot stamping line stoppage for a time period up to 2400 seconds;   the blank moves from the first section to the second section and is hot stamped after the hot stamping line stoppage is over; and   the hot stamped blank comprises an inter-diffusion layer with a thickness less than 16 μm.   
     
     
         16 . A method of treating a plurality of blanks during stoppage of a hot stamping line, the method comprising:
 heating a first section of a furnace to an inter-critical temperature between 725° C. and 825° C.;   heating a second section of the furnace to a critical temperature between 910° C. and 950° C.; and   moving a plurality of blanks on a conveyer line through the first section and the second section of the furnace to a hot stamping press and hot stamping the plurality of blanks;   wherein:
 the conveyer line stops moving during stoppage of the hot stamping line such that a subset of blanks in the first section of the furnace do not move into the second section of the furnace; and 
 the conveyer line starts moving after the stoppage of the hot stamping line is over such that the subset of blanks in the first section of the furnace move into and through the second section of the furnace and to the hot stamping press. 
   
     
     
         17 . The method according to  claim 16 , wherein the plurality of blanks is formed from aluminized press hardenable steel and the subset of blanks hot stamped by the hot stamping press after the stoppage of the hot stamping line is over comprise an inter-diffusion layer thickness less than 16 μm. 
     
     
         18 . The method according to  claim 17 , wherein the stoppage of the hot stamping line is for a time up to 1800 seconds. 
     
     
         19 . A method of hot stamping a blank after stoppage of a hot stamping line comprising:
 heating a blank formed from a coated press hardenable steel in a first section of a roller hearth furnace to an inter-critical temperature for a first time period;   heating the blank in a second section of the roller hearth furnace to a critical temperature greater than the inter-critical temperature for a second time period less than the first time period;   stopping the blank from moving from the first section to the second section of the roller hearth furnace during stoppage of the hot stamping line;   moving the blank from the first section to the second section of the roller hearth furnace after the stoppage of the hot stamping line is over; and   hot stamping the blank after it moves through the second section of the furnace, wherein the blank is positioned in the first section of the roller hearth furnace for up to 2400 seconds and the hot stamped blank has an inter-diffusion layer less than 16 μm.   
     
     
         20 . The method according to  claim 19 , wherein the inter-critical temperature is between 725° C. and 825° C., and the critical temperature is above 910° C.