Differential heat shaping and hardening using infrared light

Abstract

A shaped part having at least two structural regions of different ductility is made from one unitary blank of a hardenable steel alloy by first heating the entire blank to an elevated temperature below an AC 3 point of the alloy. Then only first regions of the blank are heated by a plurality of infrared lamps to above the AC 3 point of the alloy while maintaining the rest of the blank below the AC 3 point of the alloy. Finally the first regions are hardened in a thermoshaping and hardening tool.

1 . A method of making a shaped part having at least two structural regions of different ductility from one unitary blank of a hardenable steel alloy, the method comprising the steps of sequentially:
 heating the entire blank with a plurality of infrared lamps to an elevated temperature below an AC 3  point of the alloy;   differentially heating only first regions of the blank to above the AC 3  point of the alloy while maintaining the rest of the blank below the AC 3  point of the alloy;   hardening the first regions in a thermoshaping and hardening tool.   
   
   
       2 . The method defined in  claim 1  wherein the entire blank is heated to the elevated temperature below the AC 3  point in a pass-through furnace. 
   
   
       3 . The method defined in  claim 1  wherein the elevated temperature is at most the AC 1  point of the alloy. 
   
   
       4 . The method defined in  claim 1  wherein the elevated temperature is above the AC 1  point and below the AC 3  point of the alloy. 
   
   
       5 . The method defined in  claim 2  wherein the alloy consists essentially of by weight percent:
 Carbon (C) 0.18% to 0.3%   Silicon (Si) 0.1% to 0.7%   Manganese (Mn) 1.0% to 2.5%   Phosphorus (P) maximum 0.025%   Chromium (Cr) up to 0.8%   Molybdenum (Mo) up to 0.5%   Sulfur (S) maximum 0.01%   Titanium (Ti) 0.02% to 0.05%   Boron (B) 0.002% to 0.005%   Aluminum (Al) 0.01% to 0.06% and   remainder iron and impurities resulting from melting.   
   
   
       6 . The method defined in  claim 1 , further comprising the steps, before heating the blank to the elevated temperature, coating the blank; and
 completely alloying the coating of the blank.   
   
   
       7 . The method defined in  claim 6  wherein the coating is aluminum. 
   
   
       8 . The method defined in  claim 1  wherein the first regions are differentially heated by a plurality of infrared-light sources, the method further comprising the step of:
 providing shields between the regions at the sources.   
   
   
       9 . A method of making a shaped part, the method comprising the steps of sequentially:
 making an elongated workpiece blank of alloyed sheet steel;   heating the entire workpiece blank to an elevated temperature at most equal to the AC 1  point and below an AC 3  point of the alloy;   heating only a center region of the blank to above the AC 3  point of the alloy before any part of the blank cools below the AC 1  point, the end regions remaining below the AC 3  point; and   hardening the center in a thermoshaping and hardening tool.