Austempering Of Structural Components

Abstract

An austempered structural steel component for an automotive vehicle, and a method for manufacturing the component, is provided. The structural component can be a twist axle, spring link, control arm, pillar, trailer hitch, bumper, body or suspension attachment bracket for a truck frame, or other chassis, body in white, or safety-related component. The structural component is at least partially formed of medium carbon steel having a bainitic microstructure. The medium carbon steel can include 0.2 to 1.0 wt. % carbon, 0.1 to 3.0 wt. % manganese, not greater than 2.0 wt. % silicon, 0.0 to 0.010 wt. % boron, not greater than 0.1 wt. % sulfur, and not greater than 0.2 wt. % phosphorous. The medium carbon steel provides a yield strength of 900 to 1500 MPa. The structural component is also lighter and can potentially be manufactured with reduced costs, compared to structural components formed from other steel materials.

1 . A method of manufacturing a structural component for an automotive vehicle or truck, comprising the steps of:
 providing a shaped component formed at least partially from a medium carbon steel material; and   austempering the shaped component, wherein the austempering step includes transforming the microstructure of the medium carbon steel material to a microstructure consisting predominantly of bainite.   
     
     
         2 . The method of  claim 1 , wherein the medium carbon steel material includes 0.2 to 1.0 wt. % carbon (C), 0.1 to 3.0 wt. % manganese (Mn), not greater than 2.0 wt. % silicon (Si), not greater than 0.010 wt. % boron, not greater than 0.1 wt. % sulfur (S), and not greater than 0.2 wt. % phosphorous (P), based on the total weight of the medium carbon steel material. 
     
     
         3 . The method of  claim 2 , wherein the medium carbon steel material includes 0.25 to 0.45 wt. % carbon (C), 0.4 to 2.0 wt. % manganese (Mn), not greater than 1.0 wt. % silicon (Si), not greater than 0.01 wt. % boron (B), not greater than 0.05 wt. % sulfur (S), and not greater than 0.1 wt. % phosphorous (P), based on the total weight of the medium carbon steel material. 
     
     
         4 . The method of  claim 1 , wherein the austempering step includes heating the shaped component until the microstructure of the medium carbon steel material includes austenite, and quenching the heated shaped component until the microstructure of the medium carbon steel material transforms to the microstructure consisting predominantly of bainite. 
     
     
         5 . The method of  claim 4 , wherein the heating step includes heating the medium carbon steel material to a temperature above 750° C., and the quenching step includes cooling the medium carbon steel material to a temperature of 300 to 600° C. 
     
     
         6 . The method of  claim 1 , wherein the shaped component is partially formed of at least one second steel material different from the medium carbon steel material. 
     
     
         7 . The method of  claim 6 , wherein the step of providing the shaped component includes mixing the medium carbon steel material and the at least one second steel material to provide a single workpiece, and shaping the single workpiece. 
     
     
         8 . The method of  claim 6 , wherein the step of providing the shaped component includes providing a first workpiece formed of the medium carbon steel material, providing a second workpiece formed of the at least one second steel material, and joining the workpieces together. 
     
     
         9 . The method of  claim 6 , wherein the austempering step includes heating the medium carbon steel material and the at least one second steel material together until the microstructure of both steel materials includes austenite, and quenching the medium carbon steel material and the at least one second steel material together until the medium carbon steel material has a microstructure consisting predominantly of bainite and the at least one second steel material has a microstructure different from the microstructure consisting predominantly of bainite. 
     
     
         10 . The method of  claim 1 , wherein the step of providing the shaped component includes providing a workpiece formed at least partially from the medium carbon steel material, and shaping the workpiece to the shape of a twist axle, spring link, control arm, pillar, trailer hitch, bumper, body or suspension attachment bracket, or other chassis, body in white, or safety-related component. 
     
     
         11 . The method of  claim 1 , wherein the step of providing the shaped component includes providing a workpiece formed at least partially from the medium carbon steel material and shaping the workpiece to the shape of a twist axle, spring link, control arm, pillar, trailer hitch, bumper, body or suspension attachment bracket, or other chassis, body in white, or safety-related component;
 the medium carbon steel material includes 0.25 to 0.45 wt. % carbon (C), 0.4 to 2.0 wt. % manganese (Mn), not greater than 1.0 wt. % silicon (Si), not greater than 0.01 wt. % boron (B), not greater than 0.05 wt. % sulfur (S), and not greater than 0.1 wt. % phosphorous (P), based on the total weight of the medium carbon steel material;   the austempering step includes heating the shaped component to a temperature above 750° C. in an oven until the microstructure of the medium carbon steel material consists essentially of austenite;   the austempering step further includes quenching the heated shaped component to a temperature of 300 to 600° C. in a nitrite and/or nitrate salt bath, and holding the quenched shaped component at a temperature of 300 to 600° C. until the microstructure of the medium carbon steel material transforms from the microstructure consisting essentially of austenite to the microstructure consisting predominantly of bainite; and   the microstructure consisting predominantly of bainite includes at least one of upper bainite and lower bainite.   
     
     
         12 . A method of manufacturing a structural component for an automotive vehicle or truck, comprising the steps of:
 providing a shaped component formed at least partially from a medium carbon steel material, the medium carbon steel material including 0.2 to 1.0 wt. % carbon (C), 0.1 to 3.0 wt. % manganese (Mn), not greater than 2.0 wt. % silicon (Si), not greater than 0.010 wt. % boron (B), not greater than 0.1 wt. % sulfur (S), and not greater than 0.2 wt. % phosphorous (P), based on the total weight of the medium carbon steel material; and   austempering the shaped component, wherein the austempering step includes transforming the microstructure of the medium carbon steel material to a microstructure including bainite.   
     
     
         13 . The method of  claim 12 , wherein the medium carbon steel material includes 0.25 to 0.45 wt. % carbon (C), 0.4 to 2.0 wt. % manganese (Mn), not greater than 1.0 wt. % silicon (Si), not greater than 0.01 wt. % boron (B), not greater than 0.05 wt. % sulfur (S), and not greater than 0.1 wt. % phosphorous (P), based on the total weight of the medium carbon steel material. 
     
     
         14 . A structural component for an automotive vehicle or truck, comprising:
 a medium carbon steel material, the medium carbon steel material being austempered and having a microstructure consisting predominantly of bainite.   
     
     
         15 . The structural component of  claim 14 , wherein the medium carbon steel material includes 0.2 to 1.0 wt. % carbon (C), 0.1 to 3.0 wt. % manganese (Mn), not greater than 2.0 wt. % silicon (Si), 0.0 to 0.010 wt. % boron (B), not greater than 0.1 wt. % sulfur (S), and not greater than 0.2 wt. % phosphorous (P), based on the total weight of the medium carbon steel material. 
     
     
         16 . The structural component of  claim 15 , wherein the medium carbon steel material includes 0.25 to 0.45 wt. % carbon (C), 0.4 to 2.0 wt. % manganese (Mn), not greater than 1.0 wt. % silicon (Si), 0.0 to 0.010 wt. % boron (B), not greater than 0.05 wt. % sulfur (S), and not greater than 0.1 wt. % phosphorous (P), based on the total weight of the medium carbon steel material. 
     
     
         17 . The structural component of  claim 14 , wherein the medium carbon steel material is shaped to form a twist axle, spring link, control arm, pillar, trailer hitch, bumper, body or suspension attachment bracket, or other chassis, body in white, or safety-related component. 
     
     
         18 . The structural component of  claim 14  further including at least one second steel material different from the medium carbon steel material, wherein the at least one second steel material is mixed with or joined to the medium carbon steel material, and the at least one second steel material has a microstructure different from the microstructure of the medium carbon steel material consisting predominantly of bainite. 
     
     
         19 . (canceled) 
     
     
         20 . (canceled) 
     
     
         21 . (canceled) 
     
     
         22 . A structural component for an automotive vehicle or truck, comprising:
 a medium carbon steel material including 0.2 to 1.0 wt. % carbon (C), 0.1 to 3.0 wt. % manganese (Mn), not greater than 2.0 wt. % silicon (Si), 0.0 to 0.010 wt. % boron (B), not greater than 0.1 wt. % sulfur (S), and not greater than 0.2 wt. % phosphorous (P), based on the total weight of the medium carbon steel material; and   the medium carbon steel material being austempered and having a microstructure including bainite.   
     
     
         23 . (canceled)