Microstructural optimization of automotive structures

Abstract

A process for hot stamping a steel component is described. The hot stamping process enables the formation of one or more regions of the component to exhibit specific physical properties different than other regions of the component. The various processes are particularly well suited for forming a variety of automobile structural members.

1 . A process for forming a high strength martensite microstructure in only a portion of a steel component after stamping in a die, and without removal of the component from the die, the process comprising:
 stamping a steel component in a die, the steel component having a temperature greater than about 850° C. and an austenite microstructure throughout the entire component;   while the component is in the die, cooling a desired portion of the steel component at a cooling rate of greater than about 27° C. per second and cooling a remainder portion of the steel component at a cooling rate of less than about 27° C. per second, the die contacting the entire surface of the steel component, so that the microstructure of the steel component in the desired portion undergoing cooling is transformed into a martensite microstructure; and   after formation of the martensite microstructure in the desired portion, removing the component from the die.   
   
   
       2 . The process of  claim 1  wherein the temperature of the steel component during stamping is from 900° C. to 950° C.. 
   
   
       3 . The process of  claim 1  wherein the desired portion of the steel component is cooled at a cooling rate of from about 30° C. per second to about 100° C. per second. 
   
   
       4 . The process of  claim 1  wherein the desired portion of the steel component is a first portion, and the cooling step further includes cooling a second desired portion of the steel component while the component is in the die at a cooling rate of greater than about 27° C. per second, so that the microstructure of the steel component in the second desired portion undergoing cooling is also transformed into a martensite microstructure. 
   
   
       5 . The process of  claim 1  wherein the steel component has a composition including 0.14-0.32% carbon, 0-0.50% silicon, 0.60-1.60% manganese, 0.04-0.45% chromium, 0-0.15% titanium, 0-0.10% sulfur, 0-0.01% boron, and 0.001-2.00% of other agents. 
   
   
       6 . The process of  claim 1  wherein the steel component has a composition including 0.18-0.28% carbon, 0.10-0.40% silicon, 0.80-1.45% manganese, 0.08-0.40% chromium, 0.01-0.10% titanium, 0-0.010% sulfur, 0.002-0.004%, and 0.001-1.00% of other agents. 
   
   
       7 . The process of  claim 1  further comprising:
 prior to stamping, identifying a region of the die corresponding to the desired portion of the steel component; and   wherein the cooling step is performed by reducing the temperature in the region of the die to thereby cool the desired portion of the steel component.   
   
   
       8 . A process for forming a desired microstructure in a region of a steel component different than the microstructure in remaining regions of the component, after stamping in a die and without removal of the component from the die, the process comprising:
 identifying a region of a steel sheet to exhibit a desired microstructure in a steel component formed from the sheet, the microstructure being different than a microstructure in remaining regions of the component;   identifying an area in a die corresponding to the identified region of the steel sheet;   stamping a heated steel sheet in the die to form the steel component;   cooling the area in the die so as to achieve the desired microstructure in the identified region of the steel component different than the microstructure in the remaining regions of the steel component, the die contacting the entire surface of the steel component.   
   
   
       9 . The process of  claim 8  wherein the cooling is performed such that the identified region of the steel component undergoes a cooling rate greater than 27° C. per second. 
   
   
       10 . The process of  claim 9  wherein the remaining regions of the steel component undergo a cooling rate less than 27° C. per second. 
   
   
       11 . The process of  claim 8  wherein the temperature of the steel sheet prior to stamping, is from 900° C. to 950° C. and after stamping, the identified region of the steel component undergoes a cooling rate of from about 30° C. per second to about 100° C. per second. 
   
   
       12 . The process of  claim 8  wherein the steel component has a composition including 0.14-0.32% carbon, 0-0.50% silicon, 0.60-1.60% manganese, 0.04-0.45% chromium, 0-0.15% titanium, 0-0.10% sulfur, 0-0.01% boron, and 0.001-2.00% of other agents. 
   
   
       13 . The process of  claim 8  wherein the steel component has a composition including 0.18-0.28% carbon, 0.10-0.40% silicon, 0.80-1.45% manganese, 0.08-0.40% chromium, 0.01-0.10% titanium, 0-0.010% sulfur, 0.002-0.004%, and 0.001-1.00% of other agents. 
   
   
       14 . The process of  claim 8  wherein the heated steel sheet is in an austenite phase. 
   
   
       15 . A process for obtaining a martensite microstructure in a region of a steel component and which is different than the microstructure in remaining regions of the component, after stamping in a die and without removal of the component from the die, the process comprising:
 providing a steel sheet to be subsequently formed into a steel component;   identifying a region of a steel sheet to exhibit a martensite microstructure in a steel component formed from the sheet, the martensite microstructure being different than a microstructure in remaining regions of the component, wherein the die contacts the entire surface of the steel component during cooling;   identifying an area in a die corresponding to the identified region of the steel sheet;   heating the steel sheet to a temperature of at least 900° C.;   stamping the steel sheet in the die to form the steel component;   cooling the area in the die so that the identified region in the steel component cools at a rate greater than 27° C. per second so as to achieve the martensite microstructure in the identified region of the steel component and which is different than the microstructure in the remaining regions of the steel component.   
   
   
       16 . The process of  claim 15  wherein the steel component has a composition including 0.14-0.32% carbon, 0-0.50% silicon, 0.60-1.60% manganese, 0.04-0.45% chromium, 0-0.15% titanium, 0-0.10% sulfur, 0-0.01% boron, and 0.001-2.00% of other agents. 
   
   
       17 . The process of  claim 15  wherein the steel component has a composition including 0.18-0.28% carbon, 0.10-0.40% silicon, 0.80-1.45% manganese, 0.08-0.40% chromium, 0.01-0.10% titanium, 0-0.010% sulfur, 0.002-0.004%, and 0.001-1.00% of other agents. 
   
   
       18 . The process of  claim 15  wherein prior to stamping, the steel is in an austenite phase. 
   
   
       19 . The process of  claim 15  further comprising:
 identifying a second region of the steel sheet to exhibit a martensite microstructure in the steel component formed from the steel sheet;   identifying a second area in a die corresponding to the identified second region of the steel sheet;   cooling the second area in the die so that the identified second region in the steel component cools at a rate greater than 27° C. per second so as to achieve the martensite microstructure in the identified second region of the steel component.   
   
   
       20 . The process of  claim 15  wherein cooling is performed at a rate of from about 30° C. per second to about 100° C. per second.