Laser spot hardening

Abstract

A hardened/stiffened steel component includes a steel substrate having a bulk region and a steel substrate surface. Plurality of localized martensite-enriched regions is located at the steel substrate surface. Characteristically, the plurality of localized martensite-enriched regions has higher martensite content than the bulk region. Centers of adjacent localized martensite-enriched regions in the plurality of martensite-enriched localized regions are separated by a separation distance that is from about 0.5 to 5 mm. A method for forming the steel component by laser spot hardening is also provided.

What is claimed is: 
     
         1 . A steel component comprising:
 a steel substrate having a bulk region and a steel substrate surface; and   a plurality of localized martensite-enriched regions located at the steel substrate surface, the plurality of localized martensite-enriched regions having higher martensite content than the bulk region, wherein centers of adjacent localized martensite-enriched regions in the plurality of martensite-enriched localized region are separated by a separation distance that is from about 0.5 to 5 mm.   
     
     
         2 . The steel component of  claim 1  wherein the separation distance is from about 1 to 4 mm. 
     
     
         3 . The steel component of  claim 1  wherein the separation distance is from about 1.5 to 3 mm. 
     
     
         4 . The steel component of  claim 1  wherein at least a portion of the plurality of martensite-enriched localized regions are arranged in a rectangular array. 
     
     
         5 . The steel component of  claim 1  wherein at least a portion of the plurality of martensite-enriched localized regions are arranged in a hexagonal array. 
     
     
         6 . The steel component of  claim 1  wherein each localized martensite-enriched region has a maximum spatial extent parallel to the steel substrate surface less than 4 mm. 
     
     
         7 . The steel component of  claim 1  wherein the steel substrate comprises a multiphase steel or dual phase steel. 
     
     
         8 . The steel component of  claim 1  wherein the localized martensite-enriched regions have a maximum spatial extent parallel to the steel substrate surface less than 3 mm. 
     
     
         9 . The steel component of  claim 1  wherein the localized martensite-enriched regions have an average Rockwell hardness value from about 35 to 60 HRC as measured on the C scale and the bulk region has an average Rockwell hardness value less 35 HRC as measured on the C scale. 
     
     
         10 . The steel component of  claim 1  wherein the localized martensite-enriched regions extend below the steel substrate surface to a depth from about 50 to 600 micrometers. 
     
     
         11 . A method for hardening a steel component comprising:
 providing a steel substrate having a bulk region and a steel substrate surface; and   laser spot hardening the steel substrate at a plurality of locations on the steel substrate surface with a laser welding system that includes a laser to form a plurality of localized martensite-enriched regions located at the steel substrate surface, the plurality of localized martensite-enriched regions having higher martensite contents than the bulk region, wherein centers of adjacent localized martensite-enriched regions in the plurality of localized martensite-enriched region are separated by a separation distance that is from about 0.5 to 5 mm.   
     
     
         12 . The method of  claim 11  wherein the laser melts the steel substrate within 5 ms which upon solidification creates the plurality of localized martensite-enriched regions. 
     
     
         13 . The method of  claim 11  wherein the laser welding system includes a fiber laser. 
     
     
         14 . The method of  claim 11  wherein the laser has a power output from about 0.1 to 3 MW/cm2. 
     
     
         15 . The method of  claim 11  wherein light from the laser is sequentially directed to the plurality of locations on the steel substrate surface. 
     
     
         16 . The method of  claim 11  wherein the steel substrate is sequentially moved to direct light onto a plurality of locations on the steel substrate surface. 
     
     
         17 . The method of  claim 11  wherein the separation distance is from about 1 to 4 mm. 
     
     
         18 . The method of  claim 11  wherein the separation distance is from about 1.5 to 3 mm. 
     
     
         19 . The method of  claim 11  wherein at least a portion of the plurality of martensite-enriched localized regions are arranged in a rectangular array or a hexagonal array. 
     
     
         20 . The method of  claim 11  wherein the steel substrate comprises a multiphase steel, dual phase and HSLA grades of steel.