Heat treated steel strips. 
"Harper Steel Strips specializes in customized hardened and tempered high-carbon and stainless steel strips, ensuring exceptional flatness, tensile strength, and fatigue endurance." 
https://www.harpersteelstrips.....com/about-harper-ste
 
        
 
					 
						 
                                     
         
         
         
         
             
             
             
             
             
             
       
       
       
       
       
       
       
       
       
         
         