Catalytic converters-metal foil material for use therin, and a method of making the material

Abstract

A metal foil substrate material with improved formability properties for catalytic converters and a method of making the material in which layers of ferritic stainless steel and aluminum are solid state metallurgically bonded together forming a composite material. Such composite material is further rolled to an intermediate foil gauge and then subjected to a thermal in situ reaction to form a resulting uniform solid solution foil material with superior high temperature corrosion resistance. This uniform solid solution material is then rolled to the final foil gauge.

We claim:  
     
         1 . A method for making a foil substrate material with excellent formability having various metal constituents for catalytic converters comprising the steps of: 
 providing a layer of a first material chosen from the group consisting of chromium containing ferrous metals and aluminum and aluminum alloys, sandwiching said layer of first material between first and second layers of a second material chosen from the group consisting of chromium containing ferrous metals and aluminum and aluminum alloys not chosen for the first material, metallurgically bonding said layers together by reducing thickness of said layers thereby forming a multilayer composite material of said first and second materials, reducing thickness of the composite material to an intermediate thickness between the bonding thickness and a finish thickness; heating said composite material in situ at a temperature between 900° C. and about 1050° C. for a sufficient period of time to cause diffusion of various metal constituents of said layers throughout the composite material thereby providing a uniform solid material and rolling said uniform solid solution material to said finish thickness.    
     
     
         2 . The method according to  claim 1  wherein said heating said muitilayer composite material is about less than 1000° C.  
     
     
         3 . The method according to  claim 1  wherein said first material is a ferritic stainless steel and said second material is aluminum.  
     
     
         4 . The method according to  claim 1  wherein said time for heating said multilayer composite material at peak temperature is between 1 and 60 minutes.  
     
     
         5 . The method according to  claim 1  wherein a chemical composition of the uniform solid solution material generally is between 18 and 22 wt. percent Cr, at least 5 wt. percent Al and the balance Fe.  
     
     
         6 . The method according to  claim 5  wherein the chemical composition further includes rare earth metals as a minor constituent.  
     
     
         7 . The method according to  claim 6  wherein said minor constituent of rare earth metals is between 0.01 and 0.10 wt. percent.  
     
     
         8 . The method according to  claim 7  wherein the chemical composition further includes a content of S of less than 0.003 wt. percent.  
     
     
         9 . The method according to  claim 1  wherein said intermediate thickness is between 0.002 of an inch and 0.008 of an inch.  
     
     
         10 . The method according to  claim 9  wherein said finish thickness is between 0.0010 of an inch and 0.0025 of an inch.  
     
     
         11 . The method of  claim 1  wherein the reduction from said intermediate thickness and said finish thickness is between about 50 percent and 75 percent.  
     
     
         12 . The method according to  claim 1  further including annealing said uniform solid solution material after rolling to finish thickness to recrystallize the microstructure.  
     
     
         13 . A foil substrate material with excellent formability made according to the method of  claim 1 .  
     
     
         14 . A method for making an easily formable substrate material for use in catalytic converters comprising the steps of: 
 providing a metallurgically bonded multilayer composite material having layers of at least two different materials, reducing the thickness of the composite material to between about 0.002 of an inch and 0.008 of an inch, heating said composite material at a temperature and for a sufficient period of time to cause diffusion of various metal constituents of said layers throughout the composite material thereby providing a uniform solid material, rolling said uniform solid solution material to a finish thickness of between about 0.0010 of an inch and 0.0025 of an inch and annealing said uniform solid solution material to obtain recrystallization of the material microstructure.