Iron-based brazing filler metals

Abstract

A plurality of parts is brazed using an iron-based brazing filler metal. The parts generally include stainless steel, and the brazed assembly forms a heat exchanger characterized by effective corrosion resistance and low rates of leaching of nickel into fluids passing therethrough. The heat exchanger is especially suited for use in processing items intended to be ingested by humans or animals.

1 . A brazing filler metal consisting essentially of a composition with a formula Fe a Cr b B c Si d X e , wherein X is molybdenum, tungsten, or a combination of molybdenum and tungsten, and incidental impurities, wherein the subscripts “a”, “b”, “c”, “d”, “e” are all in atom percent, and wherein “b” is between about 0 and 5, “c” is between about 10 and about 17, “d” is between about 4 and about 10, “e” is between about 0 and about 5, and a sum “a”+“b”+“c”+“d”+“e” is approximately equal to 100.  
   
   
       2 . The brazing filler metal as recited by  claim 1 , said metal being in a form of one of: a homogeneous, ductile ribbon; a powder; a foil; a wire; or a preform.  
   
   
       3 . A brazing filler metal material for joining objects by brazing, characterized in that the brazing material consists of an alloy which contains at least 63% iron and includes 0-5% chromium, 10-17% boron, 4-10% silicon, and 0-5% X, wherein X is molybdenum, tungsten, or a combination of molybdenum and tungsten, and incidental impurities, all stated in weight percent, and wherein amounts of boron and silicon are varied to adjust liquidus and solidus temperatures of the brazing filler metal material to desired liquidus and solidus temperatures.  
   
   
       4 . The brazing filler metal as recited by  claim 3 , wherein the brazing filler metal material is in a form of one of: a homogeneous, ductile ribbon; a powder; a foil; a wire; or a preform.  
   
   
       5 . A brazing filler metal foil for joining objects by brazing, characterized in that the brazing foil consists of an alloy which contains at least 63% iron and includes 0-5% chromium, 10-17% boron, 4-10% silicon, and 0-5% X, wherein X is molybdenum, tungsten, or a combination of molybdenum and tungsten, and incidental impurities, all stated in weight percent, and wherein the foil is a metastable material having at least a 50% glassy structure.  
   
   
       6 . The brazing filler metal foil of  claim 5 , wherein the foil has a thickness ranging from about 18 to 50 μm.  
   
   
       7 . A brazing filler metal composition for joining objects by brazing, the brazing filler metal composition consisting of an alloy which contains at least 63% iron and includes 0-5% chromium, 10-17% boron, 4-10% silicon, and 0-5% X, wherein X is molybdenum, tungsten, or a combination of molybdenum and tungsten, and incidental impurities, all stated in weight percent, and wherein the composition is characterized by a solidus temperature range of approximately 1042° C. through approximately 1174° C. and a liquidus temperature range of approximately 1148° C. through 1182° C.  
   
   
       8 . The brazing filler metal composition as recited by  claim 7 , said metal being in a form of one of: a homogeneous, ductile ribbon; a powder; a foil; a wire; or a preform.  
   
   
       9 . An iron-boron-silicon alloy, the alloy especially useful for brazing stainless steel assemblies, and exhibiting effective corrosion resistance and minimized rates of leaching of nickel into fluids passing through either side of the stainless steel assemblies, the iron-boron-silicon alloy consisting essentially of (in weight %) about 10-17% boron, 4-10% silicon, and a balance of: 
 iron,    0-5% chromium, and    0-5% molybdenum or tungsten.    
   
   
       10 . A brazed product manufactured by brazing objects with the brazing filler metal of  claim 1 , characterized in that the material in the objects to be brazed is stainless steel.  
   
   
       11 . A brazed product manufactured by brazing objects with the brazing filler metal of  claim 1 , characterized in that the product is a shell-and-tube type heat exchanger intended for at least two heat exchanging media.  
   
   
       12 . A brazed product manufactured by brazing objects with the brazing filler metal of  claim 1 , characterized in that the product is a plate-plate type heat exchanger intended for at least two heat-exchanging media, which comprises at least one plate package manufactured by brazing together a plurality of thin-walled heat exchanger plates of a stainless steel material via the brazing filler metal at which the heat exchanger plates between themselves define plate inter-spaces intended for the heat-exchanging media.  
   
   
       13 . A brazed product manufactured by brazing objects with the brazing filler metal of  claim 1 , characterized in that the product is a plate and fin type heat exchanger intended for at least two heat-exchanging media.  
   
   
       14 . A method of manufacturing a heat exchanger and an apparatus having brazed parts, comprising: 
 juxtaposing at least two parts to define one or more joints therebetween;    supplying to said one or more joints an iron-boron-silicon brazing filler metal alloy wherein amounts of boron and silicon are varied to adjust liquidus and solidus temperatures of the brazing filler metal material to desired liquidus and solidus temperatures;    heating said juxtaposed parts and said brazing filler metal under predetermined conditions to melt said brazing filler metal; and    cooling said brazing filler metal to produce a brazed joint.    
   
   
       15 . The method as recited by  claim 14 , wherein the iron-boron-silicon brazing filler metal alloy consists essentially of a composition with the formula Fe a Cr b B c Si d X e , wherein X is molybdenum or tungsten, and incidental impurities, wherein the subscripts “a”, “b”, “c”, “d”, “e” are all in atom percent, and wherein “b” is between about 0 and 5, “c” is between about 10 and about 17, “d” is between about 4 and about 10, “e” is between about 0 and about 5, and a sum “a”+“b”+“c”+“d”+“e” is approximately equal to 100.  
   
   
       16 . A corrosion-resistant heat exchanger which provides a low rate of nickel leaching, comprising at least one joint brazed with the iron-boron-silicon brazing filler metal alloy in accordance with the process of  claim 14 .  
   
   
       17 . The heat exchanger as recited by  claim 16 , wherein said iron-boron-silicon brazing filler metal alloy consists essentially of a composition with the formula Fe a Cr b B c Si d X e , wherein X is molybdenum or tungsten, and incidental impurities, wherein the subscripts “a”, “b”, “c”, “d”, “e” are all in atom percent, and wherein “b” is between about 0 and 5, “c” is between about 10 and about 17, “d” is between about 4 and about 10, “e” is between about 0 and about 5, and a sum “a”+“b”+“c”+“d”+“e” is approximately equal to 100.  
   
   
       18 . A heat exchanger as recited in  claim 17  comprising at least two parts forming one of a plurality of brazed joints in a brazed assembly, said heat exchanger being produced by a process comprising: 
 juxtaposing said at least two parts to define one or more joints therebetween;    supplying to said one or more joints the iron-boron-silicon brazing filler metal alloy in the form of a ductile, amorphous brazing foil;    heating said juxtaposed parts and said brazing filler metal alloy to melt the brazing filler metal alloy; and    cooling the melted brazing filler metal alloy to produce the brazed assembly having a brazed joint.