Brazing material, a method of brazing, a brazed article, and a paste comprising this brazing material

Abstract

A method is provided for brazing products of stainless steel. The method comprises applying an iron-based brazing material to parts of stainless steel wherein the brazing material comprises an alloy consisting essentially of chromium (Cr); manganese (Mn); nickel (Ni); molybdenum (Mo); copper (Cu); nitrogen (N); silicon (Si); boron (B); phosphorus (P). The alloy is balanced with Fe, wherein Si, B and P are in amounts effective to lower melting temperature. The method comprises a step of optionally assembling these parts. The method comprises a step of heating the parts in a non-oxidizing atmosphere, in a reducing atmosphere, in a vacuum, or in combinations thereof, up to a temperature of at least 900° C., and brazing the parts at the temperature of at least 1070° C. for at least 15 minutes. The method further comprises optionally repeating one or more of these steps.

What is claimed is: 
     
         1 . A method for brazing products of stainless steel, comprising the following steps:
 step (1) applying an iron based brazing material to parts of stainless steel wherein the brazing material comprises an alloy consisting essentially of:
 (i) 15 wt % to 30 wt % chromium (Cr); 
 (ii) 0.1 wt % to 4.5 wt % manganese (Mn); 
 (iii) 15 wt % to 30 wt % nickel (Ni); 
 (iv) 1.0 wt % to 12 wt % molybdenum (Mo); 
 (v) 0.1 wt % to 4.0 wt % copper (Cu); 
 (vi) 0 wt % to 1.0 wt % nitrogen (N); 
 (vii) 2.5 wt % to 12 wt % silicon (Si); 
 (viii) 0 wt % to 2.0 wt % boron (B); 
 (ix) 0 wt % to 16 wt % phosphorus (P); 
   
       optionally one or more of elements selected from the group consisting of carbon (C), vanadium (V), titanium (Ti), tungsten (W), aluminium (Al), niobium (Nb), hafnium (Hf), and tantalum (Ta), wherein the amount of each element is within the range from 0.0 to 2.5 wt %; the alloy being balanced with Fe, and small inevitable amounts of contaminating elements such as carbon (C), oxygen (O), and sulphur (S); and wherein Si, B and P are in amounts effective to lower melting temperature, and Si, B, and P are contained in amounts according to the following formula: Index=wt % P+1.1×wt % Si+3×wt % B, and the value of the Index is within the range of from 5 wt % to 20 wt %;
 step (2) optionally assembling the parts; 
 step (3) heating the parts from step (1) or step (2) in a non-oxidizing atmosphere, in a reducing atmosphere, in vacuum or combinations thereof, up to a temperature of at least 900° C., and brazing the parts at the temperature of at least 1070° C. for at least 15 minutes; 
 step (4) and optionally repeating one or more of step (1), step (2) and step (3). 
 
     
     
         2 . The method of brazing according to  claim 1 , wherein the parts in step (3) are preheated to a temperature below 1120° C. before brazing at a temperature within the range from 1150° C. to 1250° C. for at least 30 minutes. 
     
     
         3 . The method of brazing according to  claim 1 , wherein the parts in step (3) are preheated to a temperature below 1040° C. before brazing at a temperature within the range from 1050° C. to 1150° C. for at least 15 minutes. 
     
     
         4 . The method of brazing according to  claim 1 , wherein the brazing alloy contains an amount of chromium (Cr), an amount of nickel (Ni), and an amount of molybdenum (Mo), which being defined by the formula (wt % Cr+wt % Ni+wt % Mo)≧33 wt %. 
     
     
         5 . The method of brazing according to  claim 1 , wherein the brazing alloy contains chromium within the range from 18 wt % to 26 wt %, nickel within the range of from 16 wt % to 26 wt %, and molybdenum within the range from 2.0 wt % to 12.0 wt %. 
     
     
         6 . The method of brazing according to  claim 1 , wherein the brazing alloy contains silicon within the range from 6.0 wt % to 12 wt %. 
     
     
         7 . The method of brazing according to  claim 6 , wherein the brazing alloy contains silicon within the range from 8.0 wt % to 12 wt %. 
     
     
         8 . The method of brazing according to  claim 1 , wherein the brazing alloy contains boron within the range from 0.1 wt % to 1.5 wt %. 
     
     
         9 . The method of brazing according to  claim 1 , wherein the brazing alloy contains silicon within the range from 6.0 wt % to 12 wt % and boron within the range from 0.1 wt % to 1.5 wt %. 
     
     
         10 . The method of brazing according to  claim 1 , wherein the brazing alloy contains phosphorus within the range from 2.5 wt % to 14 wt %. 
     
     
         11 . The method of brazing according to  claim 1 , wherein the brazing alloy contains phosphorus within the range from 5.0 wt % to 14 wt %. 
     
     
         12 . The method of brazing according to  claim 1 , wherein the brazing alloy contains silicon within the range from 6.0 wt % to 12 wt % and phosphorus within the range from 2.5 wt % to 14 wt %. 
     
     
         13 . The method of brazing according to  claim 1 , wherein the alloy of the brazing material is produced by gas-atomising or water-atomising or melt-spinning 
     
     
         14 . The method of brazing according to  claim 1 , wherein the brazing material is a paste with a binder selected from an aqueous binder system, an organic binder system, an oil-based binder system, or combinations thereof. 
     
     
         15 . The method of brazing according to  claim 1 , wherein the brazing material is a paste with a binder selected from polymers, poly (met) acrylate, biopolymers, cellulose derivatives, starches, waxes, or combinations thereof. 
     
     
         16 . The method of brazing according to  claim 1 , wherein the value of the Index is within the range of from 6.6 wt % to 20 wt %. 
     
     
         17 . The method of brazing according to  claim 16 , wherein the value of the Index is within the range of from 9.1 wt % to 20 wt %. 
     
     
         18 . A brazed product obtained by the method according to  claim 1 . 
     
     
         19 . The brazed product according to  claim 18 , wherein the article is a heat exchanger.