Method for treating a part made of iron alloy for improving the anti-corrosion properties thereof

Abstract

The present invention relates to a method for treating a part (P) made of iron alloy for improving the anti-corrosion and mechanical strength properties thereof, the method comprising: a salt bath nitriding or salt bath nitrocarburising step, to form a combination layer ( 1 ) on the part (P), and subsequently a step of phosphating the part (P), to form a phosphating layer ( 2 ) on the surface of the part, characterised in that the bath of molten salts contains chlorides, and the phosphating step is carried out in a phosphating bath which contains zinc ions and/or manganese ions, and iron ions.

1 - 13 . (canceled) 
     
     
         14 . A method of increasing anti-corrosion and mechanical strength of an iron alloy part, the method comprising:
 forming a combination layer on the iron alloy part by using a nitriding molten salt bath and a nitrocarburising molten salt bath, wherein the nitriding molten salt bath and the nitrocarburising molten salt bath comprise chlorides; and   phosphating the iron alloy part to form a phosphating layer on a surface of the iron alloy part, wherein the phosphating is carried out in a phosphating bath comprising zinc ions and/or manganese ions, and iron ions.   
     
     
         15 . The method according to  claim 14 , wherein the molten salt bath does not contain sulphur. 
     
     
         16 . The method according to  claim 14 , wherein the chlorides comprise alkaline metal chlorides. 
     
     
         17 . The method according to  claim 16 , wherein the alkaline metal chlorides are lithium, sodium, potassium chlorides, or a combination thereof. 
     
     
         18 . The method according to  claim 14 , wherein the molten salt bath comprises:
 25% w/w to 60% w/w of alkaline metal chlorides;   10% w/w to 40% w/w of alkaline metal carbonates;   20% w/w to 50% w/w of alkaline metal cyanates; and   3% w/w or less of cyanide ions.   
     
     
         19 . The method according to  claim 14 , wherein the iron ions are present in the phosphating bath at a mass concentration of between 1 g/l and 8 g/l, and wherein:
 the phosphating bath contains zinc ions but no manganese ions, and said zinc ions are present at a mass concentration of between 1 g/l and 40 g/l with respect to the total volume of the phosphating bath;   the phosphating bath contains manganese ions but no zinc ions, and said manganese ions are present at a mass concentration of between 1 g/l and 40 g/l with respect to the total volume of the phosphating bath; or   the phosphating bath contains zinc ions and manganese ions, and the total of these ions is present at a mass concentration of between 1 g/l and 40 g/l.   
     
     
         20 . The method according to  claim 19 , wherein the phosphating bath contains zinc ions but no manganese ions, and said zinc ions are present at a mass concentration of between 5 g/l and 20 g/l with respect to the total volume of the phosphating bath. 
     
     
         21 . The method according to  claim 19 , wherein the phosphating bath contains manganese ions but no zinc ions, and said manganese ions are present at a mass concentration of between 5 g/l and 20 g/l with respect to the total volume of the phosphating bath. 
     
     
         22 . The method according to  claim 19 , wherein the phosphating bath contains zinc ions and manganese ions, and the total of these ions is present at a mass concentration of between 5 g/l and 20 g/l. 
     
     
         23 . The method according to  claim 19 , wherein the iron ions are present in the phosphating bath at a mass concentration of between 1 g/l and 6 g/l. 
     
     
         24 . The method according to  claim 14 , wherein the phosphating layer has a thickness of between 3 μm and 40 μm. 
     
     
         25 . The method according to  claim 24 , wherein the phosphating layer has a thickness of between 5 μm and 30 μm. 
     
     
         26 . The method according to  claim 25 , wherein the phosphating layer has a thickness of between 5 μm and 20 μm. 
     
     
         27 . The method according to  claim 14 , wherein the combination layer has a thickness of between 5 μm and 40 μm. 
     
     
         28 . The method according to  claim 27 , wherein the combination layer has a thickness of between 15 μm and 25 μm. 
     
     
         29 . The method according to  claim 14 , wherein the iron alloy part is made of grey cast iron. 
     
     
         30 . A part made of grey cast iron, comprising:
 a nitriding layer in contact with the grey cast iron, comprising a combination layer containing nitrides; and   a phosphating layer arranged on and in contact with the combination layer, comprising metal phosphates, wherein the metal phosphates comprise zinc, manganese, or a combination thereof, and iron.   
     
     
         31 . The part according to  claim 30 , wherein the phosphating layer has a thickness of between 3 μm and 40 μm. 
     
     
         32 . The part according to  claim 30 , wherein said part comprises graphite inclusions at a surface of the part on which the combination layer is formed. 
     
     
         33 . The part according to  claim 30 , wherein the part comprises a brake disc.