Inoculation alloy against micro-shrinkage cracking for treating cast iron castings

Abstract

Inoculation alloys for treating cast iron castings containing, by weight, 0.005% to 3% of an element selected from the group consisting of bismuth, lead and antimony, 0.3 to 10% of metals of the rare-earth group and optionally aluminum up to 5%, and calcium up to 1.5%, the remainder being ferro-silicon, lanthanum constituting more than 90% of the rare-earth metals contained in the composition. The inventive alloys enable efficient inoculation of cast iron and avoid occurrence of micro-shrinkage cracking in the cast parts. The alloys are conditioned in the form of slugs or powder.

1 . Inoculating alloy for cast iron containing (by weight) 0.005 to 3% of an element in the bismuth, lead and antimony group, 0.3 to 10% of metals in the group consisting of rare earths and possibly up to 5% of aluminium and up to 1.5% of calcium, the remainder being ferro-silicon, characterised in that lanthanum accounts for more than 90% of the rare earth metals used in its composition.  
     
     
         2 . Alloy according to  claim 1 , characterised in that it contains from 0.3 to 8% of lanthanum and from 0.2 to 1.5% of bismuth.  
     
     
         3 . Alloy according to  claim 1 , characterised in that it contains between 0.7 and 1.3% of bismuth.  
     
     
         4 . Alloy according to  claim 1 , characterised in that it contains between 0.5 and 5% of lanthanum.  
     
     
         5 . Alloy according to  claim 1 , characterised in that it contains between 0.8 and 5% of aluminium.  
     
     
         6 . Alloy according to  claim 5 , characterised in that it contains between 1 and 3.5% of aluminium.  
     
     
         7 . Alloy according to  claim 1 , characterised in that it is conditioned in the form of a powder.  
     
     
         8 . Alloy according to  claim 1 , characterised in that it is conditioned in the form of slugs for treatment “in the mould”.  
     
     
         9 . Alloy according to  claim 8 , characterised in that the slug is obtained by moulding from molten alloy.  
     
     
         10 . Alloy according to  claim 8 , characterised in that the slug is obtained by agglomeration of a powder.  
     
     
         11 . Alloy according to  claim 10 , characterised in that the powder grain size is smaller than 1 mm, with the size grading fraction between 50 and 250 μm accounting for more than 35% of the total weight, and the fraction smaller than 50 μm representing less than 25%.  
     
     
         12 . Alloy according to  claim 10 , characterised in that the average composition of the alloy is obtained by a mix of alloy powders with different compositions