WELDING & CUTTING
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Buffering
 
Buffer layers are used as intermediate deposits between the base material and the actual hardfacing weldmetal so that the following aspects are taken care of
  • Good bonding with the base material
  • Hydrogen-induced underbead cracking is avoided, even on preheated workpieces
  • Stress consequences are minimized
  • Effect of dilution is limited
  • Spalling in subsequent hard layers is avoided
  • Prevention of cracks or relief checks from the hardfaced layers running into the base material
Generally, austenitic consumables are widely used as ductile buffer layers in hardfacing applications. The choice of consumables depends on the base material and the type of hardfacing alloy given the wear factors.
 
The hardfacing layer tends to sink under high load conditions if the base material is a soft one like mild steel. This can result in the hardfacing layer spalling off. A tough and strong buffer layer is applied to prevent this occurence.
   
In case of hardfacing with very hard and brittle alloys like the ones containing chromium carbides or with cobaltbased alloys, there should be a buffering by an austenitic consumable for one or two layers. The compression stresses generated in the subsequent hard layers during cooling are thus accommodated, reducing the risk of cracks in the hard weld metal.
  The "relief checks" present in many hardfacing deposits can propagate into the base metal under heavy impact or flexing. High strength steels are most prone to such crack propagation. This is prevented by applying a tough buffer layer.
   
Build-up Layers
In case of heavy wear, the component has to be builtup to its original dimensions. But hardfacing layers are limited to 2-3 layers. In that case, a similar type of alloy can be used to build it up before applying the hardfacing deposit. Otherwise, alternate layers of hard and ductile deposits can be made finishing off with the hard layer. E.g. hammers, crushers, cold shearing tools and excavator teeth.
   
 
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