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| 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
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| 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.
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| 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. |
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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. |
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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. |
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| 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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