Guidelines for Applying Hardfacing Alloys - Part 4 of 5
Cushion Layers and Buffer Layers
Hard surfacing alloys are usually much harder and of a much higher alloy content than the base metal. Applying a cushion or buffer layer provides a transition between the softer parent metal and the hard overlay.
The cushion layer has several purposes
1. Most hard surfacing alloys are limited to two or three layers, some only one. Therefore, some applications require that an intermediate layer be used to build up the part close to finish dimensions prior to depositing a harder, more abrasion resistant alloy.
2. When hard materials are used on soft base metals, such as mild steel, there is a tendency for the hardfacing layer to “sink” into the soft base metal under high load conditions. This may result in spalling of the hardfacing alloy. An intermediate buffer layer will help to prevent this from happening.
3. Hard surfacing alloys check-crack throughout the deposit. The buffer layer helps to prevent these cracks from propagating into the parent metal.
4. If the surface conditions involve thermal cycling, large thermal property differences between the parent metal and the overlay can lead to fatigue problems and spalling. The deposition of a buffer layer provides a very effective transition between the weld and the overlay.
5. Never use 7018 as a cushion or build-up. It does not have the hardness and strength for hardfacing applications.
Alloys in this category are used on many different parts and components
Base Metal Wire Electrode
Manganese Postalloy®2860-FCO Postalloy®205
Low alloy and Carbon Steel Postalloy®2865-FCO Postalloy®207
Look for Part 5 in the November Newsletter – Hardfacing Patterns
The Cushion Layer