FOR INTERNAL USE ONLY
14 APPLICATION OF WEAR PROTECTIVE COATINGS Once the wear resistant alloy type and process have been selected, see Section 7, the method of application needs evaluation. Included in this is the preparation of the base metal.
14.1 BASE METAL PREPARATION
The preparation will depend upon the condition of the base metal. If the component has not previously been wear protected, only slight mechanical cleaning may be necessary. Alternatively, previously cracked and damaged “hardfacing� may be present, which should be removed by grinding, gouging, etc. depending upon extent. If the old hardfacing is left on and covered, this may cause chipping of the deposit while in service. All sharp corners and edges should be radiused, if that area is to be surfaced.
14.2 PREHEAT
This will depend upon the type, (e.g. never preheat 13% manganese steel), and thickness of the base metal, i.e. if the part is large there is a greater heat sink effect therefore more likelihood of hardening and crack susceptibility of the heat affected zone, therefore preheat is advisable. Preheat will also depend upon available facilities and if a highly alloyed buttering layer is used which reduces (although not usually eliminates) the need for preheat. Preheating carbon steels is usually based on the Carbon Equivalent When to Preheat
CE
Weldability
Preheat
Postheat
<0.45 0.45-0.60 >0.6
Good Fair Care
Optional 150-250oC >250oC
Optional Preferable Necessary
WELDING AND COATING METALLURGY2
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