Choosing a Hardface Overlay
Here are some guidelines when choosing a Hardface Overlay.
A. Never put a soft, ductile weld metal or a work-hardening manganese alloy on top of a harder, more brittle hardfacing alloy. Deposits may spall and come loose. The softer alloy should always be applied beneath the harder deposit. Never use 7018 as a cushion or build-up. It does not have the hardness and strength for hardfacing applications.
B. When two metal parts meet each other, the following guideline is suggested. The part that is easiest to change out or hardface should be about 10 points softer than the part that is more complicated to work on.
C. Never use a mild or low alloy steel on manganese. The weld deposit will be brittle.
D. If a manganese part is to be repaired repeatedly, such as hammers or railroad frogs and switches, applying one or two layers of Postalloy® 2865-FCO (Postalloy® 207 electrode) the first time is very beneficial.
E. The more wear resistant the deposit and the higher the alloy content and hardness, the greater will be the tendency to crosscheck. They appear during cooling and are due to the different shrinkage rates between the hard surfacing material and the base material. A regular check patters is desirable as it will reduce or even eliminate the tendency for distortion. These cracks do not normally extend into the base material and do not weaken the bond to the base. Cracks should be transverse across the weld and less than 1” apart. If not, increase the travel speed.
Hardness and number of layers
Limit deposit thickness. Thick hardfacing deposits may crack and break off rapidly in service. Furthermore, as hardface overlays increase in hardness, they tend to be more brittle. Unless an alloy has been specifically designed and tested for multi-layer weld overlays, the following guidelines should be useful to determine the number of hardface layers that should be applied. If it is necessary to apply more layers than is specified for the alloy, a build-up material should be applied first.
Deposited Hardness of Overlay Maximum Layers
65Rc or higher 1-2
Look for Part 3 in the September Newsletter – Dilution and Preheating