Some machinery parts may get out of shape due to one or more wearing
mechanisms such us abrasion, adhesion, erosion, fatigue or corrosion.
build-up welding is used advantageously for these and for the rebuilding
of broken parts.

As it can be performed with ease in most welding workshops, the most
widely used building- up method is hard surfacing with coated electrodes.

Coated hard surfacing electrodes have various types and are easily
available.

D.C. or A. C. is used depending on the type of electrode.

Hard surfacing rutile or basic electrodes contain alloying elements such
as Cr, Mn, Ni, V, Mo, and W. Hard carbides formed by these elements or
the cold deformation that occurs as the parts are used produce the
required wear-resistance.

The wear resistant coated electrodes are classified in DIN 8555 and AWS
A5.13.

Moisture in the coating of hard surfacing electrodes could produce porosity
in the weld. The fore these electrodes should preferably be dried, according
to the recommendations of the manufacturer, before usage.

Hard surfacing welding with coated electrodes is done with a rather low
current, short length of arc and the electrode held nearly perpendicular to
the work piece. Hardfacing electrodes of high quality melt easily at low
currents and provide a wide seam.

As the compositions of the filler and base metals could be different, low
penetration is preferred to prevent dissolution of alloying elements which
produces a loss of hardness and could cause hot cracking. Sometimes
a buffer layer should be welded before the build-up. The selection of the
buffer is important and it is done in accordance with the base metal.