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 PREHEAT (Continued)
Prior to hard-facing, badly worn parts must be restored
Table 2-1 shows recommended preheat temperatures for
with an appropriate buildup material to within 2/16 -
welding. Temperatures higher than those indicated on
3/8 in. of their finished size. The buildup material
this chart are sometimes required when hard-facing,
must have sufficient mechanical strength to sustain
depending on the size and shape of the part and the type
structural requirements. It must resist cold flowing,
of hard-facing alloy to be applied.
mushing under high compressive loads and plastic
deformation under heavy impact. If the buildup
WELDING ON CAST IRON
material doesn't possess these properties, a hard-facing
overlay, which has comparatively little ductility, will
Rebuilding and hard-facing of cast iron is not generally
span for lack of support. In addition to these
recommended since it is extremely crack sensitive.
mechanical requirements, a buildup material must be
However, some cast iron parts, primarily those subject to
compatible with the base metal and the hard-facing
straight abrasion, are being successfully hard-faced.
overlay.
Under any circumstances, cast iron parts require high
preheat temperatures, from 1000- 1200F (dull red),
Use electrode on page 1-24 as the primary source and
and must be slow cooled after welding. Weld deposits on
cast iron should be peened to help relieve stresses.
electrodes on pages 1-5 and 1-3, in that order, as
alternate sources to rebuild carbon steel parts prior to
overlaying with hard-facing electrodes. When
BUILDUP MATERIALS AND BASE METALS
hard-facing with the high alloy group, apply the
recommended hard-facing material before placing it in
Considerable differences exist between welding materials
service and do not allow it to wear more than 1/4 in.
used to buildup worn equipment and those used for
(two layers) before hard-facing. If carbon steel parts
hard-facing overlays.
2-3
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