©
COPYRIGHT 2000 THE ESAB GROUP, INC. LESSON
VIII
burying gas lines to homes in an area
where the topsoil is a sandy loam, and the sub-soil is a
soft gumbo-like clay. For this application, only abrasion need be considered.
If this back-hoe
is moved to work in a new area where the soil contains shale and quartz rock in
small and large pieces, impact and
abrasion must be considered. 8.1.5
Base
Metals -
Basically, there are three types of steel used in the manufacture
of equipment and parts subjected to
heavy impact, compressive loads, and abrasive wear. These
are the straight carbon steels, the low alloy
high strength steels, and the austen- itic
manganese steels. All of these steels possess good deformation resistance
and lend themselves
well to the application of hardfacing alloys if the proper welding procedures
are followed.
8.1.5.1 Carbon
Steels -
If the base metal is a mild carbon steel with a carbon content of
.20% to .30%, preheat temperatures
from 200°F to 300°F are recommended. If the carbon
content of the base metal ranges from
.30% to .45%, preheating to 300°F for thin sections,
to 500°F for heavy sections, is
necessary. For base metals to .45% to .80% carbon con-
tent, preheat temperatures of 500°F
for thin sections, to 800°F for heavy sections, are
necessary. High carbon tool steels
containing carbon up to 1.7% are difficult to hardface because
they are prone to cracking. After hardfacing, parts should be allowed to
cool slowly.
8.1.5.2 Low
Alloy High
Strength Steels
- Low alloy steels may be hardfaced as long as
the proper welding procedure is followed.
Preheat and postheat temperatures must be maintained.
In some alloys, stress relieving may be necessary. As a rule of thumb,
the welding procedure
becomes more critical as the alloy and carbon content increases. Pre-
heat temperatures of 100°F to
600°F are used for most alloys, although some low alloys
with carbon content over .35% require
preheat temperatures in the 800°F to 1100°F range.
8.1.5.3 Austenitic
Manganese Steel
- Austenitic manganese steel (known as Hadfield
steel) is a high alloy containing 11-14%
manganese and approximately 1.2% carbon. It is non-magnetic,
unless it has been work-hardened. It is characterized by high strength,
high ductility,
and good wear resistance. It has no equal in its ability to work harden.
It is widely used
in equipment and parts that are subjected to heavy impact and compressive loads.
These loads actually harden the new
surface as the old is slowly worn away. It may actu-
ally have a shorter service life when
used in sand where there are no impact loads to work harden
the surface. 8.1.5.4
Unlike carbon and low alloy steels,
preheating of high manganese steels is not
recommended. Temperatures above
500°F to 600°F will induce embrittlement if sustained
