©
COPYRIGHT 1999 THE ESAB GROUP, INC. LESSON
I, PART A elements
are added to improve strength and toughness, to decrease or increase the
response to heat treatment, and to
retard rusting and corrosion. Low alloy steel is gener-
ally defined as having a 1.5% to 5%
total alloy content. Common alloying elements are manganese,
silicon, chromium, nickel, molybdenum, and vanadium. Low alloy steels may
contain as many as four or five of
these alloys in varying amounts. 1.2.2.1
Low alloy steels have higher tensile
and yield strengths than mild steel or carbon structural
steel. Since they have high strength-to-weight ratios, they reduce dead
weight in railroad
cars, truck frames, heavy equipment, etc. 1.2.2.2
Ordinary carbon steels, that exhibit
brittleness at low temperatures, are unreliable in
critical applications. Therefore, low alloy steels with nickel additions
are often used for low
temperature situations. 1.2.2.3
Steels lose much of their strength
at high temperatures. To provide for this loss of
strength at elevated temperatures, small amounts of chromium or molybdenum are
added. 1.2.3
High
Alloy Steel
- This group of expensive and specialized steels contain
alloy levels
in excess of 10%, giving them outstanding properties. 1.2.3.1
Austenitic manganese steel contains
high carbon and manganese levels, that give
it two exceptional qualities, the ability to harden while undergoing cold work
and great toughness.
The term austenitic refers to the crystalline structure of these steels.
1.2.3.2 Stainless
steels are high alloy steels that have the ability to resist corrosion. This
characteristic is mainly due to the
high chromium content, i.e., 10% or greater. Nickel is
also used in substantial quantities
in some stainless steels. 1.2.3.3
Tool steels are used for cutting and
forming operations. They are high quality steels
used in making tools, punches, forming dies, extruding dies, forgings and so forth.
Depending upon their properties and
usage, they are sometimes referred to as water hardening,
shock resisting, oil hardening, air hardening, and hot work tool steel.
1.2.3.4 Because
of the high levels of alloying elements, special care and practices are
required when welding high alloy steels.
