©
COPYRIGHT 1999 THE ESAB GROUP, INC. LESSON
I, PART A
1.7.11
Columbium
- Columbium is used in austenitic stainless steel to
act as a stabi- lizer.
Since the carbon in the stainless steel decreases the corrosion resistance,
a means of making
carbon ineffective must be found. Columbium has a greater affinity for carbon
than chromium, leaving the chromium
free for corrosion protection. 1.7.12
Tungsten
- Tungsten is used in steel to given strength at high
temperatures. Tungsten
also joins with carbon to form carbides that are exceptionally hard, and therefore
have exceptional resistance to wear.
1.7.13
Vanadium
- Vanadium helps keep steel in the desirable fine grain
condition after heat
treatment. It also helps increase the depth of hardening and resists softening
of the steel during
tempering treatments. 1.7.14
Nitrogen
- Usually, efforts are made to eliminate hydrogen, oxygen
and nitrogen from
steel because their presence can cause brittleness. Nitrogen has the ability
to form austenitic
structures; therefore, it is sometimes added to austenitic stainless steel to
reduce the amount
of nickel needed, and therefore, the production costs of that steel.
1.7.15
Alloying
Elements Summary
- It should be understood that the addition of
elements to a pure metal may influence
the crystalline form of the resultant alloy. If a pure
metal has allotropic characteristics
(the ability of a metal to change its crystal structure) at a
specific temperature, then that characteristic
will occur over a range of temperatures with the
alloyed metal. The range in which the change takes place may be wide or
narrow, depending
on the alloys and the quantities in which they are added. The alloying element
may also effect the crystalline changes
by either suppressing the appearance of certain crystalline
forms or even by creating entirely new forms. All these transformations
induced by alloying
elements are dependent on heat input and cooling rates. These factors are
closely controlled at the steel mill,
but since the welding operation involves a nonuniform heating
and cooling of metal, special care is often needed in the welding of low and high
alloy steel.
