©
COPYRIGHT 1999 THE ESAB GROUP, INC. LESSON
I, PART A that
require excellent surfaces, a more homogenous composition, and better mechanical
properties than rimmed steel.
1.1.3
Killed
Steel - Unlike rimmed or capped steel, killed
steel is made by completely removing
or tying up the oxygen before the ingot solidifies to prevent the rimming action.
This removal is accomplished by adding
a ferro-silicon alloy that combines with oxygen to form
a slag, leaving a dense and homogenous metal. 1.1.4
Semi-killed
Steel - Semi-killed steel is a compromise between
rimmed and killed steel.
A small amount of deoxidizing agent, generally ferro-silicon or aluminum,
is added. The
amount is just sufficient to kill any rimming action, leaving some dissolved oxygen.
1.1.5
Vacuum
Deoxidized Steel - The object of vacuum deoxidation
is to remove oxygen
from the molten steel without adding an element that forms nonmetallic inclusions.
This is done by increasing the carbon
content of the steel and then subjecting the molten metal
to vacuum pouring or steam degassing. The carbon reacts with the oxygen
to form carbon
monoxide, and as a result, the carbon and oxygen levels fall within specified
limits. Because
no deoxidizing elements that form solid oxides are used, the steel produced by
this process is quite clean.
1.2 CLASSIFICATIONS
OF STEEL The
three commonly used classifications for steel are: carbon, low alloy, and
high alloy. These
are referred to as the “type” of steel.
1.2.1
Carbon
Steel - Steel is basically an alloy of iron and
carbon, and it attains its strength
and hardness levels primarily through the addition of carbon. Carbon steels
are classed into
four groups, depending on their carbon levels. Low
Carbon Up
to 0.15% carbon Mild
Carbon Steels .15%
to 0.29% carbon Medium
Carbon Steels .30% to 0.59% carbon High
Carbon Steels .60%
to 1.70% carbon 1.2.1.1
The largest tonnage of steel produced
falls into the low and mild carbon steel groups.
They are popular because of their relative strength and ease with which
they can be welded.
1.2.2
Low
Alloy Steel - Low alloy steel, as the name implies,
contains small amounts of
alloying elements that produce remarkable improvements in their properties. Alloying
