Metallurgy is the science and study of metals, especially
involving welding. Everyone should know basic metallurgy before they weld. When
welding, you can alter the steel you are working on affecting it adversely. A
good example is stainless which is alloyed with chromium to make it rust-resistant,
and nickel to make it hard. If you burn the chromium out of the steel when welding,
it will then rust. Stainless will also warp very easily from the heat if precautions
are not taken.
Many people will put way too much weld on a joint thinking
that more is better. Actually more can be worse because of the added heat. You
are also wasting time and materials which wastes money. Studying metallurgy will
help you know what amount of weld metal should be deposited.
involves the chemical, mechanical, and physical properties of metals.
- One form of chemical metallurgy most everyone has heard of is rust. Rust is
the oxidation of metal, or where oxygen gets into the metal and corrodes it. There
is also corrosion where the atmosphere wastes away the metal. And in welding we
are concerned with reduction, which is the removal of oxygen from the molten puddle.
OXYGEN AFFECTS THE WELD POOL ADVERSLEY! WE WANT TO KEEP OXYGEN OUT OF OUR
MOLTEN WELD POOL!
Mechanical - Mechanical metallurgy involves the way that
metal acts under stresses and loads. Welding rods are numbered with the first
2 or 3 numbers telling the tensile strength of the rod per square inch of deposited
metal. Tensile strength is the ability to resist being pulled apart. There are
many different loads and stresses involving brittleness, toughness, ductility,
malleability, plasticity, shear, and others.
Physical - Physical properties
in metallurgy involve the metals being affected by the heat applied when welding.
Grain size affects strength in metals, and grain size can be affected when welding.
A good welder needs to know the thermal conductivity, melting point, and grain
characteristics of the metal they are going to weld on.
One of the first
things learned in metallurgy is the atomic structure of the metals. These structures
consist of different "space lattices" which form different crystals.
After you get a general idea of different structures in metals it will help you
to understand the changes metals and steels go through when heated.
metallurgy we find that carbon plays a big part in the strength of the steel we
weld on. Steel is made harder by adding more carbon, but the more carbon added
also makes it less ductile, thus more brittle. There are low, medium and high-carbon
steels used in industry. The more carbon steel has, the more difficult to weld
it will be.
Most hobbyist will use low-carbon steel with around .30% carbon
There are technical journals, textbooks, and countless internet
sites available to help with the study of metallurgy. The more you learn about
the steel you are welding on, the better the welder you will be!