Metallurgy Defined

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.

Welding metallurgy involves the chemical, mechanical, and physical properties of metals.

Chemical - 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.

In studying 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 in it.

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!