Metallurgy is the science that explores why metals behave the way they do. It explains the properties, behavior and internal structure of metals. Metallurgy also describes the treatments and processes that allow us to tailor a metal’s properties to a specific application.
Metallurgy is a relatively broad and, at times, complex subject. Most welders do not need to be experts. However, all welders should have a good grasp on basic metallurgical principals. Why? Because welding involves the heating and cooling of metals, and the heating and cooling of metals affects the mechanical properties of the resulting part.
For example, carbon and low alloy steels like 4130, tool steel, cast iron, and some 400 series stainless steels, harden by quick cooling from a red hot temperature. But most other stainless steels, nickel alloys, aluminum, magnesium, titanium, cobalt, and copper alloys will actually soften and lose properties by heating up red hot and quickly cooling.
This is just a generalization. A welding procedure, technique, or filler metal may be entirely appropriate for one these materials and disastrous for another. In other words, you really have to be familiar with different types of base materials and how they are affected by heating and cooling processes in order to avoid lack of fusion, cracking, porosity, and other weld defects that can lead to mechanical failures and deadly disasters like the San Bruno pipeline explosion that killed 8 people in 2010.
Most welders come by their knowledge of metals and a metal’s weldability over many years on the job. However, this knowledge is often incomplete because it is limited to the processes and materials used in a particular shop or industry. A more complete understanding of metallurgical principles, such as the relationship between a metal’s properties and its composition, and the function of processes such as cold working, alloying, and heat treatments, will not only allow you to master the process and materials that he or she is accustomed to working with, but it will also allow you to take the next step in their career. Whether it’s welding space age alloys in the aerospace industry or becoming a Certified Welding Inspector, the future is in your hands.