Metallurgy is the study of metal. Welding Metallurgy is the study of how welding affects the microstructure of metal.
Did you know that there are metallurgists who devote their lives to only studying carbon steels? So what about all the other metals like Stainless steel, nickel alloys, aluminum, magnesium, titanium, cobalt, and copper alloys?
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Metallurgy is such a deep and mysterious subject that it takes a lifetime to completely understand carbon steels much less all the rest.
So if is such a deep subject, what chance does a welder have in understanding enough about metallurgy in order to be a better welder.
There is good news. And its not that I saved a bunch of money on my car insurance by switching to GEICO.
The good news is that you dont have to understand everything about metallurgy. You just need to understand some basic principles.
The absolute fundamental thing to understand is that heat from welding affects metal. That sounds really simple but it is profound. Why? Because heat affects different metals in different ways.
When you heat a piece of metal to red hot, and then quench it by dunking it in a bucket of cold water, what do you think happens? If you answer "it hardens" you are only partially right. Only a few metals harden by heating and quick cooling. Most other metals react totally differently.
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 quick cooling.
So what does this mean to you the welder?
If you are doing a weld on 4130 chromoly, you need to know not to speed cool the weld or it will harden.
If you are welding 6061 t6 aluminum, you need to know that the weld area will soften if it gets too hot for too long, and strength will be lost and never regained unless a full heat treatment can be done.
Welding 301 full hard stainless steel is easy to do, but heat from welding recrystallizes the work hardened microstructure and the strength and hardness goes right out the window.
Welding 304 stainless can cause carbon and chromium to bind up and form chromium carbides if the weld area stays too hot for too long.
So do you get the picture. Heat affects different metals in different ways.
Welding Metallurgy studies exactly how the heat from welding affects metal and if you the welder take the time to study metallurgy, the knowledge gained will make you better.