Metal fabricators, or at least those in charge of welding operations, must have a sound understanding of metallurgy. Metallurgy is the study of metals, their properties and their behaviors, especially when undergoing the welding process.
Below are 6 areas of fabrication for which an understanding of the metallurgical properties of metals is vital.
- Material Selection – although many fabricators build to their customer specifications, some build based on their own designs. Choosing the right material for a particular application is no uncomplicated matter. The mechanical and physical properties of a base metal are of utmost importance, but so is cost. All these must be considered when selecting the right base metal for a specific use.
- Heat Treatment – when fabricators use base metals that are quench and tempered or simply have a high carbon content they normally need to apply some sort of post weld heat treatment (PWHT). PWHT is necessary to restore or improve the mechanical properties of a weldment, the heat affected zone and the unaffected base metal. Knowing metallurgical characteristics of the base metal is necessary to specify the right PWHT.
- Welding – The welding process has a huge impact on the metallurgical properties of the metal being welded. Understanding the implications of welding (how it changes the microstructure of the base metal) is very important. The higher the carbon content in steels the more important it is to have a sound understanding of its metallurgical characteristics. This is especially important when welding aluminum, nickel alloys, copper alloys and other exotic metals.
- Corrosion – understanding how metals interact with the atmosphere and service conditions as well as the effects of the welding process is very important. In certain applications, such as marine applications, it is sometimes necessary to select materials that will resist corrosion. The selection of weathering steels is also an example of material selection with corrosion in mind. These steels are typically used in bridges and other highway structures.
- Mechanical Properties – understanding the mechanical properties of base metals is crucial to fabricators. Strength, ductility, hardness and toughness are all material properties that a fabricator must understand. More importantly, how these mechanical properties are affected by the welding process.
- Fatigue and Fracture – the mechanical properties of a base metal combined with the effects of the welding process and any welding discontinuities has a huge impact on the fatigue life of welded components. All fabricators, but especially design engineers, must understand the implications of the selected base metal when it comes to fatigue life.
It is important to note that metallurgy is a science that must be understood fully by designers. But, welding metallurgy goes far beyond basic metallurgy. Someone once said that welding metallurgy is metallurgy at high speed. And this is very true. The welding process introduces extremely quick heating and cooling cycles that occur at rates much higher than those experienced in the steel making process and subsequent heat treatments. All welding engineers must be proficient in welding metallurgy, but not all fabricators have the luxury of having one in staff. However, it does not take a degree to understand the basic principles that can lead to successful fabrication. Seeking advice from experts or other knowledgeable resources is all you need.