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Welding is a process used to fuse or join materials such as metals or thermoplastics together, usually by melting them and adding so-called filler material to the area being welded in order to form a strong joint, or weld, once the material cools. A material's weldability, or jointability, can refer to whether it can be welded together without cracks, and in this case a weldable material is a material that can be welded together creating a crack-free weld. Weldability can also refer to more qualitative characteristics of how easy or difficult it is to achieve a functional weld. This kind of weldability is not easily quantified, and can depend on a variety of factors, including the welding method, the physical specifics of the joint created, and what the welded structure is to be used for. There are several welding methods, and knowledge of a material's weldability is important in order to choose the proper welding process.
The goal of the welding process is to produce a crack-free joint that is functional and able to withstand the wear and tear it will be subjected to. Common welding methods include arc welding, soldering, and oxy-acetylene welding. What method is chosen depends mainly on what material is being welded. Copper is a weldable material that produces a good weld if soldering is used. Oxy-acetylene welding is preferable when working with cast iron, and arc welding works well for stainless steel.
Weldability testing is the study of how materials are affected by different welding methods. This testing has to take many factors into account, because the quality of a weld is influenced not only by the materials and the welding method used, but also by other factors such as how fast the material cools after welding, and the speed of the welding process itself. For example, aluminum is susceptible to cracking from the heat of welding, and produces a better weld with a shorter welding time and less heat-input. Various charts and comparisons are available that list and rate the weldability of various materials when using various welding methods.
Steel is commonly welded in various industrial processes, and different welding methods can be used for this material. The weldability of various types of steel vary, and depends on what materials, such as carbon, nickel and chromium, were used to create the specific steel alloy. Common problems affecting the weldability rating of steel is spot-weld peeling, lamellar tearing, and hydrogen-induced cold cracking.