In arc welding, as the weld metal needs mechanical properties to match the parent metal, the welder must avoid forming defects in the weld. Imperfections are principally caused by:
• insufficient measures to accommodate the material or welding process;
• high stress in the component.
Techniques to avoid imperfections such as lack of fusion and slag inclusions, which result from poor welder techniques, are relatively well known. However, the welder should be aware that the material itself may be susceptible to formation of imperfections caused by the welding process. In the materials section of the Job Knowledge for Welders, guidelines are given on material weldability and precautions to be taken to avoid defects.
Material types
In terms of weldability, commonly used materials can be divided into the following types:
• Steels
• Stainless steels
• Aluminium and its alloys
• Nickel and its alloys
• Copper and its alloys
• Titanium and its alloys
• Cast iron
Fusion welding processes can be used to weld most alloys of these materials, in a wide range of thickness. When imperfections are formed, they will be located in either the weld metal or the parent material immediately adjacent to the weld, called the heat affected zone (HAZ). As chemical composition of the weld metal determines the risk of imperfections, the choice of filler metal may be crucial not only in achieving adequate mechanical properties and corrosion resistance but also in producing a sound weld. However, HAZ imperfections are caused by the adverse effect of the heat generated during welding and can only be avoided by strict adherence to the welding procedure.
This part of the materials section of Job Knowledge for Welders considers the weldability of carbon-manganese (C-Mn) steels and low alloy steels.
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