Weldability also is known as joinability. Weldability is the capacity of metal or combination of metals to be welded into a suitably designed structure. As the resulting weld joints to keep the required metallurgical properties to perform adequately in the proposed service.
Weldability simply is the measure of how easy to make a weld in a specific material without cracks. If it is easy to avoid cracking, the material is supposed weldable.
Factors affecting weldability:
Good weldability is characterized by the ease with which the welding process is accomplished, the absence of weld defects, and acceptable strength, toughness, and ductility in the welded joint.
Factors that affect weldability include the following main factors:
(1) Welding process
(2) Base metal properties
(3) Filler metal
(4) Surface conditions
The welding process is significant. Some metals or metal combinations that can be readily welded with one process are difficult to weld with others. For example, stainless steel can be easily welded by most arc welding processes but is considered a difficult metal for Oxyfuel welding.
Base Metal Properties:
Properties of the base metal affect welding performance. Important properties include melting point, thermal conductivity, and coefficient of thermal expansion.
A metal with a lower melting point would mean easier to weld. However, some metals melt too easily for good welding (e.g., aluminum). Metals with high thermal conductivity tend to transfer heat away from the weld zone, which can make them hard to weld (e.g., copper). Therefore, metals with high thermal conductivity considered to be difficult to weld. High thermal expansion and contraction in the metal cause distortion problems in the welding assembly. So, materials with a high thermal expansion coefficient also become hard to weld.
Dissimilar metals pose special problems in welding when their physical and/or mechanical properties are considerably different. Differences in melting temperatures are an obvious problem. Differences in strength or coefficient of thermal expansion may result in high residual stresses that can lead to cracking. If a filler metal is used, it must be compatible with the base metals. In general, elements mixed in the liquid state that form a solid solution upon solidification will not cause a problem. Embrittlement in the weld joint may occur if the solubility limits exceeded. Proper use of filler metal is also an important factor that affects the weldability of metals.
Surface conditions of the base metals can harmfully affect the operation. For example, moisture can result in porosity in the fusion zone. Oxides and other solid also films on the metal surfaces can prevent adequate contact and fusion from occurring. Similarly, the material with a dirty surface becomes also difficult to weld.
How to Increase Weldability of metals:
Weldability of metals increased or improved with the help of following steps:
- Proper shielding of Atmosphere
- Proper use of fluxing materials
- Suitable selection of filler metals
- Proper use of the welding process with the help of welding chart
- Before and after welding, proper heat treatment of metals
- However, proper use of welding procedure also improves weldability of metals
The weldability of some metals in descending order is an under:
- Cast Iron
- Low Alloy Steel
- Stainless Steel