Welding is a complex yet essential procedure used to join pieces of metal together. On a functional level, it is a form of energy transfer between workpieces which, when joined with a good weld, can create strong, reliable connections. In terms of energy, welding requires specific levels of heat, usually in the range of 5,000-7,000°F, to create the weld.
Along with temperatures this high, come consequences called heat affected zones (HAZ) which can compromise the strength of the final weld and place major limitations on the design decisions of welders. Heat affected zones affect 3
5% of welded industry components and have a direct impact on the quality of work produced. Therefore, it is important to understand the effect of heat on the surrounding metal and how it impacts the weld. In this article, we will discuss the concept of a Heat Affected Zone (HAZ) and outline the factors that contribute to it.
What is the Heat Affected Zone in Welding?Welding is a process which is used to join metal or thermoplastic components together by melting them.
Welding produces heat which can cause damage to the metal surrounding the weld joint, and this area of damage is referred to as the Heat Affected Zone (HAZ). It is defined as the area of metal that has been heated above critical temperatures by the welding arc.
Importance of Heat Affected ZoneThe Heat Affected Zone is an important consideration in the welding process as it can influence the mechanical properties of the welded joint.
For example, in worked parts, the transformation of structure, such as the formation of martensite and embrittlement of the material, can reduce the strength and toughness of the joint. The HAZ can also affect the corrosion and fatigue properties of the welded joint, which can reduce its service life. For this reason, it is important to consider the heat affected zone when welding.
Factors which Affect Heat Affected ZoneThere are several factors which can affect the size and shape of the Heat Affected Zone. These include the welding parameters such as welding current, speed and travel, as well as the welding process and the type of material being welded.
The welding process has the most influence on the HAZ, as some processes generate more heat than others. In general, Gas Tungsten Arc Welding (GTAW) produces the smallest HAZ, while Shielded Metal Arc Welding (SMAW) produces the largest.
Reactions in Heat Affected ZoneWhen the Heat Affected Zone is heated up, several reactions take place in the metal, including melting, solidification, diffusion and chemical transformations.
When the metal is cooled, some or all of these reactions can occur, depending on the temperature and amount of time the metal was subjected to the heat. These reactions can alter the properties of the welded joint, such as its strength, hardness and ductility.