Metal has so many great properties that allow it to perform superbly in many applications, but it’s also susceptible to damage as well. Heat, particularly excessive heat, can wear away at metal surfaces and objects as well as put people at risk. In plant and factory settings, where employees work and walk by every day, heat management and damage control are necessary not only to promote well-functioning equipment but also a safe workplace for all.
What is the Heat Affected Zone?
The heat-affected zone (HAZ) is the part of a metal surface that is exposed to high heat levels. When this surface is put under high temperatures, it’s prone to changing its chemical structure. This can be seen by warping, bending, or wearing away at the surface. It’s common to find HAZs in welding applications, but machinery of all sorts can (and often do) create HAZs via thermal cutting and mechanical cutting, for instance.
Welding involves the joining together or melting of metal parts and connection points. As such, extreme heat temperature from the welded surfaces can inherently weaken the metal and therefore proper welding techniques must account for HAZs.
Furthermore, thermal cutting, as the name implies, is the act of shearing through metal surfaces with extreme heat. Like a hot knife through butter, in a sense. The HAZ of the cut metal may warp or bend if the extreme heats are not sufficiently controlled.
How Does the Heat Affected Zone Change Metals?
A chain is only as strong as the weakest link. So too are metal surfaces. When a metal’s material properties have been compromised due to excessive heat on the HAZ, the surface is only as durable as that affected area.
The easiest way to identify the HAZ on a metal surface is to look for coloured bands. These colours tend to be bright and are therefore easy to identify. Just have a look at the HAZ and notice how it goes from a bright yellow to a purple and ultimately into a dark blue at the end of the HAZ.
The HAZ plays an important role in not only the operational safety of equipment and metal surfaces within the plant, but also the design and manufacture of products themselves.
When specific engineering load-bearing requirements need to be met, for example, an HAZ may reduce the structural integrity of the object and thus the product may be unsafe and unsuitable for sale.
Heat Affected Zone Effects to Look For
In addition to colour, the HAZ has additional characteristics that any responsible engineer, equipment technician, and quality control employee needs to know about. The question of whether remediation needs to be performed or not will depend on the decision of an engineer and this decision can make a big difference. Here are some effects to look out for:
- Distortion/Warping: while fundamental chemical and metallurgical changes cannot be seen by the naked eye, excessive heats on a metal surface can be seen by distorting and warping of the surface. Like all surfaces, metal has diffusivity properties that enable heat to be diffused quickly across a surface area, so HAZs tend to be large on metal surfaces since heat is transmitted so quickly.
- Oxidation: high temperatures from cutting, for example, can promote oxidation of the metal surface. The result are bands of colours ranging from bright yellow to dark blue within the HAZ.
- Hydrogen Embrittlement: heat in the HAZ can introduce hydrogen into the chemical composition of the metal and thus lead to a more brittle, less ductile metal. Engineering standards for construction, for example, needs to meet certain criteria and a brittle I-beam can’t be used since it isn’t up to standards. This phenomenon can be seen by cracking, which can make itself visible after only a day.
- Corrosion: corroded metals don’t just look unsightly, they’re also weaker and a potential safety hazard. The HAZ can be exposed to corrosion, which further promotes more corrosion within and less of an ability of the metal to protect against further corrosion.
What Can Be Done to Control the Heat Affected Zone?
If the HAZ poses a risk of compromising your plant, equipment, or manufactured products, then it’s time to look for a solution. Of course, there are so many possible problems and solutions depending on the industry and the product as well as the standards that may be required. For example, waterjet cutting tends to produce no HAZ and may be a viable solution for sheet metal cutting, whereas thermal cutting produces too large a HAZ on sheet metal and therefore should not be used.
Speed
Reduce the surface’s exposure to high heats and the HAZ will not spread as quickly.
Treatment
If a HAZ has already formed on the surface, there’s often a solution that can keep it under control and prevent the negative effects from spreading.
For instance, solution annealing is a process that evenly distributes heat across steel in order to forge stronger chemical bonds. This can be done before the steel is shaped and cut to produce a stronger and higher quality material that’s more resistant to the HAZ.
Sometimes, the only way to deal with a HAZ is to remove it completely. If possible, the metal surface will need to be cut or ground away so that it doesn’t spread and further compromise the metal surface.
Product Solutions
Often, industrial products are able to keep the HAZ in check, but this isn’t always the case either. Most of the time, products are used strategically to solve symptoms of the HAZ. That’s fine, since these products can prolong the lifespan of equipment and keep metal surfaces looking great for years.
Metal Coating
Brushable ceramics and similar epoxy-based compounds can be applied to surfaces in order to protect against wear and tear, corrosion, and they’re often sold with high temperature thresholds that can resist the formation of the HAZ in the first place.
Epoxy Patching Products
Sometimes, the damage has already been done and it seems that action wasn’t taken fast enough. In many cases, metal-filled epoxy patching and repair products such as Plastic Steel Putty can get the job done well and to fill in metal surfaces that have worn away due to exposure to high temperatures or from acute damage.
Need a Practical Solution? Contact Cotter Marketing
It can be challenging to find the right product solution to deal with HAZs on metal surfaces. It can be costly to ignore the problem, too, or to apply the wrong solution which can end up damaging the metal surface even more.
Consider consulting Cotter Marketing for your industrial plant product needs. Our great selection of products are designed with the needs of hardworking machinery and heavy-duty equipment in mind, and many are sold exclusively in Ireland by us so you know that you’re getting quality when you choose to do business with Cotter Marketing.
Other pages that may be of interest are metal coating, concrete coating, abrasion resistance and chemical resistant coating.