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Welding
Monday | 12 May, 2014 | 10:42 am

The research behind repairs

By Gretchen Salois

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Researchers learn how a buffer layer for a soft metal weld works

Advancements are often a result of necessity—something breaks and you need to fix it fast without sacrificing quality. Researchers at the University of Western Australia are breaking down the why behind soft metal welds, where a welder makes a repair without creating cracking, residual stresses or loss of weld strength.

“If an appropriate soft, thin metal layer is melded first, it creates a useful buffer layer between two hard metals,” explains Xiaozhi Hu, professor of applied mechanics and advanced materials, School of Mechanical and Chemical Engineering at the university. “An additional benefit of welding the thin buffer layer first is that the process also limits the development of the so-called heat-affected-zone.”

Hu recognizes that in practice, fabricators have figured out how to meld the appropriate materials together in order to fix a broken pipe, for example. “Experience is one thing but this is a scientific study—when we first did a serious literature search, we found we couldn’t find any research on the topic of soft metal welds. Uncovering the science behind it offers immediate benefits.”

Such benefits include a breakdown of a method that could be widely used in Australia’s strong mining industry, for a start, where damage to mining equipment occurs regularly. “These types of jobs are substantial repairs. We’re not just talking about joining two pieces of metal together, these pipes need to be able to withstand extreme pressures, so understanding a process that allows for a repair to be completed on-site and economically, is key.”

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Mining methods

A metal component (e.g. a shaft in a large mining equipment), can crack or fracture and to replace it would cost upwards of $300,000. In three separate reports, researchers break down how certain variations of a soft weld buffer works and what doesn’t.

Published in Journal of Materials Processing Technology, researchers investigated the relationships among welding residual stress distribution, Vickers hardness profile and microstructure of welded high-strength low-alloy steel and the effects of a soft buffering layer between the parent metal and the weld metal and its thickness variation.

By incorporating a 4 mm-thick buffering layer, researchers were able to increase the strength of the weld. “The degree of the welding softening and microstructure grains of the welded HSLA steel was improved by the incorporation of a 4 mm buffer layer,” according to the report. “In the welded HSLA steel, the hardness decreased with increasing grain size of block ferrite.”

“This research tells us that with any weld, there is a third face between weld and structure. It exists,” Hu says. “There are many situations where you might not have the material needed to repair a weld—the exact original metal. But by placing a soft layer in there, you can in a sense, improvise, use a different grade without embrittlement.

“People may not pay too much attention to this type of approach, which is why I probably couldn’t find any research on it. We tested, measured hardness and tried normal welding while measuring microhardness and compared different metals. When you’re putting in a thin layer, you alter that layer to see what works and the more we uncover, the more possibilities for improvement.” MM

 

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