July 15, 2014
Editor’s Note: This is the first article of a two-part series.
Q: I work in a midsized job shop, and we weld with the FCAW, GMAW, and SMAW processes. Occasionally we encounter weld cracking issues. What causes weld cracking, and what can I do to prevent it?
A: To ensure that the measures you take to correct weld cracking are successful, you must first thoroughly investigate why cracking is occurring in the first place. It is critical to understand what causes weld cracks if you’re going to prevent them in the future.
First, take into consideration the material type and thickness, as well as the level of residual stress in the weldment, before fabricating begins. This will help you to avoid having to repair cracks after the welding is completed. With that said, three main types of weld cracks exist: hot cracks, stress cracks, and hydrogen cracks.
Hot cracks generally occur before the weld bead is completed and are longitudinal. They are also referred to as centerline cracks because they usually appear at the weld centerline. Hot cracks most commonly occur at high travel speeds, but they are known to happen at normal travel speeds as well. When elements or compounds with a lower melting point, such as sulfur, phosphorus, copper, boron, and selenium, end up at the weld centerline during solidification, the end result is typically a hot crack.
To eliminate hot cracks you may want to consider decreasing your travel speed. By doing so you will be able to lay a weld puddle that is rounder in shape. Research verifies that a “teardrop” weld puddle may be more susceptible to hot cracking than one that is rounded.
You also should look at using filler metal with higher manganese content, or one that has a more basic slag system. For instance, if you’re experiencing hot cracks with an E7014 electrode, you could change to an E7018.
Last, consider removing the source of the low-melting-point compound. This may be difficult if the compound is part of the makeup of the material being used, but it is still an option.
We sill discuss stress and hydrogen cracks in Part II.
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