What causes weld metal solidification cracking and how to avoid it?

HOW IT WORKS

November 29, 2021

 

Question:What causes weld metal solidification cracking and how to avoid it?

Author: Nairn Barnes

Answer: Weld solidification cracking, sometimes referred to as hot cracking or shrinkage cracking, is cracking that occurs as the weld is solidifying. The reason for solidification cracking is that the amount of liquid metal in the weld pool is insufficient to fill the gaps created as the weld metal shrinks during solidification. Cracking often appears during welding or immediately following solidification and is often evidenced as centerline cracks running longitudinally (along the main length) along the weld. Some smaller peripheral longitudinal cracking may also present itself in the weld. Cracking occurs at the centerline or oriented towards the top point of the weld bead as that is the last portion to solidify. Solidification cracking may be contained within a weld and is not necessarily identifiable through visual inspection alone.

The main causes/factors of solidification cracking can be categorized as: high strain on the weld pool, insufficient quantity of liquid weld metal, and impurities.

Controlling or preventing solidification cracking can be accomplished through control over the weld metal composition, altering the weld solidification pattern, and reducing the strain on the solidifying weld metal. 

  • With the aim of reducing solidification cracking, weld metal compositions that have wide cooling ranges (i.e. different phases solidifying at different temperatures creating a wide range of solidification) will increase the risks of solidification cracking, as the remaining liquid metal may not be able to reach where it needs to properly. Research has been completed on several material systems to show which elements may have the largest effects on this. Reducing the number of impurities in the weld metal is key.

 

  • The weld solidification pattern is determined based on the weld bead shape/ joint shape. Wide and shallow weld beads will be less prone to cracking, while narrow and deep weld will be more prone to solidification cracking. Too wide a bead will also increase the risk of cracking. Generally, a weld bead shape where the width is half that of the depth will result in the best condition to avoid solidification cracking. Welding parameters such as travel speed can play a large role here as well, with lower travel speeds being preferable to minimize the weld tail length. 

 

  • Generally, a highly restrained joint will be more prone to solidification cracking. Additional factors such as yield/tensile strength of the base metal, the base material thickness (thinner plates are generally better), and the amount of preheat applied can all play major roles in the strain on a solidifying weld.

Importantly, it should noted that solidification cracking can occur in any form of welding and specific considerations outside of those listed may be relevant based on the material system, welding process/parameters, and constraints on the weld execution may need to be considered.




References

[1] 

The Welding Institute, "What is hot cracking (solidification cracking)?," [Online]. Available: https://www.twi-global.com/technical-knowledge/faqs/faq-what-is-hot-crac.... [Accessed 19 November 2021].

[2] 

The Welding Institute, "Hot (Solidification) Cracking – Definition, Process and Tests," [Online]. Available: https://theweldinginstitute.com/Hot-(Solidification)-Cracking-Definition-Process-and-Tests. [Accessed 19 November 2021].


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