Weld Cracking: Causes and Prevention

Weld cracking may occur during cooling or after welding due to excessive restraint, hydrogen, incorrect filler metal or unsuitable welding procedures. The type of crack determines the likely cause.

Identifying whether it is hot cracking, cold cracking or hydrogen cracking is essential before carrying out repairs. Using the correct consumables and welding procedures significantly reduces the risk of cracking.

Hot cracking develops while the weld metal is solidifying and is often caused by excessive heat input, unsuitable filler metals or impurities such as sulphur and phosphorus.

Correct joint design, appropriate welding parameters and compatible filler metals help minimise the risk. Hot cracking is more common in certain stainless steels, aluminium alloys and nickel alloys.

Cold cracking usually develops after the weld has cooled and is commonly associated with hydrogen, residual stress and hard microstructures.

It is often seen in higher-strength steels where preheating and low-hydrogen consumables are required. Following approved welding procedures helps prevent cold cracking.

Hydrogen cracking occurs when hydrogen becomes trapped in the weld and combines with residual stresses and susceptible microstructures. It is most common in thicker carbon steels and structural applications.

Using low-hydrogen consumables, storing electrodes correctly and applying preheat where required all help reduce the risk.

Cracking in stainless steel may result from incorrect filler metal selection, excessive heat input or poor joint design.

Using the correct filler rod, controlling heat input and following recognised welding procedures helps maintain weld integrity and corrosion resistance. Clean preparation is also essential. For grade and filler matching, see our stainless steel grade comparisons.

Aluminium is susceptible to cracking if unsuitable filler metals or incorrect welding parameters are used.

Selecting the appropriate filler wire — such as ER4043 or ER5356 depending on the alloy — and maintaining clean joint preparation helps reduce cracking. Correct heat control is equally important.

Yes. An incompatible filler metal may produce welds with unsuitable mechanical properties or increased cracking susceptibility.

Always match the filler metal to the parent material and intended application. Where dissimilar metals are joined, use filler metals specifically designed for that purpose.

Preventing weld cracking involves selecting the correct filler metal, controlling heat input, using low-hydrogen consumables where required and following approved welding procedures.

For thicker steels, preheating and controlled cooling may also be necessary. Proper joint preparation and fit-up are equally important.

Yes. Preheating slows the cooling rate, reduces residual stresses and helps hydrogen escape from the weld area.

It is commonly used when welding thicker carbon steels, alloy steels and wear-resistant materials. Always follow the recommended preheat temperature for the material being welded.

Cracked welds should normally be completely removed before rewelding. Simply depositing additional weld metal over the crack rarely provides a permanent repair.

Before repairing the weld, identify and eliminate the original cause of the cracking to prevent the defect from returning.

Cracking is heavily influenced by consumable choice — low-hydrogen electrodes for higher-strength steels, the correct aluminium filler for the alloy, and matched stainless fillers for corrosion resistance. Choosing and storing the right consumable is often the simplest, cheapest way to prevent recurring cracks.

For help matching a filler metal to your material, explore our MIG and TIG filler wire comparisons, MMA electrode comparisons, or contact the Weldability SIF technical team.