22/07/2026
Large root gap when welding? Watch your heat input and T8/5 cooling time!
When you have to execute a weld with an excessively large root gap, for example, 12 to 16 mm instead of the ideal 5 mm, the heat input rises sharply, and the cooling slows down drastically. But what does this actually mean for the strength of your weld?
In our latest blog, we dive deep into the microstructure of the metal and show you why the T8/5 cooling time is the absolute thermometer of toughness:
❄️ Cooling too fast: The metal forms an extremely hard but dangerously brittle structure, greatly increasing the risk of cold cracking.
🐢 Cooling too slow: Coarse ferrite grains form, which offer barely any resistance to crack propagation.
✅ The perfect balance: The optimal cooling time limits grain growth and allows the most desirable structure to form: acicular (needle-like) ferrite. This acts like a dense 'briar patch' that forces a crack to constantly change direction until it completely stalls.
The result? Legendary toughness, even in extreme freezing cold!.
Read our full blog on the influence of heat input and calculate your ideal cooling time directly with our advanced Welding Analyse Pro calculator.
🔗 Link to the blog & calculator in the comments!
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