Hand-warm
Hand warm is a temperature where you can still comfortably touch the workpiece with your bare hand – roughly 40 to 60 °C. For cold welding cast iron, this is the upper limit: the individual short weld beads must not heat the part hotter than this.
What does Hand-warm mean
Hand-warm describes a temperature where you can still comfortably touch the metal with your bare hand – roughly 40 to 60 °C. It's the line between "warm, but not critical" and "starting to get hot."
Why it matters for cast iron
When cold welding cast iron, you want to introduce as little heat as possible. Every weld bead heats the part – if you let it get too hot, the temperature difference to the cold surroundings increases, and so does the risk of cracking.
The practical rule
Only lay short stitch welds and then wait until the part is Hand-warm again before laying the next bead. It's slow, but exactly right: whoever welds cast iron cold has to take plenty of time.