Hot enough for a mirror weld? I doubt it

I keep seeing folks online brag about hitting 'mirror' finish welds on mild steel with just a propane torch and flux. In my experience, that's rarely true below 1400 degrees, and I've tested this at a shop in Dayton. A forge weld needs that dull red glow you can barely see in daylight, not a cherry color you can spot from across the room. Has anyone else actually checked their weld temp with a pyrometer, or are we all just guessing from the color?

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evab521mo ago

Weld color alone can fool you pretty easy since lighting changes everything. A dull red in a dim shop might read as invisible in daylight, but the actual temp needs to be right around 2200F for steel to forge weld, way hotter than 1400. So if you were checking with a pyrometer and getting those low numbers, something else was off with the setup.

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