Old timer told me I was grinding too hot on a job site last week

Was prepping a boiler tube weld in Gary, Indiana and this guy named Frank walked over. Said my grinder speed was creating micro-cracks in the heat affected zone. Never even thought about that in 5 years of doing this. Anyone else have a senior guy drop some knowledge that completely changed how you work?

2 comments

2 Comments

rosew374h ago

So Frank's got a point but not quite right about the micro-cracks thing. I'm a metallurgist by trade and I spent 10 years in power plants dealing with this exact thing. Grinding too hot won't create micro-cracks in the HAZ from just the heat alone, it's more about the grinding burns that change the surface hardness and then that can lead to stress corrosion cracking later on, especially in boiler tubes where you got that caustic environment. The real trick Frank might have been getting at is the discoloration of the metal - if you see that blue or purple color from overheating, you've basically hardened that spot and set yourself up for cracking under thermal cycling. So yeah, slow it down and keep your grinder moving, but the issue is more about surface hardening from burns than actual micro-cracks from the heat itself.

ryanprice2h ago

Yeah except the discoloration thing isn't always that simple, I've seen blue temper colors show up from grinding on stainless that actually didn't hurt anything because the guy kept the wheel wet and moving. The real danger is when the burn goes deep enough to change the microstructure below the surface, which you can't always see just by looking at the color. So Frank was close but he was mixing up the visible signs with the actual metallurgical damage, which is way harder to spot without etching or hardness testing.