I overheard a guy at the steel yard warning about bad 4140 stock

Was picking up some flat bar yesterday at Atlas Steel in Denver when this old-timer was telling the guy behind the counter that a whole pallet of 4140 from a certain batch has been cracking under heat treat. He said the mill certs were faked on lot #B27 and the carbon content was off by 0.15%. Made me think I should double-check my own stock before my next big project. Anybody else run into counterfeit certs lately?

2 comments

2 Comments

leo2381mo ago

Hold up, you sure about that 0.15% carbon being off? Most 4140 runs about 0.38 to 0.43 carbon, so a 0.15% swing would put it way outside normal range, more like 0.23 or 0.58 which would be pretty obvious even before heat treat. I've seen fake certs before but usually the numbers are closer to spec, just slightly off to save money on alloying. A 0.15% carbon error would make the steel behave completely different, like you'd notice right away on a grinder spark test. You should probably test a piece of your own stock with a portable analyzer if you're worried about that batch.

wrenstone1mo ago

Yeah but I've seen 4140 certs off by that much before, it happens more than people think.