why did it crack? Hey guys, I’m completely stumped. We…
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why did it crack?
Hey guys, I’m completely stumped.
We forged a medium‑carbon alloy steel part (approx. 12” round). Did a full ultrasonic inspection right after forging – absolutely clean. No indications, no echoes, nothing. Looked perfect.
Then we sent it for heat treatment (quench + temper). After HT, we saw a VISIBLE crack right in the center of the cross‑section. Ran UT again just to see how bad it is – and it’s showing a very deep, strong reflection, practically from the core.
So now the same piece:
· Forging + UT → ✅ clean
· After heat treatment → ❌ deep internal crack
I’m trying to figure out what could cause a crack that deep after HT when there was zero sign of it before. Some ideas I had:
· Quench cracking from excessive thermal stress? But why would it initiate in the very center?
· Hydrogen flaking (delayed cracking)? We did slow cool after forging, but maybe not enough?
· Microstructural changes during HT (e.g., untempered martensite cracking)?
Has anyone seen something similar? Could the crack have been there in a “closed” or tight form after forging, and HT just opened it up? Or could it be something like centerline segregation / internal bursts that UT missed because the crack faces were welded shut?
Would love to hear your theories – and what you’d check next (metallography? fracture surface? hydrogen analysis?).
Thanks in advance!
#industry
Hey guys, I’m completely stumped.
We forged a medium‑carbon alloy steel part (approx. 12” round). Did a full ultrasonic inspection right after forging – absolutely clean. No indications, no echoes, nothing. Looked perfect.
Then we sent it for heat treatment (quench + temper). After HT, we saw a VISIBLE crack right in the center of the cross‑section. Ran UT again just to see how bad it is – and it’s showing a very deep, strong reflection, practically from the core.
So now the same piece:
· Forging + UT → ✅ clean
· After heat treatment → ❌ deep internal crack
I’m trying to figure out what could cause a crack that deep after HT when there was zero sign of it before. Some ideas I had:
· Quench cracking from excessive thermal stress? But why would it initiate in the very center?
· Hydrogen flaking (delayed cracking)? We did slow cool after forging, but maybe not enough?
· Microstructural changes during HT (e.g., untempered martensite cracking)?
Has anyone seen something similar? Could the crack have been there in a “closed” or tight form after forging, and HT just opened it up? Or could it be something like centerline segregation / internal bursts that UT missed because the crack faces were welded shut?
Would love to hear your theories – and what you’d check next (metallography? fracture surface? hydrogen analysis?).
Thanks in advance!
#industry
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