ASTM A705, A564 Type 630 (17-4 PH) Severe Cracking After Heat Treat

[Macdost]

We changed ingot size from ~46" Round to ~26" square for forging of the subject line material. Forged the ingots down to H-20”, W-28”, L-21 ft, we made the switch to save time in forging (Open Die). This was the only major change in process

After cooling to 90° we placed in furnace, ramped to 1900° soak. When they came out they had massive crack along the middle of the entire piece(s) essentially splitting in half. The heat treat instruction was poor - Put in at XX Time/day, ramp to 1900°f, shut off and pull out at XX time/day, air cool.

We have two more in the furnace and have revised the heat treat; Slow heat to 1000°f, hold for 7 hrs. Increase to 1900° slowly (150°f/hr.) hold at temp for XX hours - no cracking.

It is easy to say that the new heat treat, with actual instruction was the reason for the no cracking on second lot. I just want to ask if anyone had any other ideas in their experience with 17-4 PH.

Thanks in advance for replies.

 

[EdStainless]

So you reduced the forge ratio from roughly 3 to approximately 1.2.
Massive segregation and chemical inhomogeneity could have been the cause of the cracking.
Did these receive a very long high temp homogenization soak before you tried forging them?
Sounds to me like you need a larger ingot.
Of course forge temp could be an issue, but since you have done these before I'll presume that you watch that very closely.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[metengr]

I think the lack of a proper heating cycle and cooling cycle description (deg F/hr) was probably the root cause for the cracking in ingots of this type. Also, another consideration is the forging temperature. If it falls below 1800 deg F without reheating this could also crack the forging. Nothing of this type is easy only obvious.

 

[MagBen]

Ingot size was concerned. From 26 to 20 and 28'', 28'' side must be expanded. plus, the small press ratio caused non-uniform deformation,the center of slab might get no deform at all.
cracking of this alloy is not uncommon because the formed fresh martensite is very brittle. HT to revert some ductile phase is one of trick to prevent cracking.