You don’t define breakdown so I will assume a permanent change to the original specified mechanical properties.
For ASTM A 514 Grade H steel (high yield, Q&T), above 400 deg F to 1100 deg F you will see a reduction in mechanical properties while at elevated temperature; cool to RT and properties are back to near original.
Exposure to temperatures above 1150 deg F (original minimum tempering temperature by specification) will have a step change to lower mechanical properties and upon cooling to RT will be a permanent change (lowered) to these properties unless this material is reheat treated.
metengr - Can you also comment on the reduced properties? We are considering a forming process with A514 that would require twmps of 900 deg C. Is there anyway to predict the material properties after this operation?
Also, does anyone have any experience requenching and tempering A514 or working with green material prior to Q&T (not sure if this is even possible to get)?
At 900 deg C, the UTS and YS will be close to 10% of RT properties. After cooling from this temeprature, the mechanical properties will be lower (between normalizing and annealing).
You can easily reheat treat this material to achieve the desired mechanical properties after hot forming.
