Need input regarding should anneali

[gma301221]

Need input regarding should annealing be performed on 4340 hardened bars? 4340 bars after heat treating at 1525F/oil quench/ tempered at 1190F. Hardness lower than 28hRC. IS full anneal required prior to rehardening and tempering at temperatures around 1125-1140F.

 

[bobjustbob]

From the aspect of mechanical properties, I would not anneal before rehardening. I would question your temperature prior to quench however. 1525°F seems a bit low, I would go to 1550°F minimum. Is your hardness requirement 28HRc? What hardness were you actually getting? Your 1190°F temper temperature seems about right to get around 28HRc.

Bob

 

[EdStainless]

I would not re-anneal.
1525F should be fine, provided that there is no delay in getting parts into quench.
I would look into the hold time, are you sure that you are heating long enough?
And is there any chance of surface de-carb? That would give you a lower surface hardness.

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

 

[MagBen]

Re-anneal is not needed. normalizing may give you some benefit. you can simply re-temper at higher temp to knock down hardness, but cannot re-temper lower for a higher hardness.
1525F is ok, or even lower than that. An axiom: "temper low, harden high; temper high, harden low"

 

[gma301221]

Thanks guys for your inputs.