Aisi 4340

I want to U-bent 1.5” dia rod, and proper cold bent requires to be R (radius) = 3 x rod dia that in this case is R=3 x 1.5” = 4.5”. My application requires radius to be 4”. To get that, I would need appropriate tool (press) that I unfortunately have, so I thought to heat the rod and bent it slowly. Doing that way, I am afraid I will change mechanical properties of chosen AISI 4340 material. It would be easy if I have proper furnace to heat material to 1550F and annealed it properly, but again I do not have it either.
Is there anyone who can tell me what is the maximum temperature that can be applied on alloy steel AISI 4340 that will not affect its mechanical properties?

Thanks in advance,

Zoran R.