Heat Treatment of injector body

Sunil,
IMHO the only way there can be a difference in machinability for "identical microstructures" is that there are very small precipate (sub =B5m) carbides or nitrides or intermetallics not resolvable by OM (opitical microscopy) in the microstructure.
This is the case with M2 and other tool steels. Other wise fabricating a cutting tool from 4140 Q&T to 60 - 65 HRC should be able machine a 4140 Q&T to 25-35 HRC! Hot hardness is obtained by the ppt particle hardening and not but the martensitic matrix.
Reheating after forging/cooling cycle can ppt these small particles and affect machinability - and strength (toughness). The process must be examined systematically before jumping to a conclusion.
Ed Vojcak PE (don't relpy to e-mail addresss it is a dead end)

Ed Vojcak PE,
points you mentioned are very much relevant in case of high alloy steel viz. M2 etc. or even in 4135 etc.
but material in context is S45C or C45 or 1045. a very simple steel grade with nil or negligible alloy contents.
plz let me know if hard micro structure such as carbides nitrides can be present in this steel grade.
also, as per customers requirement if we directly quench the forgings from press then at that time there is different temperatures at different locations in the forging ( simulated by software). So at different locations microstructures after quenching in polymer quench will be different. But as per our proposal, after soaking for requisite time at the autenization temp of 1045(steel grade) if we quench then there will be more uniform microstructure across the section of the forging.
then something else also come into my mind i.e. having different temp are different locations may be requisite structure is being obtained. But then our customer is a big German Automobile giant. and as per my understanding, German are the best metallurgist, so they can't think that way. What you say about my problem, Now.

You must test the the "S45 C (or AISI 1045)" to find out - CMTRs are not trust worthy and often wrong or even false!
"Simple Steel??" How much nitrogen in this "simple" steel? Most continous cast have over 30 PPM?
Is this a AK steel SK steel? Are any residuals present Ni, Cr, Mo, V, Ti, Nb present (micro-alloyed intentional/un-intentional)?
Allegheny Ludlum developed a process (I don't have the reference handy - something like 'Al-tech process') applicable to all steels (even simple steels) that increase toughness by precipating sub-micron carbides and nitrides in a controlled fashion - "special alloying" need not only apply!
Point is - even "simple steels" are not so "simple" - nature acts on its own - not to our mis-conceptions or beliefs.
Ed Vojcak PE

That a good piece of advice...thanks. I'll come back to you with more information and ambiguity .. ies I've.
Regards
Sunil