Heat Treatment of injector body

Material is S45C or C45.
It is recommended by the customer that after forging (at min850+10°C), it must fall in quenching tank with polymer quenching system. but we can't be sure that all forging will be at the same or in 850+10°C temp when fall in to quenching media.
we propose, forging will be re-heated at 860°C in our Continuous furnace and will be quenched at 860°C+10°C 9 or 850°C+10°C in the tank. in this way we can maintain exactly same temp before quenching and all forgings will have same micro structure and hardness. But customer is not agreeing, saying that micro structure obtained thus will cause problem to machining which is very minute and precise.
I just wonder how come micro same micro structure, which obtained through different process will affect machining.

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Sunil,
IMHO the only way there can be a difference in machinability for "identical microstructures" is that there are very small precipate (sub µm) 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.
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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

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