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Whiskeymike

Air temperature vs. material temperature

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I'm wondering how the temperature of the oven relates to the material temperature and if they are always the same once the right amount of time has past.  

So for instance, if you need to heat treat steel at 500 degrees for 8 hours, you set your oven to 500 degrees - 

1.  Is there a rule of thumb of how long it will take the steel to come to 500 degrees? 

2.  If the steel was in the oven when you started the oven to rise to 500 degrees, when the oven hits 500 degrees, does that mean for relative certainty that the steel is also at 500 degrees?  Or by scientific principles, will the oven not hit 500 degrees until the steel hits 500 degrees as it's effectively cooling the oven air by being heated?  

I'm thinking of using a ceramic/glass kiln to heat treat/temper steel since I already have it.  But wondering if any of the above has to be taken into account when doing these actions.   

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Given enough time; the material in a heat treat furnace will reach the same temperature as the furnace  interior.. What would prevent it from doing so?

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but no,  it wont be the same temp at the start, the materials temperature lags because air is a terrible transmitter of calories

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Sort of like asking how long does it take to boil water? Which would depend on how much water, what the starting temperature was and how many BTUs are going into the system and how many are being lost. (Altitude too; but steel doesn't care about that...)

Why not get an optical pyrometer and take reading of the temp off your piece?

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Well,  I guess I have two concerns.   1. is the time that it takes to get there.  So if you have heat it to 500 degrees for 8 hours and you place the piece into a 500 degree oven, it will take some time to also get to 500 degrees.  So I'm trying to figure out if you need to calculate this or measure it's temperature or something to accurately heat it for 8 hours.  

Secondly, it might have been a brain fart, but I was thinking that just because your oven is at 500 degrees, the steak inside the oven is not.  I guess this is due to moisture, etc.. and may not be applicable to steel, but trying to figure out if the steel is automatically at 500 degrees because the oven is 500 degrees.  

9 hours ago, ThomasPowers said:

Sort of like asking how long does it take to boil water?  Why not get an optical pyrometer and take reading of the temp off your piece?

Yep, exactly. Was just wondering how smiths deal with this and how they determine when it's the same.  

On the optical pyrometer, I have one.  I think it maxes out at 800 degrees or so.   Is there a trick to determining it after the upper limits of an OP is reached without spending a fortune?  

Perhaps i'm thinking about this too much before I get in to it.  

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where did you find a metal that needs an 8 hour temper?  Most use 1 to 2 hour cycle, 2 or 3 times.  The exact time is not critical and many people just use a thermometer or temple sticks for determining temps

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Lol, you nailed it,,, but you owe me a coffee drenched keyboard,,,  ;)  

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I'm brand new to heat treating, so my knowledge comes from the dozen articles/posts I've read over the past few days.  (so very little, and I'm still in that zone of confusion and not knowing what's accurate and internet conjecture).    So the comment of temperature and timing was off the top of my head from one of the articles I read, but isn't particular to the metal I'm working with.   I understood from reading that each metal will have a different temperature and timing and it will be different for normalizing versus quenching, etc..  But as you mention, perhaps an hour or two is the appropriate time line and doesn't need to be timed to the minute.  

It may be a detriment to myself, but when getting into something new, I do an extensive amount of reading and then pick the project to implement on.  That process seems to conjure up tons of questions in the process.  Sometimes it works really well as I recognize issues before they occur.  In other situations, I find that I've over complicated it and if I just did it following a simple one page guide that I would have been further along in the process of learning.  

I appreciate the guidance guys.  I'll give it a shot on a few pieces and see what happens. 

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NO holding steel at high temperatures for long periods of time is NOT good for it's structure! If you do not have an inert atmosphere furnace then you also get scaling and decarburization!

Did you have to stick it in the forge for an hour or two to get it up to forging heat?

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