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c.baum

continuous cooling transformation diagram

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c.baum   

Hi folks, 

got a question concerning the cooling times in CCT. If you have a look at the diagram there are several curves showing the composition after different cooling speeds. Everything ok for me but how do i know how fast a cooling medium does the cooling? Are there any rough rules of thumb (e.g. cooling in oil does xxx K/s, cooling in water yyy K/s,...)? Many thanks in advance!!! 

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John B   

I don;'t know if this helps, but it is a section from the handout and general notes I work to when taking a toolmaking course

HARDENING To harden steel, the metal must be brought from hot to cold quickly , and this rapid rate of cooling is done by quenching

The more rapid the rate of cooling, the harder the steel will become, but care must be taken in choosing the appropriate quenching medium, because certain steels will crack if quenched too quickly, or if the item being quenched is of an intricate shape

The quenching medium is chosen according to the rate at which it is desired to cool the steel

For most steels we use oil or water,

Water should be clean and fresh from a tap, warm water will give a much slower rate of cooling but will be somewhat more rapid than oil,

Warm oil is more rapid than cold oil, Mineral oils are more rapid than Animal oils, and Animal oils are quicker than Vegetable oils.

Air is also used and results in a very slow rate of cooling and is referred to as Air Hardening.

If extreme hardness is required, 5% caustic soda solution,  or 5—20% brine solution can be used.

 

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c.baum   
On 14.9.2016 at 5:57 PM, John B said:

Warm oil is more rapid than cold oil, Mineral oils are more rapid than Animal oils, and Animal oils are quicker than Vegetable oils.

Nice info, never heard of that. But it still is just a relation. Many thanks anyway! 

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c.baum   

I actually got the following information: water does 200 K/s, oil 100 K/s. The "source" doesn't say which kind of oil. But after thinking about the whole thing i don't know if it is that simple. Quenching a thing with a high mass will take longer cause there's more heat saved in the core beeing conducted to the outside, so in my eyes you can't say "quenching in water at 800°C takes 4 sec". Seems to be a bit more difficult...

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c.baum   
14 hours ago, ThomasPowers said:

 

yup factoring in the leidenfrost effect can make a big difference.

 

Of course Leidenfrost is a additional factor. But in my eyes even moving the tool in the quenching medium will show different cooling speeds at different diameters, not to mention the warming of the medium resulting a alteration of the cooling speed...

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saw a funny video where a guy was attempting to compensate for this effect by rapid motion,  which would have been fine if he were not swishing it around like a child attempting to get nasty sticky goo stuff off his hand. and he wondered why it came out bent and warped?  forgetting a red hot knife is about as solid as wet pasta, and bends just as easily.

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JHCC   
31 minutes ago, Steve Sells said:

saw a funny video where a guy was attempting to compensate for this effect by rapid motion,  which would have been fine if he were not swishing it around like a child attempting to get nasty sticky thing off his hand. and he wondered why it came out bent and warped?  forgetting a red hot knife is about as solid as wet pasta, and bends just as easily.

Kind of like the video of the guy trying to harden a sword by heating it in a lava flow?

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Or the old urban legend about quenching sword blades in people.  If it had any validity you'd have folks still doing it using farm animals.  (Now blood works as a weak brine IF you use it before it clots; urine works better and has such an amusing smell...)  When I was researching the old UL I would run into a reference that basically said "While we NEVER did it our terrible enemies would do it" and sometimes I could track down the exact same thing in the other culture about the first one.  Never found one saying "yup that's the way *we* do it"  but then who likes to admit they are stupid as a red hot sword is about as solid as wet pasta and people are NOT a uniform density quench!

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