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kb0fhp

Calculating CCT/TTT diagrams

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I think the 'calculator' was designed for the metallurgist among us as I have tried to use it and the results do not look like any TTT nor CCT chart I have seen before. Can anyone offer a brief tutorial on how to use it? The upper portion of the calculator is the input area for the percentage by weight of the makeup of the material. That is self explanatory. The bottom portion seems to be the area causing me trouble. Thanks...

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When I input values of known materials, the graph that comes out is not at all like it should be. It is possible that I do not understand. How does Kelvin comare to centigrade ? (thought it was the same). It is also possible that the cooling rate needs to be increased substantially ?

 

This thing has always confounded me. :(

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When I input values of known materials, the graph that comes out is not at all like it should be. It is possible that I do not understand. How does Kelvin comare to centigrade ? (thought it was the same). It is also possible that the cooling rate needs to be increased substantially ? This thing has always confounded me. :(

 

Zero in Kelvin is rock bottom and equals -273.15 degrees Centigrade and -459.67 Fahrenheit. No molecular movement (and it's really a hypothetical point, at least to current science). Space is warmer at 2.7 Kelvin.

 

Hmpf, didn't know that button worked. My Halfzheimer's is not yet complete...

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Actually - it doesn't look too bad. When you input "0" into the temperature - it defines the austenitizing temperature as Ae3...let me try and find a simple one and I can compare data.

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OK - when looking at a common steel that you might encounter/use - I chose 6150, and used the same parameters for each - same chemistry, austenitizing temperature, time scales, etc. Within the limitations of the calculations, it doesn't look too bad. Remember in the calculated file to subtract 273K to get the C temperatures. The basic phase fields tend to correspond with temperature and time - actually pretty well. THere seems to be a disconnect with the TTT diagram and the Bainite start temperatures. But overall - I find that it is pretty close on the whole - good enough that I would use the calculated data with a bit of understanding and caution. Certainly, I would compare several more to verify - but on this first comparison - it is pretty good. The CCT diagram appears to match pretty well....One thing that you have to pay attention to is the maximum cooling rate - note the differences when I changed the maximum cooling rate from 100K/s to 35 K/s

6150_CCT.jpg

6150_TTT.jpg

calculations.ewi.org.png

6150_calculate.jpg

Edited by kb0fhp

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Guest Kyle Hershey

Oh! Man!! The link is down!! Damn damn damn!!! :wacko:

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Guest Kyle Hershey

Thank you kindly Don!! I have been looking for a calculator like that!!

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Am I correct in thinking that this could help you heat treat damascus more accurately? Average the percents of alloys in the different steels you use (by weight) and enter those figures in. Or would the fact that only carbon migrates quickly make that inaccurate?

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That might work if you are making damascus with just 10XX series steel. If you have other types of steel, let us say O1 with 1070, the carbon will equalize and, assuming equal parts, you will end up with around 80 points of carbon evenly distributed throughout. The nickel and tungsten from the O1 and the manganese from both steels diffuse very slowly in austinite. Extremely slowly might be more accurate and you will have bands of these alloys in different concentrations thoughout the damascus billet. The ITT diagrams can still be of an assistance in choosing which of the steels that you are going to heat treat for as a starting point. You may have to experiment a bit to get the best heat treatment.

 

Doug Lester

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These calculators can be very usefull but it is hard to take into consideration all the factors that influence the shape of a TTT or CCT curve (there are MANY). Usually they are only really usefull if used in the "context" they are designed to be used in... i.e. they are based on a combination of empirical data and theoretical physics in a certain application or composition range and can tell you what the result of a certain degree of variation would probably be. Some of the variables they don't give you an option to input may very well be making a difference because in your application it is varied but in the intended application it is a constant or at least a different typical value.

 

Usually the TTT's are a bit more accurate than the CCTs due to a very variable cooling rate being taken into consideration on CCTs but not TTTs.

 

Even if nothing looks the way it "should", it is very interesting playing with these to get a bit of a gut feel for what does what :)

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THE LINK IS DOWN GAYS ... ANYONE HAS NEW LINK PLEASE,,, I REALLY NEED IT FOR MY RESEARCH ????????

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It has been broken for a while.  I sent an email to the folks at EWI a couple years ago asking about it, but never heard back.  

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