TTT Chart for W1

J

JoshEarl

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Sep 30, 2007
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197
Does anybody have a TTT chart for W1 that they'd be willing to send me? My copy of the Atlas of Isothermal Transformation Diagrams is from 1951, and it doesn't have W1. (Unless they had another name for it then?)

I'm working on nailing down the heat-treatments for my steels in my new Ellis forge. :D

Josh
 
I can send you a copy of a page from a HTG, Josh. I need an email addy.
 
I found this online w/o much trouble :thumbup: Hope it helps :D
found it here: http://www.kaker.com/std/ctt/html/1397.html



1397.jpg



says this is from Atlas of Isothermal Transformation Diagrams 1961


Jason
 
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Thanks, guys. Believe it or not, I did make a (weak, apparently) effort to find it online. I had trouble locating an O1 chart a few months back, too. Sad. :o

Josh
 
So if I read this right, to miss the "pearlite nose", you have to get from critical to under roughly 800 degrees in the first second, and then you can slow down from there? And best case scenario, you'll be at 62 rockwell? What am I supposed to be getting out of a diagram like this?
 
All kinds of fun stuff, actually, much of which I can't make use of with my relatively simple equipment. But for starters...

First, it shows that you really can't miss the pearlite nose, because it runs off the chart. That's why it's a shallow hardening steel.

Getting it to about 800 F in one second will give you maximum martensite formation, but you still end up with a mixed structure (probably more in the core of a thick blade, not so much in thinner cross-sections.)

What I was wanting to know was the Ms point, just over 400 F, which is when the martensite actually begins to form.

You're right about being able to cool more slowly once you get it under 800 F. If you quenched to 500 F you could hold it there for 15 to 30 minutes and still get full martensite formation. If you held it longer than that, it would creep into the curve zone and you would start to get bainite, which is cool for some blades.

The as-quenched hardness for W1 that I have in another reference is RWC 68. I think the numbers running down the side represent a range of hardnesses that you could end up with. In designing a heat-treatment, you draw a cooling curve on the chart, and there are different intersection points... I'm a little fuzzy on the details at this late hour. :) It gives you some ballpark hardness figures, which don't mean much to us because we can't control the temperatures as precisely as the industry guys can.

Basically, the TTT chart gives you all the info you need to design a heat treatment for a given application. You can figure out how to get your steel annealed, semi-hardened or hardened, depending on your application. For us, it shows the conditions we have to meet to achieve a fully hardened blade. There are variations that will work--that's why we get different approaches thrown around so much. :)

Hopefully someone will correct me where I'm off...

Josh
 
Wow...

Looking at this, even getting the steel to under 800 in a second, you're still dipping deep enough into the pearlite / austenite zone to approach a 50% mix. I am beginning to rethink water and brine quenching...
 
Dan how do you read that? I found it but can't understand some of it yet. are you saying water brine would be good or no?
 
You can't 'miss the pearlite nose' because the curve goes right through it. Therefore you'll always have pearlite no matter how fast the quench.
 
Mr Carter

If you look at the pearlite "nose" that is clearly defined on the chart, you'll see a dash line that follows it just to the left of it, and another well defined pair of lines even farther to the left. The farthest to the right one is the 100% pearlite nose. The dashed line represents the 50% pearlite curve, and the "pair" of lines that follows the same curve, only off the left of the chart is the actual nose that tells you where you will form some pearlite.

The F+C in the middle of the whole chart is Ferrite and Cementite. This is the "separated" low stress stuff we commonly call pearlite. That big F+C is placed where it is to show that everything to the right of the darkly defined line is pearlite. The A+F+C between the dark lines (the dotted line region) is Austenite + Ferrite + Cementite. As you cool steel too fast to make pure pearlite, the austenite is still hanging around, waiting to make something else. If you pass through the leftmost line and into the middle region, you will make varying amounts of pearlite.

Since the far left portion of the curve (where you begin to make at least some pearlite) goes off the left of the chart, there will be some pearlite no matter what. You simply cannot quench the steel fast enough to avoid it. However, studying this, I am getting a much clearer picture of why it is designated a water quenching steel!

Water is pretty harsh, brine is too, but in a slightly different way. Water is real quick, but also uneven. This causes a lot of problems with micro cracks, larger cracks, and warpage. Brine is less uneven, but faster even than water. Being less uneven is rather helpful, but being faster is problematic too.

There's even a formula for a brine and soap mix floating around that's even faster than brine, but I'd be willing to bet that using it is tantamount to sticking an as quenched blade on the anvil and hitting it real hard with a hammer!
 
Wow thank you very much Dan! I had thought that the F-C and the A-F-C had ment those things, but were unsure as to what it was telling me. Now that you say that it pops right out there (Doh!) This opens up a lot more questions for me though...Now correct me if I'm wrong but isnt this chart based on a Jominy test where the test piece is a 1" drill rod. 3" long? which gives it about 1/8th thick martensite shell on the outside and then a layer of pearlite for the slower cooling part and finally retained austenite core? Which could explain why the nose goes off the chart and pearlite is achieved instead of mostly martensite? Wouldnt we get a fully hardened martensite blade since we work with 1/4" (usually) and less cross sections? Shouldnt this nullify these TTT charts for us since they are based on a 1" cross section? GAH! :eek::barf::foot:

Jason
 
MAYBE it's based on a Jominy test.

Alternatively, MAYBE it's based on calculations given specific chemistry of the steel (likely the "ideal" chemistry as designated).

Would this "nullify" the curve for our use, because of the thin section? no. The "shell" on the outside of the jomoiny sample is actually a gradient. In it's most dramatic (or least dramatic, if you prefer) form, the "skin" would be 100% martensite and the exact core 100% pearlite, with a nice, even gradual mix of more and more martensite as you move away from the core.

The thin sections we work with help us a bit in that regard, but they do not change the laws of thermodynamics!
 
I see your point Dan. the gradient example really helped. so basically these charts give us an informed guess at best, (all variables considered) See I'm a very black and white person, theres a right way and a wrong way kinda guy. This hobby is helping open me up to some gray shades that's for sure. Thanks for taken the time to educate me on this. Dan and the rest of ya'll to. I appreciate it all greatly.
 
The Jominy test is to determine hardenability .That's not how they get the TTT curve." retained austenite core" No the core will transform to either martensite or pearlite depending on the hardenability.
 
Thank you very much Mete :thumbup: I understand now I think, so with W1 it's near impossible to get a martensite core? but say 5160/52100 with all the chromium to make it deep hardening would get a full martensite core. (given you did everything else right;)
 
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