Some heat treating questions from Larrin's Book

[weo]

Hello all. I hope everyone is staying safe and happy these days.

I was re-reading Larrin's book, and have a question about Fig 22.16 on p.283. I shoot for a HRC of 61-62 for my kitchen knives, and I've been using the tempering info I got off of Kevin Cashen's website. He has a chart that says tempering at 400F will yield 60-61 and tempering at 350F will yield 63-64 HRC. So using this info and the general guideline of doing two 2-hour tempering cycles, I've been tempering twice at 375F for 2 hours.

From the graph in Larrin's book, it looks to me that I ought to be able to get the same result by tempering for only 30 min at 400F. In the interest of minimizing energy costs, would I be safe cutting my tempering time by 75% and doing 2 - 30 minute cycles at 400F?

Thanks

 

[weo]

My second question has to do with the cooling rate of Parks 50 in Figure 21.17 on p259.

Looking at the chart, I'm estimating that the cooling rate at 1485F (807C) is 86F/sec (30C/sec). So:
After 1 sec, the steel is 1400F (760C). I'm now estimating the cooling rate is now ~75F/sec (24C/sec)
after 2 sec, the steel is 1325F (718C) and cooling rate is now ~ 70F/sec (21C/sec)
after 3 sec, the steel is 1255F (680C) and cooling rate is still ~70F/sec (21C/sec)
after 4 sec, the steel is 1185F (641C) and cooling rate is now ~140F/sec (60C/sec)
after 5 sec, the steel is 1045F (563C) and cooling rate is now ~ 200F/sec (93C/sec)
after 6 sec, the steel is 845F (452C) and cooling rate is now ~ 140F/sec (60C/sec)
after 7 sec, the steel is ~700F (371C) and cooling rate is now ~ 100F/sec (38C/sec)
after 8 sec, the steel should be ~ 600F (316C).

Now, looking at the TTT diagram for 1080 (Fig 24.20 on p311), here's what superimposing the 2 curves should look like:

So it looks like after 7 seconds, I've avoided the nose of the curve and am now safe to take out of the oil and put between my aluminum quench plates. Am I looking at this correctly? Would I be able to change to the plates 1 or 2 seconds sooner to help minimize/avoid warping?
Thanks

 

[A.McPherson]

Man! That's way beyond me!!

I think you should treat it and found out, then tell us the results!!!

 

[DevinT]

My second question has to do with the cooling rate of Parks 50 in Figure 21.17 on p259.

Looking at the chart, I'm estimating that the cooling rate at 1485F (807C) is 86F/sec (30C/sec). So:
After 1 sec, the steel is 1400F (760C). I'm now estimating the cooling rate is now ~75F/sec (24C/sec)
after 2 sec, the steel is 1325F (718C) and cooling rate is now ~ 70F/sec (21C/sec)
after 3 sec, the steel is 1255F (680C) and cooling rate is still ~70F/sec (21C/sec)
after 4 sec, the steel is 1185F (641C) and cooling rate is now ~140F/sec (60C/sec)
after 5 sec, the steel is 1045F (563C) and cooling rate is now ~ 200F/sec (93C/sec)
after 6 sec, the steel is 845F (452C) and cooling rate is now ~ 140F/sec (60C/sec)
after 7 sec, the steel is ~700F (371C) and cooling rate is now ~ 100F/sec (38C/sec)
after 8 sec, the steel should be ~ 600F (316C).

Now, looking at the TTT diagram for 1080 (Fig 24.20 on p311), here's what the 2 curves should look like:
View attachment 1449117
So it looks like after 7 seconds, I've avoided the nose of the curve and am now safe to take out of the oil and put between my aluminum quench plates. Am I looking at this correctly? Would I be able to change to the plates 1 or 2 seconds sooner to help minimize/avoid warping?
Thanks

Please be aware that the quench temperature of that diagram is 1650’f which is much higher than normal. 1450 down to room temperature is a lot shorter.

Hoss

 

[PEU]

...
So it looks like after 7 seconds, I've avoided the nose of the curve and am now safe to take out of the oil and put between my aluminum quench plates. Am I looking at this correctly? Would I be able to change to the plates 1 or 2 seconds sooner to help minimize/avoid warping?
Thanks

Once you get past the perlite nose you can go straight to plates. I do this all the time, not with 1080 but O2 (Bohler K720) which has much higher hardenability, in fact, for 2mm thickness I could skip the oil and go straight to plates...

Pablo

 

[weo]

in fact, for 2mm thickness I could skip the oil and go straight to plates...

This is what I'm hoping to be able to do with my 1080/15N20 combination so that I can forge closer to final shape opposed to grinding to shape. Unfortunately, I haven't been able to find any comparable graphs/data for 15N20. I know L6 is supposed to be similar to 15N20, but I'm not sure it's close enough to use that data set.

 

[weo]

Please be aware that the quench temperature of that diagram is 1650’f which is much higher than normal. 1450 down to room temperature is a lot shorter.

I noticed that, but how would that change the shape of the curves? I was assuming that the TTT curve is the TTT curve and the quench temp wouldn't change the curves of the graph, but only affect the time necessary to cool sufficiently to 'avoid the nose' of the curve.

 

[DevinT]

I noticed that, but how would that change the shape of the curves? I was assuming that the TTT curve is the TTT curve and the quench temp wouldn't change the curves of the graph, but only affect the time necessary to cool sufficiently to 'avoid the nose' of the curve.

The lower the quench temperature and the larger the grain size, the farther the nose of the curve moves to the right.

Hoss

 

[weo]

Thanks Hoss. So you're saying that quenching at 1485 would give me more time to avoid the nose, eh? If so, am I correct in thinking that I don't need quite as fast of a quench as Parks 50, so perhaps I could avoid the oil and go straight to the quench plates?

Part of me wants to forge out a blade and experiment, but another part of me doesn't want to take the time to make a damascus blade and not have it harden properly. If I had a Rockwell tester I'd go for it, because then I'd have some good, solid data to tell me if the blade was hardened properly.

Thank you for your input.

Any thoughts on the shorter tempering cycles at a higher temp?

 

[DevinT]

Thanks Hoss. So you're saying that quenching at 1485 would give me more time to avoid the nose, eh? If so, am I correct in thinking that I don't need quite as fast of a quench as Parks 50, so perhaps I could avoid the oil and go straight to the quench plates?

Part of me wants to forge out a blade and experiment, but another part of me doesn't want to take the time to make a damascus blade and not have it harden properly. If I had a Rockwell tester I'd go for it, because then I'd have some good, solid data to tell me if the blade was hardened properly.

Thank you for your input.

Any thoughts on the shorter tempering cycles at a higher temp?

It’s best to make test coupons, 30 minutes is fine for simple steels.

Hoss

 

[Larrin]

Hello all. I hope everyone is staying safe and happy these days.

I was re-reading Larrin's book, and have a question about Fig 22.16 on p.283. I shoot for a HRC of 61-62 for my kitchen knives, and I've been using the tempering info I got off of Kevin Cashen's website. He has a chart that says tempering at 400F will yield 60-61 and tempering at 350F will yield 63-64 HRC. So using this info and the general guideline of doing two 2-hour tempering cycles, I've been tempering twice at 375F for 2 hours.

From the graph in Larrin's book, it looks to me that I ought to be able to get the same result by tempering for only 30 min at 400F. In the interest of minimizing energy costs, would I be safe cutting my tempering time by 75% and doing 2 - 30 minute cycles at 400F?

Thanks

There may be some decomposition of austenite in that temperature range for low alloy steels so I would probably stick with longer tempers. Also it becomes more difficult to walk the tightrope the shorter your tempers become. I checked the math and I wasn't getting quite the same number for 400F for 30 minutes vs 375F for 2 hours. Once you get up to two 2 hour tempers then things level off and don't change much with longer time.

 

[Larrin]

My second question has to do with the cooling rate of Parks 50 in Figure 21.17 on p259.

Looking at the chart, I'm estimating that the cooling rate at 1485F (807C) is 86F/sec (30C/sec). So:
After 1 sec, the steel is 1400F (760C). I'm now estimating the cooling rate is now ~75F/sec (24C/sec)
after 2 sec, the steel is 1325F (718C) and cooling rate is now ~ 70F/sec (21C/sec)
after 3 sec, the steel is 1255F (680C) and cooling rate is still ~70F/sec (21C/sec)
after 4 sec, the steel is 1185F (641C) and cooling rate is now ~140F/sec (60C/sec)
after 5 sec, the steel is 1045F (563C) and cooling rate is now ~ 200F/sec (93C/sec)
after 6 sec, the steel is 845F (452C) and cooling rate is now ~ 140F/sec (60C/sec)
after 7 sec, the steel is ~700F (371C) and cooling rate is now ~ 100F/sec (38C/sec)
after 8 sec, the steel should be ~ 600F (316C).

Now, looking at the TTT diagram for 1080 (Fig 24.20 on p311), here's what superimposing the 2 curves should look like:

So it looks like after 7 seconds, I've avoided the nose of the curve and am now safe to take out of the oil and put between my aluminum quench plates. Am I looking at this correctly? Would I be able to change to the plates 1 or 2 seconds sooner to help minimize/avoid warping?
Thanks

That is a TTT diagram for 1080 not a CCT diagram. The two diagrams are different, and TTT does not show you what happens during quenching. The TTT diagram provides relative hardenability only from that standpoint. Which is why I have CCT diagrams in the quenching chapter and TTT diagrams in the austempering chapter so that they are clearly separated for their different uses. For example, your quenching line passes straight through the nose of the curve on the TTT diagram, that solid line that the cooling rate glances by is the 100% transformation line not the transformation start line. There is no CCT diagram for 1080 in the book, but 80CrV2 is in the same general class of hardenability and there is a CCT diagram for it. You will see that there is significantly more time to avoid the nose in the CCT diagram as opposed to the TTT. W1 and W2 have the "nose" at very short times even with the CCT as they have poor hardenability.

Learn about these different diagrams by reading pages 206-209, 226-227, 252, 256, 259-269, 299-301, and 307-11.

 

[weo]

Thanks for the reply Larrin .

That is a TTT diagram for 1080 not a CCT diagram.

hmmm....in my initial draft of this thread I used the term CCT when describing my mental gymnastics, and then changed it to TTT after rechecking the image. I got a little confused here, and realized metallurgy isn't as easy and doesn't stick in my brain as well as anatomy and biomechanics stuff.
Thank you for taking the time to redirect me, for pointing out the pages that I should refer to, (and giving me a little confidence boost that I was correct in my original thinking that I needed a CCT curve instead of TTT curve.)

PS- Do you have any interest in doing a digital demo/talk on zoom for the NWBA (Northwest Blacksmith Association) Knifemaker's corner sometime?

 

[Larrin]

PS- Do you have any interest in doing a digital demo/talk on zoom for the NWBA (Northwest Blacksmith Association) Knifemaker's corner sometime?

Sure

 

[weo]

Thanks, Larrin! PM sent

 

[PEU]

This is what I'm hoping to be able to do with my 1080/15N20 combination so that I can forge closer to final shape opposed to grinding to shape. Unfortunately, I haven't been able to find any comparable graphs/data for 15N20. I know L6 is supposed to be similar\ to 15N20, but I'm not sure it's close enough to use that data set.

With these steels you wont be able to go straight to plates, a oil quench is needed because of the low hardenability. But its game once you pass the perlite nose.

Besides what I said, I still prefer the quench in oil then plates for K720 in 2mm

Pablo

 

[weo]

With these steels you wont be able to go straight to plates, a oil quench is needed because of the low hardenability.

I'm getting closer to talking myself into experimenting with a damascus billet by forging one of my chef's blades thin (< 0.090 thick at the spine with forged bevels) and trying the quench plates to see if the extra thin cross section will cool quickly enough. I haven't quite decided if I want to make a billet just for this, though. If someone else has already tried this, feel free to chime in.

 

[Storm W]

Thanks for the reply Larrin .

hmmm....in my initial draft of this thread I used the term CCT when describing my mental gymnastics, and then changed it to TTT after rechecking the image. I got a little confused here, and realized metallurgy isn't as easy and doesn't stick in my brain as well as anatomy and biomechanics stuff.
Thank you for taking the time to redirect me, for pointing out the pages that I should refer to, (and giving me a little confidence boost that I was correct in my original thinking that I needed a CCT curve instead of TTT curve.)

PS- Do you have any interest in doing a digital demo/talk on zoom for the NWBA (Northwest Blacksmith Association) Knifemaker's corner sometime?

I would love to see that too. Any chance?

 

[weo]

I would love to see that too. Any chance?

Sure. You can see this one and others live if you join the NWBA: https://blacksmith.org/ways-to-join/
We now have a "virtual" membership just for access to the digital demos.

They will eventually end up on the NWBA YouTube page, but there will be a delay, and you won't have a chance to interact and ask questions.
https://www.youtube.com/channel/UC0GAGq48SxpBxh-95XK0LEQ?view_as=subscriber

It looks like Larrin won't be on until after the new year.

 

[Storm W]

Sure. You can see this one and others live if you join the NWBA: https://blacksmith.org/ways-to-join/
We now have a "virtual" membership just for access to the digital demos.

They will eventually end up on the NWBA YouTube page, but there will be a delay, and you won't have a chance to interact and ask questions.
https://www.youtube.com/channel/UC0GAGq48SxpBxh-95XK0LEQ?view_as=subscriber

It looks like Larrin won't be on until after the new year.

Thats awesome. As you know I live on the east coast but Washington state is home. If I could ever find the right job out in Eastern Washington I would move back.

Hey you probably know this already but when you are looking for wood vine maple and yew are very sought after by bow makers. Just one more thing you could make a few bucks off of.