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Hi all, 

 

So I started doing my first chefs knife, a Damascus 1060/15n20. But I found it to warp a LOT. I left it a bit thick for quenching but I saw it warping since the normalizing (I treated it like 1060 steel) maybe that was my mistake. So when I quenched it I quickly put it in my straightening jig and let it cool there and it was straight. But when I started grinding it started to warp I was cooling the blade in water and that started to make it curve. But I wasn't letting it get hot. That's what has me wondering.. 

Do any of you know where I took a misstep or what I should do differently? 

 

Check the Pics20210323_200753.jpg20210325_101456.jpg

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There are people far more qualified to  explain why metal does what it does. If you haven't tempered yet you can clean up a majority of the metal. It doesn't have to be perfect. Clamp it to a piece of straight stock  and run it through what ever your tempering cycle is. If it takes  a curve after that try blue backing it while in a straightening jig. 

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6 minutes ago, vlegski said:

There are people far more qualified to  explain why metal does what it does.

I agree, but a little more info might be useful?  How many layers and what was the pattern? 

In my experience with damascus, I've had this happen, not all the time, but enough of the time to come to the conclusion that it's the nature of the steel.  The different steels used have different properties and there is a lot of stresses in the steel that can get relieved through grinding.  Proper thermal cycling/grain refinement seems to help significantly, but won't guarantee a warp free experience. 

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Thanks vlegski! 

BillyO caught my drift a bit better. 

 

It was a mere 216 layer Damascus nothing fancy. 

I did my thermal cycling perfectly but I did it to suit the 1060 steel, here's where I get my doubts. Maybe 15b20 needs different treating than 1060 and I'm either quenching too hot, Or too cold. 

 

In waiting for a response from the forum I started messing around with the knife pre tempering. (it was at 60 hrc) so I wanted to leave it as such to get a great sharpness. But in my lack of patience I broke it. So we might think this discussion is no longer a moot point, but I think it will help to know more for future reference. 

My grain was smooth as silk check the pics 

 

Maybe I made all the mistakes that had to be made for making Damascus chefs knives. 

 

I would love all your feedbacks and tips. 

 

Thanks 

 

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Paul, your grain is actually a little on the big side of good.  That is, it's still good, but could be better.  

I can't help with the warping, some blades just seem to want to warp.  But, what was your normalizing sequence and hardening temperature?  That will help perfect your grain.

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Hey Alan! 

 

So I did 3 normalizing cycles 

1. 1650 and cooled in air

2. 1600 and put it in the jig and let it cool 

3. 1550 in the jig again 

 

Quenched at 1565 in 150º cooking oil and straight to the jig. 

 

And this was all in my evenheat oven 

 

And the second time I hardened 

 

I normalized once at 1550 and them quenched. 

Maybe I should have done the 3 cycles again right? 

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I don't have experience with 1060, using 1080 in my damscus, but if they have (my guess) similar critical temps, then I think your 'grain refining' cycles are a bit on the high side, causing the larger grain than expected.

I'm still not an expert, but my understanding, after reading Dr Larrin Thomas's book, is that when doing grain refinement/thermal cycling, you do one cycle at a temp a bit higher than critical temp to get all the carbides in solution and as evenly distributed throughout the steel as possible (your first 1650F cycle). It's also my understanding that for those of us forging blades, this isn't necessary because we typically forge at temps higher than this.  Then, the next 3 cycles should be slightly below the critical temp (and air cool to black) to shrink the grain, and while many smiths do descending temps, it's un-necessary.  For my damascus (1080/15N20), the critical temp is right around 1475F, so I do 3 cycles at 1400F.

Edited by billyO
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You stated you determined the hrc as 60 prior to tempering. I'm curious as to your method to determine Hrc prior to tempering as all I've ever done was file tests to check for hardening. Usually prior to tempering my files won't cut, unless I have a decarb problem 

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1 minute ago, vlegski said:

You stated you determined the hrc as 60 prior to tempering. I'm curious as to your method to determine Hrc prior to tempering as all I've ever done was file tests to check for hardening. Usually prior to tempering my files won't cut, unless I have a decarb problem 

I use this little miracle I found, I know it's not gonna be totally accurate but it skated right off on 60 and bit in with the 65. So I say 60 but it might be in between. 

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15 minutes ago, billyO said:

I don't have experience with 1060, using 1080 in my damscus, but if they have (my guess) similar critical temps, then I think your 'grain refining' cycles are a bit on the high side, causing the larger grain than expected.

I'm still not an expert, but my understanding, after reading Dr Larrin Thomas's book, is that when doing grain refinement/thermal cycling, you do one cycle at a temp a bit higher than critical temp to get all the carbides in solution and as evenly distributed throughout the steel as possible (your first 1650F cycle). It's also my understanding that for those of us forging blades, this isn't necessary because we typically forge at temps higher than this.  Then, the next 3 cycles should be slightly below the critical temp (and air cool to black) to shrink the grain, and while many smiths do descending temps, it's un-necessary.  For my damascus (1080/15N20), the critical temp is right around 1475F, so I do 3 cycles at 1400F.

I understand perfectly. But we need to remember we do put a lot of stress into the steel when forging and even more being Damascus steel. That's why the high temp the 3 cycles and the bringing the tem down with each cycle. 

It has actually proven to be a faultless technique with my other blades. I actually developed a quick guide for treating steel with Alan Longmire's "supervision". 

 

Check it out, it can be very helpful it's printable and I have it next to my oven to look at when I'm doing this if I don't have the schedules programmed into my evenheat kiln. 

 

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I still can't help with the warping, but Billy is right, your normalizations and hardening temps are a little high.  To get the best grain refinement you need to rock it back and forth across critical a few times, and with your steel combo that would be around 1450-1475 F.  Try taking it to 1500, air cool to at least 700 and quench, then 1475 and air cool to below 700 and quench at least twice.  Then harden from 1475.  I bet you'll get grain so fine you can't even see it.  You might lose a point or two of hardness, but you'll gain toughness.

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Well, since we understand the metal stresses could be a cause. And the temps are controlled by the oven it leaves a couple areas to look at. 

1. Your normalizing numbers may be to high. For 15n20 the  1650 seems to agree with various documents.  The second and third are high when compared to other heat treat sources. But since temps vary all over the board because if personal opinions it trial and error.

2. Oil contamination or deterioration.

3. Oil temp to high

4. Quench technique might lend itself to warp.

4. Blade configuration. Thin to thick.

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I believe 

7 minutes ago, vlegski said:

Well, since we understand the metal stresses could be a cause. And the temps are controlled by the oven it leaves a couple areas to look at. 

1. Your normalizing numbers may be to high. For 15n20 the  1650 seems to agree with various documents.  The second and third are high when compared to other heat treat sources. But since temps vary all over the board because if personal opinions it trial and error.

2. Oil contamination or deterioration.

3. Oil temp to high

4. Quench technique might lend itself to warp.

4. Blade configuration. Thin to thick.

I believe everything you said is true.

So in summation... 15b20 gets treated as the steel it has been  welded to. 

In this case I think I have identified my mistake. 

When I requenched I didn't do the 3 cycles. And the blade was thin enough that it wanted to warp decause not only did it warp to one side but it became concave from hilt to spine. 

 

Well. Off to try again, it was only to be expected for my first time. Trial and error I always say. 

 

I'll save this Damascus billet to make some fossil Damascus in a can. 

 

 

Thanks again for all your imput 

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Personally I've had good results with warps when I clamp blade to a straight piece  of stock and given it at least 2 tempering cycles. It helps relieve the stresses in the blade from the quench. Then I use a slower grinder speed  to avoid over heating  the blade.

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2 minutes ago, vlegski said:

Personally I've had good results with warps when I clamp blade to a straight piece  of stock and given it at least 2 tempering cycles. It helps relieve the stresses in the blade from the quench. Then I use a slower grinder speed  to avoid over heating  the blade.

I will keep that in mind for my next project. Maybe it started warping cause I hadn't tempered it. And you're right I might have had to temper to release the stress. And instead it released it in the ginder. 

But I did use a slow grinding speed. 

 

Lesson learned. Ahahah 

 

Thanks again for all the comments and helpful tips! 

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Always temper fresh martensite as soon as possible (alloys that get cryo/cold treatments will be slower to get the temper, but you still temper them immediately after heating back up to room temp.  Even if you don't temper to your final temper temp.  So if you plan on tempering at 450 eventually, but you don't want to do that quite yet for some reason, temper it at 300 ASAP, and get back to it more later.  

 

Warps come from uneven stresses.  These stresses come from either geometry or uneven heat/cooling (and really, the geometry is also related to uneven heating/cooling).  Or, obviously, if you mechanically stress the blade.  So, how even were your grinds?  How even is the cooling from your jig?  How smooth is your quench?  

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Hey jerrod. 

 

Well I did everything by the book. The jig was perfectly even. My finds were as well. I mean not down to the  .0001 of a millimeter but very very honed in. 

 

My quench went perfectly. As a matter of fact when it took it out of quenching it was straight! It started warping on the grind. And I believe it's because of what you said. I should have tempered to at least 300 o 350. 

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I'm with Jerrod on this.  Definitely recommend tempering, and also a stress relief cycle (subcritical anneal at well under the transformation temperature - 1250-1350 range) before heating up to quench.  I was trained to let normalizing and stress relief cycles cool in air, not in a jig.  Your jig may be cooling the stock too quickly.  Good luck on the next one.  Kitchen knives are tricky, but straightening during the second or third tempering cycle, as other's mentioned, has worked for me as well.

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1 hour ago, Dan Hertzson said:

I'm with Jerrod on this.  Definitely recommend tempering, and also a stress relief cycle (subcritical anneal at well under the transformation temperature - 1250-1350 range) before heating up to quench.  I was trained to let normalizing and stress relief cycles cool in air, not in a jig.  Your jig may be cooling the stock too quickly.  Good luck on the next one.  Kitchen knives are tricky, but straightening during the second or third tempering cycle, as other's mentioned, has worked for me as well.

 

I will keep all of this in mind! Thanks Dan 

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