torch marks visible when etched.

timos-

timos-

Knifemaker / Craftsman / Service Provider
Joined
Oct 22, 2012
Messages
2,210
I have a couple blades made out of raindrop damascus (1095 and nickel)

I am finishing them up and very disappointed to see that the torch marks are etching darker than the rest of the blade. There are multiple torch marks from the blades being straightened after heat treat. I know this is the method used to straighten blades but had no idea this would happen. Any one ever experience this? Is there anything that can be done at this point? Ferric chloride seems to show the torch marks right away. A very light etch in plain vinegar does not but then I dont get much of a contrast in the pattern.
 
I dont think it is decarb, I have ground quite a bit off the surface. I surface ground them to 120 grit lengthwise and then took them up to A65 with gator belts. these knives were only 1/16" to begin with. I cant really take much more off the surface.
the bottom knife you can really see the problem, the other marks are just as visible depending on how you hold the blades.
RL51yMJ.jpg
 
This is an issue with any torch straightening. The torch drops the steel in the HAZ (heat affected zone) to high tempered martensite, pearlite, or a mixture of high temper martensite and pearlite. Whichever it is, it will etch different (usually darker) than the hardened steel. There is nothing to do about it besides use a blade finish that does not show it as much. I use a Scotch-Brite finish on most stainless blades that have torch "stains" on the spine.

One thing I did on a damascus blade it was showing the torch marks badly on was to use a torch and walk the red all the way down the spine, stopping about 1" from the tip. I put the edge in a shallow pan of water while using the torch. I only heated the spine to show red about 1/4" down. This gave me a temper like that was rather pleasing. From there I re-sanded the blade and etched to augment the darkness difference.

Peter's HT does torch straightening. Some folks really have a problem with it, but they clearly tell you up front that they do it. I have started doing my own HT again on many blades where it might be an issue.
 
Last edited:
ahh, It is as I feared, I just never considered this issue when i sent the damascus. I guess now i know.
 
I did a dagger with some Devin Thomas damascus. After HT at Peters some apparent torch marks showed up very noticeably when I started etching in ferric. I was very worried. However, I kept etching and by the time I finished it evened out. You can't see it in the final product.
 
Just imagine the stresses and changes in that blade from the soft torched areas and the rest of the hardened blade.

Using a torch is the quick way but not the best way to remove the bend.

Makers should not just shrug it off as being "OK", It is damaged and you can see that damage when etched.
 
AVigil said:
Just imagine the stresses and changes in that blade from the soft torched areas and the rest of the hardened blade.

Using a torch is the quick way but not the best way to remove the bend.

Makers should not just shrug it off as being "OK", It is damaged and you can see that damage when etched.
Click to expand...
Yes, I wasn't happy about it. That piece is not a user, but I would have preferred not to have the issue. Now I do more of the grinding post HT, and I haven't seen any torch marks lately.
 
same here, i ground my latest batch from peters ht post ht. i did the profile, fit the guard and drilled the holes, and the 45 degree angles at my edge then sent them out. i thought they would be "harder" to grind than soft blades, i honestly do not notice any difference. i do a lot of double edge grinds and tapered tangs, even with hi end gas purged furnaces and vacuum ovens there will still be warp. after HT seems to be the key so far.
 
There's nothing wrong with torch straightening, it's just spot tempering. If you're concerned about stress propagation from the spots you torch, then do a final stress relieving temper at the target RC temp.

The etch isn't showing "damage", it's showing the difference in hardness.

Even 2 points RC will change the color of the etch. The harder it is, the blacker the blacks will come out of the etch, and the brighter the silvers will come out. 62 and higher, most of my damascus comes out of the etch cycle dead black and silver (you don't have to clean oxides off the 15n20), assuming you've got your etchant ratio and times right.

Try differentially hardening a test coupon, you'll see a clear transition in color and clarity when you etch it, as the hardness decreases, the black will look muddier, the silver will etch darker and require more cleanup to get it back to bright.



Now, I don't spot straighten this way with damascus, because it's tricky to over-come this, however, coffee etch can mitigate this quite a bit. The coffee etch reacts much less to difference in hardness (try getting annealed damascus fittings to etch with any clarity in ferric, it'll never look great on it's own), since it's coloring mostly, and not cutting, like ferric. Etch to normal depth with ferric, then use the coffee (instant coffee and equal parts hot water mixed well), and experiment. You can go too far, and cause your blacks and silvers to take on a brownish hue, and hot etch works much differently and faster, than cold.

If it's hot, try 5 mins, pull it out, rinse it well, and look at it. Once you oil it, it'll darken up a bit more. You want to get the blacks darker without affecting the silvers. Once you get it right, neutralize lightly (just baking soda and cold water mixed), blow dry with air, and submerge in oil completely, or oil it liberally and leave it alone.

If it goes too far, just polish the blade by hand with 3m pink polishing paper until you get it back to where you started. You may have to dip back in the ferric for 30 seconds, before or after. It's tricky to get right (temp, humidity, luck, all seem to be a factor), just make sure you have a deep enough ferric etch that you can just feel a depth transition, which will allow the silvers (higher) to protect the color.
 
Thank you very much ! i am sure I will learn a whole lot more about etching and finishing damascus after experimenting. I have not come across coffee etching much, but I did notice the vinegar gave a nice even contrast without showing the torch marks, it just wasn't quite enough contrast. So, I am excited to try out that coffeee. Also thanks for clarifying the spot tempering technique a bit, I also did not think of this as "damage" so to speak, but for the type of knives Adam makes I think it could certainly be considered damage. Thanks again guys!
 
I personally don’t agree with using a torch to straighten blades. And there are other options to take care of these issues that don’t degrade the over all heat treat quality. One of these is clamping the blade stright for the first tempering. If it does not come out stright then the next temper you clamp it with alittle counter bend.
 
JT, your method is very nice but i think its also time consuming, of course at this point I dont care what it costs to get done as long as its done right. spot tempering damascus is clearly not the way to go. These blades of mine were not ground at all prior to heat treat, they had just been profiled. BTW that long thin 250mm 15n20 @ RC 63-64 blade you sent me has been excellent. I ground it pretty thin and never had a problem with it warping to one side or another. Some hardened blades will bend all over the place as they are being ground (post heat treat). The guys testing the finished knife think its some kind of high alloy cpm steel because of the great heat treat. :)
 
JTknives said:
I personally don’t agree with using a torch to straighten blades. And there are other options to take care of these issues that don’t degrade the over all heat treat quality. One of these is clamping the blade stright for the first tempering. If it does not come out stright then the next temper you clamp it with alittle counter bend.
Click to expand...

IMO there's nothing wrong with it, if used correctly; but I don't think it should be anybody's go-to method for straightening. I'm a big believer in having as many tools in my arsenal as possible, and sometimes, spot tempering and quenching is the only way to get a tiny compound warp out, of a blade that's ground too thin already, won't straighten in temper without causing a new warp, and wouldn't likely survive re-austenizing. As long as you aren't doing it near an edge, what's really different than blue backing, or using san mai with non-hardening cladding?

Bear in mind, that you're not typically spot-heating to anything like austenizing temps, just spring or slightly higher temps.


Still, I agree, there's usually an easier way to skin this cat. 90% of straightening really should be done right out of the quench, before the blade takes a set, 9% in temper, the other 1% being more extreme measures. I'm guessing that just due to the batch nature of Peter's HT, they can't individually clamp and temper straighten blades though, where as spot tempering allows one person that knows what they're doing, the ability to straighten each blade quickly, without taking up a lot of furnace real-estate, etc.
 
timos- said:
JT, your method is very nice but i think its also time consuming, of course at this point I dont care what it costs to get done as long as its done right. spot tempering damascus is clearly not the way to go. These blades of mine were not ground at all prior to heat treat, they had just been profiled. BTW that long thin 250mm 15n20 @ RC 63-64 blade you sent me has been excellent. I ground it pretty thin and never had a problem with it warping to one side or another. Some hardened blades will bend all over the place as they are being ground (post heat treat). The guys testing the finished knife think its some kind of high alloy cpm steel because of the great heat treat. :)
Click to expand...

Glad the knife is working great for you. I ment to respond to your email when I got it. But then got swamped and spaced it. Email me agian and we can go over your future plans.
 
Well, its a damn shame , nothing I do seems to make a difference on this piece, i can get it to look real good in a photo only lol.
aBR6qYm.jpg
UXVJ2l3.jpg
 
That sucks. High carbon steel straightens real easy when clamped stright for the first temper. I find that the temper needs to be in the 400° range for it work.
 
Can you send it back for heat treat with instructions not to torch straighten?
I would HOPE they would cover the cost.
Sucks that you have to deal with this, thanks for sharing though, maybe it will prevent someone else’s blade from getting stained.
 
considering this is already 100% finished and ground like a laser, no way can it be re-treated. I only post to save others this kind of trouble, and am surprised i had never come across this before. Ive spent about a million hours reading this forum
 
You must log in or register to reply here.
Back
Top