HT idea will it work?

Gahagan

Well-Known Member
ok I have a knife that I have been working on for a customer. Well I have had to make 4 blades so far becuase everytime I ht it it will warp bad and then crack. All 4 have done the same thing I have used different methods of ht such as salt brine, canola oil and parks 50,everyone has done the same thing (this is Aldos 1095). I have tripple normalized each blade before ht and they still warp real bad and all crack in the same place. . Well I had this bright idea where I am going to ht the blade first and then grind the knife without getting it too hot. Will this work?I am at the point were I am really frusterated. This has never happened to me before.Will my idea work. I know others fo it for smaller knives but this is a large bowie knife with alot of grinds.
 
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First off, I'm confident Aldo's steel is good. If you're having repetitive blade failures during the quench I'm thinking of stress risers, might be an area in your pattern with an inside corner or some other cause. Can we have a pic of the blade to look it over? I do know some makers do the grinds after the HT is done on a profiled blank, it's just harder on the abrasives.
 
Yes, You can HT first and grind after..
I second that Aldos 1095 is the best out there for knife blades!! :)
 
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I'm with Frank on this one. You are starting out with good steel that has a good reputation with other makers. Stress risers are a good possibility for the cracking. One thing to watch on the warping is heating the steel unevenly. Brine is scary stuff that can cause breakage but I would not expect problems with canola oil. Getting the steel too hot cold be another problem with warpage. It can also be caused by it not going into the quenchant straight. Also is it warping in the quenchant or is it warping in the tempering oven?

You could try clamping it flat to a thick plate of steel with C clamps and tempering. You could also shim it to over correct the bend slightly but I think that I would do at least one tempering cycle without before I tried that so that the clamping doesn break the blade.

You could also try marquenching. Heat the canola oil, deffinantly not the Parks #50, to about 425 degrees and quenching in it for about 5-10 seconds and then allowing it to finish air quenching. It will probably not do the full thickness of the blade unless it is 1/8" thick, or a little less, but the thicker parts will probably just convert to pearlite and give you differential hardening but that will also depend on grain size. What this does is allow the core temperature of the blade to equilize with the exterior temperature just above the Ms point. It will also bring the temperature of the steel down to the bay in the IT cooling curve and give you about two minutes for the steel to decend past the Mf point from the 425 degrees. The steel is most likely to warp between the Ms and the Mf points and this brings the whole thickness of the steel to the same temperature before phase change and the entire blade changes at the same time and rate. This could get around problems caused by uneven dimentions.

Just throwing some ideas out there. If you post the pictures of the failed blades we might be able to come up with other possibilities, maybe exorcising the forge. If it is any consolation, you're not the first maker who has asked that question: What the (Bleep)?

Doug
 
Oh by all means I am not questioning Aldos steel. I threw that in to show that I was infact using a quality steel and that it was not fault of using some of the mystery 1095 out there.Here are pictures of the knives with close uos of the last two which were done in canola oil and parks 50.
brokenknife001.jpg

brokenknife004.jpg

brokenknife003.jpg

brokenknife005.jpg

brokenknife002.jpg
 
I'm no expert or remotely close to one, but I have seen this issue before, for ME it was because the hollow grind got that area too thin. The hollow grind on both sides of mine resulted in the area about the same spot as yours being paper thin. Now mine didn't crack and break like yours did, mine simply folded up like an accordian, I was so upset, I was all excited about that knife, it was gorgeous, the best one I had done, my testing was too much for it, I thought it was going to be super duper tough. Cut through a 2X4, no prob, cut a small sapling down no prob, got real happy and whacked a 60 year old piece of Moc Orange (Osage Orange), BIG PROBLEM!!! I either didn't hit that spot right on the problem area, or the Moc Orange was just too much for it! Moc orange is extremely hard, I have a log of it I was going to cut into handles, it was a used as a fence post for 60+ years, recently replaced and my buddy gave me this log. I cut some handles out of it, after getting 3 blocks cut, I had to replace my band saw blade, it dulled a brand new one! I set the log outside, if I get desperate for handle material or find myself with too many bandsaw blades I'll go cut some more then! Hope this helps, do keep in mind I could be totally wrong, but it looks just like the problem I had, Rex
 
I thought that to be part of it to but the area where it is cracking is the same thickness as the rest of the blade. I measured it with a digital caliper to make sure that was not the problem. My blade is cut out of some new 1095 since i used an entire stick of 1095. I am just worried. as far as straighting the blade during temper, the blade would warp at almost a 45 deg angle way to far to straighten in like that. I have made this same knife before with no problems. It has just got me scratching my head out of pure frustration.
 
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I have a whole bunch of WTF things happening here. First is that all failures are in the same place. That might be alleviated by leaving more meat for post heat treat grinding - and also by finishing further to remove deep scratches, which can form stress risers. My next concern is heat treating before grinding. 1095 is a shallow hardening steel. The stock looks thick - 1/4"?. That won't harden through with oil and I just don't know if it will with water or brine??? I've never seen anything warp 45 degrees. BIG WTF?

The solution may be interesting, but I have to ask..... is there any reason you couldn't use Aldo's 1084? Clearly, this is becoming less about the price of wasted steel - and more about lost time.

Following this with interest. Thanks for sharing.

Rob!
 
Depending on the grain size, the 1095 might not harden all the way through with oil, water, or brine. But the edge will harden all the way through. It will harden to twice the depth of hardening. Thicker than that it will form all pearlite. Things in thin sections, like knife blades, don't harden the same way a rod of steel will harden, which will form a jacket of martensite around a core of pearlite.

You could try roughing the blade shape and then grind in the edges after heat treating. Also the 45 degree warpage would mean that there is some major stresses built up in the steel from something. You are also right that that's too much to straighten during tempering. All you could really do is to reaustinize the blade and straighten with a hammer on a makeshift anvil or even a wooden maul on a large block of wood.

I'm not trying to talk down to you but I have to ask because this is freaking me out that you had that much warpage. Did you check to see that the steel went non-magnetic and then got it just a little hotter when you normalized it?

Doug
 
So how thick are those areas? Could it be that the cross section is too thin?Also, how thick was the stock? I'm not positive you can HT it first and then grind it, if you did it would be incredibly hard and the amount of belt$ you'd be spending would be astronomical. Sharp belts will grind cooler, dipping it in water will get old quick, as much as it will have to be dipped. What was the temp you quenched at? W-2 is one of the tougher to HT steels, I've had great success with the last 3 I've made. I recently added it to my 2 HC steels, replacing 1095 with it, once Aldo is out of the 1095 he has I don't think I will use any other 1095 unless I find some that is like that he has. We'll figure this out, it may take some smarter folks than me, but I know the guys here and they will all help out.

One thing I think should be a consideration, while Aldo's steel is the best, he doesn't control all of the quality of each and every stick and I'm sure it's possible that a bad piece could get in there, not saying anything negative about his steel, it's the only steel I use. All I'm saying is could it be a bad batch? Or maybe, just a bad stick? Did all of those pieces come from the same stick? I think you probably need to email Aldo about it just to see what he might advise, I know he doesn't look it, but he's really a smart fella! If we keep plugging at this I'm sure we'll get it figured out. I don't think I've been much help, and I'm going to stay tuned to see how this turns out. Good luck, Rex
 
It is 1/4 steel all from the same stick. I ground to 220 finish before hting. i normailzed by going to 1560 for 5 min lettting it drop to 800 int he oven then going to 1460 for 5 min drop to 800 then going to 1360 for 5 min and coolin oven. For ht I tried wo different ways on was heat to 1525 for 5 min and then quench the other was heat to 1475 for 10 min and then quench.
 
We've got a real head scratcher here. Your HT times and temps look workable, what temp was your quenchant for these?
 
It really looks like your edge is just too thin at quench . It seems to crack at the upper most part of the recurve as well . Point first or edge first when quenching ?
 
It is 1/4 steel all from the same stick. I ground to 220 finish before hting. i normailzed by going to 1560 for 5 min lettting it drop to 800 in the oven then going to 1460 for 5 min drop to 800 then going to 1360 for 5 min and cool in oven. For ht I tried wo different ways on was heat to 1525 for 5 min and then quench the other was heat to 1475 for 10 min and then quench.

I have the direct quote from Don Hanson somewhere on my puter, I think I found it on Bladesmith's Forums doing a Goggle search, it said something to the effect of, (I'm quoting him as I remember it)" I soak my blades for about 5 minutes at 1450 and then quench in oil", now to take this into context, the discussion had to do with a guy having trouble getting W-2 to harden properly and if he actually had W-2. Now, I can't say anything about TT charts or the nose temp stuff, thing is I don't think that there are accurate TT diagrams for W-2 because there are so many different variations of W-2. I can see if I can find that post, I'll see if I can dig it up.

Found it!
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#5 Don Hanson


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Posted 07 August 2006 - 05:35 PM
W2 is one of my favorite steels and I've forged a good number of blades from this steel. I soak for around 5 minutes at 1425 - 1450 deg.s and quench in room temp oil. These blades come out screaming hard.

You need to drop the temp in 1 second not get it to the quench in 1 second.

Either something is way off with your heat treat or your steel is not W2. A thin cross section of W1, W2, 1095 will harden fine in a good quench oil.
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I also have my own experiences with it, I soaked mine at 1440 for 5 minutes, I did that with 2 blades that were
pretty thin, about an 1/8" thick, the other was a 1/4", all 3 came out great, all of them had great Hamons on them, and the best edge I've gotten to date, seriously sharp and tough. Hope this helps, Rex
 
The thin edge coupled with relatively radical angles and curves has most likely created the perfect storm for differential cooling rates and resulting stress that is beyond the steel's capacity to adapt. Leave more steel at the edge and use the least abrupt quenchant - canola. You can also push the preheat temp of the canola.
 
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I agree with Bush Monkey

What is look like to me (and i am not an expert)is that as the steel cools it wants to flex upward toward the tip. the spine area is a lot thicker than the edge and the area where the crack is forming looks to be the smallest section for edge to spine and it can not handle the stress. Maybe try leaving the edge a little thicker so you have more sacrificial metal for the final grind.
 
Boy I've got alotta thoughts here. I've worked Aldos 1095 alot and it's good stuff.

1. The steels most likely NOT the problem

2. I disagree with folks who say it'd be ok to HT first then grind 1/4" 1095. As Doug mentioned you will in fact have a hardened "shell" of martisite with a core of pearlite. The edge will end up in the center of the core and you'll get at the very best a mixed structure. To through harden your gonna want to be 1/8" MAX. If you grind the edge to 1/8" very shortly above the edge you'll get that core of pearlite which is not what you want. I'd grind that edge to about .050 before hardening.

3. The heavy recurve shape is probably causing the blade to crack in that particular spot (the peak of the recurve). Here is my guess as to why this is happening- When forming martinsite will expand at a much faster rate than pearlite. this fact is what causes differentially HT-ed swords to take on the upward curve that they do (think Katana). On a 1/4" blade your creating ALOT of pearlite in the core of the blade. -Note- even if you clean that blade up and etch it you wont find a temper line and it'll skate a file all over because you still have a thin (shallow) shell of martinsite on the whole blade. Basically the martinsite edge is expanding so fast in comparison the the upper portion of the blade that it's literally tearing itself apart.

4. IMHO The Parks 50 is THE choice of quenchant (I've used all 3)- Canola and Brine/water are both fast quenches. Fast enough to harden 1095. The problem with those quenchants isn't the initial speed that gets you under nose and allows martisite formation it's the second stage of the quench thats the problem. The parks is engineered to quench fast intially then slow down through the second stage while the others are not. Once your under the nose super fast speed is detrimental because it speeds through martinsite formation in violent fashion when thats not necessary therefore giving the steel less time to "adjust" to the differing expansion rates.

Speaking of quenching I'm curious how long your staying in the quench ?

5. Normalizing 3 times is good. I follow a Mastersmith's HT on 1095 with fantastic results. I'll share with ya but won't name drop just because I didn't ask his permission to do that. I do know that He's publicly given this recipe away so it's certainly not a secret-

One thing I want to mention- In my Evenheat it takes 10 minutes at temp just to get a 1/4" thick blade completely up to temp. To me 10 minutes equals zero soak in the oven because that's about the point that 1/4" thick will be heated completely through.

Normalize 1600 Grain refinement 1475 1450 1425

Here's the part I think you should definately add to your HT after grinding to reduce stress- Sub-Critical anneal- Heat to 1200 and hold for 1 hour then air cool (do not slow cool)

6. Edge cracking is always a big risk with shallow hardening steels due the extreme speed of quench needed to harden them. To counter this it's advisable to sand the edge lengthwise so no scratches are going across the edge. Where scratches meet the corner of the edge is where stress risers form (especially if you've got a deep 50 or 80 grit scratch hidden under the 220 scratch pattern. I'd recomment going even further and rounding the corners of the edge completely and sanding the edge to at least 400 grit.

7. 45 degree warp ! Yowser. I got nothing here other than thinking if the blade was laying on it's side in the oven and the floor side of the blade wasn't up to temp causing martinsite to form on one side of the blade only.

8. Something else I'd like to mention is you've got MAJOR stress risers on all of those blades right where the tang meets the back side of the riccasso. Keep that area rounded instead of 90 degrees and again make sure theres no deep scratches around the entire perimeter of the blade. I'd even leave that section a bit bulkier for HT. It's no problem at all to soften the tang after HT to make this area easy to work with files. I've cracked quite a few blades before I got my Parks and it'd be a dang shame to have your recurved section survive only to have the tang snap off !

Just one last thing- Wicked looking blades ! I sure hope you get a survivor soon.

Take care- Josh
 
Josh, correction. He will not end up with a shell of martensite over a core of pearlite. According to John Verhoeven in Steel Metallurgy for the Non-Metallurgist the blade will form martensite to a blade thickness of twice of the depth of hardening. That will be found at the edge of the blade and at the corners of the spine. In sections thicker than that it will only form pearlite. This applies to thicknesses up to about 1/4" due to what is called film heat-transfer control. I has to do with steel in thin sections the steel will cool at the core at pretty much the same rate at the surface. So if the section of the blade is thin enough to form martensite, it will form martensite all the way through. If it is too thick to form martensite then it will form pearlite all the way through in that thicker section.

Remember that his only applies to sections under approximately 1/4". Thicker than that and you will get a shell of martensite surrounding a core of pearlite. It is also very much influenced by grain size as depth of hardening increases with it. So if you have a course grained blade it may harden all the way through. Also alloying will effect this. Steels such as 1060 will deffinantly display film heat-transfer control. This is where the "natural" soft spine or hamon comes from using a shallow hardening steel. Steels such as 5160 will harden all the way through because of the alloy content, in this case chromium.

Doug
 
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