Troy-Bilt Tiller knife project finally underway

[picker77]

Changed out the tines on my 1980 model 8 HP Troy-Bilt tiller a couple of years back, and saved all the old worn tines, since they are made of what seems to be very good metal - probably 5160 or 1095. After all, they were used hard for nearly 40 years, and still had life in them. Of course this was back when Troy-Bilt tillers were 350 pounds of cast iron and heavy wall steel, unlike today's big box store versions. Before annealing, these tines would skate any file in my shop. Now that I finally have a forge up and running, I dug them out and straightened and annealed them, thinking they might make some decent utility knives. Coincidentally, last week I finally got around to adding a vertical platen to my home built 2x72 grinder, which up till now has been running with just an 8" contact wheel and a tool rest. I also put together a simple blade grinding jig.

Today I started roughing out the first sample "tiller" knife, a 9" full tang drop point. The other two flat bars in the photo were front bumper mounts for a pickup truck of some sort, from a body shop friend. Very decent steel also, haven't decided what to make with them yet. Not gonna run out of tiller tines for a while anyway, lol. Anyway, finally getting some scale generated and having lots of fun.

[BIGGUNDOCTOR]

Have you tried hardening a piece yet? Some mower blades are a high boron alloy that takes a very specific heat treat. Don't know if tiller tines are the same way. 

 

[SLAG]

18 minutes ago, BIGGUNDOCTOR said:

 Some mower blades are a high boron alloy that takes a very specific heat treat.

 

Mr. B. G.,

Is there a practical way to check if the steel is alloyed with boron?

I mean low tech.  Yes a mass spectrometer would work but it is beyond my means.

Thanks,

SLAG.

[BIGGUNDOCTOR]

I was thinking of just taking one, anneal it, then try and heat treat it and see how well it hardens. The boron alloys need an austenitic type of heat treat. If it works, fine, continue on with the project. If it doesn't, no time lost. There is one major company producing the mower / brush hog blades for many of the OEM's.

[picker77]

Nope, haven't tried it, BGD. I know for certain they WILL harden, just don't know for sure if generic HT methods will do it. I have 15 of these already annealed I can play with, so I can afford to cut one in two or three pieces and see what happens before I try anything on this first test blade. If it matters, this is steel from 40 year old technology/metallurgy, so not sure if the boron thing would be likely to apply. Besides, I only have available water or canola oil at the moment, don't have any of the fancy Parker oils, and my HT options are pretty primitive: a forge, a toaster oven, and O/A and propane torches. I don't have a real HT oven. I'll report back here after I try some things.

[ThomasPowers]

I'd think 1980 would still be a rather plain HC steel;  Stuff after 2000 I would worry about but I don't know the actual dividing line.

[picker77]

I got around to trying what BigGunDoctor suggested, with somewhat puzzling (to me) results. I pulled one of the tines from the "annealed only" group and gave it a routine HT process, i.e. heated beyond magnetic, held there for several minutes, then quenched immediately in canola oil, and (starting about 20 minutes later), tempered for 1 hour at 350 and let cool in still air. I had a standard oven thermometer on the shelf inside the oven, plus I monitored the oven temps several times with a non-contact IR thermometer by quickly opening the door, taking a reading, and closing it again. My little toaster oven's thermostat proved surprisingly accurate (at least at the 350 setting), with both thermometers. After an initial 5 min or so overshoot to 400 and back, the actual temps stayed steady at 350 the remainder of the hour. NOTE TO SELF:    Prewarm the tempering oven longer!

Anyway, the photo below is the result. The top one is the only original "unheated" tine I have left (I cut the tip off cold with a band saw back when), the middle one was annealed with it's 14 brethren in a 6-gallon pail of vermiculite for 24 hrs, and the bottom one was today's victim. It was annealed, heated, quenched in oil, and tempered to 350. What has me scratching my head is that side-by-side with a brand new file it's pretty hard to tell the difference between all three. All are very hard, the bottom two are not quite as hard as the original, although that difference is not very much. The bottom (tempered) tine did take on a nice light golden color, as expected.

I don't know quite what to make of the fact the annealed-only tines appear to have remained nearly as hard after annealing as the one I quenched and tempered, and that neither the annealed only or HT'd tines are a whole lot softer than the factory original. All three will skate a new file unless I really lean on it. The only thing I could think of is maybe this is air-hardening steel, not oil-hardening as I first thought?

Further adding to the newbie head scratching is the knife shaped object I've been working on (made from one of the bucket of "annealed-only" tines), is nowhere near as hard as any of these three, and has been relatively easy to file, shape, and grind since I started on it. It's currently in the early sanding/polishing stage. It's only difference from the others is it was repeatedly heated and pounded on the anvil while I forged it into shape. If this was air-hardening steel, why would forging and beating on it make it softer?

 

[Kozzy]

Just pondering here.  For some ground implements they used a high manganese steel...old school it was called "Hadfield steel".  The surface work hardens quite easily so that might explain why the file skates even on annealed stock.  Once you start to bite, it becomes hard and won't bite without extreme pressures no matter what the HT level.

 

 

[picker77]

Pretty interesting, Kozzy. Never hear of Hadfield steel, but the "symptoms" you mention fit the situation at least. So, if that's what this is, what's the prognosis for knife material? Seems like it would make a blade that would hold a great edge, but be hard to sharpen if it gets dull. I looked it up and it appears to be very popular with the exotic Japanese blade makers for swords. Go figure.

What doesn't fit, though, is why this annealed blade I'm working on made from this stuff has not work hardened. I've given it every opportunity to do that, but it still works like mild steel. I've hit it with a couple of grinders, some stones, files, sandpaper, ad infinitum... still feels like mild steel under a file or abrasive. Would multiple heats and forging act to negate some or all of the characteristics of manganese steel? Of course, metallurgically speaking I'm in the deep end of the pool here and way over my head.

[BIGGUNDOCTOR]

14 in a 6 gallon bucket may be the issue. They may have air hardened. My annealing barrel was half of a 55 gallon drum full of gray wood ashes and a lid. Many steels will air harden in thin sections.

I would try heating to nonmagnetic, quench, and test, no tempering. File test, try snapping one to check grain structure, etc.

Try leaving them in the forge to cool down for annealing.

 

 

[picker77]

Thanks, BGD. I'll do some more experimenting. Kinda fun to sort this stuff out (with help from IFI members like you and Kozzy) and  I'm learning a lot as I go.

[picker77]

Just for fun I finished this "tine knife". After drilling the handle holes, it hardened just fine quenched in canola and skated a new file no problem. I did NOT temper it after quenching, we'll see if that was a mistake after I use it a little to see if the edge chips up (it was not yet sharpened when these photos were taken). I'm pretty happy with it for a first-time experimental forged from scratch knife. The handle is polished and waxed ebony with stainless pins. I still have about 14 more of these tines to play with. I plan to harden and destructively test one as suggested above by BGD (but not this one, lol!). If the test tine shatters after quenching without tempering I guess I'll just have wasted some time on this one, unless I get ambitious and temper it with the handles still on it, which would certainly test the limits of good old JB weld, which according to them could take it without letting go. Anyway, I am definitely interested in seeing the grain of the test tine, looking forward to that.

 

[picker77]

Well, scratch my idle thought about the possibility of tempering with the scales still on the blade in case it's too brittle. I looked up the specs on JB Weld (I have both kinds, the regular and the "JB Quik" 6-minute stuff). Sadly, I used the Quik version on this one, and the specs say it's good to 300°F. The regular version is good to 500° with a max limit of 600. I've read elsewhere that 150°C (302°F) is about the lowest temp commercially used for tempering carbon steels, so 300°F would be walking a little close to the edge for a toaster oven.

[Steve Sells]

where did you get the idea that 302F will do much of anything as a temper? The same place that said you dont temper after hardening?

When you decide to make a knife that you want to keep read the heat treating pinned posts for how to heat treat them

[picker77]

Well, Mr. Sells, if it's important, it was the website of Industrial Metallurgists, LLC - a company that apparently creates and conducts training courses in metallurgy for the metal industry. They said "During the tempering process the steel is heated to a temperature between 125 °C (255°F) and 700 °C (1,292 °F). At these temperatures the martensite decomposes to form iron carbide particles." That, btw, differed a bit from another metallurgical engineering site in that the other one (don't remember which it was) said normally 150C is the generally accepted lower limit for tempering carbon steel. I suppose that's where I got that 150°C number.

I've read much of the heat treating info, including the pinned posts, but there is practically a lifetime of reading involved in all that, so I am still trying to absorb the huge amount of (and sometimes conflicting) expert advice on IFI and elsewhere. Most of it, however, properly pertains to known alloys, and in this particular case I'm experimenting with an unknown alloy, although it is certainly tool grade steel of some kind, and is demonstrably hardenable. 

At any rate, about an hour ago this particular knife just hacked easily (well, easily is a stretch, it took some help from a stout mallet - this is a small lightweight blade after all, not a "chopper") through a 1-1/2" x 2" piece of very hard red oak with no visible or detectable tactile damage whatsoever, and will still shave my arm. Certainly from a technical HT standpoint that simple test means nothing, but from a practical use standpoint it means a lot in my eyes. So with all due respect and appreciation for your helpful advice, I think this is still a knife I'll "want to keep" as I'm working my way up the learning curve. Have a great weekend.

[Buzzkill]

You can still temper it with the handle on if you are so inclined.  Submerge the knife (handle down) up to the transition from handle to blade in a container of water with the blade sticking out then use a torch or tempering tongs to get the color you want.  Colors run fast once they start so you have to be prepared to quickly quench it when you get the temperature you're after.

[picker77]

Thanks, Buzzkill. That makes perfect sense and if I decide I need to temper later I'll try that. Although this blade seems to be quite hard, my little "chopping" test didn't tell me much about toughness or flexibility. However, if I try a bending test, it will be with a second tine that I have set aside for just that purpose on the sage advice of BigGunDoctor. Have a great weekend and I hope everyone can (a) dodge Dorian, and (b) enjoy some cooler weather down the road soon. Tired of sweating in the shop.

[Steve Sells]

your posted reference on tempering does not say what alloy content it was talking about, and here we are talking about thin cross sections of higher carbon steels for knives, which are different than lower carbon steels and most industry specs are for thick portions, both of which are why there is a separate sections for blades heat treatment,   but keep hardening without tempering if you choose its your blade, but read up on blue embrittlement before you temper above 400C

[ThomasPowers]

Tempering temperature  is based on ALLOY, USE, HEAT TREAT PROCESS, CROSS SECTION; PERSONAL PREFERENCE, etc.  Using a broad statement as a guide is like reading that cooking ovens are used at up to 700-800 degF,  (like a commercial pizza oven), and decide to cook your casserole at 750 degF.  What is fine for one thing may be terrible for another and yet they are both "food".

[picker77]

Lol. You guys sound like you think I was arguing with you. Far from it, this was a partially done sample of one blade of unknown alloy, and I haven't even had the chance to harden and test a second sample of the same steel. I meant no pronouncement of general fact regarding tempering, just because I read about the accepted ranges of tempering for carbon steel a couple of places, and I was certainly not questioning anyone's technical knowledge on a subject I know squat about. Thanks, Steve, I'll read up on blue embrittlement (whatever that is) but there's not much danger of my tempering above 400C with my little toaster oven that struggles with 500F, ha. Please remember I'm just a few months down this road you guys have been on your whole lives. I didn't mean to imply I'm forever going to do non-tempered blades, not sure where that idea came from. Just this one blade. And if needed I'll temper it. Looking forward to learning more and experimenting more. That's how I like to learn.

[ThomasPowers]

Well I, and I'm sure Steve and others, have run into a lot of "one book wonders" who treat one book as the sole source of information and don't have the background to know where it's good and where it's not so good. I remember ; IIRC, Daryl Meier showing us the Heat Treat book he worked from and it had as nearly as many pages inserted in it as the original tome had to deal with the aspects of heat treating knives and not large cross section items. Luckily we have folks who have done a lot of the work and share the differences in hardening something less than 1/8" thick and wanting it to stay straight.

I sometimes try to research medieval and renaissance quenchents; but don't expect they will out perform modern ones...just for fun. (There's a list in "Sources for the History of the Science of Steel"  worm water or radish juice anyone?)

[picker77]

I'm more like a 10-book newbie, ha. I've read so much about forging, making knives, tools, heat treating (yes, Steve, I have read your HT posts) the past few months my brain is drowning in information. After a while it all just runs together like fruit thrown in a blender until I was able to finally heat up some metal and try to apply some of the methods and practices. I've been actually using a forge for all of about 3 weeks now, haven't even used up my first 30 lb of propane, so I'm heavily experienced, ha. A little spooky at first, had to get used to the dragon's breath, the noise, handling hot metal, etc., but every minute of it so far has been fun, even the screw ups. When things don't go like I expect it's still a blast because even failures point out new things I want to try the next day. Tomorrow I'm going to do some "destructive testing" on a couple of these tines and see what happens.

[Irondragon Forge ClayWorks]

On one of the knife forums Storm Crow gave an excellent method on heat treating/tempering 5160 steel in a "back yard" setup. I've tried it and it works. As far as tiller tines, I have a bunch and have made knives out of several. I treated them like 5160 and they came out great. Sorry no pictures as I gave them away 5 or 6 years ago and as far as I know they are still in use .

[picker77]

Thanks, IFC, I'll look up that Storm Crow post. I'm pretty sure these are likely 5160, also. I have a couple of test cases ready to go, one has been annealed, hardened, and tempered using Steve's 350/24hr/350 method, the other has been annealed only, and I plan to harden it in oil today but NOT temper it, and do a bend test on both of them to see what the grain looks like, and also to see the effects of not tempering after hardening. The one knife I just finished without tempering is a great performer but of course I haven't tried bending it. If the un-tempered test tine today breaks like a piece of glass as I sort of expect it will, then I'll probably torch-temper this finished knife using Buzzkill's methodology. I kind of wish I had a big stack of these tines, but at least I still have about a dozen to play with.

[picker77]

This morning I heated and quenched the second test tiller tine (the one that was annealed only). I then put both test tines in a heavy bench vise side by side, and using a 2-ft pipe cheater, did some bending of both of them. They were very strong, I weigh 240 and I was leaning hard on that pipe. Photos of the results are below. I tried to get some good closeups of the grain, and to my newbie eyes it actually looks pretty tight, but I'd appreciate learned opinions on that. I was surprised at how springy feeling and resilient both were (up to a point, that is), especially since I was cranking down on only the tips (about 1/3 of their length). It was odd that both bent & returned to perfectly straight a couple of times at about 25 degrees of bend, and both ultimately broke cleanly at the same pressure point (about 30-35 degrees of bend), even though only one was tempered. Could it be that the 350F temper was simply too low, and should have been 450-500? I still have the bottom 2/3 of both tines, so I could try tempering each to 500F (which would max out my little toaster oven), and see what happens. Thanks for letting me waste all of your time with this exercise, but I truly appreciate the opinions and I'm learning a lot.