Dumb question about annealing

J

Jahaworth

Joined
Jun 3, 2009
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15
Hello all.
I'm in the process of making my first knife. It's just a little kitchen utility knife. Now the steel was originally a large powered hacksaw blade from an engineering workshop. It's obviously very hard steel & I have been painstakingly grinding & sanding away shaping the blade, Spending way more hours than I feel I have to.
My question is this. I still have some more of the metal & was wondering if for my second attempt is it as simple as heating it red hot & then letting it cool at it's own pace to make it easier to work with & then paying someone who knows what they are doing to heat treat it afterwards. Sounds simple.... is it?
I've added a pic just so you know what I mean.
Also is the metal actually any good? I hope so after the amount of hours I've put into it so far.

DSCF6878.jpg


Thanks
 
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Hi there,

Firstly the shape looks good, it will be a decent paring knife.

My suggestion would be not to work with an unknown steel. As you begun with it I would suggest not to anneal it and work slowly trying not to overheat it as it is a hardened steel afterall. But judging by the picture you already overheated that so you may try to anneal it. But not knowing the steel type I dont know how you can anneal it properly. Maybe you can try your luck by heating it to nonmagnetic and a little more and leave in the ashes let it cool very slowly about 10 or more hours. It may soften it or not, but if you manage I would suggest you or a much experienced smith to harden a scrap piece of that steel before any attempt to harden your workpiece. Good luck with it...
 
MOST and I say most, cause ever once in awhile you find one that isn't.
power hacksaw blades are HSS high speed steel.

People have been making them into knives since they started making power hacksaws.

Most foks work em cold, and put pin holes in using a torch.

Makes a good blade if you work within its parameters.

google heat treat for HSS

I still have couple that Grandpa made. :D
 
Most of the power hacksaw blades are now made of something like M4 and non magnetic won't do much to make them soft and yes they are very difficult to grind.
 
M4: 1.3% C, 5.50% W, 4.50% Mo, 4.0% Cr, 4.0%V

Annealing: (pack annealing necessary to minimize decarburization) Heat to 1600F-1650F and hold 1 hour/inch of pack container thickness. Cool slowly at a rate not exceeding 40F/hr to 1200F.

Hardening: Preheat from 1350F to 1550F (double preheating from 1000F-1200F in one furnace and then 1550F-1600f in another is recommended for minimal thermal shock). Heat rapidly from preheat to austenitizing temperature. Austenitize at 2200F-2250F for 2-5 minutes. Using the lower end will impart more toughness, the higher end and resulting solution will impart form hardness and heat resistance. Quench in oil air or salt.

This is not a beginner alloy, I myself would probably be intimidated by its HT requirements.

As for HSS or hacksaw steel, what is the carbon content of HSS, or power hack saw blade steel? What is any of the chemistry? Good things to know in determining an anneal. Should it be spheroidized? should it be lamellar annealed? If it is over .84% carbon after any carbide formers get their share just heating it up and cooling it slow will cost you a bit of heartache and tooling, not to mention toughness in the finished blade. Without the chemistry sending it out for heat treat would be in vain, as any heat treater worth his salt will turn you away if the only description you have is “hacksaw blade” or “high speed steel”, if one does take on the job he is only taking your money and laughing behind your back. So I would probably go with the advice of not messing with the current heat treatment- although it is meant for hacksaws and not knives, it is still better than a stab in the dark, and keeping it cool in the grinding operation.

When I was getting started I gave a try at small knives from industrial bandsaw and hacksaw blades, I also did the file thing, as well as leaf springs and others. At the time I was prettying impressed with what the knives could do. I hacked wood, cut paper and even shaved some steel off a bed frame in front of my friends. At the time they were great knives. A couple years later I didn’t think so much about them and was much happier with the more consistent results I was getting with the next level of materials I found. A few years after that my knives could still do all of those things but much, much more and just about every time I heat treated one. Of course today so much water has passed under that bridge that all of my standards and criteria barely resemble those in the beginning. It is all a journey, how wonderful the county fair is the first time we see it, the Ferris wheel is about the biggest thing we have ever seen, our perspective changes once we have been to Disneyland or Cedar Point, and one day they are all just amusement parks and our travels bring even bigger and better things.
 
Thanks for your replies everyone. Well I'll just slowly keep working on it. I'm in New Zealand & havn't figured out where to buy the correct steel yet. Well in small amounts anyway.
Thanks again.
 
When you're done shaping and finishing it, I would see if it still had some spring left in it. If it did, I would just leave it as is. It would probably still be tougher than some of the stuff you see on store shelves these days. It is a first knife attempt anyways, you should not expect to get a perfectly tempered blade. My first knife that I ever made I made out of some unknown steel and I don't think it even got hardened at all, in fact, I think it was mild steel.:D Try using old files as a source for making knives with. Anneal them first though.
 
Old files aye.... excellent idea. To anneal them you heat it untill it goes non magnetic & then let it cool at it's own pace?
 
The slower they cool the better. After they are non magnetic place them in a pile of something like kitty litter or vermiculite of a pile of ald ashes so that it is insulated and cools very slowly.

Now to reheat treat. The absolute best way is to heat to non magnetic and let it air cool to black for a bit then to almost the color red it was when non magnetic and let cool again till black then do it again but, not quite as red as the last time and let cool to black again. This is called normalizing. This works best if you have a way to accurately control the temperatures. Then harden by heating to 1500f and hold for a few minutes then dunk tip first into a special quench oil like Parks 50. Then temper by placing in an oven for 2 hours at 450f cool and repeat the 2hours at 450f

The more you know about your steel and the better you can control the complete heat treat the better the steel will preform. That is a solid fact. But, you can get very usable results and enjoy the pleasure of making your very own knife with less refined equipment and control.

I know you do not have that much control of the heat or the Parks 50, so do this for the best you can do learning experience with what you have. Get a couple quarts of automatic transmission fluid or mineral oil. Heat it up to about 120 to 150f. Sticking a piece of old steel that has been heated up will warm the oil fine. Do the heat and cool normalizing like described above. Heat your blade up to non magnetic and a bit passed that and try to keep it at that color for a couple minutes by moving it in and out of the heat. You do not want to get it to hot as this will cause the steel to get grainy and brittle. After it has been a bit above non magnetic for a couple minutes dunk it in the heated oil. Move it back and forth the way it will cut. Do not move it side t side as that may cause it to warp. Then do the tempers at 450 f in the wife's oven. This part works best while she is unaware of what you are doing. Good luck Jim

Mess around with the finished knife. If it cuts well and the blade edge does not chip or fold over and holds and edge you did fine. If it chips you probably need to temper it at a bit higher temperature. If it folds over you tempered to high or did not get it hot enough before the quench. If it doesn't hold an edge it may be the same thing. If it breaks and the break looks coarse you had it to hot when you quenched. Enjoy
 
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You guys will probably think this abhorrent but is it true that you can anneal files in the household fireplace? Get them nice & hot while warming the house & then leave them to cool very slowly over night in the sealed firebox??
Don't shoot me for asking.... i only read it on google.
 
What ib2v4u said is fine for 1050 to 1084, but has problems with any steel above 1084. It will not work any at all on HSS ,which is what this blade is being made from.

Yes, people anneal files in the ashes, but it does a poor job on some files. It depends on the steel type used to make the file ( which you most likely don't know). If the steel is higher than .84% carbon, it may not end up as soft as you want it to be. I would say that if you have no other choice, OK, but a proper annealing is a much better choice. Read Kevin's stickies at the top of this forum for more info on hyper-eutectoid steel.

Here is what I would do with a file and no special heat treating setup:
First, consider what method you are going to use to heat up the steel. It can be a super simple charcoal forge ( look up "Brake Drum Forge", or "Tire Rim Forge"), a welding torch ( preferably with a rosebud tip),a gas forge ( plans to build one everywhere, but check out Darren Ellis's site for lots of info and all supplies - http://forgegallery.elliscustomknifeworks.com/ ), or any heat source that can be controlled enough to heat the steel to bright red.
Second ,you need some way to hold the steel. A pair of long handled needle nose pliers, a set of tongs, vise grips....whatever.
Third, something to quench the steel in . For this simple back yard work, a light oil will do. Peanut oil, canola oil, ATF,hydraulic fluid....all will work. They are not the best, but will work with simple steel. Water will do fine, but may break the blades, so it isn't a starting quenchant.

The steel - a file is an unknown steel as to the type and alloy. It is probably a hardenable steel if the file is a good quality one, but some are case hardened mild steel. Assuming the file is all good steel, it probably has somewhere between .85% and 1.00% carbon. This means it is hyper-eutectoid steel. This type of steel does not work quite as easily as simpler steels below the eutectoid. You have to deal with the extra carbon a bit. Since this is a backyard HT, we will just do the best we can.

OK, to anneal the blade you need to heat up the steel until the atoms arrange themselves in a softer structure. You could heat it to a non-magnetic red color, and just a little more. Try to keep it there for a couple minutes (if possible), and stick it in a bucket of lime, kitty litter, ashes, vermiculite, or whatever will allow a slow cooling. After it has cooled to room temp ( overnight?) try and drill a hole in it ( using a good bit). If it drills OK, then you are going to be able to proceed with shaping the knife with files and sandpaper.
If it won't drill well, it is probably a hyper-eutectoid steel, and needs a little different treatment. Try a sub critical ( sub-non-magnetic) anneal. You will need to heat the steel up to just below the point it gets non magnetic ( play with it a bit until you get the color down ) and let it cool in the air.
This is how to make the steel soft, using a sub-critical anneal:
First, heat the steel up like you did in the slow cooling anneal. Get it to the nice red color that indicates it is about 825C ( 1500+F), and quench it in the oil quenchant. let it cool off in the oil. Now you have (hopefully) made it hard...and brittle. Check the edge with a good file and see if it is glass hard. If so, the quench will work for hardening the steel later in HT, and has done its job in making the steel martensite ( the hard steel type for knife blades). You now want to convert this martensite into pearlite ( which is soft and easy to file/drill). Heat it up to the just below magnetic point and then hold it out in the air to cool down until all red color is gone ( about 15-20 seconds is fine). Dunk in the oil to finish cooling. Wipe off the oil and repeat the sub-critical heating and quench two more times. Check with a file and try and drill a hole, hopefully it is soft now. If so make the knife, leaving the edge about 1mm thick (.030-.040").Sand to 400 grit, and make sure all holes are drilled.

Hardening (HT):
Clean the blade off.
Warm your oil quenchant to about 50C (130F).
Heat the blade to non-magnetic plus about 100C as evenly as possible - about 825C ( 1500F). Hold it there for a minute if you can, and immediately quench in the oil. Move the blade back and forth like you were cutting the oil ( never side to side). Let the blade cool off in the oil for one minute, then check the edge with a file to see if it is hard. If so, it is ready to temper. If not, repeat the heat up and quench again, trying to get the temperate right.
If the blade is hard, clean it off ( be gentle, it is very brittle right now) then bake in the kitchen oven at 225C (450F) for two hours, take out and let air cool for five minutes, then put back in the oven for another two hour bake. After it cools again it should be ready to finish making the knife.


Cheers and good luck.

Stacy E. Apelt, FSA,Scot
 
Stacy, I wasn't talking about the hacksaw blade I was talking about if he used a file. Something like 1084 would be best, but if all he has is a couple of good files to make the blade out of. I should have pointed out that they are probably something like 1095 or W1 or W2 and the carbon content would be a bit high.
Your explanation is better as it explains the why. I think that it is a great way to start and gives people some experience and enjoyment. Then if they like it and chose to go on and get the full blown addiction they can get what they need to do more controlled heat treat.
 
What is the exact chemistry of "file steel?" If we can safely assume that it is not just case hardened (a big if) then we may be able to assume that it is a hypereutectoid steel in order to maintain cutting ability on steel. In which case a slow cool in the wrong range will result in unnecessary embrittlement and sill tear our tooling up. But lets say we don't give a hoot about that, the quickest and easiest way to soften it may be just to heat the untouched file to dull red several times.

When we abandon the concept of shooting for the best results possible, which is almost necessary when we don't have at least a general chemistry, we can still fall back on ease, simplicity, and expediency, which is often the general theme in recycling items into knives. And just heating the blade up to a dull red several times is much easier, simpler and quicker than chucking it in the fireplace, kitty litter, vermiculite etc... One could get to work on it within the hour instead of waiting a day and the grain size will still be fine, the carbides will still be fine, more carbon will be left in the blade, and there will be less scale and chances of overheating.
 
Thanks for the great advice guys.

Kevin R. Cashen said:
And just heating the blade up to a dull red several times is much easier, simpler and quicker than chucking it in the fireplace, kitty litter, vermiculite etc... One could get to work on it within the hour instead of waiting a day and the grain size will still be fine, the carbides will still be fine, more carbon will be left in the blade, and there will be less scale and chances of overheating.
Click to expand...

For the sake of having a play & just figuring things out... I can just heat the file as you say above & let it cool for 10 minutes and repeat several times? If I can drill it I can use it. Excellent.
That sounds fun. I'll go see a mate with a gas torch & see what we can do.
Thanks again everyone for your advice/help. I've really enjoyed what I have done so far, even though its been hard going with the HSS blade.
 
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