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Old 02-17-2011, 06:57 AM
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Default Q: Home made Knives.-hardening/tempering



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Not too long ago I pulled out some of my "Mike-Gyver" tricks and made a hommade steel forge with an old BBQ Grill, Fire Bricks, and an Air Mattress Inflator. It's worked out well thus far and my skills with shaping have improved dramatically, I've made arrowheads, spear points, and knives. I've just finished a knife I made from rebar and it's great; the feel, the balance, the size, the angle...you'd never know it was once rebar.

Now to the meat of the issue. Steel is soft (for steel) right out of the forge and requires tempering and hardening. I've watched a ton of "you tube" videos trying to get the information I want and have been through the trials of test runs with quenching in oil etc. I've learned to keep the steel in a north south orientation to reduce warping, but my confusion lies in do you "harden and temper", "Harden or Temper" if both, which order or can I simply harden the edge alone and leave the spine soft?

I've got a 4 day weekend this weekend and plan to fire it up (the forge) and try to treat the knife so I can start on the handle and sheath.
Old 02-17-2011, 07:40 AM
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From what I have read, you harden and temper

Tempering it takes some of the hardness out of the metal. It seems that tempering allows you to "fine tune" the quality of the blade.

I have been doing some research, as I was hoping to try to make some knives this year. So I have posted my findings in this thread: Knife making basics
Perhaps there is something that you can find helpful here:
http://www.survivalistboards.com/sho...d.php?t=146754

As I am still in the "learning phase", perhaps there is someone more experienced in this that might be able to speak into this question better than I can.

Welcome to the forums!
Old 02-17-2011, 07:54 AM
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Wow, OK what you have there is low carbon steel, rebar is meant to be ductile (bend not break), therefore it is inherently soft and you cannot harden it without adding carbon to it. Tempering is something you do after you harden steel, basically it is a reheat of the steel to bring its hardness down to reasonable levels, and some steels will be so hard they shatter like glass if impacted, so it is necessary to soften them a little or temper them.

You’re going to need a case hardening agent this time because you have used the wrong steel, here is a decent one for application.

http://www.centaurforge.com/Quick-Ha...tinfo/QHARD01/
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Old 02-17-2011, 02:05 PM
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I'm totally tracking with you that it's a low carbon mild steel, I'm playing and practicing with it because the price is right ($free.99). I certainly wonder how the cowboys and settlers used knives before all of the gucci steels came along. The case hardening stuff you mentioned and enclosed the link for; I've never heard of before, and sounds great. That was very useful information. Do you know what it is made of?

After I play around and get better, I'll probably order my barstock from knifekits.com where I can get the known compositions and maybe play with damascus some day (have you seen how expensive that stuff is!?!?!!). For now I have some rebar, and a little tool steel (metal files) to play with. I'ver heard I could raise the carbon content of softer steel by pounding sawdust or hay into the steel. (I guess we'll find out)...

So I'm tracking from you that I should harden it first then temper it to back it off some. I'm still learning, so I've clearly got a lot more to learn, but I'm aggressive to figuring it out especially at the price of $free.99



Thanks for your Comment
Much appreciated-Mike
Old 02-17-2011, 02:33 PM
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I found it easier to work already-tempered steel wet.. and not worry about tempering..

BUT Dad used to just heat it up to "cherry red" and drop it end first into used motor oil.. seemed to work... never noticed warping.. never cared.. he always made lots of stuff from molding plane blades to workbench knives/chisels always seemed to work for him.
Old 02-17-2011, 03:50 PM
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If you case harden a low carbon steel, it is not necessary to temper it, in fact you can't. The pounding of hay or sawdust would introduce carbon but on a very limited scale, it would be easier to use charcoal since that is almost pure carbon.

Keep in mind you must rub charcoal all over the blade surface, in fact might be easier to make a charcoal slurry or paste with a little water and paint it on the blade (while its cool) then let it dry and heat it up to red-hot and leave it red-hot for 15 minutes, remove from heat and quench in used motor oil, (also full of carbon).

At this point the blade will only have the first few thousands of an inch containing carbon at levels high enough to give it hardness, and since it is only a few thousands deep there is no need to temper the blade, I assure you the steel is still very soft in the center. The reason you have to temper higher carbon steel is that the carbon is present in high levels through-out the steel not just a coating.
Old 02-17-2011, 03:58 PM
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We'll give it a try and I'll let you know how it goes. I'll post pictures if I can. I'm still very new to the message boards.-Mike
Old 02-17-2011, 09:15 PM
gelandangan gelandangan is offline
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Quote:
Originally Posted by Mr.Emann View Post
I've learned to keep the steel in a north south orientation to reduce warping,


Reeeally! what pray is the mechanism to induce warping in this instance?
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Old 02-17-2011, 09:51 PM
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Quote:
Originally Posted by gelandangan View Post


Reeeally! what pray is the mechanism to induce warping in this instance?
It's part wives tale, and part science. some steel is worked in the presence of extremely strong magnets to get all the grains of the steal to line up just a smidgen better. On a scale of 1-1000, his gives you an improvement for certain applications of 1-2.

I doubt that the earths magnetic field is strong enough to give any measurable difference.
Old 02-18-2011, 12:14 AM
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You can get coil springs from a junk yard and heat and straighten them. Hondas seem to come up for a name fairly often but any should work. When you are done forging them you want to heat to cherry red and then quench in oil. Then you need to accurately heat them in an oven to a specified temp and then let cool very slowly. This will temper them to the final hardness you want. The temp involved will be based on the type of steel as well as the final hardness you want. If you want to differiently treat them then when they are cherry red dip the edge of the blade into the oil first and then after it has started to cool slowly lower the rest of the blade in. This allows the edge to get the full beneift of the hardening and the back to harden much less. Then temper as before. In the end the blade will be hard and the back softer. I can higly recommend this book to get you started. He is master in the world of knife making and this book gives lots of great info.
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Old 02-18-2011, 12:44 AM
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Another thing to note if you use a belt sander or similar to sharped your blade afterwards.

Remember, if you see sparks, you're de-tempering the edge.
Old 02-18-2011, 02:45 AM
arleigh arleigh is offline
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I don't want to confuse the issue here but many of the terms I see people using sound backward .
To draw the temper out for hammering into shape one brings it to a cherry read and draws the heat of very slowly I mean it should be still red 10 minuets after you started backing it away from the cherry read point and keep drawing it away very slowly and evenly the longer you take the better. It is not an instant session of work, it takes patience and time.
. Now while it is hot and red you can hammer it with out any temper and shape it and it grinds easier as well.
Hammering while hot drives the metal into a tighter bond , heating it loosenens it up again relieving it, letting align it self .
Metal high in carbon like a file were the common knife in the old days . My grand father made lots of them and gave them away ..some beautiful work.
He quenched in salt brine bringing it back to it's original hardness or pretty close .
Yes they were brittle but the edge stayed forever almost .
I've quenched in oil with softer metals making special tools for old air compressor valve removal using an impact wrench . Oil works ok . Lots of tools are oil quenched .
At work , a memory metal we make the stent out of is water quenched after being heated in a salt bath .,
Different metals need different attention . so be willing to expiriment and sacrifice a bit too.
Some of the rebar from china is a little high in carbon content , while the older american made rebar is a bit softer. Every one has their own theory as to which is better.
Case hardening is done in coke and coal usually in high heat the metal has to open up you might say to recieve it. this is where a coal forge reallly shines .
I can't remember the name of the site but there is a man that teaches engineers how metal is made , It's reallly cool . My next project is smelting steel from scratch .
One other thing I've done too Is weld hard facing rod on ax heads , After welding , grind into shape ,get it up to cherry red and quench in water , advantage = sharp for a long time . dis advantage = have to sharpen with grinder, file won't touch it .
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Old 02-18-2011, 03:26 AM
gelandangan gelandangan is offline
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You would better off starting the job using high carbon steel that can be hardened properly.
The effort you spent (including aligning the steel north and south ) would be wasted if you use mild steel to start with.

Cheap and easily available high carbon steel are:

- Car springs
- old saws
- old files
- Broken drill bits (industrial SDS drills are the best)
- Motor armatures
- gear shafts
- grade 12.9 bolts
- high tensile chain
- large ALLEN keys
- Large pry bars
- Large screwdrivers
- the list goes on..

test them on a grinder, high carbon steel would spark like the fourth of July.
Your local scrap yard is treasure trove!

If you have access to high enough temperature forge that could go to WELDING temperatures,
twisting steel cables (eg. old winch or elevator cables) could produce very pleasing pseudo damascus effect.
Or you can experiment on folding steel (japanese style) and add HARD edge on SOFT flexible core.

If you wish to give "edge" to "softer" steel, you can try to give it saw edge by sharpening using rough stone.
The groves left by the stone would help create mini saw edge that could tremendously help cutting process.

You can try to surface harden low carbon steel by containing the finish product in a small steel container,
pack with crushed bone and place in very hot fire for a long time (the longer you do this, the deeper is the hard skin going to be) then quench in water.
Hopefully the carbon would be absorbed by the steel and thus giving you better cutting edge.

Quenching does not always do good, it may create too brittle a steel that need to be drawn back.
It is an art, you got to experiment!
Old 02-18-2011, 07:27 AM
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Quote:
Originally Posted by andersed View Post
It's part wives tale, and part science. some steel is worked in the presence of extremely strong magnets to get all the grains of the steal to line up just a smidgen better. On a scale of 1-1000, his gives you an improvement for certain applications of 1-2.

I doubt that the earths magnetic field is strong enough to give any measurable difference.
I had purchased a blade blank and was playing with it in the forge and wanted to harden it based on some of the knifemaking videos I had watched. I had set up a horizontal quenching bath with used motor oil. I did not have it oriented north south. I heated it until non-magnetic and quenched it. It warped a 1/4th of an inch right there. I seemed to remember the comment in my lively forge video, went back to review it and viola there it was the recommendation to keep the quenchbath north south. Maybe it's a wives tale, but I believe it at the moment. Funny still because I snapped the blade blank trying to bend it straight again. Yes I've learned a lot the hard way but I'm still learning and having fun with it.

Thanks for your comment
-Mike
Old 02-18-2011, 07:28 AM
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Quote:
Originally Posted by NFNF View Post
Another thing to note if you use a belt sander or similar to sharped your blade afterwards.

Remember, if you see sparks, you're de-tempering the edge.
Sounds logical
Old 02-18-2011, 01:32 PM
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For the comment about quenching brine. Remember some steels are specifically spec'd to harden in water and some are specifically spec'd for oil. It has to do with the speed at which the temp is taken out of the steel.

For the comment about trying to straighten a warped blank. Since you had hardened it it was now brittle and can't be straightened as is. You would need to anneal it first to get it totally soft and then reharden and then temper. To anneal heat again to cherry red and then put in a bucket of ashes totally buried and let it sit there overnight to slow cool. This will take all the hardness out and leave it dead soft.

As for north-south quenching I have never paid any attention to it and only occasionally had any warpage though very very minor. My blades are stock removal vs forging so that may make a differience.
Old 02-18-2011, 06:55 PM
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Ok; I'm definately new to message boards so lets see if I can get these photos to post...
First is gettin the oil for quenching once I get the steel hot.
The second is the steel projects I've been working on. the knives are from rebar and the rest is from Misc steel barstock.
My humble forge is made of a BBQ grill, bricks, and an airmattress inflator....
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Old 02-18-2011, 07:06 PM
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...and here is the first hardening...

The quenching in oil I disregarded the North south orientation to see what happened. The chisel and knife came out fine but the spearpoint warped...hmmmm?? magic??

Although this is soft steel the knife cleaned up well (careful not to reheat when cleaning and polishing. I sharpened on a whetstone and did notice a difference in the hardness of the steel. It's nothing amazing, but is is harder then it was. it doesnt scratch as easily with a file....

Notes made; and the weekend is young.

-Mike
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Old 02-18-2011, 07:26 PM
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Make knifes from old steel files, and large allen wrenches. My grandfather was a blacksmith, and I wish I had paid more attention. He showed me how to make knifes when I was about 10-12 years old. Pops
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Old 02-18-2011, 09:05 PM
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The only way that you will ever make a knife worth using with rebar it to combine it with a high carbon steel and make a Damascus blade. End of story.
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