Survivalist Forum banner

Q: Home made Knives.-hardening/tempering

17K views 28 replies 14 participants last post by  WannaBePrepper 
#1 ·
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.
 
#2 ·
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/showthread.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!
 
#3 ·
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-Hard-Hardening-Powder/productinfo/QHARD01/
 
#4 ·
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
 
#5 ·
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.
 
#6 ·
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.
 
#9 ·
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.
 
#10 ·
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 Amazon.com: Wayne Goddard's $50 Knife Shop, Revised (9780896892958): Wayne Goddard: Books to get you started. He is master in the world of knife making and this book gives lots of great info.
 
#12 ·
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 .
 
#13 ·
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 :D::rolleyes: ) 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!
 
#16 ·
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.
 
#17 ·
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....
 

Attachments

#18 ·
...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
 

Attachments

#22 ·
That would have been cool to learn from your dad. Sounds like he used a lot of tool steel. I'll be playing around with that before too long. Right now I'm using softer steel and getting better at shaping and some of the processes. I hope to barter for a real anvil at some point. Once I start to get good at this I'll let my son do more of it with me and maybe he'll enjoy it a little too.
 
#21 ·
Are you hardening your blade by going down in the oil as if cutting it or on its side? On its side will definitiely cause warping. Another thought is to "normalize" the blade after forging and before hardening and tempering. This will take the stresses of forging out before you start the hardening. Go to this link
http://www.celticknot.com/ and download "HAMA handout" It is a simple PDF file that will give you lots of info on this.
 
#26 ·
Trixie;
it seems pretty hard as my files skate off of it more than they did before, but I think I'm clearly with the consensus of many of the other posts that it is still pretty soft comparitively. I've sharpened it and it cuts well, but while fooling around with it the wider beveled area of the blade seems to be holding the edge better.

I've got some higher carbon scrap tool steel to play with now, so I'll be playing with that too. Once I get good with this I'll probably order some barstock from knifekits.com but I'm comfortably learning a lot of ins and outs right now. Thanks for your support.

-Mike
 
#27 ·
Hardening and tempering are mainly about the crystal structure of the steel in the metal.

In normal steel, the crystal grains are medium sized, with the carbon (and other alloys) in the cracks in between the crystals. If heated and allowed to cool slowly, very large crystals will form, making the steel weaker.
Hardening cools the heated steel very quickly, so the crystals formed are very small - they also form an interlacing pattern.
That makes the steel very hard, but also makes it brittle.
Tempering takes hardened steel, heats it up partially, and then cools it slowly. This results in a mixture of new, large crystals and old, small ones... It's that mixture of both large and small crystals that gives tempered steel both hardness and durability.
(The exact balance between hardness/brittleness and durability/softness depends on how hot the tempering process gets, and how quickly it is cooled, which in turn depends on what kind of use you want for the knife.)


By the way, I like your BBQ grill forge!
Is it still using propane, or did you convert it to coal instead?
I've been thinking of building a forge, but coal seems like a cumbersome and tedious fuel source; I'd like to find something in liquid or gas form that could achieve the right temperatures with less trouble.
 
#28 ·
Thanks for the comments I'm certainly getting lots of help while learning this. ...as for the forge, thanks again. It's coal and it's free. the whole idea was to learn all about this stuff for free before I started paying for quality stuff just in case I really suck at it. I got the grill from someone throwing out theirs and i tossed it in the truck. I got the bricks as leftovers from someone elses project and made a box out of it, I got the air matress inflator from the closet. The coal is leftover from bbq season and it's only $5 a bag for all natural charcoal. it's really easy to use and get fired up and doesnt make a big mess...my neighbors get curious but I'm just that guy in the neighborhood who's always tinkering with something.
Mod 2 is going to use a gas pipe i found with 3 air holes instead of 1 so i can work with longer pieces of metal.
 
#29 ·
Check out MrIronman1979 on you tube, he shows and explains annealing, hardening and tempering. He does a demo on making a tomahawk from a RR spike and also start to finish on a knife, he then proceeds to abuse the crap out of the knife to prove how durable it is.

He is a blade smith and seems very knowledgeable. He will also make custom knives for anyone interested.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top