Knife blade hardining.

[Wyostikbo]

I have a concrete saw blade I want to make a knife out of. I tried one and it came out fine, I just don't think the steel is hard enough. I can drill through it without heating it up red hot and letting it slowly cool down.
Can somebody tell me the procedure for hardening steel.
Thanks.
Brent

[Gene Roberts]

Can't you get it red hot then put it in water.

[Holm-Made]

Can't help you unless I know what kind of steel it is.  Old saws work best because most of them are L6 tool steel.  Alot of the newer saws and files are case hardened and don't make good knives.  

Most high carbon steel is heat treated by heating it to 1650 degrees (cherry red) and quenched into oil heated to 120-140 degrees.  That is the hardening process.  Then the tempering process can be done in a kitchen oven.  About 1 hour at 300 degrees.  Chad

[LC]

I'd have to guess that the steel in a concrete saw is not good knife steel. Same for all blades that use diamond or carbide for the cutting action.

[Lin Rhea]

I have some concrete saw blades, but I've noticed they dont rust much. I have concluded they may be or very close to being some kind of Stainless. It's very hard to temper for someone new to working steel. I would search around and find an old sawmill blade (L-6) and I can help you with that. It's a high carbon steel and will be more likely to make you a good knife. Lin

[sticshooter]

How big of blade you looking to make?<><

[Wyostikbo]

I think you guys are right in thinking the steel isn't good enough for a knife blade. I was just hoping I could harden it somehow.
I'm not looking to build anything big, maybe 7"-8" OAL.
I don't have access to any old saw blades but would be willing to buy one if there are any available.
Thanks.
Brent

[loyd]

if i had your address i could send you some. loyd

[hickstick]

gotta be careful with that one gene.  oil hardening steels can rip apart violently if quenched in water...

aren't most concrete saws diamond blades?  if so they are relying on the hardness of the diamond powder to cut the conrete, not the steel...they are probably using a lower carbon steel for the blade part so it can stand the temperatures generated in the cutting???   just a guess.

you could do 2 tests...one like Lin said to see if its stainless...get gun blue and see if it blues...if it wipes right off its stainless and would require highly technical hardening/tempering  process....if it stains with the bluing do a 'quench test'....cut a small piece off, heat it to  red, then quench in oil (used motor oil, transmission fluid, veggie oil)  I use canola oil,  then clamp one end in a vise and whack it with hammer (donning proper safety attire, goggles gloves, apron, etc)..if it bends over it ain't hard. repeat the heat and this time quench in water....again if it bends it aint hard...no good.

if it snaps or shatters then its pretty hard...probably hard enough to make a knife.

[jindydiver]

I often use concrete cutting saws for the steel in my blades. I only use the saws that are around 2 foot across or bigger and I test the steel before I make anything worth keeping.
It is true that when the saw is doing it's original job it is the diamonds that are doing the cutting, but the saw must be strong enough to be able to take abuse AND stay in one piece while doing some serious RPM, this requires steel of pretty good quality. It might or might not be L6 used these days (it was used in times past for saw blades WITH integral cutting teeth) but either way it is hardening and tempering fine and the tempering recipe (and the knives performance) is close enough to L6 for it to make no difference.

Some blades made with concrete saws
 

And one didn't like the quench
 

The test to see how good it will perform
 
 

I had this blade over at near 80 degrees before it snapped and the handle sprung back a heap.

I don't ever use those dinky little 12 or 18 inch saws. I had no luck with them earlier and don't believe that the steel is good enough to waste time on.

[Wyostikbo]

My blade isn't 2 ft. But I think I will try the tests on a small piece and see what comes of it.
Sounds like I may need to find an old saw blade that's made out of real steel.
Thanks.
Brent

[ALW]

Not wanting to hijack the thread but I had a question.  I have been making a few knives out of 10" table saw blades.  They sharpen to a really good edge but I haven't had a chance to give them some use yet to see how well the edge will hold up.  I read on another site about doing a brass rod test on the blade to check the hardness.  Exactly what it this test?  I'm guessing you try cutting or peeling the brass with the edge to see if it will chip or hold it's sharpness.  Just wondering.  Thanks.

Aaron

[robtattoo]

The Brass Rod Test (as it appeared in BLADE Magazine) by Wayne Goddard

The brass rod test was demonstrated to me in 1959 by an old blacksmith who made knives in the 1930s. Here is my version of the brass rod test which is simple test of heat treating to help determine that a blade will hold up in normal use.

Clamp a 1/4-inch-diameter brass rod horizontally in a vise with the top half above the jaws. Or glue it to a piece of hardwood. Lay the knife edge on the brass rod at the same angle used for sharpening (about 15 degrees). Have a good light source behind the vise so that you can see the deflection caused by the rod on the edge. Apply enough pressure so that you can see the edge deflect. (When tested on a scale, the pressure works out to 35-40 lbs.) If the edge chips out with moderate pressure on the rod, the edge will most likely chip out in use. If the edge stays bent over in the deflected area, it will bend in use and be too soft to hold an edge. The edge of a superior blade will deflect on the rod and spring back straight.

The test is intended for knives in the hunting knife class. Thin filet knives or thick camp knives will not respond to the test in the same way. The blade that is too hard will chip out in normal use, too soft and the edge will bend. The brass rod test can quickly determine if the blade has a good balance of flexible strength and hardness sufficient to hold an edge.

The brass rod test as I present it is not intended to replace a hardness test to determine that a blade was fully hardened. It only applies to blades that have been tempered. I have worked out my version using it on blades made of alloy and carbon steel types that backyard heat treating methods are adequate for. The brass rod test is only a comparison test to determine what is in my opinion a hardness that will hold up in normal use. I started using is about thirty years ago and still think it is the best non field-use test I've found for testing the suitability of a blade steel and heat treatment for a working knife.

[ALW]

Robtattoo, thanks for the quick response.  So much good information here.

Aaron

[hickstick]

re: brass rod test

if you don't have a brass rod handy a croc stick (ceramic rod) will work in a pinch.  I like to do it a little differently too...instead of clamping it in a vise, I like to lay the rod on a sturdy table, place the blade edge against it at the appropriate angle and roll the edge (and rod) from choil to point...with enough pressure to actually see the edge deflect, and if it stays bent or warps at all its too soft, if it chips from the pressure...its too hard.