Tempering a circular saw blade

Status
Not open for further replies.
M

mjn

Joined
Nov 2, 2002
Messages
114
I'm working on my first knife. I started with an old 10" circular saw blade. It's marked
FULL TEMPERED
HARD COLD ROLLED US SPRING STEEL
MAY BE RESHARPENED

I cut out the shape with an abrasive metal cutting blade in a circular saw and ground in the basic bevel with a belt sander- not letting the blade get too hot to touch at any point.

Question is, do I have to temper it now? What happens if I don't?

I've seen all the comments in the archives about starting with a known steel, etc. Right now I'm just doing this for the first time to see how it works, and I didn't want to spend a ton of money on materials knowing I'm going to make a lot of mistakes.

Any thoughts?

Thanks.
 
My first several blades were made in the same way as yours, except I cut them out with a metal cutting band saw. I did not heat treat the blades and they made what I would call fair knives, they will sharpen to a good edge, but don't hold an edge as good as they could if heat treated, but are very usable. Hope this helps. J.D.
 
First I want to say that I am not a Metalurgist or even a knifemaker but I have worked with metal a good bit in various welding shops and industrial plants doing maintenance work. I would just fire up my gas bar-b-q grill and get that piece of metal good and hot then quench it in an oil bath to give it some kind of a heat treating myself.
 
Ok, so I heated it to nonmagnetic in a wood stove burning alder wood and using a boat inflator for forced air, and quenched it in canola oil (hey, I'm trying to start simple). When I got done it had a cracking/crazing pattern on the surface of the steel that didn't appear to go beyond the surface. Some of it started at the file work on the spine. What, if anything, does that mean?
 
It might mean the steel was fatigued before you started. Or it might mean you had the steel too hot when you quenched. Or it might mean oil is too fast a quench for that steel (was the oil warmed or room temp). Or if it is just on the surface it might be scale from heating (especially if there was an excess of oxygen). That which started at the file work, the file work may have had sharp corners which are potential stress risers increasing the likelyhood of cracks. There are other possibilities, pictures may help.

ron
 
Sand it down to bare steel and see if the cracks are still there, Also after you do the quench you need to temper the blade in an oven at about 375 for a couple hours, cool it then give it a couple more hours in the oven. If you do no do this the blade will be very brittle and snap easily. When heat it to magnetic you do not want it to get much hotter. Just a bit hotter but not much. The oil needs to be about the temp of good drinking coffee.When you quench. Smile
 
I have never heard of steel crazing like that before, so maybe bluegrass is right about it being scale. I think a lot of circuilar saw blades (not TCT tipped ones) are flame hardened, but only on a periphery of the blade, so I would imagine they steel would need to be fully hardened in that case. By the sounds of the tag, the whole piece of blade is cold rolled... This hardens by a different method of 'strain hardening' as such. If the blade keeps a good edge I wouldnt do any further treatments. Take some of the offcuts and smash it around a bit and see how brittle or soft it is
 
son_of_bluegrass said:
It might mean the steel was fatigued before you started. Or it might mean you had the steel too hot when you quenched. Or it might mean oil is too fast a quench for that steel (was the oil warmed or room temp). Or if it is just on the surface it might be scale from heating (especially if there was an excess of oxygen). That which started at the file work, the file work may have had sharp corners which are potential stress risers increasing the likelyhood of cracks. There are other possibilities, pictures may help.

ron
Click to expand...

7. E, All of the above
 
I hate to sound like a broken record but here goes:

You took a circular saw blade that was of some kind of steel, not necessarily usable for a knife (None of the label info says high carbon, of declares any specific alloy).
You heated it to an unknown temperature , in an atmosphere surely too high in oxygen, and quenched it in a non-standard quench oil.

In the process you spent a lot of time, work, effort,.....

From this you got a....well what did you get????.... some kind of cracked surface piece of metal.

Where did this go wrong? At steps one, two ,and three. How can it be corrected?

Get a know steel.
Heat treat it in a controlled and proper atmosphere.
Use a proper quenchant for the steel selected.

The above steps don't take any longer to perform, but will yield reproducible results. If something goes wrong with the second set of parameters, you will at least know where to look to make corrections.

I know this sounds harsh, but your time and effort are worth $2.00 in good steel. A lot of good fellows on this site repeatedly advise to use known steels (especially while learning) if you want reliable results and less heartache. For the life of me I can't understand where in these four words there is any room for doubt.

USE A KNOWN STEEL

Stacy
 
Here is a crazy concept to add to Stacy’s post (which I agree with). It took me a little bit pondering by the sound of the hammer on the steel but this is it: “You don’t know what you don’t know”.
I started my first knive with saw blades but only for the practice. I developed the techniques on steel that was free to me and I didn’t intend to make a functional blade with it because I didn’t know even the basics about the steel. A catastrophic failure of a knife in use could be very bad.
Now I am not saying that it cannot be done. Some research about what you are using (phone calls, emails, technical research online) can give you the knowledge of what the material is that you are using.
Knowing your material as well as your technique can make this tradecraft so much more fun.
Keep having fun, keep being safe, never stop learning.

Cheers,
Caleb
 
Get know steel! My time was worth more than the price of steel. Plan on throwing away some. Steel is cheap. Time is not replaceable.
 
eleven year old thread. If the OP has not figured it out by now, he never will.
Closed.
 
Status
Not open for further replies.
Back
Top