Large sawblade steel

[Golden Bay Duncan]

Hi,
Im a novice and was given a very large old sawblade. The former owner said he produced a great sharp knife from it without heat treatment so I cracked into it.
I noted the section he cut was from the outer edge so I did the same.
After many hours of working a perfect shape and bevel the bloody thing would not sharpen. As yet I haven't heat treated it to see if it will indeed harden off but my instints say no. Due to its size …{say 2 feet wide } my friend reckons that the body of the blade would be produced to flex and may have been pounded?.... therefore not possessing the hardness needed. But it has made a knife before hmmmm
Also..NB*..Can you just heat treat all recycled steel, regardless if its been done before?. I have other good old much smaller blades [ normal table saw size ] but am reluctant to go further until I know what Im doing. Can I just heat treat blades even if they may already be the correct but unknown hardness?. Will I lose that much hardness in the steel?. I know the process will release more of the carbon but I have had success before with a large, old skinny bandsaw blade. Help appreciated

 

[JTknives]

First off welcome to the form.

Now let’s get down to the nitty gritty. The blade being hard or soft does not affect if it sharpens or not. I can sharpen a knife made from soft mild steel to hair shaving sharp. It won’t hold that for very long at all. But not being able to sharpen it has more to do with geometry and sharpening techniques then the steel it’s self. It is a steel you can heat treat and make harder. You will hear lots of people say “oh all sawblades are L6”, This is not true. Sawblades generally are not very hard becaus thy need to be tough. Thy also need to be able to be sharpened by filing. That’s how thy did it back in the day. So I’m guessing in the low to mid 40s RC. Most knives are in the range of 58-62rc. But like I said above if you can’t sharpen it you have other things going on besides the steel. Post a picture so we can help better.

 

[P.Brewster]

Many large circular saw blades are made from something like 8670 and are thru hardened to ~50 RC.

They are flattened by hand by hammering with a carbide-faced hammer. The hammer face is not flat. You can read about the process and see pics here http://americancarbidesaw.com/serv.htm

 

[Ken H>]

Are you asking about making the knife from the saw blade without heat treating it again? There is no real good way to make a knife from that saw blade without heat treating it again. Could you do it - sure, but you're not going to have a very good blade.

Seems the proper method for using your saw blade would be to cut a small piece, Heat to non-magnetic, allow to cool very slowly. This puts the metal in the state you can work it with files, grinders, etc. Now to test if it will harden. Heat test piece just past non-magnetic and quench (canola oil, even water for this first test piece). See if a file skates on it. If it does, you're golden - make a knife. Perhaps to assure more, temper the test piece in oven for a couple hrs. Since you have no real idea what metal it is, do your first temper at 400⁰F. If that seems to hard after temper, raise it to 450.

 

[Golden Bay Duncan]

Thanks heaps guys. To answer JT I have ground the bevel then worked on a stone course then fine. I have no problem sharpening knives usually.
NB My question still remains a little unanswered in regard to heat treating steel that may already be hard. ie do you lose much of the steels hardness qualities by quenching it again?. THis is in regard to sawblades and other recycled steel I come across. Could I just heat and quench everything I make without losing too much from the steel itself??. Really appreciate your help

 

[Golden Bay Duncan]

Are you asking about making the knife from the saw blade without heat treating it again? There is no real good way to make a knife from that saw blade without heat treating it again. Could you do it - sure, but you're not going to have a very good blade.

Seems the proper method for using your saw blade would be to cut a small piece, Heat to non-magnetic, allow to cool very slowly. This puts the metal in the state you can work it with files, grinders, etc. Now to test if it will harden. Heat test piece just past non-magnetic and quench (canola oil, even water for this first test piece). See if a file skates on it. If it does, you're golden - make a knife. Perhaps to assure more, temper the test piece in oven for a couple hrs. Since you have no real idea what metal it is, do your first temper at 400⁰F. If that seems to hard after temper, raise it to 450.

cheers Ken

 

[Natlek]

Thanks heaps guys. To answer JT I have ground the bevel then worked on a stone course then fine. I have no problem sharpening knives usually.
NB My question still remains a little unanswered in regard to heat treating steel that may already be hard. ie do you lose much of the steels hardness qualities by quenching it again?. THis is in regard to sawblades and other recycled steel I come across. Could I just heat and quench everything I make without losing too much from the steel itself??. Really appreciate your help

Simple answer ..........no ! No , if new HT is done right

 

[12345678910]

Forget the little circular blades, have a close look they probably have carbide tips on.


Re the two foot dia blade

does it have carbide tips?

Take a scrap strip, heat it red hot, quench in oil and see if you can snap it.
repeat in water.