Home heat treat

[Waldganger]

Hi there all.

Last night I discovered that I could heat a chunk of 1075 to non magnetic in the wood fire heater.

so this has me thinking about heat treating my own blades instead of sending them away.

So I have a couple of questions.

Quenching (using oil) - do I
a) fully submerge edge first until it cools
b) fully submerge for ten seconds, remove and scrub scale off, submerge for another ten etc etc until cool?
c) some other method

Tempering, do I
a) place in an oven @ 200 celcius for a couple of hours or
b) something else


I'm not entirely sure why I temper, I think its so the blade isn't as brittle all the way to the spine.

I have very limited tools/$$ to spend, and I only want to make stuff for myself (or as gifts)
I do not own a oxy set, just have a fireplace and gas oven/stovetop

Also I plan on getting old saw blades (L6) and old files and using them, can I just use the same methods?

thanks in advance

 

[caliban]

If you can get your steel to non-magnetic, I doubt that much that it matters how you do it, some people have used propane torches. Why don't you just heat it to nonmag, stick it into a tin of warm veg oil and then clean it and wrap it in foil and stick it in your oven at the right setting for the usual time?

I think you "temper" the blade to harden it. It only gets hard at nonmag, but it's brittle like glass, so you draw the temper in the oven at lower temps, to reverse the process a bit and soften the steel to a useable hardness. Quenching stops the heating and locks in the hardness gained by the initial heat treat. Scientifically what I've told you is bound to be a load of b****cks, but that's how I understand the process.

 

[Matt.S]

Heat-treating can be a little confusing, but if I can get the basics anyone can!

When you harden a piece of high-carbon steel (heat to non-mag and quench) it becomes 'dead-hard' -- as hard as that particular piece of steel can get. For O1 or similar 1-odd-% carbon low-alloy steel that's about 64RockwellC. 1070 will be a little softer. In other words, bloody hard and bloody brittle. Tempering is the process of removng some of this hardness for whatever reason -- in this case so as to make it easier to sharpen, and to reduce the likelihood of the blade snapping.

As to actual techniqe I'll leave that to the experts -- I don't make knives very often

 

[Ogri the trog]

From my primitive standpoint.....
Yes, no, no and yes, no!
Yes to quenching edge first until cool - beware of any tilting of the hot blade as it enters the oil as this can cause it to cool on one side before the other and bend the resulting knife.
Tempering will be around 200 C (some people will temper at lower temperatures, some higher and for differing times) depending upon the qualities you want in the finished tool, but as a ballpark figure, its fine. The tempering process is effectively trading off some of the hard, brittle, glass-like qualities for ease of sharpening and tough rather than hard steel.

I can't comment on the saw steel as I've only used olf files up to now, but I recon the theory should be the same, so long as it is similar steel.

ATB

Ogri the trog

 

[Waldganger]

cool thanks for the replies. Makes sense now.

So any idea what kind of scale the tempering is done at? (like maybe every hour is 1 on the RC scale?)

I found this info

Tempering Temper, after heating and quenching, at 700 to 1300 F. However this steel is most often used in the fully hardened condition (not tempered) of Rockwell C 55 or so.

http://www.suppliersonline.com/propertypages/1075.asp

is this accurate do you think?

thanks again

 

[Mojoracinguk]

Taken from a ground flat stock of 01steel
It say's "Temper for one hour per inch of thickness" so I was treating blades of 1/8 inch thick which equates to 7.5 mins....so i left mine for 20 imins
as long as the temperature is constant in the oven and does not rise above your target temp then you can leave it in there until the cow's come home, it just ensures the heat has "soaked" the entire work piece. if you take it out too soon you'll end up with a tempered outer skin over a brittle inner core.
It also stated on the packet
150 degrees for a rockwell hardness of 62
200 degrees for a rockwell hardness of 60/61
232 degrees for a rockwell hardness of 58/59
290 degrees for a rockwell hardness of 56/57

Also if you go on line and search for 'Approximate Temp of steel by colour' you can find charts that show you the colour steels become when they oxidise at tempuratures. This is the old school method I was taught when making chisels knives scribers etc It is used in conjunction with a propane/acetlyne torch. although when using a torch you will not be able to make the work piece uniform in temp and therefore will end up with the condition as mentioned above....although in some cases having a steel with differing tempers can be benificial.

Jim

 

[Mojoracinguk]

BTW the temps metioned are all in Celsius.

 

[Waldganger]

Thanks Mojoracinguk.

http://ajh-knives.com/metals.html#springs

down the bottom has this

HEAT TREATING INFORMATION FOR SPRING STEEL

which has this info for AISI 1075
As Quenched Hardness - Rc 64

400 F - Rc 59
600 F - Rc 53

So what I'll do is get my blades quenched, and stick in @ 200 celcius and leave for one hour per inch plus some.


I'll wrap it in alfoil to help (any special foil or just kitchen stuff? Shiny side in or out?)
Also must I remove the scale left over from the quench? I kinda like it.