Thread: Last minute Heat Treat Questions

OK I’m just about ready to heat treat my file razors, but I’d just like to run my plan past some of you guys and get your opinions.
I’ve read a lot of stuff on the subject and some sources seem to contradict others, so I could be a little confused on what I need to do.
Here is the plan:

Normalizing: Heat the blade to non-magnetic and soak for a couple of minutes, remove and allow to air cool (on a steel rack?) until the blade is no longer glowing. Repeat for a total of 3 cycles.

Hardening: Heat the blade to non-magnetic and soak for a couple of minutes.
Quickly plunge the blade into warmed quenching solution and agitate. Remove when blade is cool enough to touch. Remove excess oil, test hardness with file.

Tempering: Wrap blade in foil or in tray of sand and place in pre heated toaster oven at 205C or 400F for 1 hour, allow to cool to room temp and repeat.

A few other details: Is there a preferred way to place the blade in the quenching solution? Cutting edge down, tip first etc?
I can get 4 litres of cheap motor oil or 4 litres of Canola oil for around the same price. Is either OK for this exercise, would one be better than the other?

Thanks guys
Grant

Hello Grant, your scheme seems pretty solid to me. Everything you are doing should achieve your desired results.

Every different quenchant has it's own ideal temp where it does the best job. as a very general rule, oil ~ 150F, water~100F. I have also used peanut and olive oil, and water and brine.

I always quench the blades spine down and edge up with the razor level.

Also, I do not harden the tangs any more. It is not uncommon for the tang to warp slightly. If they are unhardened, you can straighten them with good success. I have snapped several tangs off of nearly finished hardened razors and I must tell you it is quite disheartening. (read: a whole lot of cursing).

Good luck,
give my love to the family
Bob

Make sure your pliers are flat, or you will leave ribs in the tang.
I swish the the razor in the oil slowly in a spine to edge motion.
Im looking into a natural oil alternative.Motor oil stinks horribly, and has a lower flashpoint (So I have read).
Oh yes, keep an extinguisher handy just in case

Good Luck!
Eric

I use corn oil, because it was the cheapest oil around.

Canola oil should be fine. Not sure what the flash point is - that is temp at which the surface catches fire. Should probably be about 110-120F. I have always been told to quench spine up - Bob is very experienced, however, so maybe it doesn't matter. Perhaps Mike Blue will chime in - he knows more than most (all?) books on the subject. I have just tempered in our oven at around 385, with the blade laying on the rack. Fire extinguisher is a must. Good luck - let us know how it worked.

Hey Grant,
as you said, there are a lot of methods that seem to contradict. For what it's worth i use Canola or Olive Oil. Smells a lot better than motor oil.
Knives i quench edge down. You can use a rest under the oil to stop the blade at a desired depth if you want to differentially harden. Maybe the lower third of the edge. After about 10 seconds there, move it over and totally submerge. Razors do vary from knives due to the extreme change in thickness from spine to edge. For razors, follow Bob's advice.
i also do not agitate in the quenchant. i believe that increases the chance of warpage. {i could very well be wrong there- just my opinion and what i am comfortable with for my methods.
Normalising - i heat to non-magnetic, soak for two minutes, let cool to room temp. Heat to non-magnetic again, turn off forge and leave to cool extra slow as forge cools. {gas forge} i really use the same method for annnealing before working as well-want to remove stresses in steel both times.
Last thing - the tempering i just put it in the oven on a wire rack. Have not used sand or foil.
After it is back to room temperature, put in the freezer overnight, remove next day, wait until it is back to room temperature and then repeat the temper in the oven.
Most of all - try what you feel is best and makes you happy. If the results are not what you want, then try something else. They are your blades.
Best Regards, Adam

It depends. There are any number of variables in this type of equation and I don't know them all.

I'd want to know the type of steel first. There are books like "The Heat Treater's Guide" or thermal transformation graphs, that have well defined recipes for each steel type. Books like that are based on observations over years of collected data and trials of different times and temperatures to produce a guide to optimum performance for that specific steel.

But for a simple carbon steel, your plan will work. You may well settle for "good enough" rather than perfect. If it gets hard enough to hold an edge and shaves well...in the end what else matters?

As to tempering, maybe start lower and work upward. If it seems too hard or resistant to honing, then you can go back in the tempering oven at a slightly higher temperature for another hour and try again. If you go too high, you can't put hardness back in the blade unless you repeat the entire heat treatment. If you've already gotten to a shave ready edge that's a fair guarantee of having a potato chip wave along the edge. Keep good notes of how your methods are working and your results.

The most critical process for dealing with warping is the thermal cycling/normalizing ritual. I don't think a human being can hold still long enough to prevent some swishing around in the quench tank and I've not noticed that blades warp from any of that when the blade was well and truly thermal cycled in the beginning. Really swinging that baby around and banging it off the inside of the tank while it's still plastic is a sure way to produce a bend you didn't want.

In the end, it comes down to what works in your shop with your tools and what you have to do to make a blade the way you want to. Pay attention, the steel will talk to you about what works best.

Well it's 11 o'clock Saturday night and the blades are in the toaster oven for the temper cycle.
Everything seemed to go well with the hardening.
I might post some pics tomorrow.
Grant