Heat treating

[deernhog]

I have been dabbling in forging some blades for chopping tools. I formed one from a mower blade and another from a leaf spring. The blades are cut then hammered to shape. The edge is hammered not ground to the thickness I want approx 1/16". Problem is when I quench the  blade it causes the blade to warp in a wavy shape. I'm sure it has to do with the rapid cooling but what can cure the problem. I found the hard way that trying to straighten it without reheating causes you to go back to start the project over. The mower blade I salvaged after it just cracked but the leaf spring broke in half leaving me a 7" mini cleaver (still a sharp chopping tool though). Just need to see what I'm doing wrong causing the warping when quenching.  Will cold water cause this because that is what I'm using to quench and saw where someone was heating to 150*fh to quench. I have used oil that I can use also . Either way it is fun hammering steel in to a shape on an anvil like that.
 
I'm getting the heat treat down because the blades will literally cut sandstone without chipping or rolling the blade. I'm trying for a parang type of blade.

[DeckH]

deer hog-  Some steels can be hardened in water but it is ususally heated to 100-190 degrees.  I think your type of steel is best hardened in warm oil.  I use an old fire extinguisher tank (stainless steel) and used or new automatic transmission fluid.  You can heat the ATF with a red hot piece of rebar.   I guess you know that once you harden your blade it is too hard.  You then have to temper it or draw it back.   There is a wealth of heatreating info on the internet.  All you have to do is GOOGLE it.

[deernhog]

Thanks I'm tempering the metal in the oven at 400 till I get the purple color which is making for a good chopping edge. I searched the net and found most of the same suggestions you gave me but you get credit first. I noticed that most also say it is rare to get it right on the first try so back to the anvil I go after deer season winds down. My first 2 are ugly or short, but efficient choppers even on our local Bois Darc trees or a deer pelvis .
 

[Ranger99]

you may be thinning your edge too
much before you quench.


x2 with deckhand about quench fluid.


have you tried to anneal to relieve
stress from forging before you temper?

[deernhog]

I have been putting the edge on before hardening. I anneal the blank to red hot then turn the blower off to let it cool till the next day before I start putting a hammer to it.   I read where if the metal is quenched in too cold a liquid it will warp and the water has been being air temp in a large tub probably from 50 to 70 degrees depending on the air temp at the time.

[Dan308]

Deernhog, quenching in warm brine (salt) water you will most likely lose 30% to 40% of your blades to cracking and really bad warping. Cold water will be even worse. Try Canola oil heated to 120 degrees. Temper at 400 - 425 for one hour.

[deernhog]

I have given up on any water quenching except for thick stuff. I have motor oil to use but it stinks so I avoided it. Wasting a lot of time sucks worse that smelling burning oil though.  I did get one parang type blade to work though using 170 degree water quench. Very little warp and no cracking but I still plan on using the oil. I left the edge thicker than a dime which also helped a lot.

[cabledad]

I have owned a hammer forged custom knife for 20 years ,its really hard.I understand he forged it red hot on a power type hammer. Lots of knives out there but few that really hold there edge. It was built by Tom Beery from Rockdale,Texas.

[mmt7714]

Don't quench in water. That is part of your problem. You can use several different things like motor oil, trans fluid, canola oil, vegetable oil, etc. It needs to cool quickly but not too quickly. Water cools it too quickly. As far as your warping, your edge is too thin when quenching. Leave your edge about the thickness of a dime, or a little less before quenching. This will cure the warping problem. Also, heat a scrap piece of metal and put it in your oil to heat it up a little, about 120 degrees, before quenching.
 
Mike

[mmt7714]

I forgot to add that different carbon steels will act differently when quenching. The lawnmower blade is a fairly low carbon blade while the leaf spring is a pretty hard, high carbon piece of steel and would make a better tool or knife.
Mike