heat treating with a blow tourch?

marthinus

marthinus

Joined
Dec 10, 2006
Messages
5,945
I read that that Mr. Emerson heat treated his first blade with a blow torch. I started asking around and seems to be possible, but no one could give me more detail. Is this true?

Further more, if so:

How do you ensure consistancy and how would one measure the heat?

Thank you in advance for any answers.
 
Last edited:
not a good idea depends on the steel 1080, or 195 you might be able to do it but for tool steel it requires soak time and consistent heating. the temp can be mesured with a a magnet when the steel transforms to austenite it becomes non magnetic. you could also judge by colour.
 
I think to get consistency using a torch unless the blade was rather small, would be rather difficult.

I think Mr. Emerson (back in the day) was only concerned with getting the blade hard (which a torch will do). Probably didn't have any correct means of hardening otherwise. Don't think he'd do that these days !

But due to the small tip of the flame, you'd be hard pressed to have the entire blade at the same temperature when you quenched it (unless it was a small blade).

You'd be better off being a small forge and using the same torch. The heat trapped in the small say one brick or two brick forge, would be much greater and you'd get better results !
 
i have been using a torch for almost 18 years using 1075 and i have had good luck. i'm pretty consistent too getting within 63-65rc. you just have to watch the color of the blade and remember the color. i quench in used canola oil or a mix of motor oil and transmission fluid.
 
Eveness is the key. It has helped me to have the torch stationary and it's flame backstopped by an insulating brick (kiln brick 2300F to 2600F). Some scoop out the face of the brick but I've not tried that.

Mike
 
I know it can be done for 1084. I am wondering that if you had a simple one-torch mini-forge and can get the temperature high enough, can you heat treat M2/M4 with the simple torch forge? Those only require a few minutes soak time at the upper temperature range. Anyone?

I am building an electric oven anyway, but I'm curious.
 
you want to use a magnet not try to tell by colour and try to heat it as evenly as possible.
 
nullack said:
you want to use a magnet not try to tell by colour and try to heat it as evenly as possible.
Click to expand...

What's the rationale for this? The non-magnetic temperature isn't hot enough compared to the austenizing temperature.
 
Hard to get the right color in photo's I know but this is what I do.

DemoShot.jpg


No need to waste the heat loss looking for a magnet. It will be non magnetic for sure :)
 
when i heat treat i'll have a friend run the torch while i hold the blade stationary. if you get sparks coming off the blade you're getting the flame too close and blade too hot. red hot isnt enough and yellow is too hot. bright orange is the color to look for.
 
cotdt said:
What's the rationale for this? The non-magnetic temperature isn't hot enough compared to the austenizing temperature.
Click to expand...

Its my understanding that gamma iron is non magnetic and using this to indicate when the austenziing temp is reached is more reliable than judging by colour. Overheating it is not only bad for grain growth but also for carbon problems.
 
NULLACK, steel goes non-magnetic at 1414°. That is not enough heat to get a good solution in the steel. About two shades of red beyond that temp will. You want a minimum of 1475° for most common carbon steels, and often 1500° is even better. Also remember you lose some heat between the heat source and the quench.
 
Obviously skill/experience are major factors... but I used the magnet/color method for a year on 1075 and W1 and was SEVERELY overheating. Broken cross-sections looked like cast iron.
 
As a learning tool I am finding it useful to run some test sections first. I'm practicing with 1084 right now. Here's my process:

Finish your knife to the point of being ready for hardening.

Cut some 1/2" to 1" wide strips from the same stock.

Set up your torch and quench area like you will actually be using them. It helps to be in a dark room (I use my garage after dusk with the door 3/4 down and lots of open room around me).

Take one of your test strips and heat with your torch to a good red glow. Check with a magnet periodically (read on before you scream guys) and you will find that it loses it's magnetic properties at a good red color. This is the 'cherry red' everyone talks about. Go ahead and quench. It's too low of temp, but this gives you practice, warms your quench oil (which is desirable to a point), and you will be working up to find the right (but not too hot) temperature.

Check the test strip with a file. It'll probably bite easily, just like the other unhardened pieces.

Torch heat again to a slightly hotter temp, quench, repeat until you'll find suddenly that the file didn't bite! Remember that color/temperature!!!

Now, take your hardened test strip, lock it in a strong vise, and snap it in half. It should be hard to snap, not bend much at all, and snap sharply. Hopefully the break looks like really silky, wavy, smooth, etc. and not like 80 grit sandpaper. Smooth==good, rough===overheating.

Repeat until you can nail the right color each time.

Move to your knife. Note that the larger knife will take longer to heat up, and you'll have to watch the color to get it all evenly hot. A small propane torch may work fine for the test strips but not even be able to get a full blade hot enough. Ask me how I found that out...:o

Just remember, that you can UNDERheat many many times without serious damage to the steel, but OVERheat it once and it's pretty much done.

Good luck!
 
so basically my understanding is that when steel is heated beyond it's critical Range about 1400 F for most carbon steel the crystals actually change from pearlite, a softer weaker Crystal to Austenite which is among other things harder, stronger, and non magnetic this is gamma Iron, I have heard that when heating through this the steel will actually absorb heat (i.e it cools down, or doesn't heat up for a little while), and on cooling the steel will actually gain heat, sometimes visibly, this heat i suppose is used to transform pearlite to austenite. sometimes steels containing allot of nickle and manganese (20%-30% total manganese and nickle and some other elements lower the critical temp significantly) after quenching can maintain an entirely austenetic composition, or if containing enough nickle and manganes (30%-40% total) the critical temp is near atmospheric and are thus none magnetic. these steels in order to contain some martensite (the very hard crystal desired by knife makers) must be cryo treated, or left purely austenetic, if a nonmagnetic knife/tool is desired, would this be better that titanium?
 
I use 2 torch heads on camp propane bottles opposing each other so that the flame tips touch each other. This allows me to heat about 1/2" leaving the back soft. Works well for me.
 
Nebulae said:
so basically my understanding is that when steel is heated beyond it's critical Range about 1400 F for most carbon steel the crystals actually change from pearlite, a softer weaker Crystal to Austenite which is among other things harder, stronger, and non magnetic this is gamma Iron, I have heard that when heating through this the steel will actually absorb heat (i.e it cools down, or doesn't heat up for a little while), and on cooling the steel will actually gain heat, sometimes visibly, this heat i suppose is used to transform pearlite to austenite. sometimes steels containing allot of nickle and manganese (20%-30% total manganese and nickle and some other elements lower the critical temp significantly) after quenching can maintain an entirely austenetic composition, or if containing enough nickle and manganes (30%-40% total) the critical temp is near atmospheric and are thus none magnetic. these steels in order to contain some martensite (the very hard crystal desired by knife makers) must be cryo treated, or left purely austenetic, if a nonmagnetic knife/tool is desired, would this be better that titanium?
Click to expand...

You're basically on the right track, except that austenite is softer than pearlite, partly because of the arrangement of the crystal, and partly because of the temperature needed to make austenite in the first place. Most metals get weaker as their temperature goes up, though this is a general statement and many exceptions can be found. The hardness comes from the quenching and that forms another arrangement of the crystals called martensite. This is hard, strong, wear resistant, and basically what we are after when we quench. Its also brittle, so it must be handled with care. Heating again after quenching to a lower temperature, say between 300 and 1000 degrees F, takes care of the brittleness, though again this is a very general statement and many exceptions can be found. Austenitic knives have been made, but they are mostly for decoration. The nonmagnetic forms of steel are generally too soft to make knives, though some of the austenitic steels work harden when deformed and might be able to get hard enough to make a passable knife. Basically, IMO, titanium is better, plus is more corrosion resistant in salt water. The point where steel becomes non-magnetic is called the Curie point, and is not always a good indicator of when austenite forms, since the Curie point is usually below the temperature when austenite starts to form. Again this is a general statement and the Curie point is dependent on the particular alloy in question.

When heating steel, or anything else for that matter, the temperature rises until a rearrangement of the crystals/atoms occurs. This is called a phase transformation, and each distinct arrangment of crystals/atoms is a phase. In this case, pearlite to austenite is a phase transformation, since each has a distinct and different arrangement. When phase transformations occur, heat put into the material stops making the temperature go up until the transformation is complete. On cooling, then the phases go from austenite to pearlite. When this happens, the heat used to change phases on the way up is released, causing the flash. These visible indications are difficult to see even in a dark room unless you know what you're looking for.
 
Last edited:
blgoode said:
Hard to get the right color in photo's I know but this is what I do.

DemoShot.jpg


No need to waste the heat loss looking for a magnet. It will be non magnetic for sure :)
Click to expand...

Brian,

if you packed the spine with Satanite ON REAL THICK and shaped it in a wavy manner and did the same thing with your 01 tool steel, and quenched only coloring in the fire in the empty space not covered by satanite, is it possible to get a wavvy quench/hardened line?

Pohan
 
You must log in or register to reply here.
Back
Top