quench question again

B

bartblade

Joined
Nov 4, 2002
Messages
344
ok i know now what temps to get it up to but will a propane bottle with a torch head do the first quench and it is a orange glow that im looking for right and then hold that glow all over the blade for 5 minuts and quench in warm motor oil right then after that should i do the file test or is that after the heat treat in the oven for an hour? and what if after all that the file still bites into the steel?


thanks, dale
 
bartblade,

Unless you have a very thin, very small knife, that propane bottle may not be enough for the hardening operation unless you shroud the whole thing in fire brick. Most guys using a torch, use oxy/acet. Some I think use mapp. Personally, I'd add an extra hour (tempering), to be on the safe side. Total = 2 hours. The file after quench will be suitable. This will also give you an indication of whether your subsequent tempering was to your liking (i.e. too much/too little). Test again after the temper with file. Keep in mind a little bite doesn't hurt. Run some cutting tests before any attempt to re-do the whole heat treatment. The knife may be just fine. Make haste with the file test and get that blade into the tempering oven pronto!

Everything else you mentioned sounds good. Good luck. :cool:
 
ok so i should be using fire bricks and place the blade in the middle right? and then heat the bricks up and not the blade right? it is smaller than 3 inches its the blade for my second folding knife i have ever made so far. and it is flat ground pretty thin also what about the tripple quench method can you explain that to me? thanks in advance ps check out my first folder i made at http://proflies.yahoo.com/day_walker74003[/URL]
 
Bart,

You just can't do the 5 minute soak bit with a torch. The temperatures are going to vary wildly.

Many folks heattreat with a torch or forge. But, if you notice the books all say to quench "on a rising heat". In other words once the blade hits temp, quench or the torch will get it too hot.

Don't know if this is the best way, but I use the magnet test. Put the blade in and watch the color. Pull it out frequently and check with a magnet. Once it hits non-magnetic you've found the right temp (pretty much). However, now it's too cool cause you've been waving it about.

Back into the forge until you are back to that magic temp and quench.

Maybe I'm not describing properly, but I hope that helps a bit.

The file test is after the quench. If the file won't skip across the edge, then you have to do it again.

You can file test after tempering to see if it's soft enough. If it isn't you raise your temper temp. However, I don't know of a good test for too soft (which has happened to me).

BTW what kind of steel is this?

Steve
 
Brass rod test works for too soft or too hard, or such is my undrerstanding.

Anyone else can feel free to correct me on this, but here's my rough memory:

too hard: chips
too soft: deforms and stays deformed
right: deforms/deflects, then springs back.
 
I use the magnet just like itrade. I have a magnet from an old hard drive nailed to the bench next to my forge so I pull it to quench and touch the magnet on the way down. If it sticks I put it back in the forge but if it doesn't I continue the move into the quench. You will be able to tell by color soon but use the magnet to check yourself. For most people you need to heat much higher than you think.

I use the tried and true file method to see if it hardened. There is no mistaking it when you get it right. After tempering use the brass rod.
 
Yeah, heat as consistently as you can with your propane torch and check with magnet. Quench immediately in pre-heated oil (135 - 140 F.). Temper immediately in a pre-heated oven. Don't take time to look at your work. When it is at oil temperature put it in the oven without delay.

After first temper you can grind decarb if you like or go straight to the second temper after cooling to room temperature.

RL
 
its 440c so try with a magnet huh could i use this as part of my forge i have a furnase core from a gas space heater it sits horazontal but i dont have anything around it if it will work what should do to improve the heat and where should i put the fire bricks i am a newbee at making a correct forge
 
I did not know it was 440C. Since I did not see that in the original post I presumed it simple high carbon. Do it any how but hold at non-magnetic for about four minutes before quenching. Don't poor the heat to it after it becomes non-magnetic. Just try to keep it there for a very few short minutes (four). It is hard to detect exactly when the steel becomes critical this way when holding a torch in one hand and a tong in another so I say four minutes quessing you will be late in detecting non-magnetic. In the oven I would go five minutes so use your judgment as it happens and try not to exceed five minutes at critical..

Temper at 400 F. for two hours; let still air cool to room temperature and temper again as before.

Have the oil and tempering oven pre-heated before starting and use thermometers you trust to monitor their temperatures. Do not trust a oven dial setting. Get the oil to between about (within 5 degrees of) 135 - 140 F. and the tempering oven to 400 F. - not less than 400 F..

RL
 
Bart, yeah, heat up the brick. Create a hole for the torch head. Try to keep the brick as narrow inside as practical. It will be easiest to retain that heat inside when you get up to temp. There may be a way to rig it so you can leave the torch on, but really just heat up the enclosure good and bright and uniform and place in the blade, then turn off the torch. Remember, it will cool as you are heating up the knife for HT, so get it real hot so you don't lose effective heat transfer to blade. Experiment with scrap first. You are shooting for a "salmon" color on the blade though and since it is 440C after all. You may try building on open enclosure and "paint on the heat", the brick will still help to insulate. 440C may thow you some curves with the eyeball HT method, but this should provide you a serviceable blade nonetheless. :cool:

The freezer, if held long enough, make help to transform some retained austenite. But follow up with another 2 hour temper after.
 
The freezer, I guess you mean the one the ice cream is kept in, will not transform the remaining austenite. Putting in the fridge won't hurt it but if you want to help it find a local source for dry ice.

RL
 
Tempering at temperatures below about -110 F, or there abouts, will transform retained austenite in high carbon steels, both simple and stainless. I started out by using dry ice, which I believe is around -110 F., and after I was able to scrap up enough bucks got a dewar for liquid nitrogen (around -320 F.). If you can find a convenient source for dry ice you would do well to use it.

RL
 
rlinger,

Actually yes. A "home freezer" in some cases can effectively transform retained austenite. In fact, sometimes, merely refridgeration (i.e. non-subzero) will do it. Its effectiveness versus dry ice and liquid nitrogen will depend upon the steel and its prior condition. Sometimes there will be zero difference between the results. Even left at room temperature, over a period of time, austenite will transform. This is a key reason industrial practices prefer to transform as much of that retained austenite as possible. So, that the part will not change shape or fuctionality in service by transforming into martensite later down the road. Plus, dry ice and liquid nitrogen act quicker in a shorter period of time, making them more economical. Freezing and refridgeration may takes days or weeks instead of hours. Time is just as important to the factor. As well as steel, prior condition and especially cooling conditions upon quench. Lastly, quite often, even the best and most intensive cryo will not give 100% transformation.

*Edited to note that, I in no way discourage the advice on dry ice or liquid nitrogen. I've used them both and had great results. Just pointing out some little known facts on cold treatments at warmer temps. :cool:
 
how can you tell if the austenite has been retained? boy this is a heated subject this is very cool thanks for the help guys!
 
Thanks Jason,

From my days of casting lead bullets, I knew I could harden them faster by dropping them in water from the mould. Or, if I wasn't going to use them right away they would harden on their own. Don't remember how long it would take. Or even put them in the freezer to speed it up.

Don't know what internal structures form in lead alloys, but very similar issues.

It also makes me wonder about the raves of the steel in old knives. Is the steel really unchanged from it's original forging? Or did time improve its knife characteristics? "the secrets of forging 300 years ago are lost. Modern technology cannot reproduce them." etc. Is it because there was a secret or because of 300 years of aging?

Steve
 
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