1080 Heat Treating - School of Hard Knots

[Dennis Paish]

Greetings,
I have been searching Heat Treating 1080 on the web and found more then one method. What is the critical temp, how long to soak it at that temp, quench type and then how long do you temper and for what temperature?

I HT's a batch of blades (which are now completed blades) some time ago. I dipped the blades into the salt pot until the edge was past magnetic. Then put it back for 30 seconds and then edge quenched.

I guess a good rule of thumb is to do the brass rod test BEFORE you put on handles, guards and sheaths. I tempered them at 400 degrees 3 times for 30 min each.

To my surprise many of the edges are VERY Soft. The last one I tested (before the feeling of failure started) was hard at the tip but half way down the blade edge it gets softer towards the guard.

I guess I will have to start over and knock off some handles. But first I want to verify the HT process. Then I want to do a test block of 1080 and HT. Then I will use my Rockwell tester and test, then start tempering at 350 and take another Rockwell reading. I will increase my temp until I get the desired hardness. Last question....What hardness should I be shooting for?

I guess I wasted a couple 50 to 100 hours to the 'School of Hard Knots' of learning. I hope to learn from this mistake and start making this journey of knife making as relaxing and look for a quality output verses quantity in the future.

Thanks for all you replies in advance....


Dennis

[Kostoglotov]

Hate to ask but you sure it was 1080?

[Doug Lester]

Let's start out assuming that you do have 1080. First of all what was the temperature of your salt pot? You need to measure it. I don't know if you can get a thermometer that will handle that high of a temperature but but you can get a pyrometer from Amazon for about $40. I don't have the link that I saw earlier today but you should be able to find it if you look. Get a length of stailess steel tubing that the thermocouple will fit it and crip one end closed to protect it from the salts. I would get the pot up to 1500 degrees being that 1080 is essentially a eutectic steel (the austinite is saturated but not supersaturated with carbon). I would give it about a minute to heat all the way through then go immediately to the quenchant. Most 1080 has enough manganese in it to quench in oil but it is shallow hardening.

The tempering sounds about right but I would give it 2 or 3 two hour cycles. Eighty points of carbon is right about where the carbon content starts building up retained austinite but you may well be alright with 2 cycles.

I think the most probable problems here is that you did not fully austinize the steel (get it hot enough). The next most likely, not knowing any more than what you've said, is that you let it cool too much before you got it into the quenchant. After that, there's the possibility that it's not 1080; even reputable wear houses get things mixed up sometimes.

Don't feel like the Lone Ranger when it comes to discovering that it's best to test the edge before you put a handle on it. Nothing to do but take the knife apart and repeat the heat treatment. Buy the way, the best way to do the brass rod test is to put a rough edge on the blade and see if you can drive the edge into the rod by striking the spine with a mallet. It should cut into the rod without doing any more than dulling the edge. If it indents then something is wrong. If the edges of the indentation are curled then the edge is too soft. If they are brittle and chipped looking then you have it too hard.

You can correlate that result with the hardness tester. Testing the steel right out of the quench can be thrown off with any scale on the blade. 350 degrees is a little low to start tempering at. That will do little besides relieve stress in the steel. I would start out at 375 and then move up to 400 if you need to. You can take the fire scale off by soaking in white vinegar overnight and scrubbing it with a wire brush. If you want to test the hardness out of the quench then you will need to clean off a spot with sand paper or you could give it a 2 hour cycle at 300-325 degrees to relieve stress in the steel then use the vinegar soak to remove the scale before testing.

Doug

[Ed Caffrey]

It's all part of "the game" Dennis.....we've all been there. If I've learned anything at all during all these years of Bladesmithing, it's that nothing comes quick or easy. For me, failure is always a catalyst...heck, it took me 6 months of "failures" before I figured out how to San-Mai mosaic damascus and 416, and that's just the most recent one!

One of the things that I keep trying to tell folks is that "knowledge" (reading, and knowing the numbers) simply cannot "get you there" when it comes to Bladesmithing......of course the knowledge is important, but it's the experience that teaches you how to use the knowledge.

The best advice I can offer a person when starting out, is to build ONE KNIFE AT A TIME....that way you can concentrate on each step of the process, and if something does go "wrong" it's much easier to pinpoint the problem(s), and not make the error in the future. It's very easy to make mistakes when you're dealing with a "batch" of blades.

I guess a good rule of thumb is to do the brass rod test BEFORE you put on handles, guards and sheaths.

BINGO! Every blade that I build gets exactly that.

Don't fret it too much. Sometimes when we makes mistakes of that nature, it serves us well in that we are very careful not to make those same mistakes again.

[Dennis Paish]

Thanks everyone for your reply.

Yes I am sure it is 1080.

We HT them in a salt pot and used a PID controller to monitor the temp (1500)

Maybe I was not fast enough getting them into the quench. Maybe I should of had them in the salt longer to HT more of the 'meat' of the blade, not just the edge.

Still BLUE over it all!

Dennis

[Ed Tipton]

Dennis....One of the things that I always do ....even after having quite a long history with a type of steel....is to always check the hardness with a file immediately after the quench. It only takes a couple of seconds, and if the file "skates" rather than "bites", then I know my quench was effective. If you've never done this before, then I recommend that you try a file on the blade prior to quenching it....just to get an idea of what it feels like before the quench. You should be able to tell a very distinct difference between the before and after.
Another thing to watch for is to see that the scale has been "blown" off the blade during the quench. It's a good visual indicator to check for hardness. If the blade is not clean after being withdrawn from the quench, then chances are the blade did not harden. Once you're certain it has hardened sufficiently, then clean it to where "shiney" metal shows, and get it into the tempering oven ASAP. You do this cleaning step in order to see the oxidation color from the tempering cycle.
When I do my blades, I like to temper them to about the same color as beer. That degree of hardness seem to be about right for most uses, and it can still be sharpened by hand.
1080 is very forgiving, and the heat treatment of it is about as easy as it gets...but even with 1080, things can still go wrong...and that is why we do the testing...just to be certain that each phase of the process is correct before going to the next step.
Hope this helps.

[cdent]

Hey Dennis,

It may be tougher to get a good heat treat result on a thinly ground blade. Then, it'll have taken time to get the handle off and the guard will probably need redoing too. Save time and start from scratch on the knife, and I'm sure you could get close enough to use the sheaths down the road.

You're lucky to be able to rockwell test. Admiral Steel's website says 1080ish can hit Rc 65. Maybe try to get the maximum as quenched hardness possible then temper down to where you're happy. Toss out or heavily mark those soft knives, so someone doesn't pick one up in the future and wonder.

Thanks for sharing the lesson, I don't think you wasted anything, Craig