How the hell do you heat treat 1095?!

Status
Not open for further replies.
B

bkshafer

Joined
Jul 31, 2004
Messages
54
Seeing how the question of heat treating 1095 was just being discussed, I'd thought I'd bring back this thread from some time ago.

Brian


Subject says it all. I ordered 1095 from Admiral steel. I have been looking for heat treating info but it seems that there are as many methods as there are makers. Can you help a fellow out?

Thanks
starch
 
Last edited:
1)I normalize three times then soak in vermiculite.

2) Do the profile grinds

3) Heat the edge to non magnetic

4) Quench in oil

5) Temper at @425F in an oven three times for one hour letting it cool to room temp between heats

Some guys are freezing the blade between the quench and the temper in a freezer. I havent ever dont that but who know??
 
Heat to 1500f and quench in a light oil(transmission fluid is ok for baades up to 3/16" thick) temper far an hour at 400f.
I have done almost a thousand blades this way with no trouble.
Del
 
heat treated for cutting ability or toughness.

I start by one or 2 normalizing cycles then heat to non-mag give it a few seconds soak quench in warmed oil (around 120 F). Check with a file. (you only have around 1 second to cool to around 600) Then I stick it in a freezer over night. (1095 has enough retained austenite to make it worthwhile.) For tough (chopping etc) temper 475-500 F. An interesting thing from the chart is 325 F temper gives a peak in toughness without the loss of hardness of a higher temper.
 
Prior to heat treating normalize the blade 3 times.Use a pyrometer and run your heat treating kiln or forge at 1580 degrees.Place your clay coated or uncoated blade in the heat and let it stabilize at temp for 5 minutes.Quickly quench your blade because as Son of bluegrass said ,you need to reduce the temp asap.I personally like marquenching.You quench in oil or salt heated to 400-450 degrees depending on the steel and allow the blade to stabilize at temp.Then take it out and fix any warpage until the blade is about 250f.Then back in the oil/salt for an hour then fix any other warpage and back in for another hour,out again to check final straightness and back in for one last hour.I learned this procees from reading some of Kevin Cashins previous posts and it works awsomely.I also coat my blades with borax before adding the clay,a trick i got from Fred Rowe.:)
 
All good advise.The important thing about 1095 is the sharp nose on the cooling curve.You have to get it from critical temp to hardened state very fast.Have everything in place,practice how you will quench it a few dry runs,and then do it for real.If the file test after quench is not satisfactory,re-heat and quench again.Normalizing before hardening is very important with 1095.Temper immediately (soon) after quench.
 
Sometimes I can use enough techno-babble that it is easy to misinterpret it so for safety's sake I thought I would share how I do 1095, I have been working with it longer than any other alloy and have adjusted my treatments over the years to get it as close to optimum as I can. McAhron, you seem to have it but there are few points that I am not so sure on.

I start out by normalizing after the forging. I always do my first normalizing at the range that industry does (around 1600F) in order to get everything into solution and get the grains all the same size, what size that is does not matter on this heat, as long as it is uniform so the most important thing in any normalizing heat is to heat as evenly as possible and cool as evenly as possible. Then the blade is allowed to air cool until it is entirely black, this will work with 1095 for grain refinement as a new structure will be formed when you get pearlite at around 1000F. With richer alloys that have a slower curve one needs to wait until you get to around 700-800F before the reheat in order to get grain refinement. This is all because you have to recrystalize in order to get grain refinement and if you don't form something other than austenite all you are doing is reheating the same grains again and again, but it also is not necessary to go to room temp, martensite will refine grain quicker but it will also be riskier (going from 1600F to a quench can be risky with 1095). I have some images that I posted on one of the forums that clearly show what I am describing here and how it changes with alloying.

The subsequent normalizing heats are done at lower temps in order to bring that grain size down, 3 times is usually enough.

The next thing is the anneal. A lamellar anneal (wood ash, vermiculate etc...) will be fine if all you need to do is grind it, but if you will be drilling, milling, or cutting a spheroidal anneal will be in order as 1095 has enough excess carbide to be quite problematic in those areas if it isn't taken out of play. For lamellar, heat to critical and stuff in the insulating material. For spheroidal, heat your kilns to 1375F. soak for at least 45 minutes and then run a program that will drop the temp. at a rate not exceeding 50 degrees/hour until you are below 900F.

:eek: Hold on! Don't panic, if all you have is a forge; you approximate this treatment by quenching the blade on the final normalization and then repeatedly heating to a dull red (never critical!).

Move on to grinding and finishing.

For final heat treat of a spheroidized blade, heat to 1500F. and soak for at least 5 minutes in order to get complete solution, this is critical. All of my observations over the years have brought me firmly to the conclusion that if one is not able to hold a hypereutectoid accurately at temp for proper soak times, 1080 or 1084 will work just as good. If one lacks the equipment to do this they may see some benefits from the some of the multiple quenching techniques that many with just forges utilize, by bringing more carbon into solution in steps. This situation is exacerbated by spheroidal anneals which require more soak times, so a trip in the vermiculite or ash may be better for the low tech soak.

For some time I had problems ever getting the spec sheet HRC numbers to match the tempering temps. 400F would be the highest I would want to go. When I got a grip on accurate soak times all of my tempering temperatures had to increase and came in line with the spec sheets quite well. If you are using a 1095 blade that was tempered at 375F and the edge isn’t chippy, you only used a portion of the available carbon, so 1080 may be better for you. If you have extra carbon that is not in play and you don’t keep it out of the grain boundaries, things will get weak.

I have seen a few numbers mentioned in this thread, but all the curves I have seen (which also correspond to my experience) show 1095 as having around .5 second to get below the pearlite nose. 1095 lacks the manganese of many of the other 10XX steels so it is about the quickest that can still fully harden. Think about that- ½” a second from the time you go into the quench to get from 1500F to around 900F, you quench needs to be the best it can be for this stuff. I have tried and tried, with all of the methods described by others, to harden 10XX in salts and it just doesn’t work. I would be happy to share the images of choppy martensite laced with fine pearlite from those attempts. So needless to say I personally don’t use low temp salt on 10xx. Park’s #50 is simply the best for this steel in my shop, but if you were to heat it to 400F, it wouldn’t cool worth a darn and would most likely ruin good #50. They make special martempering oils that can do this but I don’t work with them and regular oils heated to 400F will give you that same pesky fine pearlite as well as singed hair.

I quench into #50 heated to 130F and keep the blade moving length wise for a count of seven and then interrupt the quench, on a good day this should be about 450F… is that nonscientific enough for you;) . I put on my gloves and eyeball things straight and tweak it if I need to. I do not stop the cooling or reheat it in any way while the martensite is forming, for fear of stabilizing austenite.

As soon as the blade is cold to the touch, I get it in the tempering process. I start out at 400F and then cool it and check the hardness before bumping up the temp and doing it again. Around three cycles will be enough and I am always certain to hold the last one for one hour.

I have sound reasons for all of my techniques and would be happy to share if folks want to know but I have run out of room in this highly verbose post.
 
Great post Kevin. I’m taking notes.:D :D

If that doesn’t answer the question it can’t be answered.

Joe
 
I really love the title of this thread :p

kevin, that was very informative, I learn something new every time I read one of your posts. Thank you :thumbup:
 
Most excellent, Kevin. Thank you! Printed that one out to put in the notebook. :)
 
Very cool Kevin.I'll drop the temp to 1500f.I use high temp oils(expensive)not salts.Thanks for the clearifications,you are a wealth of knowledge.:)
 
Thank you for all the kind words, it is nice to have long strings of ones babbling appreciated. I think it is worth my effort to take the time for this since it is a topic that is grossly misunderstood in our business and has lead to many of the seeming contradictions we have out there.

As I mentioned in my previous post, the higher above .83% carbon you get, the more critical soak times will become in getting the most out of that steel. And when you add carbide forming elements like chrome, vanadium, tungsten etc… it becomes exponentially more important.

While it is true that Heat treating books and manuals recommend soak times for thickness on the order of inches, if your temperature is under control it simply doesn’t matter, while longer soaks may not be necessary they are not detrimental in terms of grain growth so long as the grain coarsening temp is not exceeded. It is worth mentioning that the Heat Treaters guide shows hardening temp for 1095 and O1 as 1475f. but I have done just fine with 1500F for quite some time, so one can exceed recommended temps by at least 25 degrees and not grow grains;).

Grain growth is highly feared (for good reason if one ever encounters it), but is also highly overblown and misunderstood. 1095 and other hypereutectoids have a built in resistance to it, and steels with other elements (O1 being one that I also work with) have even more of that protection- carbides.

Austenite grains will reform and then equalize while taking time to dissolve the available material for solution. A carbide in the middle of this process will stabilize the grain boundary and retard its growth. Look at sink full of dishes to be washed, the bubbles in the open areas of water will be large and continually combining to become larger, but around the handle of your coffee mug there will be a ring of very fine bubbles that cannot grow due to the stabilizing effects of something unmoving in the water. Carbides stabilize grain boundaries and the more tenacious ones require much higher heat to break down and get out of the way.

Because of this, if one has control of the heat and can keep it below the temp at which the grain boundaries can move, you can literally soak a steel for HOURS with no growth of the grains. But exceed the maximum temp and things will get out of control very quickly though. This is why the bladesmith must learn to recognize temperature above all else. All the magic hammer blows and fancy quenches are worthless if one does not have control over the temperatures. If one has developed the skills to recognize proper heat, the greatest threat one needs to look out for is scaling and decarb. If you are getting that splotchy look on your blade surface- back off the air draft or whatever else you need to adjust your atmosphere. In coal I always make a firebrick tunnel over the fire until I have blue flames coming our either end. If I maintain this atmosphere correctly I can produce a piece as clean as if it came out of the salts.

I feel this attitude of softer as-quenched steel in among knifemakers is tragic. The rule of thumb that I follow is to get the steel as martensitic as one can and then adjust it in the tempering, all opinion aside this will result in the strongest blade. I am sure mete will be happy to tell you how much industry prefers homogenous structure over mixed ones, and for good reason. Be it a slitter or forming die, the steel doesn’t give a rip what shape it is as long as it is heat treated properly for the job, and there are conditions that will apply regardless. Folks with much better equipment than any of us have figured this out and recorded it for us to use, as long as I tried to prove them wrong with a coal fire and a O/A torch none of their numbers made sense, but when I started locking in the heat and the times it all worked after all, but reinventing the wheel is one of our favorite hobbies. :o
 
By the way, I thought it may be necessarry to explain the differences in my heat treating for 1095 and say O1 or another oil hardening steel. I use the interrupted quench on the 1095 because of that critical 1/2 second thing. This allows me to cool things as fast as possible from 1500F to 450F but then I stop the rapid cooling by removing it from the oil and letting things equalize a bit (it won't equalize as well as if it was actually martempered/marquenched but it is a workable substitute) before forming martensite in the air cool. Things should be hardening quite well within a few minutes.

When I harden Oil hardening steels, I use the low temp salts at around 425F. since the curve is often at 5 seconds or better they work very well. I will cool to the temp of the salts and then hold things there until the entire cross section is the same temp. before removing it and allowing it to air cool. This all but eliminates distortion due to uneven expansion when martensite forms. Some work off from the false idea that blades contract when hardening, resulting in distortion, this is the exact opposite of what actually happens.

Different mediums for different alloys, It would be nice if there was a "one size fits all" heat treat , but there is not:(
 
Thanks for the wonderful information. If I don't get it right now I think I should have a yard sale, get rid of all my tools and take up knitting. :D
 
Kevin,

Would the following be a fair summary for someone interested in heat-treating 1095 who has a propane forge (with a 3" square tube inside it, for HT), a digital pryometer and good ability monitoring and maintaining the temp?



After forging:
- Normalize (evenly heated) at 1600F (air cool to black)
- Again at 1550F
- Again at 1500F
- Anneal by first quenching then bringing up to sub-critical (dull red) 3 times

After grinding
- Hold at 1500 for 5 min.
-Quench in Parks #50at 130F for a count of seven
- Pull out & straighten (as needed)
- Let air cool
- Temper at 400F for two hours, then cool.
- Two more hours, then cool. One hour, then cool.




I noticed there is no normalizing during the HT process...just a soak....can you explain?
 
Kevin,

I have a couple questions:

1) after normalizing, can you spheroidize 1095 (or O1) by holding at 1200 for 2 hrs or so, or is that just a stress relief?

2) Any benefit for 1095 (or O1) to "snap temper" at , say, 300-325 after the quench, then soak in Liquid N2, then temper as usual? I would guess there is not too much retained austenite in 1095, but if there were it might help. O1 probably has a higher chance of retained austenite - again, is the "cryo" at all worth it or just excess?

Bill
 
meant to add, I am NOT trying to stir the "cryo stew", just asking about retained austenite!!

Bill
 
I'll take the tempering first...

Daniel, I should probably also explain that my tempering times may differ from others due to the fact that I temper in the salts. That is the other reason why bladesmiths have a harder time making heads or tails about the industry specs.- we all have different equipment. The guys who wrote the books are all pretty much on the same page of it as process and equipment goes, but we bladesmiths may have a torch, a forge, or even salts bath; our tempering could be done in a toaster oven or an industrial type with atmosphere control.

With that said I can say that I have found significant changes in HRC after just 30 minutes in the salts. Salts are very conductive and will heat things very quickly. 30 minutes in an oven would barely be enough to get some of the smaller portions of the blade warm.

My first tempers are short ones for the purpose of walking the tempering into the HRC I desire. So I may only go to 400F for 30 minutes and then check the hardness to make sure I am on track before bumping up the temperature. If you do not bump up the temp there will be no gains at this low range unless you go to the order of days.

If one has a hardness tester I highly recommend doing it this way and keeping copious notes on each batch. Then eventually one could zero in on the desired hardness much quicker. I started doing it this way so that I could develop a curve that would allow me to go right to a given temp for a given HRC and do it once for two hours and be done but...

In the process of studying this I noticed effects happening from multiple tempering and cooling cycles. After the first temper I could get as much a 2 points variation across a piece in Rockwell C, but after the second tempering I noticed only 1 point, and by the third it was 1/2 point or less. This led me to stick with the multiple tempering regimens for reasons other than walking in my HRC. Also it is possible to get a higher toughness without lowering the Rockwell by using more time at temp in tempering (I believe Krause touches on this effect in "Principles of Heat Treatment of Steel", if not I cannot remember exactly in which tome I first encountered it, but I have noticed a difference myself).

Anyhow- if you are working in an oven you may want to make the first two cycles at least an hour with the last one being the serious temper at 2 hours.
 
Status
Not open for further replies.
Back
Top