Heat Treating 1095 - Here is another way

BossDog

KnifeDogs.com & USAknifemaker.com Owner
Staff member
Note: this has been edited on the temper temperatures. In researching I found two different temper recipes from ASM. The original temper temperatures seemed too high. I am revising the temperatures down to reflect the second set of temperatures I found from ASM that seems to be more in line with what we see in the real world.

I am working on updating the heat treat information I have on my supply site. I thought I might as well post it here also.

Heat Treating 1095

Referencedata: ASM Book: Practical Heat Treating by Boyer
Written byTracy Mickley
www.USAknifemaker.com

1095 is a high carbon steel with .95% carbon (the 95 in1095) and is proven, good quality knife steel with good edge retention. 1095 isconsidered slightly “fussier” about heat treating than say 1080 or 5160. Thisisn’t a deal break at all and really can be mostly ignored. Follow the recipebelow and you shouldn’t have any problem.
Normalizing:Normalize by bringing to 1575F, soak for 5 minutes and allowing to cool instill air. Normalizing steel allows the crystalline structure to be reset andresets the carbides back to uniformity. Steel doesn’t like uneven structure. Ifthe carbides have gotten all bunched up and oversized from forging, the steelwon’t hold an edge as it potentially could. Bar stock from the mill probablyshouldn’t have to be Normalized, especially if it has been annealed. Materialthat has been forged could probably benefit. Basically, heat it in your forgeor oven and let it air cool. Done.
Annealing: Annealby heating to 1475F and cool at a rate no faster than 50F per hour. Generally,most guys heat to temperature in their forge as the last heat of the day, turnoff the forge and let the steel cool in the forge overnight. If you have otherwork you want done, I use a half size trash can full of vermiculite. I heat acouple large bars of scrap steel to add mass/heat. I heat the steel totemperature and put it all in the vermiculite to cool down slowing using thevermiculite as an insulator. Cooling slower in the forge works better butcooking in the vermiculite works fairly well also. Some guys use lime insteadof vermiculite.
Hardening: Heatto 1475F or past non-magnetic which is around 1425F. Generally, in a forge,this means heating it until a magnet doesn’t stick and then “just a little more”to get the extra heat into the steel past non-magnetic. A few minutes at this temperaturewill not grow grain but does allow the carbon to get “into solution”.Overheating steel into the 1550F 1600F range and beyond and soaking it willgrow grain. Simple, heat it to non-magnetic, give it another minute or so toheat a bit more, quench. You will see somewhere, a lot of places in fact, thatthe steel really needs to be cooled off at a high rate, like 1 to 2 seconds andthat is absolutely true. That doesn’t mean you only have 1 second to get fromyour heat source to your quench. Moving a blazing hot piece of steel from heatto oil is where a lot of fires get started. A guy knocks over the oil, dropsthe red hot steel into the oil and instant fire! The steel will retain heat andsurvive a few seconds in the air as you move from heat to quench. Do thissafely and be prepared for a flare up of fire and a large amount of smoke. Alwaysbe prepared for a fire.
Tempering: If youdid everything right quenching, your steel is around 66RC and fragile as glass.If you drop it now, it will shatter. You want to temper it as soon as it getsto room temperature. I have a left a piece of steel overnight untempered andfound it cracked the next day from the stress hardening puts into the steel. It’srare but it happens. Temper twice at 2 hours each allowing the steel to coolback to room temperature between cycles.

(note edited temps below from original post revised data from ASM Heat Treater Guide Practices and Procedures for Iron and Steels.)

· 400F yields approximately 58RC
· 500F yields approximately 57RC which is wheremost will want this steel.
· 600F yields approximately 52RC

Cryo Treatment: Cryotreatment, soaking steel after hardening but before tempering at temperaturesat least minus -90F (dry ice range) to minus -290F (liquid nitrogen range) foreight hours. Most high carbon steels aregenerally not cryo treated as the benefit to carbon steels is usually not assignificant as it is with the newer super stainless steels. Many people willsay a properly heat treated steel should not need any cryo treatment as it only“makes up for a poor heat treat” This sounds good but isn’t necessarily true.Cryo treatment is an industry recognized practice in heat treating and simplywouldn’t exist as an unnecessary expense if wasn’t a legitimate extension ofthe heat treat, quench and temper process. Big business doesn’t waste money onsteps on heat treating it doesn’t need to do. Having said all that, most don’tcryo treat carbon steels but you can if you want. Soak it in liquid nitrogenovernight or even a cooler full of dry ice. You will read about guys usingacetone in dry ice. Acetone is crazy flammable. Avoid it please. Use Kerosene oreven diesel fuel if you feel you need a liquid medium but just putting yourblade under a block of dry is all you need to do. Some guys do one low temperheat at at 300F to 350F sometimes called a “snap temper” to take some of thestress out of a hardened blade before cryo. This lowers the chance of crackingthe blade. I have never had one crack from cryo treating a blade afterquenching but that just means I have been lucky. Eventually I will, it is justa matter of time.
Austempering:This is a process of hardening steel into Bainite, something we knife guysgenerally don’t use. We are after Martinsite steel.
 
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Again, I question the tempering temperatures. Maybe you could check with some of the makers who use this steel and can check the hardness with a meter and see what they think.

Doug
 
I found another ASM publication with completely conflicting data, which is disappointing. The ASM is supposed to be the premier authority on heat treating and their data from one publication doesn't match in this case. Just another indicator that heat treating data is all over the place and two apparently conflicting points of view maybe correct.
 
Hey Boss were the 2 recipies for similar thickness stock? I use similar times and temps for heat treating and a temper at 400 seems to be a little harder than 58 as it is harder to sharpen, keeps a great edge tho. 450 gives me an edge that lasts and is a little easier to sharpen.
 
Material thickness wasn't defined in these recipes but the ASM tends to use the exterior RC hardness and in some of their data goes into softer RC in the interior of the material depending on thickness.

I suspect the real heat treat recipe is somewhere between this one and the first one I edited out. I have always used 400F and left it at that.
 
Hey boss I have a build coming up that involves 1095 and clay coating to bring the hamon out and I have been told to lower the austenizing temp to 1450 with a 10 min soak then quench. Any suggestions on the heat treating process as it partains to bringing out a hamon?
 
If you can spot decalesence in the steel as you heat it it will be easier to do a long(ish) soak on the 1095. Watch for the shadow to pass over the steel as it heats up and try to the steel at that brightness for the 10 minutes. I actually learned to spot the "shadow" as the steel cooled down, which is known as recalesence. Get the steel hot and glowing (and non-magnetic) then take it out of the forge and watch it. You will see the the color dull, starting in the thinner parts, then it will brighten slightly before changing again. This is from the heat energy in the steel being used to change the phase of the iron crystal matrix in the steel instead of being used to produce light. It looks the same as the steel gets hot, it's just a little harder to spot. If you can hold the steel just past the point where this dullness disappears as the steel is heated up you can soak it long enough for the 1095 to release enough carbon into solution to form martensite without dissolving so much that it will increase the retained austinite or overheat the steel and cause grain growth.

Doug
 
Hey boss I have a build coming up that involves 1095 and clay coating to bring the hamon out and I have been told to lower the austenizing temp to 1450 with a 10 min soak then quench. Any suggestions on the heat treating process as it partains to bringing out a hamon?

I've done two just two clay coated hamons on 1095. I didn't do anything different than I would have otherwise. I cracked the first one testing hardness, the second I didn't fiddle with and the hamon came out just fine.
 
Concerning tempering temps for 1095, I use the information found here. I give mine a through (multiple) tempering at 450-500f. I'm using parks50, probably not getting a full-length soak (2-5 minutes), and judging temperature by decalescence.
 
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It's always fascinating to read about the professed absolutes of a task that is rife with ambiguity, mutually exclusive "data" and sentences that begin with "studies show". Thank you for bringing another example of heat treating ambiguity to our attention.
 
1095 is one of my favorites.

one of these days Im going to get a kiln so I can try all these other recipies! right now I just have a propane forge, with no thermothingy to tell me what the temp is. but here is my ht.

grind or forge

then normalize twice

anneal twice in preheated wood ash {i heat up a couple sections of leaf springs, put them in the ash 30 mins or so before the blades, and then put the blades in the ash above the springs}

heat to nonmagnetic, then "just a bit higher" i look for the steel to lose the shadows and the color to even out.

edge quench in 120-130 canola, then edge quench again about 5 minutes later. I usually do batches of 2-4 blades at a time, so I quench all of them once, and then go back and quench them all again, keeping an eye on the temp of the oil

temper at about 375 for 3 hours, cool, then 2 hours, then cool then 2 more hours

test for edge flex, and cut on 1/2" manilla rope. with this ht, I set my minimum at 130-150 cuts before the edge loses its ability to shave hair from my arm.


When I came up with the tempering temp: I have a toaster for my tempering oven, I set 2 thermometers on lower and one on the rack that holds the knives. my temp knob is way off, so I started at 350 on the lower one, and the upper one is colder, tested for edge flex and it chipped. I went up in temp until the edge no longer chipped, then noted the temps on the thermometers.

I have a thought as to why everyone has different temps for tempering. I think it may be the differences is ovens. not just in the control knobs, but also that different ovens are insulated and regulated better than others. my tempering temp may be higher than what I think it is due to the fluctuation in the oven. I have watched it before, to see how much the temp guage varies, but only for a few minutes, {till I was bored to death}. my oven may fluctuate a few degrees higher than what my guages show. my last toaster was off also, and my kitchen oven isnt very accurate according to the temp setting either. so I just use the guages as a way to make sure that the oven is set to the same range as what my edge flex showed to be the optimum temper.

anyways, that is my ht for 1095 in my basic and very non-scientific shop
 
I think you may be on to something with the differences in ovens. There's no way to tell if one person's 375 is another's or not, without actually testing it. Most HT specs give a range for this reason. If my Goodwill toaster oven is off by 25-50 degrees, I won't cry too much, but if my $1500 Paragon is off by more than 5% that's a problem. Your double checking approach is a good step.
 
setting the oven by the flex test is the most accurate way Ive been able to get consitent results. the flex test doesnt change much except from summer to winter.

I still would like to try one of those fancy ovens and do some comparisons between my ht, and the soak time ht's. and see if there is any differences. of course a rockwell machine would be nice also, but for now its just the brass rod test, rope cutting tests, breaking sample blades, and the steel itself to guide me.
 
I think that you are progressively getting more carbon into solution with the double quench. I could be the reason behind a tempering temperature that is about 50° lower than what most many makers would use but your idea about problems with the toaster oven is hardly without merit. Getting that many cuts on the rope argues against not getting the edge hard enough. Admittedly, I don't have much faith in the flex test. I much rather try to cut through some soft iron wire or a 1/16" brass rod. It would be nice to see what kind of a hardness result you could get with a hardness tester but ones that will accurately measure something as thin as a knife blade are on the expensive side.

Doug
 
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The only harndness tester i have are files, regular nicholson ones, and a 8" black diamond mill file wont cut the hardened portion of the blade, even after tempering. Yet my test knives normally flex to 70 degrees or more before the edge cracks or the blade breaks depending on the depth of the quench.

My thermometers read 400 under the rack and 350 on the rack that the blades sit on. So i guess the knives would be at 375. Or the thermometers could be off, or the toaster might cycle higher during the two hour cycles, ive never switched them around to see if they read the same. I dont know much about calibrating thermometers, but ive heard that they all vary a bit. But i think thats where the biggest difference is between ht recipies is. I know no test is absolute, including the brass rod test, but its the best ive found. In addition to destructive and cut testing.
 
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