# low tech HT friendly steels?



## inferno

I'm planning on making a knife from scratch. my tools at hand will be:
belt grinder, angle grinder, stones, paper etc

and for HT i will have a 150kw handheld propane burner, acetylene torch (very big and beefy), and then i'm investing in a thermocouple and an instrument to plug it into. for tempering i will get one of these cheap tabletop mini ovens.

I was planning on putting the blade in a steel tube and crank up the heat until i get them temps i want. 
This is not really a serious/pro or very repeatable way of HT-ing steel and i know that 

So now i would like to hear from you guys which steels you think is appropriate for this way of HT-ing. Obviously SS and tool steels are out of the question.
I know 1095 and similar will work pretty well. But in reality i want to do O1, but i'm not really sure my low tech approach will be able to keep a constant temp for the longer soak times it requires to get good.

so i found these the most interesting:
UHB 20C (1095)
UHB 15N20 - C-0,75 Si-0,3 MN-0,4 Ni-2,0
80CrV2 - C=0,85 Cr=0,6 V=0,15 Mn=0,35
UHB 26C3 - C-1,25 Si-0,25 MN-0,4 Cr-0,3
Uddeholm Arne (O1)
100Cr6 (only round stock) approx C 1,0 Si 0,25 Mn 0,3 Cr 1,5 Ni ≤ 0,4
90MnCrV8 (O2) - C 0.85-0.95% Si-0.1-0.4% Mn-1.8-2.2% Cr-0.2-0.5% V-0.05-0.2%
Böhler K510, 115CrV3 (only round stock) C 1,18% Si 0,25% Mn 0,30% Cr 0,70% V 0,10%.

Which one of these is most friendly for low tech HH-ing would you guys guess (except for the 1095 of course)?
I'm guessing the lower they are alloyed the more optimal (well) i will be able to get the HT. I wonder what i can get away with here. should i forget O1 completely?


----------



## Caleb Cox

I suggest "fail fast and fail cheap" with standard 1095 bar stock very close to the final tang/spine thickness you desire. Make a few dogs while you build skills and tweak your HT setup. Another benefit besides cost is the massive amount of data on this steel, which will help your research and troubleshooting efforts. When you then try other steels you will probably find one that you like the working properties of, and your comfort/skill level is more important than steel chemistry.


----------



## RDalman

Yea, go for 80crv2 or 15n20. try to hit 850 no soak time, right to oil quench in 60c warmed canola (willys eldorado rapsolja prima billig lösning)
temper low and long, maybe in the 150-170c 2x2h. That should make a impressive blade even with those simpler steels. Have fun, use some dustmask.


----------



## milkbaby

Agree with Robin, 15N20 or 80CRV2. You can get away with a shorter soak on those whereas 1095 will do better with longer soak due to the extra carbon, as well as 1095 needs a very fast quenchant (water, brine, or fast engineered quenchant) something not practical by backyard heat treat. 15N20 and 80CrV2 should be very close to eutectoid without a lot of alloying elements to distribute and do okay without a longer soak, they also do not need as fast a quenchant, therefore warm canola oil works well. You can normalize then thermal cycle down the steel to refine the grain before the hardening step, and supposedly the V in 80CRV2 will help pin the grain boundaries to keep the grain from growing large quickly upon overheating which can easily happen near the tip in backyard heating situations. 1080/1084 is also amenable to backyard HT, though I'm not sure how easy to find where you live.

Google it, but basically I cycle like this: Normalize ~1600F (a shade or two above non-magnetic), air cool to black. Thermal cycle: ~1500F (half a shade or so above non-magnetic), air cool to black, ~1400F just below non-magnetic, air cool to black. Then you can go through your hardening heat treat.

You may want to invest in some soft refractory firebrick or other type of refractory insulation instead of trying to HT directly in a steel tube by itself. Don't use hard firebrick as it's not refractory and will just be a heat sink.

Some people are happy with their backyard HT of O1, but I doubt they get the performance out of it that very good HT can get. In that case, you just waste money by paying more for O1 over the cost of 15N20 or 80CRV2.


----------



## inferno

RDalman said:


> Yea, go for 80crv2 or 15n20. try to hit 850 no soak time, right to oil quench in 60c warmed canola (willys eldorado rapsolja prima billig lösning)
> temper low and long, maybe in the 150-170c 2x2h. That should make a impressive blade even with those simpler steels. Have fun, use some dustmask.



cool. 80crv2 and 15n20 it is then.
we have motor oil and hydraulic oils at work. will these work too?


----------



## inferno

milkbaby said:


> Google it, but basically I cycle like this: Normalize ~1600F (a shade or two above non-magnetic), air cool to black. Thermal cycle: ~1500F (half a shade or so above non-magnetic), air cool to black, ~1400F just below non-magnetic, air cool to black. Then you can go through your hardening heat treat.



are these steps necessary? 
are these for grain refinement or similar? what is the goal with these steps?

I'm thinking that after rough grinding i will have to do some type of stress relief (i'm guessing there will be some soak time here) and then cool to room temp.
then straight to austenitizing, or?

I read that one can do a double quench for grain refinement if needed. basically harden it twice in a row. But will this be needed?


----------



## milkbaby

The normalizing will result in stress relief. Basically, it helps get everything (carbon, alloying elements) into solution and redistributed which. A further issue is that the normalizing heat can be high enough heat to grow the grain size, so then you thermal cycle with descending heats to refine the grain.

I believe if you have steel that is supplied in coarse spheroidal state and you simply cut and grind, then you can just go directly to hardening HT (austenitizing). Robin or Kippington can chime in and correct me if wrong. Very fine spheroidal will have issues with lower hardenability, so if supplied in that state, you'll probably want to normalize to bring it back to a state that has higher hardenability.

Yes, you can double or triple quench and there is some advantage to that tho TBH I'm not sure if refining the grain is one of them. It should be on Larrin Thomas' website knifesteelnerds.com and he may have wrote about it here on KKF or Bladeforums bladesmith/shop talk subforum. I just do: normalization, thermal cycling with descending heats, austenitization, quench (just once on the austenization/quench). Technically each time the steel is heated above the austenitizing temp you're austenitizing it, but you get the jist...


----------



## RDalman

Yea go right for hardening with your setup. The motor oil will make a LOT of really nasty (cancerogen) smoke, but probably work. For a chef knife you want a big amount, up towards 10 l. Be wary of the risk for oil setting on fire, so have a lid handy. A electric grill lighter if you have one is practical for preheatingthe oil. Clamp the blade between a couple of flat thicker pieces during tempering for straightening if you need.


----------



## RDalman

Also on steel, since you mentioned arne as O1. You also have groundflatstock in the uk, they have really wide selection of steel, for only a pretty small premium being flat ground.


----------



## inferno

Allright I ordered some Thyssenkrupp 80crv2, 15n20 and then some Böhler O1. Should be arriving tomorrow i think. 

Today I have been looking at thermocouples. Been reading a bit on BF. And it appears many think 3mm is a good diameter.
I have also noticed that you should not put the probe in the flame. Because then the TC will not last very long.

So I was thinking about drilling a hole in my 150mm dia pipe and then welding in a stainless tube that reaches in to the center of the pipe. The end inside the pipe will be closed.
Then the TC will not be subjected to the open flame. Will this work? Is there any reason for this not to work?


----------



## inferno

I recieved my steel today. 

started working a little on the pipe "forge". basically i cut up a pipe we had laying around and then selected a few other parts i will need to make a stand for it. tomorrow i will weld it up.

also ordered a temp meter (amprobe) and 3 thermocouples. 1 fluke with 220mm probe tip and 2 longer ones (no plastic handles on these) from another company since i think i might actually melt the handle on the fluke depending on how toasty this actually gets. but it will be useful for other things.


----------



## Caleb Cox

Awesome! Keep us posted and work safe!


----------



## inferno

safety is my middle name


----------



## milkbaby

Have fun! It seems like your Tc plan is okay, but worse comes to worse you just kill the probe /shrug


----------



## inferno

I almost finished the forge today. took me about 4,5h and 1h, at least, was simply testing if it would work at all.
all material was scrap material i found at work. you can see the donor pipe there in the corner of forge1.jpg 

i'm basically commenting on the pics, and they are labelled forge1-8.

so first i had to find out if this would work at all. and it looked like it would. i'm just blasting the burner right through the pipe at full blast. the part inside got very light bright orange, almost yellow/white but not pure white. But i only ran it for about 5 minutes the first time.

after that test run of the pipe the actual pipe was 650C lol. measured this with an IR thermometer. but since i dont know the emissivity of that pipe it could be 100C higher or lower i guess. if i positioned my hand about 10cm away from it i could only hold it there for about 5-6 seconds before it got too hot for me. but i'm very used to hot stuff. since i work with the burner almost daily. ymmv i guess.

burner has a 60 or 65mm cup, all titanium.

i welded a long flat bar under the pipe since i had a feeling i would need to attach some accessories when i start using it. i just dont know what yet. but i know there will be something.

finished product can be either axial or radial fed. when i welded on the radial pipe i noticed it was snug with the cup, the exact same diameter. it made sense to build it like this. but if i pushed the cup in there so there was no gap between cup and radial feed pipe then the forge would not work. then it was just a regular flame coming out of the ends. but if i had the burner outside the radial pipe it would work. i think i starved it for oxygen. so then i had to weld on a bigger radial pipe on the first one so there would be some kind of air mix going in. then i got some juice out of it!
you live and learn.

welded in some SS tubes that i welded shut. thats where the thermocouple will reside.

welded a stand for it. the plate was not "safe" enough for me so i welded some extra long flats on the under the plate. also if you weld something onto a plate in the middle it will warp. this took care of both those problems.
it takes quite a lot for this thing to fall over now i can tell you that. not gonna happen.

another angle of the whole forge, you can see some welding marks on there. the crap esab electrodes simply did not want to start on the pipe/SS tubes interface. I prefer elga electrodes like 1000 times more than esabs crap i can tell you that.

yeah thats pretty much it.


----------



## ian

Sweet! Nice setup for an inferno.

I’ll be watching this thread—seeing people with bare bones setups is inspiring.


----------



## inferno

it sure was an inferno around that pipe today  

funny thing was this: i think it heated the part inside the pipe better if i ran on half blast kinda. 

if i run the burner open air. the yellow part (the hottest part) of the flame is about 70-80cm (30 inch) from the cup and the flame is about 10cm (4 inch) diameter. and up to that distance its a blue flame. and the blue flame is colder. 
so basically when i tested the pipe the actual yellow part of the flame was outside the pipe on the other side. unless i turned it down to half blast. 

this burner can heat about 3-400kg of steel to over 100C in about 1,5-2 minutes. and thats what i usually use it for. many things i work with is press fit when cold so you have to cool one part and heat one and then you can assemble them. and have time to adjust angles/depths and such. not a lot of time, but usually 10-20 seconds at least.


----------



## inferno

hey guys i thought i'd update the thread to let you know how its going.

I did some more testing with the mighty hell pipe of propane power and it pretty much gets too hot during use to actally use it. the ir radiation during use is really really powerful and i have to use it outside. And on top of that it kinda shoots a flame 1,5m long out of the front  so its kinda hard to see whats going on inside the pipe since you can't really stand in front of it.

Also the big burner don't really do low power very good. below 50% or so the flame is not really suited to what i want to do with it.

So i caved in and bought some fire bricks. the hard variety. which i have read you shouldn't use since they dont isolate. they still have only 1W/m*K thermal conductivity instead of the steel pipes 30-80W/m*K or whatever it now might have. the soft fire bricks are 0,1 but i could not find those here. i also bought some chamotte clay bricks. 

-------------------

i hardened my first blade today!! 
i used 15n20. its a 180mm santoku. a beefy one. dont know if i will change the profile or keep it as it is.
i decieded to just grind out the tang and leave the rest of the blade like a nakiri, no bevels no nothing, i figured it would be easier for me to get an even heat if i left it this way during HT.

i was intending to do this yesterday but we had no discarded oil since it goes into an external underground tank usually. but today i got 60l of "compressor oil" with motor oil in it from a machine someone serviced. compressor oil is a hydraulic oil that has a much higher flame point. so this is now "infernos hardening oil" 

I heated this up to 90deg C but apparently it cooled down to 60C before i got my blade inside it. 

I built a little house of the bricks and put the burner in sideways. and 2 thermocouples (these were only of limited use i noticed).
set the burner to maybe 40% or so. and immediately i noticed there would be some hot spots in the forge because the bricks started glowing orange there pretty quickly. after a few minutes i decieded to put my blade there to get some action out the steel.

got the blade to dull orange, trying to get the whole blade to this color and then checked it with a magnet. maybe 50% was non magnetic. then i put in the flame for a bit longer to a brighter color and checked again. all non magnetic. but it very quickly turned magnetic out of the forge. so i decieded i needed to go hotter still for this to work. then i quenched it in the oil. tested with a bahco file and it skidded, it worked!! but i became unsure if i managed to get the whole blade up to correct temp, so i put the blade inside again and went even hotter maybe 1-1,5 shades and made 100% sure it was the same color all over. now this only took 1 minute to get up to temp from room temp. now when i knew how to do it. quenched it once again. and now the files skidded even better i thought. so it was a double quench.

after getting to room temp i put the blade in my preheated tabletop oven. 160-165 degC for 1,5h. then i quenched it in water and ground the profile of the blade with an angle grinder and cooling it with compressed air to not over heat things. then on to the belt grinder to finsih the profile. and after the 1,5h 160deg temper the files still skidded on the surface. i even tested a red plastic mora to make sure i wasn't dreaming and the files bit in quite good on the 1095-ish steel (carbon moras are 59hrc or so). so i figured i did something right.

then inside the tempering over again for 30 minutes when i made ready to leave work. 

and now the blade is inside my home freezer. trying to dial in 160-165 on my home oven before i put it in. 

did some fracture testing to judge the grain size and to be honest i cant really see any grains at all. its just a matte platinum gray surface. and i have inspected maybe 100 cracked parts to judge if its warranty or a manufacturing defect, and none were this fine grained.

gonna do another 2h of 160-165deg C temper as soon as my oven stabilizes around there.

ok some pics. a rough approximation of the blade profile

and then some 100% pixel per pixel shots of the grain of the steel. it was very hard to crack it even though i cut it sligthly with an angle grinder. the grain4 pic has the best sharpness when going down to 100% since it was at the correct angle towards the lens (limited depth of field when doing "macro") and the lens image stabilization worked slightly better (i'm shooting this hand held).
and then the grain4b pic is just resized down so you can get a perspective of how small the pieces of steel is. its 3mm thick. i'm propping it up on a small hand held IR thermometer.
its my closest focus distance, mag is about 1/3 (this is quite good)

*i would like some input from the pros about the grain size. looks very good to me at least. what do you think?* but i dont usually examine knife steels.


----------



## inferno

trying to get a higher rez version of the grain4 pic in here. it may or may not work. (edit: it did not work) the pic is about 2k wide on my screen at home (offline) but now its like half or smaller even, go figure... i hope someone can still judge the grain size with it.


----------



## Caleb Cox

Awesome! Thanks for the update, it's not visibly warped or cracked so I would be very pleased if that was my first!!


----------



## inferno

the tang warped maybe 2mm (because i welded an L iron on there to manipulate it in the forge i guess) but i simply banged it straight taking it out of the tempering oven. i usually bang stuff straight without heating them at all (much much thicker parts up to 25mm or so), so it was no real problem straightening this.

no cracks!!


----------



## Kippington

The grain is fine, good stuff! I do find it strange that you (and many others) get breaks that look ragged compared to the smooth clean breaks that I get, but it probably has more to do with method of fracture than anything else.






milkbaby said:


> Yes, you can double or triple quench and there is some advantage to that tho TBH I'm not sure if refining the grain is one of them.


Yep, quenching twice can help grain size.
_"[Tempered martensite] produces the smallest and most evenly distributed carbides pinning the grain boundaries during hardening. The finest grain is attained austenitizing and quenching from this condition_." - DevinT
https://www.kitchenknifeforums.com/threads/triple-quench-worth-it.35683/#post-532695



milkbaby said:


> I believe if you have steel that is supplied in coarse spheroidal state and you simply cut and grind, then you can just go directly to hardening HT (austenitizing). Robin or Kippington can chime in and correct me if wrong. Very fine spheroidal will have issues with lower hardenability, so if supplied in that state, you'll probably want to normalize to bring it back to a state that has higher hardenability.


This sounds a little off to me. Super-fine grain size will lower hardenability, but fine spheroidal carbides shouldn't made the same difference. The main issue with coarse carbides is that they take a lot of time and heat to dissolve into solution - in other words, you need a longer soak time to get the same job done for large carbides over the fine ones.
Triple quenching reportedly has a similar effect as longer soak times, as you essentially spend three times longer at the soaking temperature... all while giving the alloying elements very little time to precipitate before getting frozen in place every time you quench.


----------



## inferno

hey kip i simply bent mine off. i did not bang them off with a hammer thats why you see those ragged edges i guess.
yours looks beautiful.

i think i have encountered a problem with my tempering.
i put in pieces of steel in my ovens and heat them up to act as heatsinks. i measured their temp with the ir thermometer inside the oven.
however if i quickly removed the blade from the oven and measured it outside, it would read 130ish instead of 165.

so i put in 3 pieces of charcoal to simulate something that would be of a known emissivity of about 0,95. and if i measure those charcoal pieces inside the oven i also get values ranging from 120 to 130C. I have a feeling the actual real temp in my oven is around 130C and not 165 as indicated on the steel. 

so what should i trust? the charcoal or the steel measurements?

And my thermocouples are at work so i can't really measure this with anything else to confirm.

I guess its not really a problem since i can just temper the blade once again at real 165 right?


----------



## Kippington

I would trust the charcoal. Steel often has an inaccurate reading due to fluctuating emissivity and reflectivity. Honestly the low to medium cost IR style thermometer guns are no good for this kind of job. I bought a decent IR gun for a couple of hundred dollars, but rarely use it now. Instead I use the thermocouple extension that can be plugged into the side of it.

It's not a bad idea to go back to basics and use tempering colours. Grind a bit off some carbon steel so it's nice and shiney and stick it in the oven. The colour will give a decent indication of whether you're over-tempering, but won't let you know if the temp is too low.





Also, conventional ovens have hot-spots, even if they're fan forced. It really gets hot where the elements/flames are, plus the top of the oven is generally hotter than the bottom. There's a lot going on, but I guess you'll get the hang of it in due time. Just try not to over-temper. You can always go higher later, but never lower without a re-quenching.


----------



## inferno

I went to work and picked up my meter and a few probes. dialing it in now.


----------



## inferno

btw anyone ground out a blade on stones??

At my job we only have this industrial belt grinder and its doing about 7,3 million m/s belt speed or so. the alternative is a flapdisc on an anglegrinder.


----------



## RDalman

inferno said:


> btw anyone ground out a blade on stones??
> 
> At my job we only have this industrial belt grinder and its doing about 7,3 million m/s belt speed or so. the alternative is a flapdisc on an anglegrinder.


You can be the first moahaha. I think you will find there's some reason to folks doing some grinding before heat treatment. You can use the industrial belt grinder if you spend some fresh belts - they don't heatup your blade as quickly. But be careful obviously.


----------



## RDalman

And grain looks good, seems your HT went well, grats


----------



## inferno

Yeah i guessed it would take an enormous amount of time doing on the stones.

btw my blade is now in the oven at 165. 2h. and before that i have done 120-130 2x2h.

would i make the blade overly soft by doing 2x2h at 165 now when i have already tempered it at 120-130 for 4h? or doesn't it really matter at all since i'm using a higher temp now?


----------



## inferno

RDalman said:


> And grain looks good, seems your HT went well, grats



thank you. it appears i did something right for once


----------



## inferno

allright. just tested with a file after 2h of 165C and the file is just barely starting to dig in, but not like a mora where it very clearly dug in.


----------



## RDalman

inferno said:


> allright. just tested with a file after 2h of 165C and the file is just barely starting to dig in, but not like a mora where it very clearly dug in.


2 cycles at 165 is actually not very important with 15n20 since you're not likely to have had any retained austenite transforming in your first temper. Below 150 is actually not considered tempering, so I wouldnt count those.


----------



## inferno

ok. should i do another 2h at 165?

any guesstimate as what hardness this would result in?


----------



## RDalman

inferno said:


> ok. should i do another 2h at 165?
> 
> any guesstimate as what hardness this would result in?


What I was trying to say is that it likely wont make a difference. As long as it doesn't get hotter, the hardness won't change.
Guesstimate is really difficult as it's not possible to know what as quenched hardness you had. But if we guess you where above 65 as quenched you should be in the 63-65 range I would say.


----------



## inferno

did some digging and found this chart. from brisa.fi
http://i.imgur.com/PdXBagK.jpg






this is measured in vickers 5kgf. seems like hv5 and 10 will result in similar values.
https://www.eng-tips.com/viewthread.cfm?qid=350805

wikipedia says all hv testing will result in the same values.
_Vickers values are generally independent of the test force: they will come out the same for 500 gf and 50 kgf, as long as the force is at least 200 gf_
https://en.wikipedia.org/wiki/Vickers_hardness_test
reference says:
_The indenter is the same for both ranges therefore Vickers hardness values are continuous over the total range of hardness for metals (typically HV100 to HV1000). With the exception of test forces below 200g, Vickers values are generally considered test force independent. In other words, if the material tested is uniform, the Vickers values will be the same if tested using a 500g force or a 50kg force. Below 200g, caution must be used when trying to compare results._
https://www.instron.us/our-company/library/test-types/hardness-test/vickers-test

i guess 165C is about 750-760HV5 on that first chart.
then i found this chart https://www.seeger-orbis.com/technology/hardness-conversion/
it says HV force more than 98N, that would be 10kgf i guess. and scrolling down to 740-760 equals 62-ish hrc.
would this be a good estimate?

i however most likely did not quench at 800C as the first chart suggests, nor did i quench in water. but maybe these 2 cancels each other out since i did a less aggressive quench but quite likely from a higher temp.


----------



## inferno

RDalman said:


> What I was trying to say is that it likely wont make a difference. As long as it doesn't get hotter, the hardness won't change.
> Guesstimate is really difficult as it's not possible to know what as quenched hardness you had. But if we guess you where above 65 as quenched you should be in the 63-65 range I would say.



ah i see. so basically i can do an _almost_ indefinite temper at (well maybe 10h if i wanted) at 165 and it wont get much softer?

so is there then any benefit from doing another temper.

the way i understand it is that i'm letting out a few carbon atoms from the martensite crystals to "release internal tension"
and that makes the steel a bit softer the more carbon that gets, i guess, diffused out.
_
but if the steel wont get any softer from another 2h tempering, have then anything inside the steel actually happened?_

but i still think i'm going to do another temper, since all data sheets for almost all steels seem to suggest dual tempers no matter what (even though RA might be low or even non existant in this steel).


----------



## inferno

anyway robin, kip and milkbaby thanks for helping out! I really appreciate it. we all have to start somewhere and make all the mistakes to learn.


----------



## inferno

ok last temper done. 
tested it with 2 different bahco files and they just barely dig in. 

wanting to quantify this, i tested my files on my yoshikane skd (d2) edge and also a kurosaki r2 (have to regrind these tomorrow) and its skating about as well on my blade as the edges of those other 2. so i'm satisfied with the results. i would have imagined that the files would not scratch the r2 and d2 at all but they did. the files must be over 60 hrc, maybe even 62 or so, i guess.


----------



## RDalman

inferno said:


> ok last temper done.
> tested it with 2 different bahco files and they just barely dig in.
> 
> wanting to quantify this, i tested my files on my yoshikane skd (d2) edge and also a kurosaki r2 (have to regrind these tomorrow) and its skating about as well on my blade as the edges of those other 2. so i'm satisfied with the results. i would have imagined that the files would not scratch the r2 and d2 at all but they did. the files must be over 60 hrc, maybe even 62 or so, i guess.



Files are probably 65. If you oil quenched 15n20 from 850 you got it maxed out (to my experience this is what it will test), 65 hrc sometimes even 66. At 150 temper many steels tend to bump 0,5-1 hrc up. Dunno if it's the case with 15n20 but I have seen it in many others. I would believe if your files just barely touches the steel now, you're in the 63-65 range. If you manage to not overheat it during grinding you should be getting a good knife.


----------



## milkbaby

Too late now but I know many others will temper 15N20 no higher than 300F or 150C. They are getting 66-67 HRc with optimized HT (lower end of austenitizing temp and short soak around 10 minutes?). Even backyard HT of 15N20 I've been very impressed with how nicely it performs.

Single temper of a simple carbon steel like 15N20 is sufficient as there probably won't be retained austenite to transform on the first temper that needs to be tempered with a second temper. Edited to add: Additional tempers are useful when you need to remove a warp; I clamp the blade overbent in the opposite direction of the warp and temper one or two hours, check, then repeat possibly with more increased overbending if it doesn't seem to be coming out. I don't bend before the first temper to avoid breaking the untempered blade.

Tempering is a time and temperature process but it takes extended time at temperature to negatively affect the hardness. Basically on the order of 24-48 hours and more from what I found in the scientific and engineering literature.


----------



## inferno

i did some grinding today. it took an insane amount of time. 3h to grind one bevel. and its not even flat yet. its slightly convex. but its the best i will get out of our horizontal shop grinder i feel without overheating the blade.

Did it with a 36 grit belt. So now i'm planning on tidying that bevel up on my stones, and flattening it. i'm down to 0,5mm thickness until i get a cutting edge on there.

I cooled the blade in water to room temp between each and every stroke/round on the grinder. i started at the heel and then went to the tip in one go, over and over. maybe 2 seconds per stroke.

i did burn my thumb about 8-10 times from the heel of the blade when i either pushed too hard or went too slow. I dont know what temps that could have generated but i got no burn marks or anything, i just felt it got so hot i needed to cool the blade immediately (i cooled the blade immediately after each round on the grinder anyway, 0,5sec from grinder to water). Tested it with a file just now and i dont think i lost much if any hardness at all compared to the rest of the blade. 

should i be worried i overheated it negatively those 10 times i got slightly burnt?

I also saw no discoloration but that doesn't really mean anything i suppose. it looks like the blade is discolored in this pic but its actually my camera reflecting of the bevel. its all shiny silver.


----------



## Kippington

Discoloration from tempering colours is a good indication of overheating. To be fair, if you temper really low you'll never see much of a colour change slightly above the tempering heat. It's more like if you find purple spots on your knife, you've really done goofed. 
Also, sometimes discolouration just turns out to be rust.

There's a neat trick I worked out thanks to studying phase changes - For me, judging heat by touch alone goes out the window above 80°C, but if you spray the knife with water to cool it down instead of submerging it all the way, you can more accurately work out how hot the steel is getting in the 80-150°C range by observing how the water interacts with the surface. It can do anything from steam softly to boil vigorously. Observing this, you can more spend more time on the grinder while knowing how fast it's heating up.


----------



## inferno

Kippington said:


> Discoloration from tempering colours is a good indication of overheating. To be fair, if you temper really low you'll never see much of a colour change slightly above the tempering heat. It's more like if you find purple spots on your knife, you've really done goofed.
> Also, sometimes discolouration just turns out to be rust.
> 
> There's a neat trick I worked out thanks to studying phase changes - For me, judging heat by touch alone goes out the window above 80°C, but if you spray the knife with water to cool it down instead of submerging it all the way, you can more accurately work out how hot the steel is getting in the 80-150°C range by observing how the water interacts with the surface. It can do anything from steam softly to boil vigorously. Observing this, you can more spend more time on the grinder while knowing how fast it's heating up.



I didn't really see water boiling off the blade at all. And I always made sure there was plenty of water on the blade (for extra cooling). But the actual air flow from the belt blew the water of the blade to some degree.


----------



## inferno

milkbaby said:


> Too late now but I know many others will temper 15N20 no higher than 300F or 150C. They are getting 66-67 HRc with optimized HT (lower end of austenitizing temp and short soak around 10 minutes?). Even backyard HT of 15N20 I've been very impressed with how nicely it performs.
> 
> Single temper of a simple carbon steel like 15N20 is sufficient as there probably won't be retained austenite to transform on the first temper that needs to be tempered with a second temper. Edited to add: Additional tempers are useful when you need to remove a warp; I clamp the blade overbent in the opposite direction of the warp and temper one or two hours, check, then repeat possibly with more increased overbending if it doesn't seem to be coming out. I don't bend before the first temper to avoid breaking the untempered blade.
> 
> Tempering is a time and temperature process but it takes extended time at temperature to negatively affect the hardness. Basically on the order of 24-48 hours and more from what I found in the scientific and engineering literature.



I probably wont be able to use the lower end aus since I can't control the temps good enough to soak it for any length of time.


----------



## inferno

Btw guys in the chart above it says quench in water. 

What do you think about this? How much more likely would I be to crack blades with water?
Its a lot less messy to work with at least.


----------



## Kippington

It's much more likey to crack in water, no doubt. It can work too.



inferno said:


> I didn't really see water boiling off the blade at all.


I think you're missing the part where I say this doesn't work if you submerge the blade. I'm betting you did this instead of spraying water on it.


----------



## inferno

i meant when i felt it got too hot for my thumb, the blade was on the belt. and i saw no water boiling off from the blade.

I just ground one pass - dunk - grind - dunk. repeat..


----------



## Kippington

Yeah it gets blown off when you're grinding, as you mention. You gotta observe it as you spray, not as you're grinding.
As the blade is heating up during grinding the water will generally steam off in the same way until it fully disappears. It acts as a heatsink.


----------



## stringer

inferno said:


> btw anyone ground out a blade on stones??
> 
> At my job we only have this industrial belt grinder and its doing about 7,3 million m/s belt speed or so. the alternative is a flapdisc on an anglegrinder.



I have ground a few on stones. It takes buckets of time. You will need to see your chiropractor more often. My fastest method so far. I have my Crystolon coarse and I keep it conditioned by lapping it with loose grit and a vitrified silicon carbide dressing stick that I found at the flea market. Usually I don't do it 100% start to finish any more because I have a belt sander. However, I'm not good enough with the belt sander not to burn edges, so I only do very rough shaping then everything by hand with stones and paper. I also do a lot of reprofiling and then having to thin. I do all of that on the crystolon too. And it also takes hours and hours sometimes. I would like to use the belt sander more, but for now that's not possible. Urban apartment knife making you know.


----------



## milkbaby

In my experience, I will typically see the color change if I burnt up the edge overheating while grinding post-HT. And it is often towards the tip since I prefer to grind from heel to tip. It should be easy to tell where you ended up overtempering as that portion of the edge will also be softer and less likely to hold a fine edge. The only solution is to carefully grind down past the soft steel, carefully avoiding overheating again.

For 15N20, don't bother with water quenching, canola oil or other vegetable oil is a fast enough quenchant but slow enough to reduce the chances of unwelcome fractures. It's possible that even classic water quenched steels in knife blade cross sections could be successfully quenched in oil if agitated enough in a large enough volume of heated veggie oil quenchant.


----------



## inferno

I went shopping today. 

I wanted to have my own HT setup at home so today i got a propane tank, 1-4 bar sievert regulator, some hoses and fittings and some ytong https://en.wikipedia.org/wiki/Autoclaved_aerated_concrete slabs. these are very low density. 

i wanted to get an older sievert promatic handle with a 40mm power burner into action. this burner is only 43kW so i feel its better suited for this than the 60mm one at work.

I also borrowed my personal angle grinder from work to shape a blade. its a 1700w bosch. its from the surgical series obviously  

this time i will be doing quite some grinding _before_ the steel is hard!

tomorrow i will go to ikea and get a SS "quench tank" and then a smaller casserolle to make waterglass in, to seal the ytong.

i will try out the 80crv2 this time. 

------------

i'm about 50% done with the 15n20 blade i think. i have now reverted to the diaflat plate for the bevel. since it makes actual flat bevels. only a few hours left


----------



## daizee

Are you still using motor oil?
Switch to Canola or Peanut oil. MUCH higher flash point and no carcinogens.
Preheat to ~135F.


----------



## inferno

no i use compressor oil. it has a high flash point. and i saw no flame when i quenched the 15n20 one.


----------



## Kippington

Actual quench oil smells terrible, like motor oil.
Rob (The.9) and I were talking about how when we pre-heat it for the quench, we can tell it's close to temp by the fumes it gives off.


----------



## daizee

inferno said:


> no i use compressor oil. it has a high flash point. and i saw no flame when i quenched the 15n20 one.



The trick is knowing what speed your oil is, or having a good idea.
Warm canola is the right speed oil for full hardness in 1084 and similar steels, not merely a convenient non-toxic option.


----------



## inferno

I dont know how much difference it really makes. In the old books they stated like "oil" at 80deg C. is the end result going to change much if using whatever oil vs some high end quenching oil? maybe. is it that important to get that extra 1hrc? i dont know. 

but to be honest i dont really care. I'm working with a torch and firebricks and a magnet. and it seems to have worked out all right on my very first try.

now if i were to invest in an evenheat or paragon then i might step up the game a bit. but then i sure as hell wouldn't be wasting my time on simple low alloy carbon steels. i would try all the SS, HSS, powders and tool grades because i have a feeling these are actually better.

But this is fun too. I just feel the oil i have does the job for the time being.


----------



## Kippington

Heating up the oil will decrease its viscosity, which in turn allows for better flow around the work-piece.
Another reason we do it is to stop the steel from reaching the martensite-finish point too quickly. Its good to cool it slowly once it gets below whatever tempering temperature you choose (hitting the martensite-start point but avoiding auto-tempering). It helps to reduce warping and cracks.


----------



## inferno

I heat up my oil. 80C is the target. the compressor oil i use is _almost _like water in viscosity. i think its the lightest weight common hydro oil with some added flammability suppressors. you cant have flames in a compressor, it kinda turns it into a bomb if you get a flame in there. since you are feeding that flame with compressed air. 

I have not read any steel books in a few years now but where is the Mf point of these low alloyed carbons? i guess above room temp. maybe even 100C. is there a general point here or is it vastly different between these low alloyed carbons?


----------



## Kippington

It depends on the alloying. L6 is kinda like 15n20 but with more stuff in it, and its Mf is about 80°C.
You just don't want to shock the hell out of the newly formed untempered martensite with a cold bath. Long blades do not like this one bit and will let you know about it.
But knowing all this, there's a limit to how high you can heat your quenchent before an increased vapor jacket starts to block the quench.
http://www.zknives.com/knives/steels/steelgraph.php?nm=15n20,L6&ni=,140&hrn=1&gm=0


----------



## inferno

cool, i see M95 is around 80C or so and if i interpret this right, its not very time sensitive around there either. basically you just have to get below the knee/bulge fast enough like with water steels. 10 seconds to 350-360c or so (maybe with some margin to stay safe). i think almost all oils will manage this though. but i might be wrong.


----------



## inferno

is the second lower bulge to the right the bainite bulge?? 

i'm thinking bainite katanas, bainite  the magic steel.
bainite nakiris.


----------



## Kippington

It's just an example. 15n20 is most likey different as it doesn't have chromium.


----------



## Kippington

inferno said:


> is the second lower bulge to the right the bainite bulge??
> 
> i'm thinking bainite katanas, bainite  the magic steel.
> bainite nakiris.


It is, yes. You'd need to hold the steel above Ms for an extended time, over a day at 250°C for lower bainite (the good stuff). You can see why we just temper martensite instead...


----------



## inferno

Kippington said:


> It's just an example. 15n20 is most likey different as it doesn't have chromium.


 yeah of course. getting real 15n20 TTTs is kinda hard. and i'm swedish. and know the tech lingo.


----------



## inferno

Kippington said:


> It is, yes. You'd need to hold the steel above Ms for an extended time, over a day at 250°C for lower bainite (the good stuff). You can see why we just temper martensite instead...



doesn't sound any non economical at all to me.


----------



## inferno

I made a new blade. This time i did it at home. with and angle grinder. then did most of the grinding after hardening at work. and now just now i took it out of the tempering oven. 
This time i used the 80crv2 steel. i did 2x1h at 165C yesterday (had to straighten it but didn't want to do it untempered). and still after this the bahco files just skidded. the grain looked just like the 15n20 one.
and it was very very hard to fracture after yesterdays temper. had to bring it to work and put it in a really heavy duty vise. 

i did a double quench this time too. and i felt it increased the hardness somewhat. and i kinda felt i had not gotten that even color in the blade before the first quench. the whole tang was not full hard for instance. so i did better the next time. i made a mental note of 850C and non magnetic is like 760C and kinda went from that.

turned out very well with my stone age gear though. 

BUT this time i could make it all at home!! 

ok lets have some pics of the new knife and the new setup. i have still not finished the first blade though.  i felt i needed to try this first.

this is my home burner. its sivert promatic. like 10 years old. with 45kw or so cup on it. new bottle and regulator and hose though. ran it at 2 bars this time but the reg goes to 4. 







my ytong waterglass coated "forge". also ica maxi quench tank. its the best. i'm sticking the burner in from the side about 1/3 in.






the blade. 80crv2. i can't weld at home so i drilled 2 holes in the tang and bolted it to a flat iron. to be able to manipulate it in the forge. you use what you have.







after first temp and after grinding at work. plus other angle. its a 50x180 edge, single bevel. perspective change a lot.


----------



## daizee

Cool! Nice work.

Two quenches is more likely to refine grain than to increase hardness, but depends on the starting state of your steel. If your steel required normalizing, then multiple heating cycles can help prepare it for hardening.

15N20 is really tough stuff, hard to fracture even at high hardness. That's why it gives such good fine edge stability.

Re: oils
Your oil will probably work fine for your purposes. Heating reduces the viscosity and improves convection. Quenching in actual water is quite harsh, and in fact "water-quenched" steels are usually done in a brine solution which reduces surfaces tension and vapor jacket formation, which would actually insulate and slow down cooling. Dunking in your dip bucket water to cool while grinding is a non-issue.

But I'll mention once again that if you use a food-oil that's known to be the right speed, you won't have to wonder how close to "right" it is, wonder if you're leaving anything on the table, and you won't be burning industrial products into the surface of your eating tools and into the air.

Can't wait to see that blade finished!


----------



## ForeverLearning

Caught up with all of this, hope you keep the updates coming. I am going to add a piece to my next heat treat so I can share the grain size, I've not looked in to that yet.


----------



## ForeverLearning

@RDalman would you say Groundflatstock is the best supplier for low volume in the UK?


----------



## RDalman

ForeverLearning said:


> @RDalman would you say Groundflatstock is the best supplier for low volume in the UK?


They're the only one I know of anyway


----------



## ForeverLearning

RDalman said:


> They're the only one I know of anyway



I used them before. Unfortunately used eBay, just checked their website and its near 1/2 the price!


----------



## inferno

ForeverLearning said:


> Caught up with all of this, hope you keep the updates coming. I am going to add a piece to my next heat treat so I can share the grain size, I've not looked in to that yet.



i have been grinding the blades on stones off and on like 10 minutes every few days. today i was grinding the back side of the 15n20 one on the glass 500. and it was just soo slow so i actually flattened my 220 shappro. and then the back side got flat in like 30 seconds. no shbit. thjis stone has to like 100 times faster than the 500 glass. 

so one back side completely done. next up is the 80crv2 one and its at most 10 minites left on that back side. then i flip them and do the fronts. maybe 2h in total there for both?

i also started a home utility sword project. you know for situations when you get "unwanted" maybe even violent middle of the night "guests", i made it mostly with an angle grinder on my lawn. 80crv2 too. 5mm. 
I also made a fixture for grinding knives with an angle grinder and welded up a pipe for quenching swords in. i have added an angle grinder to my arsenal of tool too. a blue one.


----------



## inferno

Doing some HT-ing now as we speak. tempering.

and about 1h ago i did some garden hardening too. getting an even temp in 50cm of steel is not exactly easy i found out. its about 10 times harder than a 20cm blade. at least with only 1 burner. ran it at maybe 25% capacity.
I tried to harden once but noticed the whole blade was not hard after quench, tested with a file. even though it was all non magnetic. obviously it cooled too much between the forge and the quench tank. i basically didn't get it hot enough to account for that. so i had to do it again.

cranked the burner up to 3 Bar, then adjusted the flow to my liking then pretty much ran it a bit hotter, back and forth, tested it several times with a magnet to really really make sure before it quenched it. and then it came out hard as a rock. all over this time...  this is important for a sword.

now i'm tempering it at 200deg C and this will result in something around 60hrc.

shot some pics too. first pic is what my camera think it looks like at 0 EV compensation, matrix measuring. second pic is what it kinda actually looks like, and then the tempering. some of you might notice the blade has a nice traditional kurouchi finish. they all do when quenching in oil somehow. i wonder why. i also lined the aerated concrete (light concrete) with hard firebricks this time. and that was not in any way better for getting things up to temp, since they soak up a lot of heat. but it saves the isolating light concrete blocks.


----------



## RDalman

Looks like fun


----------



## inferno

i'm having fun yes


----------



## inferno

thinking about doing 1 or 2 "mora" blades out of 15n20 to give away (but more like m eklund style. he really nails the true scandi look imo https://brisa.fi/knife-blades/eklund.html ) . would 165 or so temper be good for this you think robin? I found it incredibly hard to fracture 15n20 even at full hardness. so it must be some tough stuff.


----------



## inferno

looks like i'm in the scandi biz now  
spent about 1h at work on these allinall. 
2x 15n20 skinners. tempered at 170. i did these with acetylene at work since i can harden in about 2 minutes or so then. no need for a forge. double quench. seems to have worked out well before.
quenched in a cut open spray can filled with motor oil 

these are 60-70mm or so. working them on the stones now.


----------



## Caleb Cox

Very nice! Those Eklund blades are sweet too.


----------



## inferno

yeah lets just say he knows a thing or 2 more than i do about scandis. his blades look really racy and bad ass. 

i made these 2 mostly on a 8 inch wheel shop-grinder and i dont really know how to use the wheel well. so i just made them "close enough". and now i'm doing the rest on a shapton 220. But these are small and i can put high pressure on there so its quite speedy getting them to a usable shape.


----------



## Caleb Cox

There's definitely an art to grinding on a wheel, check out some videos of Kiku Matsuda grinding, pretty amazing how he uses the different surfaces and angles.


----------



## Kippington

That thing looks amazing! 
Keep it up!


----------



## inferno

Thanks!
I took the sword to work and welded on 10cm extra tang. this weekend its time for a handle, thinking masur. handguard will be Ti. or maybe g10.


----------



## inferno

you thought i died, didn't you..

ok now i'm getting quite close to finishing my first 2 knives. 
well a bit closer at least. 

i want to have completely flat back sides. so i'm doing this on stones. and to be honest some days i dont do anything at all.
these will be used as double bevels. and sharpened as such. they just look cooler.

i have finished flattening the back sides on the 220, and moved on to the 500 glass. gonna take them up to 12k superstone.
did some grinding on the 500 on the fronts too to judge how much work there is left. 
and i noticed there is a part on the 80crv2 one that i will never be able to grind out since i went to far with the angle grinder. its like a TF denka. so it kinda is what it is with this one. 
the 15n20 one will still be 100% perfect though. first and last one i make perfect, all in one. 

ok so here we have them. 

first the handle i'm making for the 15n20 one. i made if out of white methamphetamine and some mystery black material...  that i'm gluing together. i milled out the meth for the tang.
then we have the blades in their current state. i think i'm gonna name them Krösa-Maja and Tant Gredelin. yeah now they have names. Krösa-Maja is the 15n20 one.


----------



## inferno

i made something at work today. 80crv2. 50mm height for scale.

isn't it pretty? looks really usable right. i'm incorporating a skullcrusher in this one. could come in handy. you never really know.

think i'm gonna HT it tomorrow or on sunday if i'm not too hungover. it happens...
probably gonna do everything with the angle grinder and a flap disc and call it done. maybe some sand paper. gonna be my first knife with scales. i will use bicycle spokes, 2mm SS as pins. since i have that at hand.


----------

