Need a double-check on 1095 heat treat procedure

J

jdn181

Joined
Apr 10, 2010
Messages
31
Hey all! This is my first post and I thought I'd start it with a bang.

I tinkered with forging about 10yrs ago and had to get away from it due to life intervening. But, now that I've got some free time I decided to reignite an old hobby.

So I built a forge and got to work on some stock removal 1095 knives. Forge is made from a 16"L section of 9"x9" square structural tube, 2" of ceramic wool coated with furnace cement, firebrick floor, 1" pipe burner w/ brass NPT nozzle, electronic solenoid valve controlled by PID controller which uses a K-type thermocouple to regulate the temperature. I added a second controller (not shown in picture below) to just monitor the interior temperature of a section of 3" exhaust pipe I'm using for heat-treating.

Forge3.jpg



Here's the first blank I ground out of a section of 1.5"W x 12"L x 0.125"t 1095 steel.

Blade1-2.jpg


My first heat treat with this blade was clay coat and quench in ATF. After polishing and etching the surface a bit the hamon wasn't very descipt and only went up the blade about 1/4". So I decided to quench a second time (no re-anneal I might add) but in brine. Blade was heated to 1,500 and quenched in 75deg brine. Blade was left in the brine until cool to touch. A little warping to one side was noted and decided to try an fix it (cold) in my vise and some "gently coercion". You can probably figure out what came next - SNAP! i went ahead and polished/etched the blade fragment but results were same as before - non-descript hazy hamon. I'm thinking that I didn't let it soak long enough, coupled with the 1/4" layer of furnace cement I used on the blade caused a lot of probems. I also noted some significant stress cracking on the surface of the blade probably caused by me bending it in it's hardened state and not bothering with a temper.

SO, I've learned my lesson. I've ground out a another blade to heat-treat:

NewBlade1Template.jpg


NewBlade1Fit.jpg


...and here's the process I'm going to follow to complete this blade and hopefully get a hamon:

1) Anneal steel @ 1,475degF & cover with ceramic blanket. Let cool with forge. (DONE)
2) Profile grind & hand sand to 320 grit. Leave edge @ 0.020” to 0.040” (DONE)
3) Normalize @ 1,570degF 3 times allowing to air-cool between, reducing temperature for each consecutive step.
4) Apply thin was of furnace clay to whole blade. Cover hamon spine with clay to depth of 0.0625” to 0.125”. Form clay to desired hamon form.
5) Insert Exhaust tube into forge and heat forge to 1,475degF. (PID Controller setting: 1,430degF). Insert remote T/C into inlet of HT Tube. Int. HT Tube temp needs to be 1,475degF.
8) Insert blade into HT Tube and let come to 1,475degF. Soak for 5mins.
9) Quench in 75degF brine. Count to 5, pull blade out while still warm (500 to 400degF) and check for warpage. Fix immediately. Place back in quench.
10) Temper @ 400degF IMMEDIATELY! Temper for 2hrs, let cool 30mins, temper again for 2hrs, cool for 30mins.
11) Hand sand/polish to 2,000 grit.
12) Etch with one of the following:
a. Ferric Chloride (1 part FC, 4 parts H20)
b. Warm Apple Cider Vinegar
c. Warm lemon juice (heat blade to 212 degF)
13) Polish w/ red rouge
14) Etch again & repeat step 8 & 9 until hamon is acceptable.


Can anyone else who's had a lot of experiece heat treating for a hamon chime in and double-check my procedure above. I'd appreciate any input you could give since I would hate to break another blade that I just spent 4 hours sanding on in preparation of the heat-treat. I've done a fair bit of research since my first try and figured out a number of things I did wrong - Didn't anneal before second heat-treat, didn't keep the metal at the proper temperature to fix warpage (>400degF), didn't temper @ 400degF right after the quench.

School of hard knocks I guess. ;)

Thanks much!

- Jesse
 
I see two issues in your HT.
When you quench, the brine should be a tad warmer, about 100F may work better.
The biggest issue is your quench sequence. It should go ....Quench 1-2-3-4-5 pull out 1-2-3-4-5 BACK IN 1-2-3-4-5 till cool. The count is determined by experience with your equipment. I use 1-2-3, you may want to shorten your count. If you pulled the blade after the first count and did straightening, the hot spine would auto-temper the blade right down to the spine, as it would still have too much heat. The first plunge sets the edge heading toward martensite, the pull allows the spine to enter the pearlite range, and the second plunge stops the spine from allowing the heat to migrate too far toward the edge. This process makes a mix of pearlite and martensite at some point along the bevel that is called the hamon. Just the tiniest change in timing can walk the hamon right off the blade, or make it disappear altogether. I would suggest doing no straightening until after the second temper. Straighten right out of the oven with the blade at 450F. With experience, you can do many things different than this procedure, but for starters this is safer.

Nice job on the forge, but I would not put the electronics directly above it. Put the forge on a rolling MIG welder cart (HF - http://www.harborfreight.com/welding-cart-90305.html) and mount the PID and such on the bottom shelf. Your tongs, steel, and hot stuff can be put on the shelf right under the forge. You can store the propane tank on the back lip. Thee carts are regularly on sale for about $40. I buy several when on sale and use them to mount equipment on. Think of all the things you use only occasionally that could be rolled out of the way when not in use - quench tanks, forges, HT ovens,casting equipment, big stack of hammers and tongs, etc. A trick in assembling these is to take the front uprights and re-drill the holes to make the top shelf level and not inclined. You can also flip the top shelf over and have no lip on it.
Another great cart for larger forges and HT ovens is the rolling shop cart http://www.harborfreight.com/16-inch-x-30-inch-steel-service-cart-5107.html . These go on sale for around $25.
 
Wow, bladsmth,
your description about the tempering was nice and short but made me understand it all a whole lot better now.
 
bladsmth said:
I see two issues in your HT.
When you quench, the brine should be a tad warmer, about 100F may work better.
The biggest issue is your quench sequence. It should go ....Quench 1-2-3-4-5 pull out 1-2-3-4-5 BACK IN 1-2-3-4-5 till cool. The count is determined by experience with your equipment. I use 1-2-3, you may want to shorten your count. If you pulled the blade after the first count and did straightening, the hot spine would auto-temper the blade right down to the spine, as it would still have too much heat. The first plunge sets the edge heading toward martensite, the pull allows the spine to enter the pearlite range, and the second plunge stops the spine from allowing the heat to migrate too far toward the edge. This process makes a mix of pearlite and martensite at some point along the bevel that is called the hamon. Just the tiniest change in timing can walk the hamon right off the blade, or make it disappear altogether. I would suggest doing no straightening until after the second temper. Straighten right out of the oven with the blade at 450F. With experience, you can do many things different than this procedure, but for starters this is safer.

Nice job on the forge, but I would not put the electronics directly above it. Put the forge on a rolling MIG welder cart (HF - http://www.harborfreight.com/welding-cart-90305.html) and mount the PID and such on the bottom shelf. Your tongs, steel, and hot stuff can be put on the shelf right under the forge. You can store the propane tank on the back lip. Thee carts are regularly on sale for about $40. I buy several when on sale and use them to mount equipment on. Think of all the things you use only occasionally that could be rolled out of the way when not in use - quench tanks, forges, HT ovens,casting equipment, big stack of hammers and tongs, etc. A trick in assembling these is to take the front uprights and re-drill the holes to make the top shelf level and not inclined. You can also flip the top shelf over and have no lip on it.
Another great cart for larger forges and HT ovens is the rolling shop cart http://www.harborfreight.com/16-inch-x-30-inch-steel-service-cart-5107.html . These go on sale for around $25.
Click to expand...

Thanks much!! I've read through a ton of your posts recently Bladsmth and was hoping you'd chime in! :)

I understand what you mean on the brine temp and will see if I can toss in a couple hot peices of junk steel to bump the temp up a bit before quench (currently 75 here in Houston, so shouldn't be too hard).

I'll also play with the timing on the interrupted quench a bit, but I see what you mean about getting the pearlite and martensite to start - a bit of a ballancing act it seems. (Edge cool enough to get past the pearlite nose, but warm enough on the spine to promote pearlite, and a thermal balance between the two to get the hamon). I can't rely on the clay keeping the spine warm enough to promote pure pearlite.

I'm using a furnace cement very similar in composition to APG #36 which seems to dry pretty quickly with thin layers (<.125") but with a thicker layer I had to dry it in my oven @ 140degF and it puffed up in the forge. It adhered well to the blade which was ground to 400grit, so I left this second blade at 320grit since I'll be using a much thinner layer of clay and not sure if it will stay on the blade or not during quench. If you think I should go lower on the grit (220 or 120) please let me know.

I've also read suggestions that I should put the blade in the forge when I first light it up to bring the blade up to temp slowly as opposed to sticking it in the forge @ 1,475degF and "shocking" it. Should I do this or go ahead and stick it into the forge at temp?

I agree on the the mounting of the controls. Hindsight is 20/20 and after I fired up the forge for the first time I realized that I had a "major" thermal problem. Eventually I'll cut the control box off the upright bracket and mount it somewhere else, but in the meantime I just hang a small peice of sheetmetal and a section of ceramic insulation like an awning over the front of the forge and it keeps controller tems below 140degF.

Forge Experimentations:
------------------------
When I first built this forge I was using 1.5"dia pipe for the burner and 1/8"NPT fittings with a 1/16" orifice for the gas. In this config it was litterally a little dragon! If I opened it up to full-throttle it would kick a 3ft flame out the front and back. Temp got up to 1,900degF without a problem but it could only idle around 1,500 degF or so before the flame front would back up towards the nozzle. A little too much on the hot side. At this point I was controlling the forge with two valves only - needle valve for bypass circuit, and ball valve for main ON circuit (which using a ball valve is a bad idea I might add. No fine control).

Revision 1 - I added a Watlow Series 96 PID controller I had laying around (used to work for Watlow in the past) and set up a "K" T/C in the ceiling of the forge towards the rear outlet of the forge. This controller actually controls the gas solenoid in ON/OFF mode and does a pretty good job of holding the temperatures steady. Sees to be hold +/-25degF on whatever temp I specify. I also removed the 1.5" pipe and went to a 1" pipe. Changed the nozzle orifice to a 1/32" as well. Now the forge will idle around 1,200degF at the lowest (before movement of the flame front up the burner pipe) and can run it up to 1,800deg without a problem as well. I need to put on a smaller reducer or add a gate valve to the top of the burner pipe since the atmosphere in the forge with this config is a fair bit on the oxidizing side. If I cut down the airflow by 50% I can get a good reducing flame.

Revision 2 - After running the unit for a couple of sessions I noticed a nasty cold spot about 3" in diamter on the floor of the forge where the burner's flame was impinging on the firebrick. Given that the workable space in the forge is 5"W x 9"L having a 3" cold spot in the middle presented a bit of a problem. After doing a little more research I decided to cut a 9" section of 3" exhaust pipe and stick it in the forge. I also installed asecond 96 series controller, and a remote T/C, to monitor the temp inside the pipe. I tested it out on a section of low-carbon steel bar and got a much more even heat. The cold spot is still there on the roof of the exhaust pipe, but given the amount of air in the pipe I can keep the temp at a contant 1,450 to 1,500 without a problem. (The forge is set to keep the tube inner temp at 1,475degF +/- 10deg).

Anyhow, I'll update my profile here so I can stop lurking, incorporate your comments into my procedure, do a few practice runs to get the procedure ingrained to memory, heat treat, and report back my experience. Thanks again for the suggestions!!

- Jesse
 
BTW, Welcome to the BF.

APG36 furnace cement works fine. However, you do not want it any thicker than .125". Theall too common application of .25+" of refractory compound will retain too much heat. A thin wash coat on the entire blade with about .10-.125" on the spine is just right.

On you forge. The cold spot is where the inner cone of the flame is hitting the floor of the forge. That isn't too much of a problem once the forge is fully soaked....about 10-15 minutes of running is about right. On your next forge, have the burner enter the chamber on the tangent. This causes the flame envelope to swirl around the chamber. The result is no cone and much more even heating. The flame is around the entire forge wall, not in one spot. Using a muffle (pipe) is a good system. 10 minutes of running to pre-heat the forge and pipe and the HT will be spot on.

A hamon is a finicky thing. You can do it twenty times with perfect results, and then on number 21 there is no hamon???? Careful notes and records will help a lot in zeroing in on this type of HT ( actually,good records should be kept on any type of HT).
 
Yeah, I've been keeping notes on what I've done to log all the variables so if it doesn't work I'll try something different. Will log the temps that I run the heat treat at tonight.

I tested my "tempering oven" this morning (the bottom oven in my kitchen 2-oven setup), stuck a thermocouple in there, and calibrate the oven to give me 450degF. Funnu thing is that I when I set it to temperature the internal thermostat will ramp it up to +500deg, then let it cool to about 400deg before it heats back up again. Going to be interesting tempering with an oven that is accurate to +/-50deg. Sheesh. I need to get a small toaster oven and then tie in one of my PID controllers to the element to more exact control.

I also tested what it owuld take to get my brine quenchant up to 100deg. I remove 2gal from my 5gal bucket (ambient temp ~75deg right now), heat up this two gallons in a pot on my stove until I hear hissing (~200deg or so. Won't boil at 212deg due to the salt of course. didn't verify with a thermocouple as it was being used in the bottom-oven test at the time) and then dump it back into the 5gal quenchant bucket. Temperature was logged right at 100degF.

I went ahead skim-coated the blade with furnace cement and then normalized it to relieve some of the stresses caused from grinding. (Cement reduced the amount of scale on the blade...but didn't help decarb much...). I heated it to 1,575deg, pulled it out an let it air cool, then back in at 1,450, another air cool, then one more cycle at 1,300deg (just under the non-magnetic threshold), and one last air cool.

I removed all the furnace cement with a green-pad on an air grinder, sanded of some of the decarb present, then recoated the blade with furnace cement to 0.125"t. Removed the clay for the proposed hamon line and let it dry. Will be heat-treating in a couple hours or so. With any luck I'll get a suguha-ish hamon on this blade. (I'll try something a little more active next time as a suguha hamon seems to flow a little better with the wood grain of the handle scales I'm going to put on this blade).

Edit: 8pm 10/9/10
Quench is complete. Soaked blade for 5 mins between 1,500 and 1,470degF (was trying to get as close to 1,450 as possible. Started at around 1,500 and and drifted to around 1,470 before I ran to the end of 5mins). Quenched in 100deg brine for 5 secs in, 3 out, and back in till cool. The clay on one side sloughed off after I pulled out of the water, so hopefully that's going to present a problem on the metal. Blade is now sitting in my "precision" tempering oven for the next 4 hours @ 450deg (with a cool-down planned at the 2hr mark).
 
Last edited:
bladsmth said:
The biggest issue is your quench sequence. It should go ....Quench 1-2-3-4-5 pull out 1-2-3-4-5 BACK IN 1-2-3-4-5 till cool. The count is determined by experience with your equipment. I use 1-2-3, you may want to shorten your count. If you pulled the blade after the first count and did straightening, the hot spine would auto-temper the blade right down to the spine, as it would still have too much heat. The first plunge sets the edge heading toward martensite, the pull allows the spine to enter the pearlite range, and the second plunge stops the spine from allowing the heat to migrate too far toward the edge. This process makes a mix of pearlite and martensite at some point along the bevel that is called the hamon. Just the tiniest change in timing can walk the hamon right off the blade, or make it disappear altogether.
Click to expand...

Stacy
That is about the best description of an interrupted quench Ive seen. Short, simple and easy to understand, with just enough explanation of the process that is going on in the steel to make the whole process logical.

Sean
 
Well, I finished the heat-treat last night and started polishing it up this morning. I went ahead and polished one side all the way to 1200grit real quick and assessed whether or not I was successful. After a quick etch in apple cider vinegar I could see the hint of a hamon in the metal:

Blade2wFaintHamon.jpg

If you look carefully you can see the slight haze of the hamon.

Here's what the clay coat looked like beforehand:

Blade2-ClayCoated.jpg


The interrupted quench that Bladsmth outlined worked like a champ! It's interesting to note towards the tip that a clay coat 1/8"t x 1/4" wide was rather inefectual since the hamon comes back on the blade away from the tip by about 1.5" whereas the clay only came back about 1/2". I'll have to compensate for this in the future with a slightly thicker clay layer towards the tip perhaps. Or maybe bring the clay towards the edge a bit more at the tip.

Since I had proof that a hamon was present I started over and sanded both sides through all the grits until no scratches or pits remained (220g, 320g, 600g, 1000g, and finally 1200g which was the finest I had. I tries a few rubbing compounds I had on hand but they all seem to be coarser than 1200g and just hazed the surface, forcing me to hit it again with 1200g. I need to get some finer paper and some decent polishing compound).

After I hit both sides with the 220g the hamon dissapeared. I couldn't even see it after 600g which was a little disconcerting since I've seen other's work where the hamon was clearly visible after 320g. Nevertheless I polished it as fine as my tools would let me and then hit it with a Ferric Chloride etch. Pulled it out of the etchant, rinsed it with windex (ammonia-based), and polished it with 1200g again with slow, single, draw stokes. The hamon just popped out at that point! Man was I ecstatic! First successful knife, first hamon!

Here's the blade as it sits now, waiting for a handle and the rest of the fittings:

Blade2wFeClHamon.jpg


With any luck I'll have it finished tomorrow. The different effects of etching in Vinegar vs. FeCl gave me an idea for the future. A vinegar etch seems to give the hamon a lighter appearance, whereas the FeCl etch gives it a darker appearance. May make a brother to this knife but etch solely in vinegar. Light and dark. (I suppose I could make the current blade a little lighter if I had a way of getting the blacked material out of the pits caused by the etching away of the non-martensitic metal. Anyone have a good way of making the martensite in the hamon really pop?)

In summary here's what seemed to work this time (1/8"t 1095 steel):

Good anneal before cutting stock.
Grind to shape
Normalize 3 times with a cool-down in between each step. Start around 1575deg, then 1450deg, finally 1300deg.
Clay coat to 1/8"t.
Heat up to 1475deg to 1500deg. Soak 5mins @ temp.
Quench in 100deg brine.
Temper twice @ 450deg for 2hrs with a 30min cool-down in between.
Sand to 1200g.
Etch in 50/50 mix of Ferric Chloride & Water @ 75deg. (5min sessions approximately).
 
Last edited:
Could you provide me with a little bit more information on how your burner and valve is setup. I am in the process of building a new Furnace with a Honeywell UDC2500 and ASCO valves. Are you using a pilot light or does the ambient temperature inside of the chamber ignite the LP when the controller opens the valve for temp increase? Also if you could give a little bit more info on your burner i would appreciate it. I like your setup a lot and it is very similar to the plans i have drawn up and envisioned in my brain.
 
Take a look at the stickys and read about PID controlled forges. A two-stage control is far better than a simple stage solenoid control and only costs about $10 more. No need for a pilot, either, which makes it cheaper.
 
jdn181 said:
Well, I finished the heat-treat last night and started polishing it up this morning. I went ahead and polished one side all the way to 1200grit real quick and assessed whether or not I was successful. After a quick etch in apple cider vinegar I could see the hint of a hamon in the metal:

Blade2wFaintHamon.jpg

If you look carefully you can see the slight haze of the hamon.

Here's what the clay coat looked like beforehand:

Blade2-ClayCoated.jpg


The interrupted quench that Bladsmth outlined worked like a champ! It's interesting to note towards the tip that a clay coat 1/8"t x 1/4" wide was rather inefectual since the hamon comes back on the blade away from the tip by about 1.5" whereas the clay only came back about 1/2". I'll have to compensate for this in the future with a slightly thicker clay layer towards the tip perhaps. Or maybe bring the clay towards the edge a bit more at the tip.

Since I had proof that a hamon was present I started over and sanded both sides through all the grits until no scratches or pits remained (220g, 320g, 600g, 1000g, and finally 1200g which was the finest I had. I tries a few rubbing compounds I had on hand but they all seem to be coarser than 1200g and just hazed the surface, forcing me to hit it again with 1200g. I need to get some finer paper and some decent polishing compound).

After I hit both sides with the 220g the hamon dissapeared. I couldn't even see it after 600g which was a little disconcerting since I've seen other's work where the hamon was clearly visible after 320g. Nevertheless I polished it as fine as my tools would let me and then hit it with a Ferric Chloride etch. Pulled it out of the etchant, rinsed it with windex (ammonia-based), and polished it with 1200g again with slow, single, draw stokes. The hamon just popped out at that point! Man was I ecstatic! First successful knife, first hamon!

Here's the blade as it sits now, waiting for a handle and the rest of the fittings:

Blade2wFeClHamon.jpg


With any luck I'll have it finished tomorrow. The different effects of etching in Vinegar vs. FeCl gave me an idea for the future. A vinegar etch seems to give the hamon a lighter appearance, whereas the FeCl etch gives it a darker appearance. May make a brother to this knife but etch solely in vinegar. Light and dark. (I suppose I could make the current blade a little lighter if I had a way of getting the blacked material out of the pits caused by the etching away of the non-martensitic metal. Anyone have a good way of making the martensite in the hamon really pop?)

In summary here's what seemed to work this time (1/8"t 1095 steel):

Good anneal before cutting stock.
Grind to shape
Normalize 3 times with a cool-down in between each step. Start around 1575deg, then 1450deg, finally 1300deg.
Clay coat to 1/8"t.
Heat up to 1475deg to 1500deg. Soak 5mins @ temp.
Quench in 100deg brine.
Temper twice @ 450deg for 2hrs with a 30min cool-down in between.
Sand to 1200g.
Etch in 50/50 mix of Ferric Chloride & Water @ 75deg. (5min sessions approximately).
Click to expand...

I don't see any pictures that you posted.

I am glad that you got something to work out for you. What you are doing is pretty close to what I do for my hamons both in W2 and in 1095. The only other thing that I can say about it is that the geometry of the knife play a big part of how the hamon looks as well.

You asked about making a hamon pop and the etching. I find that I like 100% vinegar compared to the ferric. If you leave it in the vinegar it will turn dark just like the ferric. The polishing is what makes it pop and gives you different looks. I took this one up to 1500 grit hand sanding and then etched in hot vinegar multiple times and polished with loose silicon carbide powder (1500grit) between the etches.

0D73DD8F-39D7-4B7C-BFC4-58DE8B855E0C_zpssmvpfnip.jpg


37ABC1DA-41E8-489D-9358-BA590385A31B_zpssrkk7kz7.jpg
 
Polishing with loose grit is what makes it really pop. Have several types on hand, as no one type does every hamon. Chromium oxide, red iron oxide, black iron oxide, tin oxide, and silicon carbide ( grits from 600 to 12,000) all make a good shiagi togi/hamon kit. Gun cleaning pads and any fine oil work well for working the grit. Oils often used are clove, olive, 3-in-1, gun oil, knife oil.
 
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