heat treating 1084

[bushcraftbasics]

hey guys...so i am making knives out of 1084 and attempting my own HT. What i have is an old kiln rated at 1650*, a quench in oil heated to 125* and a toaster oven for temper at 400*...here's my dilemma:

pictured below is my kiln with a table inside...

...and this is a picture of what would have been the knife's orientation inside of the kiln with orton pyrometric cones 014 (1485* melted) and 013 (1539* almost perfect, slightly under-fired)...

...now for the nitty-gritty: when the kiln comes to temp i have to open the lid (obviously) and upon doing so the edge of the knife appears to immediately darken from the near orange color and almost appears black...there is NO WAY to bring the knife to the quenchant any faster, this is happening AS SOON AS I OPEN THE LID! is this normal? is this a problem? the steel appears to be hardening because i can pass a file over the blade without any significant "grab", as you can see in this picture...:les:

 

[Doug Lester]

There is some information missing here. How long are you soaking the blade at temperature for? How are you timing that soak? Are you using the pyrometric cone to tell you when the kiln has come up to temperature before you put the knife blanks in or are you putting the blanks in cold and heating them up with the kiln?

A couple of suggestions. One, loose the heat cones and replace them with a pyrometer and monitor the actual temperature of the kiln with that. Just make sure that the thermocouple (probe) is rated to at least 1600°. If there is no hole in the wall of the kiln to stick the thermocouple through you will have to drill one but make sure you do not hit the heating coils. The best place that I've run into for pyrometers and thermocouples rated that high a temperature is Ebay.

You might also want to soak the knife blank that you heat treated in white vinegar overnight and scrub off the fire scale. That could be what making the file skate off the steel.

The next suggestion is more of a safety notice. Do not reach into the kiln to place the knives in or take them out with the power one. You could receive a nasty shock if you make contact with the coils with the knife blank or your tongs.

Other than that I would say that your temperatures are about right just be aware that the 1084 that you get from The New Jersey Steel Baron is not the classical 1084 that you will find the data sheets for. What Aldo stocks has some chromium, silicon, and nickel in it that's not in the classical assay. You might want to soak it just a little longer to get good break down of the non-cementite carbides. I would say at least 5 minutes after the pyrometer hits the target temperature but I don't think that I would exceed 10.

Doug

 

[bushcraftbasics]

There is some information missing here. How long are you soaking the blade at temperature for? How are you timing that soak? Are you using the pyrometric cone to tell you when the kiln has come up to temperature before you put the knife blanks in or are you putting the blanks in cold and heating them up with the kiln?

A couple of suggestions. One, loose the heat cones and replace them with a pyrometer and monitor the actual temperature of the kiln with that. Just make sure that the thermocouple (probe) is rated to at least 1600°. If there is no hole in the wall of the kiln to stick the thermocouple through you will have to drill one but make sure you do not hit the heating coils. The best place that I've run into for pyrometers and thermocouples rated that high a temperature is Ebay.

You might also want to soak the knife blank that you heat treated in white vinegar overnight and scrub off the fire scale. That could be what making the file skate off the steel.

The next suggestion is more of a safety notice. Do not reach into the kiln to place the knives in or take them out with the power one. You could receive a nasty shock if you make contact with the coils with the knife blank or your tongs.

Other than that I would say that your temperatures are about right just be aware that the 1084 that you get from The New Jersey Steel Baron is not the classical 1084 that you will find the data sheets for. What Aldo stocks has some chromium, silicon, and nickel in it that's not in the classical assay. You might want to soak it just a little longer to get good break down of the non-cementite carbides. I would say at least 5 minutes after the pyrometer hits the target temperature but I don't think that I would exceed 10.

Doug

hey thanks Doug for your response! let me break this down.

1. i am putting the steel in beforehand and heating it up with the kiln to temp.(takes about an hour), between 1475*-1540* is close to 10 minutes

2. i am not saying you are wrong, I CANT WAIT TO GET A PYROMETER! but fwiw every source i have found actually states that pyrometric cones are more accurate...

3. i believe the scale is coming off in the oil, if in fact that is the thin flaky stuff that sluffs off during quench

4. when the kiln comes to temp at 1540* i shut it down, open the lid and immediately pull the blade out and dip in the oil, tip first, and move back-and-forth to prevent air-jacketing

that being said, everything "seems" to be as it should...i just dont like the fact that the edge appears to be falling from temp before i can even get the blade out of the kiln...and thus far i have no way to test for hardness...:001_unsure:

 

[Doug Lester]

The heat cones could quite possibly be more accurate but a pyrometer is much easier to monitor.

Yes, you do have a way to check for hardness but it requires sacrificing a blade. After you quench the blade, strike it with a hammer. If it shatters you are probably getting good hardening. Another way is to go ahead and temper the blade as you normally do, and in this test your blade will probably survive, then sharpen it to a course edge and try to drive it through a piece of bailing wire or a thin brass rod. If it indents with a folded edge then it's too soft. However, that could be due to over tempering but you could try to re-harden and tempering at 25° lower. If you repeat this step a couple of times, especially once you reach a tempering temperature of 350°, then you probably didn't get it hard enough to start with. Less than 350° and you're doing little but stress relieving the steel. Sometimes there is no substitute to wasting a blade to check your process.

If, however, the blade chips out after tempering your hardening process is adequate but your tempering temperature is too low. You could grind out the chip and re-temper the blade at 25° degree higher increments until you have no more that a very slight flatting of the edge as you try to drive it through the soft metal.

These methods are not as good as a hardness tester but the ones that can test something the thickness of a knife blade run $2000+. You can get a use Aimes hardness tester for around half that but a lot of them are on the market because they are so old that Aimes will no longer service them. You could also check to see if there is a shop in the area that has a hardness tester that will work on knife blades and will do it for you. Another possibility is sending of to a lab but make sure that they can do the testing on thin steel. Any way you want to have your blades instrument tested for hardness, it's going to cost you some money. You might look up to see if you have a Fastnall store in your area.

Doug

 

[Knifemaker.ca]

You cones are indeed accurate, but they don't measure temperature. They measure heat work. They are excellent for the potters but not so good for knife makers. Orton makes another product - name not coming to me right now, but a disc that can be used for verifying a kiln by acurately indicating max temp reached by size change of the disc. It isn't something that can be used to check to see if you are at temp yet. I would suggest that a pyrometer isn't all that expensive - it measures what you want measure - no peeking inside required - and unless you have a lot of experience reading cones, is probably less subjective.

Neither the cones or discs are helpful in keeping your kiln at an even temperature and as Doug pointed out, even 1084 does well with 5 - 10 minutes at temp.

As for hardness testers, you can buy brand new for under a thousand bucks and less when they go on sale. There ae probably also a lot of makers on this board who would check a few for you without it costing more than postage.

I'm not sure what to suggest for your problem with the edge cooling. If you think it is because of thickness, you might consider leaving the blade thick and grinding hard. Pottery kilns are made to empty when they are cool, so getting blades out fast is tricky and the chamber opening is HUGE compared to a knife kiln. Edge down in the rack might protect it a bit from the in-rush of cold air. I think you are right to seek some solutions, because if the edge has cooled to black before you even get to the oil, you have probably missed the nose.

Oh yes - once you have a pyrometer, I would be inclined to preheat the kiln - put the blade in - let it come back to temperature and then do the 5 minute soak. You'll get less decarb than with your curent 1 hour + setup.

 

[One]

The lighting in the shop could be a factor. If direct sunlight or any bright light is hitting the blade when you open the door it could appear cooler than you'd expect. When I pull a blade out of a dark muffle, the color drops as soon as the ambient light can reach it.

Other than that, the door on the kiln is quite a bit larger than needed to get the blade out and the blade is clear down at the bottom. This is just a thought, maybe raise the table up so you only need to crack the door open to get it out. Incorporating a muffle tube for the blade inside the chamber could also help stabilize the heat when the door is opened.

 

[Doug Lester]

One thing to remember when buying a hardness tester is to make sure that they will measure something as thin as a knife blade, probably down to at least 1/8". There are plenty out there that are rated to measure at 1/2" or more and quite a few that need the material to be a few inches thick but ones to measure thin material, especially portable ones, are not all that common, though they are out there. You could also look at table top models. They come on very heavy bases, like about 200 lbs or more, so you're not going to be carting one around. They too can be had used but, again, they may be too old for the manufacturer to service them. I've seen the same thing with medical lab instruments. They're working just fine but the manufacturer decides that the instrument is too old and they'll no longer support them, though they might support them in a veterinarian's office or in Europe. Most knife makers have to use subjective testing to determine hardness, like the file test, wire cutting test, or breaking blades.

If you can find a hardness tester that can do the job on sale, go for it. "Sale" is one of my favorite words. It's right up there with "50% off". You will just have to keep checking and maybe you'll have to as a distributor when a model that you're interested in generally goes on sale. It might be worth your effort to do so, just check out the specs to make sure the instrument will do the job you want it to do.

Doug

 

[One]

Here’s an idea:

You have the kiln, so why not make a vertical ceramic muffle tube for the inside of the chamber? You could also drop a piece of hardwood down the muffle for a shielded atmosphere.

... could help solve several problems.

 

[bushcraftbasics]

Here’s an idea:

You have the kiln, so why not make a vertical ceramic muffle tube for the inside of the chamber? You could also drop a piece of hardwood down the muffle for a shielded atmosphere.

... could help solve several problems.

not quite following you...pics?

 

[bushcraftbasics]

You cones are indeed accurate, but they don't measure temperature. They measure heat work. They are excellent for the potters but not so good for knife makers. Orton makes another product - name not coming to me right now, but a disc that can be used for verifying a kiln by acurately indicating max temp reached by size change of the disc. It isn't something that can be used to check to see if you are at temp yet. I would suggest that a pyrometer isn't all that expensive - it measures what you want measure - no peeking inside required - and unless you have a lot of experience reading cones, is probably less subjective.

Neither the cones or discs are helpful in keeping your kiln at an even temperature and as Doug pointed out, even 1084 does well with 5 - 10 minutes at temp.

As for hardness testers, you can buy brand new for under a thousand bucks and less when they go on sale. There ae probably also a lot of makers on this board who would check a few for you without it costing more than postage.

I'm not sure what to suggest for your problem with the edge cooling. If you think it is because of thickness, you might consider leaving the blade thick and grinding hard. Pottery kilns are made to empty when they are cool, so getting blades out fast is tricky and the chamber opening is HUGE compared to a knife kiln. Edge down in the rack might protect it a bit from the in-rush of cold air. I think you are right to seek some solutions, because if the edge has cooled to black before you even get to the oil, you have probably missed the nose.

Oh yes - once you have a pyrometer, I would be inclined to preheat the kiln - put the blade in - let it come back to temperature and then do the 5 minute soak. You'll get less decarb than with your curent 1 hour + setup.

thanks a bunch...saving my pennies for a pyrometer...seems to be around $100...as is, i have no way of maintaining any temp reference or consistency...i have been simply bringing up to temp and then attempting to quench

 

[One]

It's just an idea to adapt the kiln for blades.

The muffle would be a vertical ceramic tube standing upright inside the chamber. The blade would go inside the muffle. The muffle would act as a heat reservoir and baffle with a relatively small opening at the top compared to the big door and help even out temperature fluctuations. It would also make the blade quicker/easier to get out, and at the same time give you more time. I think with this arrangement less ambient light would hit the blade, not be as likely to trick your eye, and you could also create a reducing atmosphere inside the muffle with a piece of wood.

 

[Doug Lester]

Where are you looking for pyrometers? I'm certain that I didn't pay in the neighborhood of $100 even after I purchased the thermocouples separately. It wouldn't make sense to get a thermocouple that is rated for over 1600° if that's all the kiln is rated for. You might even be able to find one on Ebay or even Amazon that comes with a thermocouple rated that high. Just be sure to check.

Doug

 

[bushcraftbasics]

It's just an idea to adapt the kiln for blades.

The muffle would be a vertical ceramic tube standing upright inside the chamber. The blade would go inside the muffle. The muffle would act as a heat reservoir and baffle with a relatively small opening at the top compared to the big door and help even out temperature fluctuations. It would also make the blade quicker/easier to get out, and at the same time give you more time. I think with this arrangement less ambient light would hit the blade, not be as likely to trick your eye, and you could also create a reducing atmosphere inside the muffle with a piece of wood.

ok i get that...i dont have enough vertical space inside the kiln to put medium sized knife vertically...

 

[bushcraftbasics]

Where are you looking for pyrometers? I'm certain that I didn't pay in the neighborhood of $100 even after I purchased the thermocouples separately. It wouldn't make sense to get a thermocouple that is rated for over 1600° if that's all the kiln is rated for. You might even be able to find one on Ebay or even Amazon that comes with a thermocouple rated that high. Just be sure to check.

Doug

i was looking at the ones at Geargies ceramic shop in Portland, OR...they are local so it was easy to go put my hands on it and check it out..thanks doug

 

[One]

You could try setting it up diagonally, from a bottom corner to a top corner for more length. Maybe form the ends at an angle to set flush with the top and bottom. You can use a fairly thick walled mild steel pipe, round, square or rectangular in cross section. I think it would be easier and less likely to sag than ceramic. I use a horizontal mild steel muffle in my forge.

Just don’t use galvanized steel.

 

[Doug Lester]

I just did a quick search on Ebay. It's no endorsement, but there is an outfit listing there, Auber Instruments, that lists pyrometers with a thermocouple rated at 2000° ready to plug and play for less than $60 plus shipping. You might not be able to get one at this time but it is an example of what's out there. They also have some PID controllers for less than that, but they come without thermocouples. You could set that up to regulate the kiln if you ever use a steel that needs to be preheated and then soaked at temperature like O1. You could also switch it to a hotter kiln at a later date if you wanted to expand into the more complex air quenching tool or stainless steels that often require a preheat and a long soak at austinizing temperature.

Doug

 

[bushcraftbasics]

You could try setting it up diagonally, from a bottom corner to a top corner for more length. Maybe form the ends at an angle to set flush with the top and bottom. You can use a fairly thick walled mild steel pipe, round, square or rectangular in cross section. I think it would be easier and less likely to sag than ceramic. I use a horizontal mild steel muffle in my forge.

Just don’t use galvanized steel.

this is brilliant...so i will get a piece of round (so its easier to pick the blade out) mild steel pipe and scribe it to fit flush at the top and bottom at an angle from corner to corner (rear left bottom - top front right, for example) this should help with the rapid cooling upon opening the lid, and should also help with the over heating due to the radiant heat? also i am going to turn the lights out before i open the lid to see if its the light playing tricks on me...

 

[One]

this should help with the rapid cooling upon opening the lid, and should also help with the over heating due to the radiant heat?

Yes, and it should make it easier/faster to get the blade out (and give you a bit more time). For shorter blades maybe just drop a piece of fire brick down to the bottom to take up some space. You can also put a piece of wood inside the muffle to help cut out oxygen and reduce scaling.

You might need to experiment with it a little, but easy enough and worth a try.