Testing W2 Hardness Quenched with Parks 50 and 9% Brine Solution.

[me2]

There are a couple of opposing issues that could be happening. Those who find optimal hardness at a lower temperature are fighting excess retained austenite after quenching. Too high a temperature for them dissolved too much carbide and frees too much carbon, resulting in enough retained austenite after quenching to lower the hardness.

The other issue is you have to dissolve enough carbon to fully harden the steel, and you have to allow time for it to evenly distribute. You may be battling this instead, which is why you're getting higher hardness that is spotty. A longer soak might help, or as Stuart has said a high normalization might be needed. Or your oven could just be off. Choices, choices.

 

[stezann]

I'd be careful when "calibrating" a kiln by melting salt...it will only show you if you are in the ballpark.
When you find melting temp data you should account that it is NaCl melting temperature, measured with hi tech laboratory equipment and conditions...the TC it is also submerged into the NaCl to record the plateau and the precise freezing point.
That means when you actually "see" the salt starting to melt it is too late, the temperature your oven's TC it's reading is already above the melting temp....your +7°F TC may be indeed already well calibrated...or even a couple degree colder!!!

 

[Jeff the Millwright]

This really drives home the point of testing yourself, in your shop, your equipment. With W2, +/- 10f names a difference, and you go be a sweet spot 30f out from myself and Don. (He's using 1460 now Iirc. ) With these steels, just following a recipe won't cut it. In the end, the reading on the kiln is irrelevant. The final condition of the steel is what's important. Use what your testing says is best.

Yes Willie I totally agree that testing yourself is crucial if a person is to do their own heat treating because at practically every turn I have gotten results different from what I expected. I initially started heat treating with a homemade natural gas oven with a pyrometer and I thought I was getting pretty good results until I bought my hardness tester and realized that my hardnesses were all over the place.

It was a good way to get started because I didn’t want to spend a lot of money initially before I knew how much I wanted to get into knife making but buying my hardness tester really taught me how finicky heat treating can be and how unexpected results can be.

Obviously I have had a lot of trouble nailing down the proper treat for W2 but I actually enjoy the investigating and testing process as much as I do the knife making so I am determined to get this right and find the challenge fun.

 

[Jeff the Millwright]

There are a couple of opposing issues that could be happening. Those who find optimal hardness at a lower temperature are fighting excess retained austenite after quenching. Too high a temperature for them dissolved too much carbide and frees too much carbon, resulting in enough retained austenite after quenching to lower the hardness.

The other issue is you have to dissolve enough carbon to fully harden the steel, and you have to allow time for it to evenly distribute. You may be battling this instead, which is why you're getting higher hardness that is spotty. A longer soak might help, or as Stuart has said a high normalization might be needed. Or your oven could just be off. Choices, choices.

Yes me2 at this point I really don’t know what my issue is and it could be what you mentioned or it could be just my oven being off so obviously before I proceed I have to figure out what the problem is so I ordered online a tempil stick with a melt point of 1450°F so I can do an accurate calibration. And yes I think you are right that the soak time may also be an issue so once I get the best aust. Temperature down I will test different soak times.

And yes stezann I agree that the salt test does have issues which is why I ordered the tempil stick and I also broke down and ordered 5 gallons of Parks 50 from Texas and more W2 from Aldo so it’s full steam ahead, lol….

 

[Don Hanson III]

From that thread I am going to use Don Hanson’s heat treat recommendations as it sounds like he has really nailed it down. I will do some experimenting with aust. temperatures because although he recommends 1450°F my oven may not be calibrated the same as his.

I was really surprised to read that he doesn’t put his steel in while the oven is ramping up but instead puts it in once it’s up to temperature and only leaves it in for three minutes. I was surprised it would even fully get up to temperature in that little time unless of course I misread that but I will try it his way and ramping one up and compare the two. I will probably post my results but that won’t be for a while as I am working pretty steady lately.

Jeff, I've never ramp the oven up with a blade in it, always have put the blade in after oven reaches temp. Now for the soak time. My oven takes about 5-10 minutes to reach temp after the drop (back up to 1460). I let the blade soak for around 3-5 minutes after the temp hits it's mark. So the blade is in the oven for 8-15 minutes.

 

[Jeff the Millwright]

Thank you for clarifying Don about the fact you don’t have your blade in the oven during ramp-up and the duration of your soak times. I do find it surprising you leave them in so little time after your temp hits its mark again but obviously you are getting excellent results so I will take that as my baseline when I do some soak time tests for myself.

I can’t believe it but my temp stick arrived today and I only ordered it on Monday so tomorrow I will do some testing to try and figure out how accurate my oven’s temperature readout is. Thanks again Don for the input.

 

[kuraki]

That's how I did it with mine Jeff. I found out that on the floor of my furnace I was -25F of the readout temp, and I have to put two 4" fire bricks and stay in the rear 75% of the chamber to get the actual temp my readout is calling for. Makes me want to try one of those sand pots.

 

[Jeff the Millwright]

That's how I did it with mine Jeff. I found out that on the floor of my furnace I was -25F of the readout temp, and I have to put two 4" fire bricks and stay in the rear 75% of the chamber to get the actual temp my readout is calling for. Makes me want to try one of those sand pots.

After my tests today kuraki I understand you wanting to try a sand pot instead of an oven even though I have no idea what a sand pot is, LOL. Because what I realized today is that my pyrometer in my oven is not so much out but that there is enormous variation in temperature within the oven.

I got my 1450°F tempil stick yesterday and today did some experiments. From my hardness tests using W-2 I thought the oven was reading high so I started my test at the temperature of the stick or 1450°F thinking it would really be cooler than that in the oven. But what I didn’t realize was that I thought this because I was heating my pieces in the front of the oven.

I placed three pieces out of curiosity in different places. I have a 22 ½ inch Evenheat tap control oven and I placed one midway in the oven directly under the sensor and another 4 inches from the door and a third between those two. I expected that at 1450°F none would melt yet but in fact the one farthest in directly under the sensor melted at that temperature.

I cut off small pieces of the stick to place in the oven.

I then raised the temperature by 10°F and found out that the front one 4 inches from the door melted at 1470°F. So all I could say at that point was there was a minimum of 20°F difference between 4 inches from the front of the oven and midway because I don’t know where the midway one began to melt.

Realizing position varies in temperature more than I expected I then did a test placing five pieces with one in the center one at each end 4 inches from either end and then two others between those so basically I covered the whole length of the oven about every 4 inches with five pieces.

This time I lower the temperature to 1430°F which was 20° below melting point of my temp stick. To my surprise the back three including the center one again melted so obviously if I want to know the real difference from front to back I have to do another test but that tells me that from the center to the front is at least 40°F difference so from the front to the back I would not be surprised if it’s 100°F.

I think it’s kind of ironic that this company calls itself Evenheat because their ovens are anything but. I always thought it might be a problem that they have three sides with heating elements being the two sides and the back with the front door side not being heated. So the farther you go in the more heat you get.

It seems to me a solution would be to cover up the back wall so that way I would have two parallel sides heating and I would think the center of the oven would be the sweet spot and if I place the middle of my blade there it would fall off evenly in both directions. I have some one inch thick high temperature wool insulation good to 2300°F and I was thinking of putting a layer of that with a ceramic tile against that and then another layer of insulation and that way the back element wouldn’t be heating which I would think would make a much more even oven temperature.

My only fear though is that blocking off part of the element may cause it to overheat and burnout so at this point I am not really sure what to do. I find it frustrating that they sell a furnace with such a poor design; all they would’ve had to do was instead of having one big element that wraps around is to have two that just heat the sides.

Because if it is around 100° hotter from front to back as I suspect that means that the temperature varies about 4 ½° every inch so just a 10 inch knife would have a 45°F variance over its length. Pretty hard to get a proper heat treat especially when people agree that 10°F makes a difference with W-2.

 

[Natlek]

After my tests today kuraki I understand you wanting to try a sand pot instead of an oven even though I have no idea what a sand pot is, LOL. Because what I realized today is that my pyrometer in my oven is not so much out but that there is enormous variation in temperature within the oven.

I got my 1450°F tempil stick yesterday and today did some experiments. From my hardness tests using W-2 I thought the oven was reading high so I started my test at the temperature of the stick or 1450°F thinking it would really be cooler than that in the oven. But what I didn’t realize was that I thought this because I was heating my pieces in the front of the oven.

I placed three pieces out of curiosity in different places. I have a 22 ½ inch Evenheat tap control oven and I placed one midway in the oven directly under the sensor and another 4 inches from the door and a third between those two. I expected that at 1450°F none would melt yet but in fact the one farthest in directly under the sensor melted at that temperature.

I cut off small pieces of the stick to place in the oven.

I then raised the temperature by 10°F and found out that the front one 4 inches from the door melted at 1470°F. So all I could say at that point was there was a minimum of 20°F difference between 4 inches from the front of the oven and midway because I don’t know where the midway one began to melt.

Realizing position varies in temperature more than I expected I then did a test placing five pieces with one in the center one at each end 4 inches from either end and then two others between those so basically I covered the whole length of the oven about every 4 inches with five pieces.

This time I lower the temperature to 1430°F which was 20° below melting point of my temp stick. To my surprise the back three including the center one again melted so obviously if I want to know the real difference from front to back I have to do another test but that tells me that from the center to the front is at least 40°F difference so from the front to the back I would not be surprised if it’s 100°F.

I think it’s kind of ironic that this company calls itself Evenheat because their ovens are anything but. I always thought it might be a problem that they have three sides with heating elements being the two sides and the back with the front door side not being heated. So the farther you go in the more heat you get.

It seems to me a solution would be to cover up the back wall so that way I would have two parallel sides heating and I would think the center of the oven would be the sweet spot and if I place the middle of my blade there it would fall off evenly in both directions. I have some one inch thick high temperature wool insulation good to 2300°F and I was thinking of putting a layer of that with a ceramic tile against that and then another layer of insulation and that way the back element wouldn’t be heating which I would think would make a much more even oven temperature.

My only fear though is that blocking off part of the element may cause it to overheat and burnout so at this point I am not really sure what to do. I find it frustrating that they sell a furnace with such a poor design; all they would’ve had to do was instead of having one big element that wraps around is to have two that just heat the sides.

Because if it is around 100° hotter from front to back as I suspect that means that the temperature varies about 4 ½° every inch so just a 10 inch knife would have a 45°F variance over its length. Pretty hard to get a proper heat treat especially when people agree that 10°F makes a difference with W-2.

Sometimes I use Ht oven in my friend workshop . His oven was isolated from inside , you can not see heat element .I don t know what is isolation , but it s not a wool .......... it s something like very fine thin bricks ? I don t know maybe I am wrong about what was isolation ... Here is picture , but sorry not good one .....

PS . Wait, it's the same as what is seen outside on front wall of oven.........

 

[Jeff the Millwright]

Sometimes I use Ht oven in my friend workshop . His oven was isolated from inside , you can not see heat element .I don t know what is isolation , but it s not a wool .......... it s something like very fine thin bricks ? I don t know maybe I am wrong about what was isolation ... Here is picture , but sorry not good one .....

PS . Wait, it's the same as what is seen outside on front wall of oven.........

Thank you Natlek for your assurance that I should be able to cover up my element without having it burn out. I know I am taking my chances and only have myself to blame if it goes wrong but I appreciate your opinion and the fact you know someone who has done it. I was looking online and I can get fire bricks about an inch and a half thick so I think I will make a wall out of them in the back of my oven to cover up the element on the back wall.

I’m thinking if I leave an inch or two of space between the wall I build and the back wall the elements won’t heat up too much and I was thinking of leaving a little gap at the top so the convection currents could disperse the heat somewhat but I wouldn’t have the radiant heat directly from the element. Maybe not a perfect solution but it should help. I might also attach some high temperature wool to the side of the wall facing inside the furnace for extra insulation.

 

[Natlek]

Jeff , it s was purchased Oven from factory not home made :thumbup:

 

[Jeff the Millwright]

I retested my furnace with the temp stick doing the full-length this time and found there was a 50°F variance along its full-length with the worst section being the front section where it fell off 20° in 3 5/8 of an inch four inches from the front. The best spot only fell off 20°F over a 7 ¼ inch section coming to 2.76°F per inch.

I placed a fire brick in the back of the oven to block the rear element hoping that would even out the temperature. The brick is 2 inches thick and I left a 2 inch gap to try to avoid overheating the element so I lost 4 inches leaving me and 18 ½ inch space of usable oven as opposed to the 22 ½ for the first test.

This time the overall difference from front to back was only 30°F. The best spot which was 6 ¼ inches long had only a 10°F variation which equals 1.53°F per inch which is a 45% improvement over the temperature variance without the brick. This should be large enough to do most of my blades and a 10°F difference I think is acceptable.

For longer blades in a 9 3/8 inch section there is a 20°F variance which comes out to 2.13°F per inch. Not ideal but probably will produce an acceptable blade. If anybody is using and Evenheat oven I would recommend blocking off the rear element unless of course mine burns up rather quickly at which time I will modify my recommendation, LOL.

It’s not ideal but at least I know where I stand and what my parameters are so tomorrow I am going to test a few pieces of W-2 along the length of my oven to see how much the hardness varies. I have coated some samples with a skim coat of furnace cement to see if that will lessen my scaling and even out my hardness readings.

This test does answer why my sweet spot for hardening W-2 seem to be 20° hotter than most people and that is because I was testing my samples in the first 6 inches of the front of the furnace which is significantly cooler.

 

[Willie71]

I have two 1/8" x2" x20" strips of steel on the floor of my kiln. I also let the kikn soak for 30 min before I put the blade in.this should equalize the temps in the kiln.

 

[Jeff the Millwright]

I have two 1/8" x2" x20" strips of steel on the floor of my kiln. I also let the kikn soak for 30 min before I put the blade in.this should equalize the temps in the kiln.

I actually started these latest tests at 1370°F and held the temperature for five minutes at each 10°F interval for five minutes after the temperature rebounded from opening the door to inspect whether my pieces had melted are not so by the time I got up to the range where they started to melt the oven was already up to temperature for half an hour so these tests are probably pretty close to what they would be if I let the oven soak for half an hour but I was opening the door to inspect so it wasn’t a true soak so I may test that better.

I am really tempted to do something I don’t want to do and that is to drill a small hole in the door of my oven because I have a pyrometer with a digital readout from when I was heat treating with my homemade natural gas oven. The probe has a very rigid wire and I know I could push it in and out the length of my furnace so I could find out the temperature variation throughout the whole oven without opening the door.

My fear is because I would have to use a hammer drill with a concrete bit I could possibly crack the bricks in my door but I think it is worth it because if I go slow and gentle it probably won’t crack and then I would definitively know what the variation is as soon as it gets up to temp and with a good long soak. I think I’m going to have to do this despite my reservations.

From these last experiments I do know that my pyrometer on my oven is actually quite accurate probably within 5 to 10°F because the pieces melted near the pyrometer very close to the melt temperature of the temp stick but I really am curious exactly how much variation I have so I think I’m going to do this today.

 

[Don Hanson III]

That kiln is made from soft fire brick, you can use regular dill & bits. No worries.

 

[Jeff the Millwright]

That kiln is made from soft fire brick, you can use regular dill & bits. No worries.

Thanks Don; after your reassurance will definitely be drilling today. I am really curious about the results. I think I will test every two inches throughout the length of the oven as soon as it reaches temp and then every 15 minutes up to an hour.

 

[JeffreyFogleboch]

Interesting test with the tempilstiks. However, these are accurate within +/- 1%. At 1450F that's still 14.5 degrees in either way. Can we really trust these when shooting for such specific temperatures?


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[kuraki]

I think that's partly why Stacy recommends using 3 sticks. I have a 1450, 1475, and 1500. When I did my testing I found the point in my furnace where all sticks melted at the indicated temperature, and they were all within 10F. That was close enough for me because it resolved all of the issues I had with heat treating 1095 and getting variable results.

So it may not tell you the exact temperature you're at +-1F, but if your results are as expected and repeatable, that's really the point.

 

[Jeff the Millwright]

I was actually curious about the accuracy of tempilsticks 705 so I appreciate the info but I do plan before I start knife making again doing some tests with actual W-2 pieces to make sure I am getting the sweet spot so as kuraki says the exact temperature really doesn’t matter as long as I am getting expected and repeatable results but at least now I know I am in the ballpark to begin that testing and I understand now why I was getting such higher temps than others for the sweet spot.

It was both I was using the cool front part of my oven to test and the other is I don't think anyone really knows exactly how hot their oven is but just have to find the sweet spot through experimenting and use whatever arbitrary temp their particular oven dictates it is.

 

[samuraistuart]

Jeff, let us know how the "peep hole" drilling goes. Also, Warren mentioned it, but not sure if you caught it. It may be of benefit to you to put some scrap steel on the floor of the kiln to act as a heat sink. That scrap steel will retain heat inside the oven, and possibly mitigate your temp differential. Worth a shot, anyway.

I had bought a glass kiln a few years ago. 110V, big chamber. Slow to ramp to temp, but extremely accurate and holds a very even consistent heat, and this is triple verified every month or so with 3 different probe readings. It "was" a top loader, with elements in the lid (read....no fun to retrieve blade at all). It also had a "peep hole", but I got the idea to extend that peep hole and create a permanently open gateway to slide blade in/out. I was concerned about heat loss...but there is no heat loss at all. It is made from the soft fire brick, I simply used a hacksaw (blade only...no frame) to cut that little slot.