Marquenching ..... Martempering .... Austempering and Bainite

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Natlek

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Jun 9, 2015
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OK guys , simple question . Can it be done with two HT oven ?? Quench blade in oil for short time and then fast IN oven with right temperature already set ? So instead of quench in molten salt to use oil and continue the process in the other oven with right temperature ?
 
In theory, yes. In practicality, it will require some guesswork. Two of your tubular HT ovens might work well for this.

The issue will being having control on the exact temperature of the metal when you pull from the oil and stick in the second oven.
The temperature range for some transformations is pretty narrow.

Molten salt drops the temperature to an exact point and holds it there. Oil and air aren't as rapid or controlled. The temperature drop from opening the second oven would have to be taken into consideration, too. Again, your tube ovens might be good here because of their rapid response rate.

All that said, your idea should work if you:
Austenitize the blade at the target temperature ( 1500F/815C for example)
Quench the steel quickly in oil and give it only enough time to drop below 900F/480C.
Immediately place in a pre-heated oven at the secondary soak temperature (450F/230C for example).

Issues to deal with:
1) The oil covered blade may send out a flash of flame or lots of smoke when inserted in a hot oven. Give it a fast wipe off with an old towel and toss the towel in a metal can, as it may catch fire. Have an assistant cover the can with a tight lid.
2) It may be hard to guess the temperature of the blade exactly when pulling from the oil. Try to have it in the range of 600F/300C and 800F/425C. My best guess would be that three to five seconds in the oil would drop a blade from austenitization to about that range. The time in air after pulling from the oil isn't as critical as long as you don't delay excessively. A quick wipe off and immediate insertion into the second oven will be fine.
3) You will have to figure the bainitic structure desired and temperature/hold times needed. My study on this has indicated that at temperatures around 50F/10C above the Ms the type of bainite desirable in a blade will form in a period of time from 30 minutes to 6 hours. The length of time and exact temperature will determine the amount of bainite and its structure.




I am preparing to start a series of exhaustive testing on this very subject. Final results will take a year or more, but I may have preliminary information in a few months. My target is to attain a martensite/bainite mixed structure somewhat similar to a blade with differential hardening having a martensite/pearlite mixed structure. The desired result is a blade with a very hard edge (Rc 60+) and a very tough and hard to break body. As a part of the research, we will try and see how hard we can make bainitic blades. Preliminary thoughts are we can make bainitic blades that can reach around Rc 58-59.



If you are want to mentally play with this, think about what might happen with three pots/ovens set up. One to austenitize …. one to marquench at slightly below the Ms …. one to quickly raise the blade to the bainitic range. Timing and temperature control will be absolute and completely controlled, so a salt pot may be the best way to do this. The timing/temperature in the sub-Ms range and the temperature in the bainitic range will determine the martensite/bainite mix. After two hours in the bainite pot, the blade should be tempered and done (no need for a second temper). Since there will be virtually no decarb and warping should be minimal, this could produce a blade that is ready for finish sanding after a couple hours of HT. The martensite/bainite mix should be interesting to test for impact resistance and overall toughness. Another plus of the hyper-Ms hold is you can straighten the blade and return to the tank as much as needed.
 
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There is a knife company in Thailand who quench L6 knife/sword in 500F with 3 hours soak for full bainite structure then gas torch edge to get martensite edge (He made his own double torch equipment with polymer added water as quench media to get very consistence result) As much as I remember the edge is 60-61HRC and around 50-52 in the spine.
 
Stacy E. Apelt - Bladesmith said:
In theory, yes. In practicality, it will require some guesswork. Two of your tubular HT ovens might work well for this.

The issue will being having control on the exact temperature of the metal when you pull from the oil and stick in the second oven.
The temperature range for some transformations is pretty narrow.

Molten salt drops the temperature to an exact point and holds it there. Oil and air aren't as rapid or controlled. The temperature drop from opening the second oven would have to be taken into consideration, too. Again, your tube ovens might be good here because of their rapid response rate.

All that said, your idea should work if you:
Austenitize the blade at the target temperature ( 1500F/815C for example)
Quench the steel quickly in oil and give it only enough time to drop below 900F/480C.
Immediately place in a pre-heated oven at the secondary soak temperature (450F/230C for example).

Issues to deal with:
1) The oil covered blade may send out a flash of flame or lots of smoke when inserted in a hot oven. Give it a fast wipe off with an old towel and toss the towel in a metal can, as it may catch fire. Have an assistant cover the can with a tight lid.
2) It may be hard to guess the temperature of the blade exactly when pulling from the oil. Try to have it in the range of 600F/300C and 800F/425C. My best guess would be that three to five seconds in the oil would drop a blade from austenitization to about that range. The time in air after pulling from the oil isn't as critical as long as you don't delay excessively. A quick wipe off and immediate insertion into the second oven will be fine.
3) You will have to figure the bainitic structure desired and temperature/hold times needed. My study on this has indicated that at temperatures around 50F/10C above the Ms the type of bainite desirable in a blade will form in a period of time from 30 minutes to 6 hours. The length of time and exact temperature will determine the amount of bainite and its structure.




I am preparing to start a series of exhaustive testing on this very subject. Final results will take a year or more, but I may have preliminary information in a few months. My target is to attain a martensite/bainite mixed structure somewhat similar to a blade with differential hardening having a martensite/pearlite mixed structure. The desired result is a blade with a very hard edge (Rc 60+) and a very tough and hard to break body. As a part of the research, we will try and see how hard we can make bainitic blades. Preliminary thoughts are we can make bainitic blades that can reach around Rc 58-59.



If you are want to mentally play with this, think about what might happen with three pots/ovens set up. One to austenitize …. one to marquench at slightly below the Ms …. one to quickly raise the blade to the bainitic range. Timing and temperature control will be absolute and completely controlled, so a salt pot may be the best way to do this. The timing/temperature in the sub-Ms range and the temperature in the bainitic range will determine the martensite/bainite mix. After two hours in the bainite pot, the blade should be tempered and done (no need for a second temper). Since there will be virtually no decarb and warping should be minimal, this could produce a blade that is ready for finish sanding after a couple hours of HT. The martensite/bainite mix should be interesting to test for impact resistance and overall toughness. Another plus of the hyper-Ms hold is you can straighten the blade and return to the tank as much as needed.
Click to expand...

Thanks Stacy :thumbsup: Which steel would you use for this kind of experiment ? What do you think about 52100 steel ?
I have these two guns,big one is Thermal Camera /they are extremely precise/ available any time I need them ,so I think that I will easy/fast find how much time I need to quench before I pull out steel ...
6my7PwO.jpg

Im researching water -soluble polymer quenchant , that s what I plan to use in my new quench tank I m working on .They eliminates fire hazard ....
 
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We have heard of people possibly using that torch method. I wonder if you could use an induction coil for the second phase assuming that the blade wasn't too long? I have seen video of a guy edge heating blades in the 8 inch range with a coil. I was thinking that would be an interesting way to HT say an integral tactical tomahawk or "breaching tool" where you wanted a decent cutting edge somewhere. In recent years, we have seen some folks switching from say 4140 to steels like 80CrV2 in order to get a better cutting edge on their hawks. Are they giving up some of the characteristics that tactical hawk buyers are looking for when they do this and would this perhaps solve that issue?
shqxk said:
There is a knife company in Thailand who quench L6 knife/sword in 500F with 3 hours soak for full bainite structure then gas torch edge to get martensite edge (He made his own double torch equipment with polymer added water as quench media to get very consistence result) As much as I remember the edge is 60-61HRC and around 50-52 in the spine.
Click to expand...
 
I'm curious what specifically you're hoping to achieve here. Are you trying to get a bainite-martensite mix or pure martensite with less stress/cracking risk?

The book "Practical Heat Treating" has a free things to say about martempering (as well as austempering):

Martempering of steel consists of (1) quenching from the austenitizing temperature into a hot fluid medium (hot oil, molten salt, molten metal, or a fluidized particle bed) at a temperature usually above the martensitic range (M, point); (2) holding in the quenching medium until the temperature throughout the steel is substantially uniform; and then (3) cooling (usually in air) at a moderate rate to prevent large differences in temperature between the outside and the center of the section. Formation of martensite occurs fairly uniformly throughout the workpiece during cooling to room temperature, thereby avoiding formation of excessive amounts of residual stress. The microstructure after martempering is essentially primary martensite, which is untempered and brittle for most applications. After being air cooled to room temperature, martempered parts are tempered in the same manner as if they had been coventionally quenched.
...

Generally, any steel that has sufficient hardenability to harden by oil quenching can be successfully martempered. It must be emphasized that martempering does not in any way eliminate the need for tempering.

...

Although hot oil is invariably the quenchant employed for modified martempering at 175 C (350 F) and lower, molten nitrate-nitrite salts (with water addition and agitation) are effective at temperatures as low as 175 C(350F).
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It seems to me that a hot oil bath that you quench in, then leave to stabilize, could be well-suited. I wonder even if a used deep fryer could be adapted to this purpose, perhaps including the addition of a PID controller.
 
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I would think that a deep fryer would not be hot enough.
Nick Dunham said:
I'm curious what specifically you're hoping to achieve here. Are you trying to get a bainite-martensite mix or pure martensite with less stress/cracking risk?

The book "Practical Heat Treating" has a free things to say about martempering (as well as austempering):



It seems to me that a hot oil bath that you quench in, then leave to stabilize, could be well-suited. I wonder even if a used deep fryer could be adapted to this purpose, perhaps including the addition of a PID controller.
Click to expand...
 
Be very careful heating oil to that temp and leaving it to soak a blade. I can think of at least one guy I know that lost a shop trying to temper in oil.
 
Hey Natlek, did you ever get the fluidized sand thing working? I think this would be the perfect application for it...
 
A.McPherson said:
Hey Natlek, did you ever get the fluidized sand thing working? I think this would be the perfect application for it...
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I m melting bronze in it this days :)This winter I will convert it to electricity , I have no way to control gas and temperature .But now I have two HT oven and very soon I will finish third one ........ I will use that sand pot for melting lead , I need it for what I plan to do .... Bainite here I come :D
 
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