heat treating and tempering 1084 for beginner

Cojab

Well-Known Member
I am going to be heat treating my first knife soon (1084) I have purchased a kiln (thanks USAKMS) and the heating part seems pretty strait forward but I have a few questions.
First, does 1084 need to be foil wrapped for heat treating.
Second, I have been reading that the tempering sequence needs to happen very soon after HT.How soon is very soon? I was planning on being able to use my kiln for both HT and tempering. Will the kiln cool down to the proper tempering temp soon enough to temper after HT or do I need a seperate tempering oven.
Third, If I need to get the steel from quench to tempering soon, what kind of temp should the steel be at that time. Should it be basically room temp or something else.
Thanks for the help. I have been reading as much as I can on this but havn't specifically seen this.
 
With 1084 you should be fine waiting until the kiln cools down. I would let the kiln cool with the door closed because I've heard that rapid cooling with the door open is hard on the coils. I use my kitchen oven for tempering. I have two oven thermometers in the oven and go by them instead of the dial. I bring the oven up to the proper temp. and let it set 10-15 minutes before putting the blade in. You'll have to experiment with your equipment to see what works best for you.
 
I am going to be heat treating my first knife soon (1084) I have purchased a kiln (thanks USAKMS) and the heating part seems pretty strait forward but I have a few questions.
First, does 1084 need to be foil wrapped for heat treating.
Second, I have been reading that the tempering sequence needs to happen very soon after HT.How soon is very soon? I was planning on being able to use my kiln for both HT and tempering. Will the kiln cool down to the proper tempering temp soon enough to temper after HT or do I need a seperate tempering oven.
Third, If I need to get the steel from quench to tempering soon, what kind of temp should the steel be at that time. Should it be basically room temp or something else.
Thanks for the help. I have been reading as much as I can on this but havn't specifically seen this.

I was once asked what things I would change if I could do the knifemaker thing it all over again. I didn’t take very long to assess the two easiest things that I felt would have eliminated years from my learning curve and put me that far ahead of the game with little to no effort, or expenditure, on my part:

1. Using a good known steel, (both chemistry and heat treatment history).

2. Using a predictably consistent and reliable quenchant (note the lack of mention of speed alone).

These answers immediately elicited an overly defensive debate that continues to this day. The underlying psychology for such strong resistance for control over what are arguably the most critical aspects in the making of a quality cutting tool is beyond my area of expertise and the scope of bladesmithing forums, however, occasionally I see a self-professed new maker who I envy for naturally having the keen insight that I lacked.

Of course, with the most critical part of heat treating any steel being the ability to control temperature, a good oven undoubtably ranks up with the other two, but iIts omission from the list is due to its expense. Most beginners understandably rank cost equally with the effectiveness of the tool so the two items listed above top the list simply because of their “bang for the buck” factor cannot be beat.

But you, Cojab, are not the average beginner with how serious you appear to be about heat treating your first knife and what you have invested in obtaining the most control over the heat as you can; you have a good steel and a good heat source. Spending some time learning to do it by eye does have its benefits but so does the determination to have the most control possible. Now with your heat source in place you are looking for knowledge on improving the heating conditions and follow up treatments, a good systematic approach that I hope we can assist with.

Although some steel are more prone to problems from the atmosphere when at heat, all steels can benefit from some shielding in a kiln. While foil may be a bit much for 1084, I think a standard anti-scale compound would be nice. The iron-oxide scaling in a kiln can often offset the more dreaded effect of decarburization, but it will still create a headache for you in the subsequent cleanup, not to mention affect the conditions in the quench.

Your tempering should always be ASAP after the steel has assumed room temperature with any alloy exceeding .6% Carbon. It gets quite complicated, but high carbon steels will form a particular type of martensite (the hard stuff) that has an awful lot of stress points and internal “concerns” and the sooner these are addressed, the better.

However many folks get too jumpy over this and are too hasty to temper steel that is not done hardening. High carbon steel does not actually begin to harden in the quenching process until it reaches 500F or below at which point a very stressful and dramatic process requiring heavy deformation of the microscopic structure begins. This process is entirely temperature dependent and requires continuous cooling until it is complete, if you stop the cooling or reheat before it is complete the hardening will not be complete, it is that simple. Remember this- the higher the carbon content the lower the temperature that the hardening will be complete and this is even more so with added alloying. 1084 is an easy one, it will begin hardening around 430F and will be all done around 200F.*

I am a very big proponent of the kitchen oven Darrin suggested, but if that is out of the question, and you need to use the same kiln, you could use a modified method of quenching to give yourself a cushion. At any point from 450F down you can remove the blade from the quench and allow it to air cool; remember, so long as the cooling is continuous things will work, that doesn’t mean that cooling has to be as fast. When air cooling, the thermal mass of the steel will allow a jump start on the tempering and as much as 50% of the hard stuff can be exposed to some tempering effects. This will give an enormous amount of wiggle room over traditionally quenched steel to allow your kiln to cool to tempering temperatures.

*Those who want to get an idea of how noticeable this process is can quench a piece of steel and interrupt at around 450F to check it with a file, it will bite like it is dead soft. Allowing it to air cool, you will notice the file biting less with every minute that goes by until the steel is cool and fully hard. You can also play with the magnet and watch the non-magnetic unhardened steel slowly grab the magnet more and more as the temperature drops.
 
Thanks for the replies. Darrin. The oven makes perfect sense and not an additional expense other than a couple of thermometers. I like that. Kevin,,,,wow. Thanks for taking the time for that reply. Very helpful. With my thick skull I will reread it a couple times for maximum benefit!!! I have also been reading your other posts and stickys and thank you for sharing the info. I cant wait to get this thing going and show off a couple of knives. First one will be for my son then the next one for me. After that, who knows.
 
Go to the sticky on the top of this board, if you already haven't and print it out. That's enough to give you a good start. When you think that you need to know more, there are some good books out there. I have four of them.

Doug
 
Haha Kevin the last paragraph is the answer I have been looking for. Does removing the blade at the Ms line 450* and allowing it to cool to 200* over 15 minutes form more martensite in the blade instead of leaving it in the oil to cool to the ambient temp of the quenchant?
 
Haha Kevin the last paragraph is the answer I have been looking for. Does removing the blade at the Ms line 450* and allowing it to cool to 200* over 15 minutes form more martensite in the blade instead of leaving it in the oil to cool to the ambient temp of the quenchant?

No, not at all. It just forms it at a different rate with less stress and allows a little head start on the tempering.
 
So being less stressful lessens the chances for stress fractures forming during the tempering process. Does removing 1084 at or below the Ms lines add any other benifit to the blade?
 
So being less stressful lessens the chances for stress fractures forming during the tempering process. Does removing 1084 at or below the Ms lines add any other benifit to the blade?

One shouldn't get fractures from tempering at all, you may have micro-fractures from the hardening that reveal themselves in the tempering but tempering should offer no mechanisms for fracture. The process you describe is known as "marquenching" and has been a very common practice in industry for decades, if not centuries. The idea is that you have now avoided pearlite with a successful quench so if the steel is allowed to continuously cool it is going to harden, regardless of what rate it cools at, so why not give the most stressful transformation the least amount of unnecessary introduced stress? It works with any liquid quenched steel, not just 10XX series. The advantages are significant reduction in distortion or danger of cracking due to the more even transformation; if you have shapes with very thin parts next to very thick parts this alleviates the thin parts blasting through the quench and expanding totally out of sync with the still hardening thicker parts. In the air cooling it is possible to form as much as 40% martensite that will then be exposed to the steels own thermal mass and be tempered to some extent. There are lots on internal things going on from this that would be a long boring metallurgical tome so I will just leave it at that. In the end you do gain some impact strength from the whole process and have straighter and more stable blades awaiting the proper tempering.
 
One thing to remember about marquenching a shallow hardening simple steel, like the 10XX series, is that there is still a maximum thickness that it will work with, depending on the carbon and manganese levels. I'm assuming, correct me if I'm wrong anyone, that what you will be left with when this limit is exceeded is just like oil or water quenching to below Mf, a blade that will form martensite until the steel becomes too thick to cool fast enough and then it will convert to pearlite.

Doug
 
Sorry to sound like the complete rookie here but one more question. How long am I supposed to hold the blade in the quench oil and agitate. It sounds from Kevins response that it needs to stay in until the metal reaches at least 450* for it to begin hardening. Is there a general time frame for this. Ive heard some people saying hold it in quench for 30 seconds, others say much shorter, and others say about 5 seconds in oil then a water quench. If it makes a difference I have decided to spend the extra cash and order some Parks 50 (if I can find it) for its ease of use and consistency.
Kevin and Doug, I cant thank both of you enough for your time and effort on this forum. You have both contributed hours and hours of info here and I appreciate it.
 
It will depend on the quenchant and the temperature of the quenchant and probably the volume of the quenchant too. You might just have to experiment with your setup, which is going to be a bit of a pain, but I don't see a way around it. You would be looking for the shortest time in the oil that will produce good hardening, as tested by a file or non-impacting hardness tester. Kevin has a big advantage on the rest of use because he has been able to invest in the equipment to do his own microscopic examination of his blades to determine their crystalline structure as well as having a rather expensive hardness tester. Microscopic examination is something that is very labor intensive as well as requires expensive instruments and tools to do and would cost the rest of us a lot of money to have done.

Maybe Kevin can give you a better idea on how to handle this but right now he might be busy getting ready for a symposium that he'll be teaching at next weekend.

Doug
 
I'm no expert and free advice on the net is sometimes scary.
I have been quenching my 1084 blades in 120 deg mineral oil. To be on the safe side I leave the blades in the oil until it reaches room temp or until I can hold them with my hands. Then I go to the oven right away for my tempering cycles.
 
Actually, due to my teaching and lecturing schedule coupled with my research, I can assure you with some certainty that I make much less money than even the average knifemaker, a group that already puts one at poverty level, so I can promise that more capitol to invest in research equipment is an advantage I have never possessed. I am essentially a backwoods redneck hick from a little white trash town in the sticks of Michigan. My advantage has been pure stubbornness and willpower to know more about what I do. Thus I have had to become an amateur microscope technician to put my metallographs together from used ones I could afford, learn more about electronics and gas apparatus than I ever wanted to in order to build my own salt baths, and my hardness tester is actually one of the cheapest on the market- but secret is that my test blocks to calibrate it are the best I could get.

That really is what it is all about, carefully applying your limited money in the places where it will have the most effect, this is why I am such a proponent of buying good known steel and a solidly consistent and reliable heat treating materials. They are very inexpensive compered to machinery but give you the greatest leverage in improving your product. I find myself often reminding people that I started out with an old file or leaf spring and a bucket of water or 10W40 just like so many others, but 30+ years has allowed me to advance and accumulate better tools and knowledge as to where to apply them. But I am still just a Michigan hick with an unhealthily obsessive need to always know more about what I do.

Now onto the 1084 quench thing. Cojab, you do have an easier time of it due to your choice of 1084 since the actual temperatures at which the steel will start and finish hardening in the quench will be pretty stable and not move all around as in our discussion about 52100 in another thread. The magic numbers for .84% carbon with .8 Mn are 425F-450F and around 200F respectively. You will not want to slow the cooling before 450F and you will not want to stop the cooling (either air or oil) until you reach 200F or below. This is where the common terminology of “cool to hand warm” comes from in the heat treating literature.

If you want to try to approximate a marquench with the Parks #50 you want to cool as close to 450F as possible and then allow it to air cool. I have found that a seven to eight second count with proper agitation in the Parks should get you in that range, and you can then let it air cool.
 
Yes, but you still have more money tied up in testing equipment than the average person can afford, even if you had to build/assemble a lot of it yourself. Even used Ames Rockwell hardness tester run north of $1.2K, though you might luck out and get one cheaper. I got a cheap Brinell tester from China and I'm going to have to slow down enough one day to sit down with those knives I've just tested to distruction and see what reading I can get from them. If I can get the handle on working with that thing, I'll try correlating it with a Rockwell reading at the local Fastenal store. I'll also check to see what it will cost to at least have that austempered blade sent to a lab for microscopic testing. If I can swing it also I'll have the marquenched one checked for pearlite formation too. Though that seemed to be one strong blade.

Hope to see you next weekend at Troy.

Doug
 
A quick follow up question on this subject if you all dont mind. After the tempering cycles, do you take the steel out and cool outside of the oven or keep it in the oven and allow it to reach room temp with the oven? Does it make a difference and what difference does it make if so?
Thanks
 
If I'm reading your question right you are asking about leaving the blade in the oven after you have completed the cycles. I've done it both ways. Unless there's something that I'm overlooking, the temperatures that were dealing with are too low to cause anything like carbide clumping.

Doug
 
I think thats what I was looking for Doug. Yes, I was referring to leaving the blades in the oven while it cooled down to room temp as compared to removing the bladesfrom the oven after the soak time to room temp and allowing to cool that way. Thanks Doug
 
One point I may make about this sub-topic if you have the attention span of a gnat, like I do. I once left the blades in the kiln to cool all the way down, I then felt it may be the safest place for them until I could get back to them- a very dry, clean and out of the way space after all. I think you may already have an idea as to where I am going...

The next heat treat I did, I simply punched in the high temp number and walked away to let the unit come up to temp. It wasn't until I went to use the kiln that I noticed I had a whole batch of blades that I had cooked.

But if you actually have short term memory left to speak of, there still is no real benefit to a slow cool from the temper. I actually quench all of my blades from the temper and get back to work as soon as possible. There are also some metallurgical reasons why I do this just for insurance, but that would be a whole other thread. But suffice to say that just cooling the blades and getting on with making the knife is the most effective use of time and resources.
 
I guess that's one of the advantages of using the kitchen oven. I'm not likely to make something in the oven that requires a higher temperature the the blades need to temper. I usually don't turn the broiler on until what I'm cooking goes in. It would be a bummer to accidentally leave the blade in the kiln and then prepare it to austinize another blade and wipe out the heat treatment on the one that you forgot and left it in. A good point to remember.

Doug
 
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