1084 tempering question

A

AJH_Knives

Well-Known Member
so after my first temper i am at the hardness i want. do I temper again at the same temp? can I call it good with the 1 temper cycle. I am at 59 rc right now after a hour at temperature.. i am inclined to leave it at 1 temper cycle and move on... any comments for or against???

Aaron
 
Some really like to do a triple cycle, however I think most just go for one temp cycle. Personally, I would leave it there. Maybe make up a test blade or two and see how you like multiple cycles?
 
the concensus seems 2 be temper for 1 hour at a standard temp you will use everytime, say 325F. with 1084 this should give Rc62-64. quench in cold tap water, water temp not critical, just less than room temperature. also a good time to clean off any scale. on your second cycle, increase your temp for your final hardness.
scott
 
AJH_Knives said:
so after my first temper i am at the hardness i want. do I temper again at the same temp? can I call it good with the 1 temper cycle. I am at 59 rc right now after a hour at temperature.. i am inclined to leave it at 1 temper cycle and move on... any comments for or against???

Aaron
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What is your tempering medium, oven? The standard time for tempering on an oven is a total of two hours. I use different mediums but will walk my temper temperature in to the exact hardness I want and then give it a good long soak at that temperature so that I do indeed have at least two hours. Tempering is perhaps the most complex of all heat treating operations as far as all the things going on inside. You will want to convert you alpha martensite to a more stable form as well as evenly precipitate the secondary tempering carbides. I personally like to err on the low side with longer times, it tends to yield greater gains in toughness for a given Rockwell.
 
Kevin, I have a digitally controlled kiln i turned into an oven. i did 1 hour at 350 should i repeat 350* will i lower the hardness..
also i do not quench in water after tempering, i let the blade air cool.. is there any benefit in quenching after tempering?
 
In a period of just one hour there should be no difference in hardness at the same temperature. I emphasize "should" because I know there wouldn't be in my shop but I cannot account for variables in your shop or your process, and I say this because there is already an variable that I cannot account for in your process- 350F should not get you to 59HRC. 350F should barely shave a point of the top end, 375F will get you around 62-63HRC after an hour in an oven. The water quench is a matter of splitting hairs just in case. There are genuine effects of rapid cooling from the temper for more complex steels that could have some TE (tempering embrittlement), but 1084 could only be effected by TME (tempered martensite embrittlement), in which case its slightly elevated Mn numbers could come into play. It is a matter of whether you are one of us neurotic individuals who are kept awake a night over that last 5% that you could get or your conscience won't allow you to look a customer in the face and say "eh, good enough! next..." If you quick cool you may prevent some negative secondary precipitates or the decomposition of a small percentage of retained austenite into the same, but the rule of "first do no harm" comes into play and there really is nothing can be harmed by fast cooling from the temper. If nothing else, it allows you get back to work on that blade immediately- and time is money.
 
Kevin,
I heat treated the 1084 at 1480*F it soaked for 10 minutes then i quenched in peanut oil heated to 120*... this batch did not get tempered till the next morning.. i was up late doing the heat treat. the 59 rc came from a fastener shop in town. the old guy that owns it had a lab set up, 20 years ago he needed it, now it collects dust. So I do not know how accurate his machine is or when it was last calibrated. in my opinion the blade feels hard, like when i do O1 steel with the same heat treat temp and a 400* temper.
I have had another forum member test my O1 and it is in the low 60s (60-63)
 
AJH_Knives said:
Kevin,
I heat treated the 1084 at 1480*F it soaked for 10 minutes then i quenched in peanut oil heated to 120*... this batch did not get tempered till the next morning.. i was up late doing the heat treat. the 59 rc came from a fastener shop in town. the old guy that owns it had a lab set up, 20 years ago he needed it, now it collects dust. So I do not know how accurate his machine is or when it was last calibrated. in my opinion the blade feels hard, like when i do O1 steel with the same heat treat temp and a 400* temper.
I have had another forum member test my O1 and it is in the low 60s (60-63)
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Here is where the quirks would be in my shop with what you describe. I have done enough testing with peanut oil to determine that it is too slow for my tastes for 10XX series steel, take that for what you want or leave it. In order for a Rockwell reading to be any good it really must be done on a flat even surface that is as perpendicular as possible to the penetrator, i.e. 90 degrees, so it can’t be the edge bevels. Thus it is areas like a flat near the spine, ricasso, or the guard seat area that yield the best readings, but even with a good fast oil these areas will seldom reach maximum hardness in a 10XX series steel unless the whole blade is particularly thin. I have had folks send me 1095 blades to heat treat in the past that only offered a ricasso area in excess of ¼” to test on, and thus I has no precise data on the very edge… I would get twitchy and walk in circles like Rainman for an hour. Also remember that Rockwell numbers really must be averaged to be accurate, thus you want around five readings to get a good idea. I know that most folks make one dimple and call it good, but it is not until you average a number of readings that you start to see patterns in the deviation of the test and how heat treatments can tighten your grouping.

From what you describe it sounds like your edge did reach a good hardness and other thicker portions are degrees of duplexed martensite/pearlite, which would also lose Rockwell as a quicker rate in tempering that a fully martensitic edge. I don’t think a second temper at 350F would hurt much, and it may even prevent some brittle behavior.
 
Kevin, is canola, or olive oil any faster than peanut oil..
we did 3 tests and they were all in the tang. and the were 58, 58.5 ,59 1/8" thick 1084
 
AJH_Knives said:
Kevin, is canola, or olive oil any faster than peanut oil..
we did 3 tests and they were all in the tang. and the were 58, 58.5 ,59 1/8" thick 1084
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Canola has a better cooling curve, peanut has a higher flash point and that is the main reason for its popularity in many hot working operations. You may want to give the canola a try if you have decided to work with the vegetable oils, 1/8" should have much less pearlite formation than a thicker cross section would.

Edited to add- it occurred to me that I have failed to address the obvious in Rockwell testing. Most folks will often only Rockwell after the temper when all is said and done, but this is another case of trying to understand the big picture with only one piece of the puzzle. To be honest a post temper number is only useful in qualifying a heat treatment when it is compared to an as-quenched number. If all you have is the post temper you cannot make any determination about your temper cycles or your hardening cycle. But if you have an as-quenched number of 63HRC and a tempering number of 58HRC you know you can stay with your current tempering regimen but your hardening process needs some attention. With a solid as-quenched number of 65HRC or better, you know you have nailed he hardening and now can use the tempering for the fine tuning you want. If I had to give up one of those number sets (which I would never do) I would stay with the as-quenched numbers and use files and field type testing to check my tempering, as tempering becomes very predictable once you are starting from a homogenous martensitic structure, but if there is pearlite mixed in it is anybody’s guess.
 
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The canola is also one of the more stable vegetable oils, but I'm not sure how it compares with peanut in that respect. At any rate, it's very important to use/keep it as fresh as possible for the most consistent results.

Kevin, do you charge for that last elusive 5%, neurosis and sleepless nights or do they get that part for free? :)
 
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