Jump to content
Will Leavitt

Long Soak Temper vs Multiple Short tempering

Recommended Posts

I'm going to probably go ahead and conduct this experiment but was wondering what experiences and the metallurgical reasoning on what happens during a long (8 hours or more) tempering soak versus the 3 1 hour soaks I do know?

 

Thanks,

Will

Share this post


Link to post
Share on other sites

The point to using three seperate cycles is to reduce the possibility of temper embrittlement. Sometimes, especially with higher alloy steels, as the steel cools from the tempering cycle it precipitates the formation of martensite from retained austenite. So, in laymans terms... When you quench steel (harden it) not always does it form 100% hard steel, otherwise known as martensite. Instead of martensite you have some percentage of retained austenite, austenite being the state steel must reach prior to hardening (austenite is non-magnetic.) Retained austenite is not stable and will, over time change into martensite but, this new martensite will be untempered and, therefore, brittle. Well, when steel is cooling after tempering it tends to cause retained austenite to convert to martensite. So, now you have a blade with mostly tempered martensite but, some percentage of untempered martensite. How do you take care of the untempered stuff? Temper it again! The idea behind multiple tempers is that with each temper cycle, more of the retained austenite will convert to martensite. After three cycles you have pretty much hit the point where, if there is still retained austenite, it is such a small percentage as to be a non-issue.

 

~Bruce~

Share this post


Link to post
Share on other sites

Thanks for the info, Bruce. This is something that I hadn't picked up un Verhoeven's book but what you pointed out does make a lot of sense. I guess I'll go back to three cycles for tempering.

 

Doug Lester

Share this post


Link to post
Share on other sites

Thanks Bruce... I shouldn't try and think when I get home on night shift. I forgot to think about the cooling cycle being an integral part of the martensite conversion process. From now on I vow not to think while drinking a lot of beer and after working night shift. :D

Share this post


Link to post
Share on other sites

What bruce said above clearly makes sense. But I have a question. I was reading on Wikipedia :unsure: , and also found this refered to on ther sites. It states that temper embrittlement is more likely to happen when tempering between 500 & 700F. I would think that tempering at that range would be good for swords, giving around 52-57Rc. Is it true that that range is more likely to give temper embrittlement?

From Wikipedia: steel is then tempered by heating between the ranges of 150°C-260°C (300°F-500°F) and 370°C-650°C (700°F-1200°F). Tempering in the range of 260°C-370°C (500°F-700°F) is sometimes avoided to reduce temper brittling.

Share this post


Link to post
Share on other sites
What bruce said above clearly makes sense. But I have a question. I was reading on Wikipedia :unsure: , and also found this refered to on ther sites. It states that temper embrittlement is more likely to happen when tempering between 500 & 700F. I would think that tempering at that range would be good for swords, giving around 52-57Rc. Is it true that that range is more likely to give temper embrittlement?

 

The key phrase (that Bruce noted) is high alloy steels. Meaning those with chromium (stain resistant, high speed etc.) or other alloying elements (moly, tungsten, lots of vanadium etc.) versus low alloy steels like the 10xx series where those elements are minimal. If you read the tempering diagrams for HAS you will often see a double curve where you can choose between a lower or higher tempering temperature and still hit the hardness value you want. Each steel has its own diagram and one diagram will not do for all steels and the principle applied to high alloy steels does not apply to low alloy varieties.

 

There is a discussion about the possibility that even LASs can retain austenite. However if the heat treatment is done correctly, that should be minimized at the outset. HASs are very much more susceptible to retained austenite. So processes like multiple tempering cycles or even cryogenic treatments are needed to convert the retained austenite. I have a steel sample on my bench that even with the most rigourous heat treatment and tempering regimen still retains somewhere between 25-30% austenite and it is some tough stuff even then. So, retained austenite is not an automatic reason for blade failure.

 

These are not things to fear, but only have to be accounted for in your approach to the material.

Share this post


Link to post
Share on other sites
The key phrase (that Bruce noted) is high alloy steels. Meaning those with chromium (stain resistant, high speed etc.) or other alloying elements (moly, tungsten, lots of vanadium etc.) versus low alloy steels like the 10xx series where those elements are minimal. If you read the tempering diagrams for HAS you will often see a double curve where you can choose between a lower or higher tempering temperature and still hit the hardness value you want. Each steel has its own diagram and one diagram will not do for all steels and the principle applied to high alloy steels does not apply to low alloy varieties.

 

There is a discussion about the possibility that even LASs can retain austenite. However if the heat treatment is done correctly, that should be minimized at the outset. HASs are very much more susceptible to retained austenite. So processes like multiple tempering cycles or even cryogenic treatments are needed to convert the retained austenite. I have a steel sample on my bench that even with the most rigourous heat treatment and tempering regimen still retains somewhere between 25-30% austenite and it is some tough stuff even then. So, retained austenite is not an automatic reason for blade failure.

 

These are not things to fear, but only have to be accounted for in your approach to the material.

Thanks Mike

I'm using XK9258S, which is very similar to 9260. Is there anywhere I can go to find information regarding the treatment of that specific steel type? I've done a tonne of searches, but come up short.

 

It's qualities are:

Carbon. = 0.55 - 0.65

Si = 1.6 - 2.2

Mn = 0.7 - 1.05

P = Max 0.04

S = Max 0.04

Cr = Nil

 

Thanks for any help you all can offer. I am building a kiln right now, and will be wanting to heat treat swords and knives pretty soon, so all info is appreciated. Previously I quenched my knives from the forge and tempered at 280C in the oven. Swords were sent to a suspension factory, but they kept stuffing them up.

My kiln will be in two (570mm high) halves, and the blades will hang vertically.

 

Thanks friends

Share this post


Link to post
Share on other sites
870-930C seems a little high to quench from.

Most information I've found calls for quenching from the high end of austenitic for hardening. You should be alright quenching from a lower temp. but, with a longer soak near or at temperature. I wonder if the silicon has anything to do with the temperature? Here is a link to Crucibles' information for S5. S5 is very similiar to 9260, just has a little Chromium, Molybdenum, and Vanadium that the 9260 doesn't have. Labelle Silicon #2 The temperature listed for austenitic is a bit lower. I think that the 870-930C temp, may be a typo.

 

~Bruce~

Edited by B. Norris

Share this post


Link to post
Share on other sites

I have no experience with 9260 or S5/S4, but according to the ASM Heat Treater's Guide, 9260 should be quenched in oil/polymers from 870C (1600F). Again, lower temps with longer soaks are usually acceptable, as Bruce said. Looking at the IT digram, you'll want a fast quench (~ 1 second), and AS ~ 1350F.

 

Thanks,

Brian K.

Share this post


Link to post
Share on other sites

There you go, 870 it is. Thanks Red and Bruce.

I don't know how I'll go with maneuvering a red hot 4ft sword from the kiln into a narrow quench tube in less than a second, but I'm sure it'll go fine with a bit of leeway on that.

Share this post


Link to post
Share on other sites
There you go, 870 it is. Thanks Red and Bruce.

I don't know how I'll go with maneuvering a red hot 4ft sword from the kiln into a narrow quench tube in less than a second, but I'm sure it'll go fine with a bit of leeway on that.

You do not have to go from the kiln to the quench in less than one second. As long as the blade is at austenitic when you quench, everything is good. The one second or less time refers to how quickly the steel must cool, in the quench, from austenitic, to about 800-900 degrees Fahrenheit. That said, it is no good to take too long going from forge to quench because the thin parts will be cooler than the thick and this can cause warping or failure of the edge to harden. Go from austenitic to the 800-900F point in less than 1 second and the steel will harden. Once past the 800-900F temperature, the rate of cooling is not as crucial. You can, in fact, pull the steel from the quench and let it air cool. It will still harden. Many makers will do this and straighten out any warps in the blade before it cools to the point that martensite has formed. Going from austenitic to the 800-900F point too slowly (longer than 1 second) will cause the blade to not harden at all or to only form a fraction of the martensite that it could.

 

Quenching from the lower austenitic helps to maintain a fine grain structure. Most recommendations in heat treating manuals are the lowest common denominator, in other words the easiest, most foolproof way to get the steel hard. Quenching from the lower austenitic is a more difficult technique because, it requires a longer time at temperature for the steel to fully austenitize. In other words it is easier to mess up and so the information is left out of the heat treat manuals. Knives and swords are rather specialized and most heat treating information is geared towards tools that do not have long, thin, sections. Bigger pieces of metal tend to be more forgiving if the heat treat is not done exactly right.

 

Fine grain structure is very important, especially in a 4ft. sword. Two pieces of steel, both at the same hardness, one with fine grain structure and one with coarse, will behave very differently. The fine grained piece will stand up to much more abuse than the coarse grained sample. This is something easy for you to test with your kiln as you have much better controls than somebody heating blades by eye. I suggest that you take some sample pieces of your 9260 and try several heat treat routines, followed by testing the samples to destruction. Prepare one sample at the 1600F austenitizing temperature. A second sample austenitized at 1450F with about a 5-10 minute soak at temperature. A third sample just like the second but, with three cycles of austenitizing and hardening. I am assuming three cycles of normalization on all samples prior to hardening. Temper all three pieces at the same time and temperature and then put them in a vise and break them. The benefits of a fine grain structure and the lower austenitizing temperature should be immediately obvious.

 

~Bruce~

Share this post


Link to post
Share on other sites

If your material does behave like EN45 then then you might have to austenise at a higher temperature than you are used to . I use it quite a bit and it did not responded well to longer soaks at lower temperatures (almost all the other steel types do ) it does make good tough blades though .I have stoped using it for classes as its damned red hard and a little hard on students arms!

Every steel really is its own fish.

It is worth noting that the high tempering ranges quoted on the west yorkshire steel charts are for making springs not knives or swords I temper this stuff in the 190C to 240C range .

Share this post


Link to post
Share on other sites

Folks,

 

I was kind of an idiot when quoting the chart. Bruce, thanks for clarifying the details of the lower temp, longer soak (among other critical details). Thanks to Owen on the temp comments.

 

I quoted an AS (Austenite-Start) temp, but not the AF (Austenite-Finish) temp, which is keenly important for the Aust. soak. So, the AS ~1350F (732C), and AF ~ 1480F (804C). However, AC3 ~1500F (816C, at 28C/hr heating rate), so at any reasonable heating rate, soak should theoretically be between 1500F and 1600F (816C to 870C). As Bruce quite eloquently stated, the REAL temp is mighty variable, so test pieces would be the best way to go. I've done a lot of test pieces, and almost no real blades yet...

 

Thanks,

Brian K.

Share this post


Link to post
Share on other sites

Gotcha. Thanks for that Fellas, I'm sure that amount of guidance should save any intelligent person from steering off a cliff. I will set about doing a bunch of test pieces shortly and figure out what works best first hand.

 

I have previously snapped a few knives I quenched from the forge, trying to straighten them, and have found a nice fine grain structure so far. Never any sand size crystals. But getting some direct comparisons will be great.

 

As quench speed is paramount would y'all mind chiming in with a few pointers on my quench tube. It is 2" x 6" wide, and 44" deep. Which means it holds a little over 2 gallons of oil (8.25 litres). Does that sound like a fair size?

 

I haven't located any supplier in Western Australia of dedicated quenching mediums like Parkes etc. So I have been using canola oil as I know it has a high flash point. It seems to have worked pretty good so far.

 

Does that sound like a good setup? Our ambient temperatures are pretty warm, about 25C (77F). Do you support preheating the oil with a couple of bars considering the 9260 steel? I see most people have their quenchant at about 50C (120F).

 

I will enjoy the trials as the best way, but being on the right road to begin with will help me to my destination.

 

Thanks for all the input fellas.

Brendan

Edited by Brenno

Share this post


Link to post
Share on other sites
I have previously snapped a few knives I quenched from the forge, trying to straighten them, and have found a nice fine grain structure so far. Never any sand size crystals. But getting some direct comparisons will be great.

Once it gets to a certain point you will no longer be able to determine grain size accurately by eye. Any grain that you can see by eye is too big!

As quench speed is paramount would y'all mind chiming in with a few pointers on my quench tube. It is 2" x 6" wide, and 44" deep. Which means it holds a little over 2 gallons of oil (8.25 litres). Does that sound like a fair size?

Volume is king. I have 9 gallons of peanut oil in my quench tank and after three or four knives it needs to cool off a bit. You should be good for one go with your setup and then it will need to cool off some.

Does that sound like a good setup? Our ambient temperatures are pretty warm, about 25C (77F). Do you support preheating the oil with a couple of bars considering the 9260 steel? I see most people have their quenchant at about 50C (120F).

This one is sort of counter-intuitive. When you heat the oil up it thins out and becomes less viscous. The thinner, more fluid, hot oil will flow and circulate better around the quenched blade and cools the steel faster.

I will enjoy the trials as the best way, but being on the right road to begin with will help me to my destination.

That is what this forum is all about. I broke some blades early on when I started forging and couldn't figure out why most of them had snapped pretty easy but, one blade was just a bear to break. I hammered on it and bent it back and forth probably 6 or 8 times before it broke. I was stumped about why that was. They were all from the same steel. All heat treated the same way (or so I thought.) Why was one so tough? Turns out it one was the one that kept warping on me in the quench and I'd heated it up, straightened, and then rehardened 3 or 4 times. Everything I am telling you has been sponged off the other members here and it is my pleasure to be able to give something back.

 

~Bruce~

Share this post


Link to post
Share on other sites
Once it gets to a certain point you will no longer be able to determine grain size accurately by eye. Any grain that you can see by eye is too big!

 

I hot cut a rail anchor last week (appx. 1060 per the manufacturer). When I snapped the thin section, I looked to see what the 'grain size' might be by eye. It appears fine and powdery...sort of like, well...the picture below will show you. A few weeks ago I was messing around while forging the rail clips flat, and in between the much thicker rail clips heating I was pounding out a spike knife for practice. One spike seemed to want to overheat. Anything over a very low orange would blister it. I finally quenched it from that heat and busted the tip off to take a look. The grains were...somewhat visible to say the least lol. Brenno may have seen this picture on another forum (and I might be sidetracking the thread...if so I apologize and we'll get right back to it asap), but I'm curious what you think of the comparison. You said any 'grain' you can see by eye is too large, but I think the rail clip type grain is what Brenno meant, just powdery looking broken steel. See, it's not totally off topic!

 

Here's the picture:

 

Grain2.jpg

 

Is the rail clip 'enlarged' grain? It was quenched straight from a good bit above critical I suppose, and didn't have the benefit of any normalization etc due to it simply being hot cut.

 

Anyhow, just curious, and since the thread touched on the subject I thought I'd ask =).

 

Cris

Share this post


Link to post
Share on other sites

Thanks for the info Bruce.

It's so good to be able to pick the brains of more experienced makers. What did we do 10 years ago before the net? I'll watch how the temp shifts on my quench tube and see about a bigger one. My friend Jeff uses a 100lb gas bottle with the top cut off, filled with used ATF from mechanics. I understand about the counter intuitive reasoning behind the prewarmed oil, now.

 

Hey Cris.

That pic was on my mind. I couldn't believe that those grains on the right are so big and so look kind of sand sized.

The blades I've broken looked like that middle section - a powdery texture, looking very fine, and not discernable to the eye. Hence I couldn't tell if they had 'grown' or not. And with a thin outer crust which hasn't broken quite with the body, just like you can see on yours.

 

I'm kind of safe that I was HTing those knives on brickettes which struggled to get my steel to orange, let alone yellow, so there wasn't a big danger of overheating. I now have Coke which gets way hotter, but I'll be using my kiln for HTs so that will be safer. Having a pyrometer (thermometer) on it takes alot of the guess work out of it too.

 

The electric kiln was easy to build, though very time consuming. It cost about $550 in parts. I did it in 2 sections each 550mm (22") internal height - so I can do knives or stack it for swords. The blades hang in from above. I saw Howard Clark's kiln on the Discovery Channel show Weapon Masters (those guys were loose hey?). So I know I'm on the right track. There's a thread at SBG forum where my friend Jeff showed us how to build one, then I added my experiences.

Has anyone else done anything like this?

 

Cheers

Brendan

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×
×
  • Create New...