Tempering Question

[tomh]

Thanks Karl I have thought a lot about this, but now you have given me much more to consider! Good stuff!!

[Montauks]

Thanks again

[kbaknife]

OK - I hope nobody is mad at me.
Or confused.
I really, really like this forum - a lot. (It helps that I'm a traditional bowhunter, too!) And everybody here is doing some fantastic work.
Sometimes the creativity overwhelms me.
I just felt compelled to share some of my experiences.
Making knives has got to be about the most enjoyable thing I've ever done. And it aggrivated me to only have infrequent and un-sure results.
I had a coal forge and a bucket of mineral oil. Actually, I made some decent knives! Then I got an acetylene torch for hardening purposes, and my results improved - somewhat.
After struggling along and wondering why this didn't work every time, or maybe changing that a little bit, and get more exasperated, I decided to make a few changes.
Piece of cake!
Overnight, my knife making took on a whole new meaning!
I just started donig what the other professionals were telling me to do!
I built a simple vertical propane forge. I got almost all of the pieces from scraps behind "shops" around town. The body was an 8 inch pipe from a well drilling company. About the only thing I bought was a few plumbing components and a blower. I probably put 70 bucks in it.
Then, after reading what others had posted similar to what I wrote up above, about a zillion times, it became evident that I needed to get the correct oils!
It's not cheap. 5 gallons cost me $75.00.
But that was three years ago and I'm still using the same oil!!!!
After only those tiny changes, and learning just the fewest of simple things, my success in making the type of knives I wanted to, became almost a 100% success rate.
And, on top of that, I KNEW that what I was doing was the right thing.
The confidence that gives a person really made a huge difference.  
I in no way intend to change any person's successful actions that they are already confident with. that has not been my intent at all.
I just wanted to share my experiences and success.
The biggest thing I had to do was kick my ego out of the equation and do what the poeple who are a LOT smarter than me were trying to tell me to do!
The steel industry has been around over a century. They've got all types of processes to evaluate and predict and control the steel in making it do what they designed it to do.
And we're using their steel!
Those processes are easily obtainable on a small scale.
I just had to do what they said!
Presto! Repeatable success.

[kbaknife]

I just "stole" this info from another knife site that was written by a fellow who really understands a great deal about heat treating and metallurgy.
I was on a discussion about heat treating 1084, and specifically on tempering FULLY HARDENED 1084. I am using NO LINKS, nor am I quoting anyone:

You may notice that (I) often quote higher tempering temps than the usual, "375-400F", stated by many others. In years past, I quoted lower temps. I have done the research and determined that it is counterintuitive to go low for a sharper blade. Sharpness has little to do with hardness, but toughness has a lot to do with edge durability.

The purpose of the temper cycle is to reduce the unstable and overly brittle martensite to a more stable mix of structures. It also is to convert any unconverted Austenite to Martensite. These conversion come at the cost of a small amount of hardness, but yield an increase in toughness, and a reduction in brittleness.

Using 1084 as an example:
As quenched the steel will be Rc64....but is quite brittle.
Tempered at 300F it is Rc 63....and still pretty brittle
Tempered at 400F it is Rc 61-62... and less brittle, but not a huge amount tougher.
Tempered at 450F it is Rc 60-61 and getting a lot tougher
Tempered at 500F it is Rc59-60 and the toughness is rising still.
Tempered at 600F the Rc is 57-58 and it is spring tough.

Now, I don't know about you, but a RC 57-58 knife will get real sharp in my shop. The edge will hold pretty well, and the edge will take a lot of abuse before damage.
For a kitchen blade, which should receive much less edge abuse, is desirable to have a harderer and longer lasting edge,Rc 60-61 will make a top grade chef's blade.

The reason to temper at 400F( or lower) is not really defendable. 500F will get the blade within two Rockwell points of that, again, at the gain of a much tougher blade.


Now, as to time and repition:
The temper cycle is a function of time and temperature. Temperature has a much greater effect than the time, but there needs to be enough time for the conversions to happen. Some of these conversions take an hour or more. So, tempering for two hours is a safe time to use as a standard.
Running a flame across the blade and getting the spine to turn blue ( all done in 15-20 seconds) may well drop the hardness, and it will do some tempering, but it will not replace a proper temper cycle. It takes time to do somethings, and tempering is one of them.

Why repeat the temper if two hours is enough to make the conversions?
The retained austenite that is converting to martensite does not finish the conversion until it gets down to room temperature (actually by the time it gets below 200F is pretty much done). Then it is untempered martensite. It now needs another temper to temper it. On complex stainless steel with high allow contents, it may take three tempers to clear out all the unconverted austenite and temper it.

So a good procedure to follow is to temper on the higher numbers,two hours ,twice. It will work with lower temps and shorted temper cycles....but not as well.

[Wampus]

Lots of great info Karl.  I've been using water to quench 52100 for a long time and haven't had any problems with cracking or warping.  I always just wiped the edge under to kill the color and then quickly transferred it to warm oil to finish cooling.  I bought 5 gal of Parks 50 about a year ago for W2 blades and now I use that at room temp for 52100 also with no problems, just dunk the whole blade under.  
I haven't been able to get any Texaco A so I always used motor oil diluted with trans fluid for 5160(I know, not a great idea).  I've tried using the P50 at about 70 degrees for the 5160 and I did get a little warping so I'm still looking for some appropriate quench oil.  
If you get a chance to compare 52100 blades quenched in Parks 50 vs Texaco A, I'd really be interested in the results.

[kbaknife]

Personally, I wouldn't even attempt 52100 in #50. If you are having success - don't change anything.
Parks #50 is "water speed" at room temperature. According to Crucible Steel:
"Oil quench from 1550 degrees F should give a hardness of 67 Rc. Water quenching is said to be risky, introducing too much stress."
So, if #50 is "water speed", ......?
I wish the diagram I have was more legible, or I'd figure out a way to post it. The hardening "nose" on the diagram to achive full hardness looks to abe about 6 seconds to get it to around 900 degrees, and Parks #50 will get it there in around 1-2 seconds. Might be adding too much stress.
As well, the high chromium content of 52100 makes it alittle more deep hardening and #50 and water/brine work best on shallow hardening steels.
But, I have heard of guys doing what you are suggesting, doing a short water quench and then eeeeeeaaaaaaassssssing it in with oil. I just have absolutely no experience with it.
I would use the Parks AAA which is obtainlable and is more suited to deep hardening steels as it has a slower cooling rate.
You won't get any of the Tex. "A" unless you order about 2000 gallons. It's just not made much anymore except for special order.
I know a few guys that have some barrels of it, so I got lucky.
You got warping on the 5160 BECAUSE you used the Parks #50. It's water speed AT ROOM TEMPERATURE.
that's just waaaaaaaaayy to fast for 5160. There's no need to heat it up like is sometimes necessary with other oils.
I think your success with water/oil on the 52100 is cool!!
I'm just not that adventurous.
You're my hero.

[Wampus]

I'm just a backyard hobby maker doing what I've seen others have success with.  I started using 52100 after I saw Al Pendray give a lecture about heat treating it various ways at a hammer-in back in the early 90's.  That guy seems to have a lot of extra brain somehow stuffed in that normal sized head.  I picked up the water wipe thing from watching Charles Ochs demonstrate somewhere but he doesn't use oil to finish, which scares me even to watch.  
A lot of what Pendray says goes along with what you typed in that knifemakers tend to try a lot of almost "witchcraft" type made up methods and quenchants when they would be better off just using what's been suggested and written by the steel industry for decades.  They spent a lot of time and money using some pretty smart engineers to come up with all that metallurgy stuff.  The main problem seems to be finding the proper quenchants in small quantities.  
It's still fun to play around with different methods and quenching goops and old found pieces of farm steel as long as we realize it won't make the best blade we could using modern methods and materials.  I guess it's a lot different for a hobby guy like me goofing around in his garage making a few knives for friends and family and a pro depending of repeat business for quality blades.

[kbaknife]

You are correct - using unknown materials and un-proven methods might be fun, but they are always far more expensive and time consuming in the long run.

[OconeeDan]

THANKS for all your time and expertise, guys!
Dan

[Lin Rhea]

Karl, I'v been away for a couple of days.

You have layed it all out pretty well to me. This subject is the most fascinating part of knifemaking to me.

From what you have said, I am even more convinced that I had heated the oil too much. Just a little. The two blades in question did harden, but not to that crisp, file skating hardness.

Back to oils, I have been using 5160 and 1084 quenching in the same oil. This has been successful for me, except for the above mentioned blades. The small variance in hardness, is probably a temperature related thing involving, perhaps, two different batches of 5160. I say this because the two that are giving me the problem are from a different size bar stock. I heat treated three from that stock. One did acceptable, the other two not. The only difference being that I probably had not heated the oil so much on the good blade.

My oil has always been successful for me till the above temperature thing. I am using a water soluable oil, believe it or not. I use very little water in it, maybe a quart to a gallon and a half. I had not had any experience with such an oil and will probably phase it out, but I have used it with success and dont want to get rid of it yet. It's has low flash point and does'nt seem to have a vapor jacket problem.

I have some Texaco Super quench that I want to use soon and see how that works too. Someone gave that to me so I'm not sure if Texaco A and Super Quench is the same oil or not. I will get me some in either case, because it's time for it.

This stuff is not magic and it should be as predictable as we can make it. The information shared here really helps. I hope that all reading will stick to the main stream, but not be too afraid to experiment for themselves.

Good stuff. Lin

[Doug Campbell]

After 20+ years of using mineral and veg oils, (I think successfully), I'm going to bite the bullet and get some real HT oil. We do owe it to ourselves and our customers to narrow down all the variables we can.

Thanks guys for all the info!

[kbaknife]

That's the great thing about 1084! Get it hot and quench it in something wet!
Not really, but almost.
You can heat up some "slow" oil or keep some "fast" oil room temp.
1084 will harden!
But, above all, keep this stuff simple, everybody. Once you get your "stuff" figured out, where you are "shop-wise", then improve things one item at a time.
Your fun and pleasure will improve as well!

[loyd]

man this is good stuff. loyd

[Bryant Hollinger]

I’m a new maker trying to learn. I have quenched a couple of 1095 blades in water and they seem to have hardened well. They where defiantly brittle as I broke one of them in two with my bare hands! Is water acceptable for 1095? If not what should I get? What in your opinion is the best/easiest to HT steel for a maker with only a coal forge and oven for heat treating? 1084? What about 1095?

[Lin Rhea]

Bryant,
        In my opinion, the simple steels are the easiest to quench successfully. Even these can have variations in alloy consistancy and will affect hardenability, but not by much. 1084 is a good one. I would use oil, not water, but water will certainly harden it. That includes 1095. The problem is, water will often stress it so much that it cracks or breaks.
      Go back through this thread and also read some of the other threads about heat treating various steels with various oils and get a better idea of what you need to do. All of the steels you mentioned are great steels. Lin

[Wampus]

Hey Bryant,

I grew up in Thomasville and my brother works at the Weyerhaeuser mill (old McMillan Blodel mill) up near you.  
If the blade broke before you tempered it in the oven, then that's pretty normal for a dead hard blade.  I've heard of them breaking just sitting on the bench after hardening because somebody waited a few hours before putting them in the oven for a temper cycle.

[Bryant Hollinger]

Thanks guys
 I think that after I use up my 1095 I might try to find some 1084. I have some D2 but plan on sending it to Mr. Paul Bos for HT. One day I would like to get a knife oven but just cant justifiy it yet. What supplier do yall get your quenchant from?

[Lin Rhea]

I'm having trouble getting it in 5 gallon quantities. I'm looking too. You may have to try veggie oil. Transmission fluid works too, but smells pretty bad. Lin

[Jeremy]

I've been using veggie oil (corn) to harden 1095 for a few years now.  For small blades (<5" and under 3/16" thick) it works fine, just make sure to heat the oil beforehand.  Try it with a larger knife where there's more heat to extract and you will run into problems.

[imskippy]

You guys are awesome. Such an amazing knowledge of the art and willing to share with those of us who are just tinkering for fun.                  

What would be the prefered oil of choice if I were to be using o1 tool steel less than 1/8" thick no larger a blade than say 4 to 5"?

Thanks for your knowledge guys. I've been using old saw blades and such and have decided it's time to try and put some consistency in my work. As I think Karl mentioned I owe it to the people who end up with my knives to be as consistent as possible. I was planning on buying o1 since it's easliy available from jantz but 1084 is sounding somewhat "foolproof" maybe I'll look for that instead. Thanks again guys. SKippy