O1 steel heat treat and tempering question re- visited

AJH_Knives

Well-Known Member
So I heat treat my O1 in a kiln. I normalize at 1200* for 10 minutes let cool to room temp. I place in the kiln at 1480* for about 10 minutes then quench in 120* canola oil. I let cool to room temp, and cold soak in a bath of alcohol and dry ice -80*F. (read a white paper on the benefits of cryo and cold baths). That usually sets overnight. then I temper at 400* 2 hours 3 times. the steel is 3/32 think and i do not get much bend in the steel before it brakes. it takes some pressure to brake should i be worried? it brakes cleanly and the grain of the brake cross section looks uniform and nice and tight. is this the nature of O1. if someone would use the knife as a pry bay it will brake. I am now wondering if someone tries to pop a knee joint on an elk, like some people i have seen, they jam the knife in the joint and start prying on it, well my blade might brake.. am I doing something wrong? Do they seem a little brittle? This is a small skinning knife about a 3.5" blade, 7.5" oal
 
Aaron,
If I read correctly, you are going from quench to room temp, and then cryo. I am surprised that the O-1 doesn't self destruct in the cryo.

From the sound of it, you have fine and uniform grain when breaking the blade.

Couple of thoughts...........

Although I have never used canola, it is said to be a pretty fast oil that works well with 1095, w2, and a few other simple carbon steels. Could it be a bit fast for O-1? Maybe, maybe not. I use AAA for O-1 with great results.

If you think you are gaining something with cryo, I would suggest at least a "snap-temper" around 350° - 375° for at least an hour prior to a cryo bath.

A 400° temper is a good starting place. I would check for edge chipping, then work it up by 10° at a time until I reached what I thought was satisfactory.

Robert
 
First of all I would say that you are not actually normalizing at 1200°, just stress relieving. To normalize you have to achieve phase conversion and that won't happen until about 1430° and most people will normalize at around 1500-1550°. However, if you are doing stock removal and your steel is coming to you with fine grain then stress relieving may be all you need.

Strength and toughness are a trade-off with each other. A temperature of 400° may give you better edge retention with O-1 but 450° may leave it a little less likely to break if the blade is use like a crow bar.

Did the white paper that you read about cryogenic treatment of steel happen to mention which steel was used in the test? Not all steels can benefit from such treatment and many of those will require liquid nitrogen to get them cold enough. This has been discussed rather extensively on Kevin Cashen's site Hypefree Blades Forum.

Doug
 
So is what i am experiencing normal for the thickness of O1 I am using?
When i brake the blade, i tighten the bench vise on the tip most quarter of the blade and I grab the handle with 2 hands and pull it. I cannot gauge how much force i am exerting and maybe i am worried about nothing. I am thinking about tempering at 425*

the paper I read listed the tool steel that was tested and O1 was one of them. I am know expert on this, but I can say the starrett steel metallurgist said that it would help as well. He actually brought it up in the phone conversation. I don't have to do it. my kids get a kick out of it though...
Aaron
 
I temper O1 at 500 deg. and that consistently gives me HRC 59 which is great for a hunter (in my opinion). I find that to be a good balance of toughness and edge holding.
 
O-1 was specifically designed for high hardness abrasion resistant applications, so its “sweet spot” for hardness to toughness ratio is actually up around 61-63 HRC, to bring it softer is fine but it would probably be more effective to switch to another alloy that would have its toughness peak at a lower hardness level.

The cryo debate will rage on for the foreseeable future, and all we have to go on are the verifiable facts that can be entirely explained at this time. Among these are that one should not see a noticeable jump in HRC from freezing simple alloys (O-1 being one of them), and if you do, the easiest way to fix it is to just lower your hardening soak temperature to avoid the unnecessary retained austenite. The other verifiable fact is that the VAST majority of papers, studies and findings on the benefits of cryo have been provided by folks who sell cryo services and thus it is portrayed as a panacea capable of everything from improving trombone sounds to women’s stockings. I take everything written on the topic with a huge grain of salt and suggest others to do the same.

Heavily alloyed stainless steels do indeed benefit from cold treatments since the chemistry makes retained austenite unavoidable. But simple tool steels are not in the same category and I feel safe in saying that increases in basic Rockwell in these steels are symptomatic of less than adequate controls in the hardening operation. There may be crystalline lattice “things” occurring with deep cryo that I keep an open mind about, but this is in the purview of serious cold, as in liquid nitrogen cold, and not just dry ice or the freezer.

Tempering for 2 hours 3 times (for a total of six hours) is gross overkill. Save on your time, and electricity bill, by at least limiting each cycle to 1 hour. Multiple cycles are good but much more than 2 hours total has little value in the long run.

Just about any oil will work for O-1 and the real fast stuff is overkill, if vegetable oils are your thing perhaps peanut oil instead of canola. If you do not get much bend before the blade breaks- congratulations! You have a fully hardened blade and not a ductile blade like object, celebrate your success and be happy, while ignoring the blade benders! For what it is worth how many springs or pry-bars has anybody seen that bent like a noodle? If you want to protect the blade from the point abusing joint splitters, the secret is in increasing the materials thickness and not compromising the heat treatment.
 
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Kevin Cashen,
One of the things that I would like to understand about O1 is the soak time. 15 minutes for blades 3/16th" thick seems awful long. Could you tell me more about what is going on in the O1 that requires something like that?
AJH, sorry to side track this, if you prefer I will start another thread.
Thanks,
Fred
 
Kevin Cashen,
One of the things that I would like to understand about O1 is the soak time. 15 minutes for blades 3/16th" thick seems awful long. Could you tell me more about what is going on in the O1 that requires something like that?
AJH, sorry to side track this, if you prefer I will start another thread.
Thanks,
Fred

Do not feel alone if you misunderstand some of the concepts of soak times, it is a very common source of confusion. The main confusion comes from thinking of it in terms of mere thermal dynamics. Yes thicker sections do take more time to come to heat, but that really doesn’t play the major factor in the soak time; in fact it shouldn’t play a factor at all when you think that soak time only applies to time at temperature.

What is actually at play is chemistry. In order to fully harden steel you need to get around .8% of its carbon into solution in the form of austenite and then trap it there by quenching to create a super saturated solution at room temperature. When carbon is not into these solutions it is locked up in the form of carbides. With simple steels with no alloying (1075, 1080, 1084, 1095 etc…) the carbide is simple iron carbide (known as cementite), which has weaker bonds that will break at relatively low temperatures. So heating to the 1400F-1500F will dissolves them and put the carbon into solution rather easily.

But with alloyed steel there are other elements present that form more complex carbides with much stronger bonds. These carbides require much greater temperatures to free up the carbon but if they are broken entirely you will get bad things like retained austenite and dramatic grain growth. So in order to stay safely within the safe austentizing range you rely on time to do the work instead of temperature. In O-1 the main culprit is chromium. If you overheated to the point the chromium carbides were entirely dissolved it would be too quick to control and it would be very bad when you lost that control. But if you heat to 1475F the chemical actions are much slower and you can simply use soak time to achieve your desired results with total control.

O-1 has from .9% to 1% carbon, but will behave very similar to 1060 or 1070 without a soak since the carbon is not freed. With a soak it will behave more like 1084 or 1095 with a greater abrasion resistance, due to the added, but greatly refined, chromium carbides and grain refining tungsten or vanadium carbides. Due to the fine controls it gives, heat treating most steel without a soak time is like driving a car that only has two accelerator positions- park, and all the way to the floor. Soak times allow us to cruise comfortably at 55mph while staying in total control of the vehicle.
 
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Kevin, I enjoy every one of yours posts. Thank you for taking the time to share your knowledge. If you ever wrote a book, man I know a lot of us would be VERY interested.

Again thank you
 
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