Shallow vs deep hardening steel

Greenberg Woods

Greenberg Woods

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Hey guys, thereso always talk about this subject but I was wondering if anyone could elaborate.

What makes a steel shallow or deep hardening? Why is 1084 deep but 1095 is shallow?

Is it simply the manganese percentage?

What are the advantages or disadvantages? I've heard people say you should use 1084 cause it deep hardening g and therefore easier to work, but O1 is super deep hardening and as is often mentioned needs a good controlled heat treat.

What application differences does it have? Would a shallow hardness blade be tougher since the core is less hard?
 
The property is called "hardenability." The term refers to how thick a section of steel can be hardened throughout or alternatively how slow you can cool the steel while still reaching maximum or near-maximum hardness. For full hardness you need 100% martensite. If cooled more slowly you get other transformations on the way down such as to pearlite which will lower hardness. With high hardenability you can avoid those transformations even when cooling thick sections in air. Manganese is one major element that increases hardenability; chromium, molybdenum and others do also.

References to "deep hardening" steels needing more control could be referring to lots of things, though they may be conflating different things that sometimes correlate with hardenability. One thing might be that it is easier to normalize in air with low hardenability, where higher hardenability steels would be martensitic. However higher hardenability steels have more alloy requiring longer soak times which might be why they are perceived as requiring more control.

A shallow hardness blade may be tougher with a soft core but controlling such heat treatments would be difficult because small changes in chemistry, quenchant, and material thickness would all change the degree to which it was hardened.
 
But what makes 1084 so good for a simple HT? I thought it had added manganese. Wouldn't that make it deep hardening and therefore need a more complex ht?
 
1084 is still a 'simple carbon steel' as we call it. So it can be HT'd a simple way. That makes it good for a beginner but at the same time still makes a fine blade for the experienced maker. It stays away from some of the problems that can occur with 1095.
When coupled with 15N20 ,1084 makes a very nice damascus !!
 
1084 is at the euctoid point, where there is enough carbon to go into solution without a soak, as there are few alloying elements, but there isn't extra carbon that can end up in the wrong places. With good heat treat equipment, the extra alloys in O1 can be brought into solution and evenly distributed. The extra alloys give combinations of wear resistance and toughness, but only if they end up where they are supposed to be. 1095 has extra carbon that can form carbides with the right heat treat, but over or under heat the blade and it would perform worse than 1084. With a non controlled forge, you are better off with 1075 to 1084, enough, but not too much carbon, and few alloying elements to mess up. 1084 is still a shallow hardening steel, it's just deeper hardening than 1075 or 1095 by a small amount.
 
Alloy elements that slow down the carbon precipitation kinetic give more time for "supercooling" the austenite through the usual 1000-900 °F window. If the steel cools faster than the carbon is able to precipitate out of solution within that °F range, the steel will transform in something else than pearlite....providing continuous cooling it will be martensite. Those are the deep hardening steels.

For steels that don't benefit of those alloy "retarder" the austenite will be very quick to squeeze out the carbon through that °F magic window....faster than you could quench the steel with a medium speed oil. Those are the shallow hardening steels.

Any consideration of performance shouldn't be related to the shallow/deep hardening thing, and of course alloy elements have a lot more business than just quenching speed influence.
 
I would not call 1084 REALLY deep hardening compared to some other steels. i still use #50 for it, but it will work with the "medium fast" 11-13 second oils like Tough Quench at their optimum temperature of about 150F where you are down to that 11 second "speed". As other have said, it has lower carbon content and also tends to have a much higher manganese content than say W2. I think that people recommend it for beginners because it is SUFFICIENTLY deep hardening and perhaps more importantly, as previously mentioned, it doesn't have much the way of other alloying elements that can complicate the life of someone using simple HT methods. Unlike say O1, you can get much closer to the max performance potential of 1084 with simple gear.
 
People use terms pretty liberally. 1084 can be described as deep hardening only compared to 1095. A knife blade of 1084 will fully harden when quenched in fast oil while 1095 may not.
 
My 2 cents; you can really only compare hardenability if the material is thick enough for there to be a significant temperature difference at different material depths. For a knife blade which typically has a large surface area compared to maximum thickness, most of the heat will be lost fast enough to achieve through hardness.

This also assumes you keep the rest of the quench variables as close together as possible.
 
The above is all pretty much right.


The terms deep and shallow when used with the word hardening refers to a test where a 1" round rod is quenched and the depth of the hardened steel is measured in a lab. If it goes most of the way to the core, it is deep hardening. If it goes only a little below the surface, it is shallow hardening. These things matter a lot in industrial HT of parts for tools and equipment.

In the thicknesses of knife blades, the depth of hardening isn't usually significant. Even very shallow hardening steels will likely harden all the way through.

What is significant to knifemakers in these steels is the quench rate. The shallower the hardening, the faster the quenchant needs to be. Simple carbon steels from .80% carbon up need a fast quench. They are all considered shallow hardening. Steels with alloying that helps give increased toughness will harden with a slower quench. Two of these are O-1 and 5160. Other simple carbon steels are alloyed with elements that allow a slower quench as well as create finer grain. Vanadium is the main alloy used for this purpose.

Many new knifemakers want to buy a HT oven and hardness tester to improve their HT. The first thing they should get to improve their HT is five gallons of Parks #50 ad five gallons of a medium speed quenchant. Put these into two five gallon quench tanks, and use them with the proper steels. Quench fast quench steels fast and slower quench steels slower. The parks should be between 70 and 90 degrees F and the medium speed quenchant is usually used at 120-130 F.
 
How does Parks 50 compare to sat, the 11 second quench oil tru grit sells? Is parks really the only good faith quench oil?
 
Maxim DT-48 is fast like Parks 50. Iirc they are 7-9 second oils.

Edit: I looked it up and DT48 is about a 6.5 second oil.
 
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Ben, Tough Quench, is repackaged 11-13 second Houghton. There are other types that some of the supply companies sell
Greenberg Woods said:
How does Parks 50 compare to sat, the 11 second quench oil tru grit sells? Is parks really the only good faith quench oil?
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Greenberg Woods said:
Would they work for w2
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From what I've read from those in the know, 10-12 second oil is on the cusp of working or not. It's not ideal, but you will likely get a hardened blade. You'll give up some hamon potential.

Does Kelly Couples still sell parks 50? If he does, that would be your best bet.
 
Stacy,

What is the issue with using a slower quenching steel like 5160 in Parks #50? Is it too much stress for the steel to cool that fast?
 
The standard test for hardenability is the Jominy End Quench Hardenability Test .That gives you comparitive numbers for the steels .There have been Standard H Steels which are melted within chemical composition but to specific hardenability levels.
The simple way for some of the tool steels the letters A, O ,W tell you to quench in air , oil or water !! Too fast a quench and it may crack.Too slow a quench and it won't harden properly !
 
Not all that well. It will work okay for 1084 at the 11 second level which is like 150F. That is the "sweet sport' for that oil. 120 or 180 gets you 13 seconds. Don't be a cheap bastid, Ben. Sell some more of your stash and buy the oil that you need. :D
Greenberg Woods said:
Would they work for w2
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PING!!!!! Not always, but the risk is there. I had a catastrophic failure on a very thin CruForge V blade using #50. On thicker blades, I had not had that problem.
i4Marc said:
Stacy,

What is the issue with using a slower quenching steel like 5160 in Parks #50? Is it too much stress for the steel to cool that fast?
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