Question for Mete.

Troop

Troop

Joined
Oct 26, 2006
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Mete, I followed your recommendation and picked up a copy of Tool Steels, by Roberts, Hamaker, & Johnson; 3rd edition (1962).
Under Cold Work Die Steels, under Hardening, p. 481, it states, in ref. to A2 and other chromium alloyed steels, " The chromium steels can be oil quenched from lower hardening temperatures (1600 to 1650F) with correspondingly less decarburization, but dimensional changes are likely to be greater than with air."
I don't get it. Either you're dissolving the alloying elements/carbides, or not, right? For air quenching A2, 1750-1800F is recommended.
If I quench A2 at 1600F into oil, I don't think it will get properly hardened.
Can you please help me to understand?:confused:
- Thanks
 
Troop,
I'm sure mete will chime in with a more complete answer, but A-2 can be quenched from 1600F to 1900F. The surface hardness is the major affected factor. At 1600F the surface gets to around Rc47. It moves up rapidly to Rc65 at 1760F. and falls off to Rc59 at 1900F. Notice I said "surface" hardness. The section you are reading is for tool and die process. These don't need the same requirements as knives. The dimensional characteristics may affect some items more than others. In industry, if you can make it at a lower temperature ( cheaper) and quench it in oil ( faster) then you can save money. That means little to a custom knife maker. Stick with 1695-1795F and plate quenching for knives.
Stacy
 
"properly hardened" that's the question.But for what ? Some of the HT procedures used by knifemakers would be laughed at on the basis of cost alone in industry.Running a HT shop with a large number of furnaces in operation is very costly so it's a big consideration. Another is the use.Do you care about optimum hardness ,retained austenite etc ? It's all a balance .Will you go for a steel or process that costs 20 % more but only gives you 10 % better properties ? I've learned on these forums to look at things from a little different perspective !!
 
Stacy, With A2 at 1600F, are you getting the the alloying elements partially into solution? Is that why the surface HRC is less?
-Thanks again.
 
I'm going out of my direct knowledge here, but let's look at A-2 and figure this out.

First, all A-2 is not the same. The formula can vary a lot. Basically:
It has about 1% carbon
It has about 5% chromium
It has about 1% to 1.5% molybdenum
It can have small amounts of nickel, vanadium, manganese, and silicon.

None of these have extensive solution requirements like the super alloy ingredients (W,V,Cr above 5%,Co, etc.)

At 1600F ,with proper heating and a long soak, all the chromium should go into solution with the hypereutectoid carbon. This is probably much more active at 1750F, but still should be in some sort of solution at 1600F. Where the chromium and carbon are may vary a lot depending on the temperature. For a large stamping die, that should do the job fine. For a knife it won't cut it ( bad pun).

OK, that is about all I can posit....mete? Help??
Stacy
 
Stacy, thanks for the reply. But, what I'm trying to figure out is the Principle at work behind the operation. What exactly is occurring within the matrix of the steel with two exact samples of A2?
What occurs at 1600F, and at 1800F, for the surfaces to be so different with regards to hardness after the quench?
This knowledge is important to me, for some reason that I don't fully grasp as yet.:)
 
As you go up it temperature you will dissolve more of the carbides. This in turn makes for a stronger and harder matrix .You will also get more retained austenite .BTW Mo is also a strong carbide former like W and V.At the max you will find RA levels have reached an unacceptable level and grain growth becomes a problem also. I would make sure that you have dissolved enough carbides [time and temperature ] to get a full strength matrix.
So there also you have to make choices. That is why I always suggest that when you choose a steel experiment with different HT to get the best properties for you and the use of the blade.
 
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