Marquenching A2 Phenomena

[Troop]

Hi guys, I have been doing some forging of A2 for a while, and I noticed something that I stumbled upon, that I was hoping you could help me understand a little better, and to share with you.
When I forge A2, which I know to be an air hardening steel, the steel gets harder with every heat. I then marquench it in oil, then temper at 400 for an hour, then at 425 for an additional hour. The A2 comes out unbelievable with this process; very tough and holds an incredible edge.
Which now brings me to the point.... I made a stock removal knife for my daughter using the A2, marquenched, then tempered as above, but....it did not hold the edge for as nearly as long as the forged blade.
So, I had the idea to try and "fool" the A2, by using simulated heats, as if I was forging the blade. Bright orange....black heat....bright orange...black heat...etc., then marquenching it, then finally tempering it.
Well....wouldn't you know it...IT WORKED!!!
Now, did this work only because A2 is an air hardening steel, meaning it got harder after letting it cool to room temperature after the marquenching? (As well as it getting harder between heats.) Would this work with 10xx steels as well? At least the repeated heats would refine grain structure, right?
Oh yeah....one more thing. Why do many people say to temper A2 at 500, when, when I temper at 400, then 425, it comes out unbelievable? Is it because of the marquenching? Does the marquenching relax the steel to the degree that it's "softened up" (so to speak) prior to the tempering?
Thanks.
- Mitch

 

[mete]

The recent post " A2 HT" has a graph which shows a good hardness/toughness combination at a 500 F temper. Below that toughness falls off....There is some auto tempering during the marquenching process...Repeated hardening refines grain thus increases hardness.... There is no benefit to marquenching an air hardening steel as the air quench hardens the blade fully with minimal stress..... Experiments like this ,as well as HTing any complex steel ,requires a properly temperature controlled furnace !!!!

 

[Troop]

The recent post " A2 HT" has a graph which shows a good hardness/toughness combination at a 500 F temper. Below that toughness falls off....There is some auto tempering during the marquenching process...Repeated hardening refines grain thus increases hardness.... There is no benefit to marquenching an air hardening steel as the air quench hardens the blade fully with minimal stress..... Experiments like this ,as well as HTing any complex steel ,requires a properly temperature controlled furnace !!!!

O.K., Robert. Thank you for the teaching....always willing to learn.:thumbup: Do you think that this result would happen with 10xx series steel? Thanks.
- Mitch
P.S. Does what you said about "repeated hardening refines grain thus increases hardness" always apply? That is extremely important information if that is always true.

 

[mete]

Finer grain gives higher strength and hardness and toughness but after 3 times the hardenability is reduced.That's why we stop at 3x ! It works on all the steels but is more significant with the 10xx steels as they have no alloying elements in them to reduce grain size.A-2 already has fine grain, 1075 doesn't.

 

[hardheart]

AFAIK, normalizing and hardening both refine grain, but hardening does it a bit better. You could do like some; triple normalize, triple quench, triple temper. Depending on the steel, you might just be wasting fuel. But, since A2 is air hardening and you were quenching in air, I'd guess you'd need to dunk 10xx steels in oil to do similar.

 

[Troop]

AFAIK, normalizing and hardening both refine grain, but hardening does it a bit better. You could do like some; triple normalize, triple quench, triple temper. Depending on the steel, you might just be wasting fuel. But, since A2 is air hardening and you were quenching in air, I'd guess you'd need to dunk 10xx steels in oil to do similar.

HardHeart, I'm marquenching the A2 in oil. Not really sure what you mean when you say I'm quenching the A2 in air. Do you mean after the marquenching in oil, then allowing it to cool in the air to room temp....is that what you're calling the "air quench"? Let me know. Thanks.
- Mitch

 

[hardheart]

depends on how cool it gets between heats, I should have asked for clarification before I mentioned it, sorry.

 

[Troop]

depends on how cool it gets between heats, I should have asked for clarification before I mentioned it, sorry.

I just let it get to black heat between heats, like I was simulating forging it.
Thanks for the reply.
- Mitch

 

[Kevin R. Cashen]

... So, I had the idea to try and "fool" the A2, by using simulated heats, as if I was forging the blade. Bright orange....black heat....bright orange...black heat...etc., then marquenching it, then finally tempering it.
Well....wouldn't you know it...IT WORKED!!!...

:thumbup: Way to go troop! It seems whenever this sort of experimenting is tried by smiths they find the result that supports the "hammered steel is better steel," notion and just stop there in order to maintain their forging fantasies and another bunch of anectotal evidence is piled on the myth. You went the extra step of asking whether it was heat or hammer and tested to determine that! Your results are exactly as I would have predicted. The difference in the blades that this is done to would be a matter of grain refinement and carbide/alloy distributaion.

 

[Troop]

Thank you for the reply, Kevin. I really enjoy discovering the "Hidden Principles" at work behind the scenes, for myself, when I'm working/learning with different steels.
- Mitch
P.S. I just received the book you recommended, "Tool Steel Simplified." Wow....that book really explains a lot of things in a very "easy-to-understand", non-mystical way. Thanks again. :thumbup: