Grain refinement and other pre HT steps for High Alloy Steels

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Skiller1nc

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Ok so I've done a ton of reading on knife steel nerds, I've read Larrin Larrin book, plenty of reading on the forum but something I cant find or understand from reading is what steps to take for higher alloy steels. I understand the processes and benefits from normalizing, grain refining, and annealing for something like say forged 26c3. My current process is a normalize at the recommended temp in the Knife steel nerds book, 2 grain refinements, a fast det anneal and then austenitize.

For something like z-wear or magnacut (or any other high alloy steel, elmax, 4E, rex 121) what steps should we be taking prior to the final austenitize? I know Larrin has mentioned that a fast det anneal probably isnt the best for air-hardening steels and recommends a temper or datasheet anneal. but as far as reducing grain to the smallest point and distributing carbides evenly, getting the right things in solution for final aus, etc. what steps should be taken before the final aus/cryo/temper?
 
For the high alloy steels you mentioned they have enough carbide where the grains are very well pinned at typical forging temperatures. It just needs annealed after forging, a datasheet anneal would work just fine. For example, MagnaCut austenitized at even 2150F led to an ASTM prior austenite grain size of 12, which is very fine.

If you are using the steels for stock removal of course there are no required steps prior to austenitizing unless you do a stress relief treatment after grinding.
 
Larrin said:
For the high alloy steels you mentioned they have enough carbide where the grains are very well pinned at typical forging temperatures. It just needs annealed after forging, a datasheet anneal would work just fine. For example, MagnaCut austenitized at even 2150F led to an ASTM prior austenite grain size of 12, which is very fine.

If you are using the steels for stock removal of course there are no required steps prior to austenitizing unless you do a stress relief treatment after grinding.
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Interesting, okay I was not sure if the as received mill condition was the best place to start or not. Not to jump topics but your comment sparked another question. If the carbide is helping keep grain pinned and small, as far as toughness is concerned, with high aus temps (like higher than recommended say 2250 for magnacut) , is retained austenite the main culprit for lower toughness rather than large grain?
 
Skiller1nc said:
Interesting, okay I was not sure if the as received mill condition was the best place to start or not. Not to jump topics but your comment sparked another question. If the carbide is helping keep grain pinned and small, as far as toughness is concerned, with high aus temps (like higher than recommended say 2250 for magnacut) , is retained austenite the main culprit for lower toughness rather than large grain?
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Austenitizing high leads to reduced toughness from higher hardness and higher carbon in solution. Plate martensite is a possibility as a result from the high carbon in solution. Retained austenite will generally improve toughness though in excess amounts the opposite can happen.
 
Some studies show that pre-quenching from 1700-1800 before doing your final austenitize and quench will reduce grain size. D2, M2, AEB-L works with a pre-quench. Other steels will probably work also. My guess is that some of the fancy heat treatments for 3V include a pre-quench and tempering at the lower end.

Hoss
 
Yeah I am 90% sure the "Delta" heat treat does include a prequench. The idea being to reduce the soak time for the final austenitize. When I read that study on D2 and how much the prequench refined the grain, I started using a prequench on all stainless and higher alloy tool steels.
 
DevinT said:
Some studies show that pre-quenching from 1700-1800 before doing your final austenitize and quench will reduce grain size. D2, M2, AEB-L works with a pre-quench. Other steels will probably work also. My guess is that some of the fancy heat treatments for 3V include a pre-quench and tempering at the lower end.

Hoss
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samuraistuart samuraistuart Are you saying they are using a just prequench followed by the final austenitize ( I don't have a lot of knowledge about quenching from a martensitic structure) or do you think they (Delta) are doing a temper anneal then final austenitize? I also know Larrin Larrin has stated a temper anneal is good for high alloy steel but judging by the second post on this thread the time it takes and power required for running an oven 13 or so hours might be for nothing if grain size and microstructure are fine as is.
 
I stress relieve the material first at 1200 and let the bars cool off in the furnace overnight
 
Skiller1nc said:
samuraistuart samuraistuart Are you saying they are using a just prequench followed by the final austenitize ( I don't have a lot of knowledge about quenching from a martensitic structure) or do you think they (Delta) are doing a temper anneal then final austenitize? I also know Larrin Larrin has stated a temper anneal is good for high alloy steel but judging by the second post on this thread the time it takes and power required for running an oven 13 or so hours might be for nothing if grain size and microstructure are fine as is.
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Excellent question. To be 100% sure I would need to ask Nathan if the delta HT includes an anneal after the prequench, but I don't think so, as I would think that the anneal would be erasing what we are trying to accomplish with the prequench. I do not perform any anneal after the pre quench, but rather go right to austenitizing once the blade is cool.

Also, I think a "temper anneal" is ~1200°F for 2 hours (starting from martensite microstructure).

And as Harbeer mentioned in the post above, I also recently started making sure that I do a stress relief prior to the prequench, even on the PM steels. That stress relief is the same as a temper anneal (1200°F for 2 hours), but it's from the spheroidized microstructure.
 
So will there be a huge difference in grain size or results austenitizing from martensite vs spherodized pearlite? How would this affect the required soak times?
 
A material's response to pre-quenching is affected by both the particular alloy and its heat condition. You can't safely pre-quench something in a mixed condition such as a forging without annealing it first because you can get a wide range of response including drastic grain growth in areas such as the point where more of the carbides may be dissolved due to higher heats and extended time at temperature. And prequench from a regular anneal is different than pre-quenching from spheroidized annealed.

With stock removal it's also risky pre-quenching something you're not familiar with because (D2 for example) different manufacturers and even different lots can have different ingredients in the hotdog. A low vanadium verson of D2 will need lower temperatures or your attempt at grain refinement will backfire on you. I have seen this with my own eyes. Some testing and experimentation is needed first.

In my experiments, CPM D2 does not respond well to pre-quenching. I use regular old school Crucible D2. The cost difference is negligible, I use the conventional melt because (in a knife) it works better (for me).

Yes, I do pre-quench many materials. It started as an attempt to refine grain (which I think, beyond a certain point, probably serves no real purpose) but there are other side effects of this process that can have other benefits, depending on what you're doing with it.
 
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