Forging higher alloyed steels

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I'm curious about the prospect of forging something with higher content of alloys than the normal, 10xx series, 01, w1/2, 52100, etc. Etc.

What I'm curious about is if someone was to take on something like forging d2, a2, 154cm, things like that, basically anything that isn't particle metallurgy really.

The thing that has me curious is the guys in japan, like masashi. He likes to forge skd steels (basically a2, d2 over here, and whatever skd magic is equivalent to) and I believe he also does sld.

Now I know this can be done obviously, but what I'm wondering is about the growth of carbides in the steel. And knowing that the amount of alloying elements in these steels doesn't allow for completely dissolving them into solution below melting temperatures. So how does someone forge them without having giant carbides remaining throughout the steel effecting toughness?

Do the super long anneal times allow for the dissolving, and redistribution of smaller carbides just over a much longer period of time than what would happen during a normalization cycle in a simpler steel?

Also on a different note that I'll throw in. I watched an interview with masashi a little while back, on a live stream, and asked him if he used cryo, and wanted to hear what he thought about using it. (Just curious because of the seeming differences in the knifemaking culture over there). He mentioned that he found he could use cryo in a way other than what is traditionally done, to improve knife properties. This was through a translation done by the interviewer. Masashi refused to go into it much further (not wanting to give away too much info, to potential competitors I guess), but encouraged people to do experiments to find out more about it.

I've been racking my brain about this ever since. What could he possibly be doing? If I remember he was implying that he might be actually using it before austenizing and quenching. From what I understand, the guy does know, and understand metallurgy quite well, has a family history of knife makers, and he is one of the few makers over their willing to experiment with new stuff. So I tend to think maybe he's is somehow onto something. I just don't know what.

Tl;dr I'm dumb and want you guys to make me smarter.

 

[BluntCut MetalWorks]

Yoshikane & Masashi SKD/D2 are good knives (I bought them in 2005) and one of them still in my kitchen knife block (unused for the last 2+ years), no magics observed! Maybe much has improved/innovated since. Nevertheless arm waving...

Crystal transformations triggered by LN2 are diffusionless, which will be reset at temperature can dissolve(LN2 carbide/structure) & diffuse carbon. i.e. med-to-high alloyed steels: LN2 steps prior to hardening austenite would reset => not beneficial to final outcome. One could employ pre-hardening LN2 and aust via inductor to optimize low alloy steels but probably bad ROI.

 

[A.McPherson]

I can't speak to Japanese "maker" culture, but if it's anything like Japanese martial culture, expect any sort of interview to be laced with quite a bit of vagueness and statements that can have multiple meanings.

My experience with this only extends to martial arts, so take it with a grain of salt. I've noticed that when speaking publicly, the higher ranking Japanese masters tend to say things in a way that if taken literally, will directly contradict things that they say in private.

Not that they are lying, they are just saying things in a way that will mislead if you aren't already in the know.

 

[fitzo]

Sean McWilliams has long forged SS. Check website.
I forged one blade of 440C back in the day. Cutesy, but it was the only time I tried that by hand.

 

[Blankblank]

I can't speak to Japanese "maker" culture, but if it's anything like Japanese martial culture, expect any sort of interview to be laced with quite a bit of vagueness and statements that can have multiple meanings.

My experience with this only extends to martial arts, so take it with a grain of salt. I've noticed that when speaking publicly, the higher ranking Japanese masters tend to say things in a way that if taken literally, will directly contradict things that they say in private.

Not that they are lying, they are just saying things in a way that will mislead if you aren't already in the know.

Makes sense. I was thought it was a bit of a dubious claim, to say he is seeing increased properties using the cryo treatment in this new way, at the same time he, or at least the person translating was very vague. So like you said, it could be interpreted a number of ways. I asked if they would think about doing an edited version of that interview, with subtitles. They said they will work on it. So I would definitely like to see it again, after that.

 

[Blankblank]

Yoshikane & Masashi SKD/D2 are good knives (I bought them in 2005) and one of them still in my kitchen knife block (unused for the last 2+ years), no magics observed! Maybe much has improved/innovated since. Nevertheless arm waving...

Crystal transformations triggered by LN2 are diffusionless, which will be reset at temperature can dissolve(LN2 carbide/structure) & diffuse carbon. i.e. med-to-high alloyed steels: LN2 steps prior to hardening austenite would reset => not beneficial to final outcome. One could employ pre-hardening LN2 and aust via inductor to optimize low alloy steels but probably bad ROI.

The knives he is talking about doing this on would be very knew, if they have been sold yet at all. Again idk how much I necessarily believe everything. I just find it interesting.

Edit: also what you're saying is any effect that could be seen through whatever process is done with the ln2 before austenizing wouldn't be seen by the time the steel has be austinitized, quenched (possibly ran through ln2 again) and tempered? This could possibly make sense.

Stoping to think about it, I remember reading an article about doing preaustenization cycles on high alloy steels, and how toughness can be effected, on larrins site. If I recall, some positive effects could be seen if done at the right temperatures, but grain size was increased (I forget about how carbides were effected) if done at too high of a temperature, decreasing toughness. I wonder if he is just doing a low temperature austenization, quench, then cryo, before doing the final austenization.

 

[Blankblank]

Sean McWilliams has long forged SS. Check website.
I forged one blade of 440C back in the day. Cutesy, but it was the only time I tried that by hand.

I'll definitely give it a look. Does he going to anything about dealing with increased carbide size, or how to get good properties out of a steel like that when forging?

My thoughts are that the toughness could be effected by forging these steels. Although by how much, I'm not so sure. Also, how much the anneal needed after forging can work to bring the carbide size back down, if it does at all, or for all the carbide that is present in a given steel, just drawn out over a much longer period of time, compared to normalizing a carbon steel, then doing a few thermal cycles.

 

[DevinT]

Grain size is reduced by forging at lower temperatures,

Carbides get larger when forging at lower temperatures,

The sweet spot is between 1850-2050’f for most high alloy steels.

Most smiths forge too hot.

Cryo should be done immediately after the quench and before tempering.

Some research suggests that longer cryo soaks and cryo in between tempers has some benefits. It’s probably not enough to measure though.

Rules: don’t forge high alloy steels too hot or too cold.

Soak high alloy steels longer than simple steels at temperature because high alloy steels have lower thermal conductivity.

Do not normalize high alloy steels.

Annealing is a must after forging and before heat treating.

Do not heat treat high alloy steels in a forge.

Enough for now.

Hoss

 

[Stacy E. Apelt - Bladesmith]

Well, Hoss said it all.
My comments are that the chance of making a worse blade are far higher than making a better blade, The best possible is likely a blade even to stock removal and standard HT. So, why would you do it?

 

[Blankblank]

Well, Hoss said it all.
My comments are that the chance of making a worse blade are far higher than making a better blade, The best possible is likely a blade even to stock removal and standard HT. So, why would you do it?

I would likely never forge with these steels. I'm more wanting to know more about the process of it. Mostly out of curiosity, but also to learn more about steel, and metallurgy in general.

I do have a question for devin. Why would forging at higher temperatures keep the carbide size small? Is it because it's hot enough for the carbides to dissolve, and reform? My understanding was higher heat, means larger carbide size, as well as grain size.

 

[DevinT]

I would likely never forge with these steels. I'm more wanting to know more about the process of it. Mostly out of curiosity, but also to learn more about steel, and metallurgy in general.

I do have a question for devin. Why would forging at higher temperatures keep the carbide size small? Is it because it's hot enough for the carbides to dissolve, and reform? My understanding was higher heat, means larger carbide size, as well as grain size.

I’m not sure what the actual mechanism is that causes carbide coarsening. It can happen in all steels and is the same thing that causes carbide banding like in wootz.

Things that can affect carbide size; solidification of the initial ingot, ingot size, alloy/composition, forging temperature, amount of reduction, type of reduction, hammer roll or press, type of anneal etc.

Some high alloy steels like AEB-L and A2 have mostly secondary precipitated carbides because the temperature at which the carbides dissolve is low enough to be close to forging temperatures.

Steels like D2, 440c, 154 cm have mostly primary carbides after heat treating.

Steels in the annealed condition have twice the carbide volume as in the hardened and tempered condition. During austenitizing, some carbides dissolve putting carbon and alloy into the matrix.

MC carbides don’t dissolve at normal forging or heat treating temperatures.

Hoss

 

[Blankblank]

I’m not sure what the actual mechanism is that causes carbide coarsening. It can happen in all steels and is the same thing that causes carbide banding like in wootz.

Things that can affect carbide size; solidification of the initial ingot, ingot size, alloy/composition, forging temperature, amount of reduction, type of reduction, hammer roll or press, type of anneal etc.

Some high alloy steels like AEB-L and A2 have mostly secondary precipitated carbides because the temperature at which the carbides dissolve is low enough to be close to forging temperatures.

Steels like D2, 440c, 154 cm have mostly primary carbides after heat treating.

Steels in the annealed condition have twice the carbide volume as in the hardened and tempered condition. During austenitizing, some carbides dissolve putting carbon and alloy into the matrix.

MC carbides don’t dissolve at normal forging or heat treating temperatures.

Hoss

Ok. That does clear up some things. It brings up more questions at the same time though.

I'll have to look into some research papers, or something possibly if I'm going to get a complete understanding of this I think. I may do some searching on Google, if I end up with some extra time, and energy, to see what kind of studies I can pull up.

Sorry to anyone if posts like these are annoying. I just want to learn as much as I can, and I know there are a lot of people with a lot of experience, and knowledge here, that are kind enough to be willing to share.

 

[Larrin]

Carbides that dissolve at forging temperature reform at lower temperature and therefore are smaller, or at least are still small in size. Carbides that do not dissolve can sometimes be broken up through mechanical forging. But carbides will grow in size at temperature. The process is known as Ostwald ripening: https://en.wikipedia.org/wiki/Ostwald_ripening

 

[Blankblank]

Carbides that dissolve at forging temperature reform at lower temperature and therefore are smaller, or at least are still small in size. Carbides that do not dissolve can sometimes be broken up through mechanical forging. But carbides will grow in size at temperature. The process is known as Ostwald ripening: https://en.wikipedia.org/wiki/Ostwald_ripening

Ok. That makes sense. At least from the understanding I had of how steel responds to being heated.

So I wonder if someone forging one of these steels could do something like cold forge, with the intent of breaking up large carbides that weren't dissolved. So they get broken up, before going on to the annealing. I wonder If this would have any positive effects on carbide size. Or at least maybe the placement of the carbides throughout the structure of the steel.

Edit:I was rushed when i originally typed this. What I was trying to say is probably more legible now.

 

[DevinT]

Ok. That makes sense. At least from the understanding I had of how steel responds to being heated.

So I wonder if someone forging one of these steels could do something like cold forge, with the intent of breaking up large carbides that weren't dissolved. So they get broken up, before going on to the annealing. I wonder If this would have any positive effects on carbide size. Or at least maybe the placement of the carbides throughout the structure of the steel.

Edit:I was rushed when i originally typed this. What I was trying to say is probably more legible now.

Hot forging under a power hammer breaks up large carbides best.

Hoss