A2 steel - History and Properties

[jdm61]

I would be interesting to see how salt treated lower bainite 52100 compares to the L6 version and even the modern attempts to reproduce Frank Richtig's HT procedures using 1095 and molten lead for quenching. I saw one report on an attempt to figure out what old Frank was dogging, They got the same hardness levels and some straight characteristics, bit not some others. One reason may have been that their 1095 was heavy sphereoididzed and although they austenized for 30 minutes, the steel never got any hotter than 815C/500F and a lot of the samples were lower than that. Two things show dup. First, the sample where they did not skim the layer of lead oxide from the top of the pot cause said oxides to coat the blade and slow down the quench so it didn't work well. The second surprise was that The original Richtig knives used for comparison were different hardness. The small knife was like 51Rc and the big one 46Rc. There is a maker who claims to be austempering 1095. So does that mean, yeah, you can do it, but the results may not be as desired;e as you might expect?

@Stacy E. Apelt - Bladesmith is working on some salt pot heat treated 52100.

 

[hugofeynman]

Self reliance essentials works mostly with austempered 1095 steel, but they outsource their heat treatment, if I’m not mistaken. In some knives, their hrc is somewhat low, wish for me means nothing, just a number, steel microstructure is the king and their knives are well regarded by a lot of people.

 

[Larrin]

I would be interesting to see how salt treated lower bainite 52100 compares to the L6 version and even the modern attempts to reproduce Frank Richtig's HT procedures using 1095 and molten lead for quenching. I saw one report on an attempt to figure out what old Frank was dogging, They got the same hardness levels and some straight characteristics, bit not some others. One reason may have been that their 1095 was heavy sphereoididzed and although they austenized for 30 minutes, the steel never got any hotter than 815C/500F and a lot of the samples were lower than that. Two things show dup. First, the sample where they did not skim the layer of lead oxide from the top of the pot cause said oxides to coat the blade and slow down the quench so it didn't work well. The second surprise was that The original Richtig knives used for comparison were different hardness. The small knife was like 51Rc and the big one 46Rc. There is a maker who claims to be austempering 1095. So does that mean, yeah, you can do it, but the results may not be as desired;e as you might expect?

Writing about Richtig is on the list. I think the metallurgists are missing the forest for the trees with the focus on heat treatment, though.

 

[hugofeynman]

Austempered L6 would be interesting to see, too. Later I think I can ship a bar of 1.2714, conforms with L6 and has only 0.55% carbon, should be interesting to test. I’ll buy this bar from Achim Wirtz.

 

[samuraistuart]

If you would have asked me, "Which is tougher, O1 or A2, at the same hardness", I would have put $$$ down on O1 being tougher. It's carbide/grain structure is much finer, and has less carbide %. But just about every chart shows A2 as being tougher than O1. Hard for me to wrap my brain around that one.

 

[jdm61]

The assumption in that test that I mentioned was that he was likely not forging but just doing stock removal and austempering. The "forest " that they might have missed on that one was where they di not appear to normalize/thermal cycled the shperoidized steel and ended up with a witches brew of lower bainite with dashes of pearlite and still intact spheroidized carbides.

Writing about Richtig is on the list. I think the metallurgists are missing the forest for the trees with the focus on heat treatment, though.

 

[jdm61]

That is who I was referring too, but I knew them as Omnivore.

Self reliance essentials works mostly with austempered 1095 steel, but they outsource their heat treatment, if I’m not mistaken. In some knives, their hrc is somewhat low, wish for me means nothing, just a number, steel microstructure is the king and their knives are well regarded by a lot of people.

 

[Larrin]

The assumption in that test that I mentioned was that he was likely not forging but just doing stock removal and austempering. The "forest " that they might have missed on that one was where they di not appear to normalize/thermal cycled the shperoidized steel and ended up with a witches brew of lower bainite with dashes of pearlite and still intact spheroidized carbides.

I mean the edge geometry matters more than the steel.

 

[hugofeynman]

That is who I was referring too, but I knew them as Omnivore.

Ah, ok, their company is Self Reliance Essentials. They make a very nice survival sword, the Kodiak, Cliff Stamp approved, if I remember correctly, so they are probably making things right.

 

[Willie71]

If you would have asked me, "Which is tougher, O1 or A2, at the same hardness", I would have put $$$ down on O1 being tougher. It's carbide/grain structure is much finer, and has less carbide %. But just about every chart shows A2 as being tougher than O1. Hard for me to wrap my brain around that one.

I thought the same thing until I read about A2 in Tool Steels. I have the fourth edition iirc.

 

[jdm61]

I like the design of that sword, although I would probably expect a different steel at that $675 price point for a base model.

Ah, ok, their company is Self Reliance Essentials. They make a very nice survival sword, the Kodiak, Cliff Stamp approved, if I remember correctly, so they are probably making things right.

 

[hugofeynman]

I like the design of that sword, although I would probably expect a different steel at that $675 price point for a base model.

You’re probably right, but nowadays I much prefer to invest in the maker, rather than in the steel. They use cpm3v, too, a highly regarded steel by most people (not my first choice for anything, though).

 

[jdm61]

Hugo, the guys at Bestar list their "L6" as having that same lower carbon content.much lower than their 8760.

Austempered L6 would be interesting to see, too. Later I think I can ship a bar of 1.2714, conforms with L6 and has only 0.55% carbon, should be interesting to test. I’ll buy this bar from Achim Wirtz.

 

[jdm61]

On the other hand, Jimmy Fikes made those Jungle Honeys from 1095 IIRC. I would wonder if you would be better off going for martensite and just taking what 1095 will give you in a bigger blade with the "accidental hamon" thing where the core of the blade doesn't get fully hard anyway.

You’re probably right, but nowadays I much prefer to invest in the maker, rather than in the steel. They use cpm3v, too, a highly regarded steel by most people (not my first choice for anything, though).

 

[hugofeynman]

Hugo, the guys at Bestar list their "L6" as having that same lower carbon content.much lower than their 8760.

Yes, you’re right, jdm61. But most L6 I see in US steel suppliers has a carbon content around 0,7%, if I’m not mistaken. Like here: http://www.zknives.com/knives/steels/steelgraph.php?nm=l6 Never tried any, but I think I would prefer the 0.55% carbon one, my focus is always on toughness. For big choppers, my favorite maker uses Bohler K600, it’s like L6 with even less carbon (0.45/0.48%) and more Nickel (4%). Some would call it L6 “on steroids”!

 

[Storm W]

Well A2 is tougher than both D2 and O1 which is what it typically replaces.

I guess what I was trying to say is that since it didn't beat out some other tougher steels does that imply some sort of bias, or does it establish a baseline of required toughness? I was also wondering if the fact that it is very forgiving with the heat treatment possibly help its reputation since there are fewer poorly HT'd blades out there?

 

[Larrin]

I guess what I was trying to say is that since it didn't beat out some other tougher steels does that imply some sort of bias, or does it establish a baseline of required toughness? I was also wondering if the fact that it is very forgiving with the heat treatment possibly help its reputation since there are fewer poorly HT'd blades out there?

It's always hard to establish what "required toughness" is. It's tough enough until it isn't. It could be that a forgiving heat treatment helps. Though I don't think D2 is any less forgiving.

 

[Nick Dunham]

When Larrin first published this article, I started looking at historical sources for molybdenum-alloyed tool steels. I find that there was plenty of experimentation revolving around the use of molybdenum as a replacement - or partial replacement - for tungsten in high speed steels. The consensus at the time seemed to be that molybdenum worked, but was more expensive than tungsten - so it never caught on commercially. Examples without tungsten all had several percent of molybdenum. That left me somewhat in the dark on what triggered the acceptance of molybdenum-alloyed steels. I presumed that perhaps some innovation in molybdenum production drove down the cost, but couldn't find any readily available sources to confirm that.

Today, however, I think I found part anof the answer: during WW2, use of imported tungsten was restricted, which lead to more use of molybdenum and molybdenum-tungsten HSS.

I don't think there was much drive behind development of air-hardening cold work steels in the very early 20th century - HSS was very much on trend as a replacement for the earlier "self hardening" steels. Obviously at some point there was a realization that cold work die steels would be useful. One source claimed that high alloy cold work die steels originate in "wortle die steels", but the alloys were fairly different, with greater than 2% carbon.

Sources from 1923 onward are still copyrighted, so there's a bit of a gap right as A2 was developing, which is more difficult to acquire information from.

 

[JTknives]

A2 is one of my favorite steels.

 

[Larrin]

When Larrin first published this article, I started looking at historical sources for molybdenum-alloyed tool steels. I find that there was plenty of experimentation revolving around the use of molybdenum as a replacement - or partial replacement - for tungsten in high speed steels. The consensus at the time seemed to be that molybdenum worked, but was more expensive than tungsten - so it never caught on commercially. Examples without tungsten all had several percent of molybdenum. That left me somewhat in the dark on what triggered the acceptance of molybdenum-alloyed steels. I presumed that perhaps some innovation in molybdenum production drove down the cost, but couldn't find any readily available sources to confirm that.

Today, however, I think I found part anof the answer: during WW2, use of imported tungsten was restricted, which lead to more use of molybdenum and molybdenum-tungsten HSS.

I don't think there was much drive behind development of air-hardening cold work steels in the very early 20th century - HSS was very much on trend as a replacement for the earlier "self hardening" steels. Obviously at some point there was a realization that cold work die steels would be useful. One source claimed that high alloy cold work die steels originate in "wortle die steels", but the alloys were fairly different, with greater than 2% carbon.

Sources from 1923 onward are still copyrighted, so there's a bit of a gap right as A2 was developing, which is more difficult to acquire information from.

You should have read my article on the development of M4: https://knifesteelnerds.com/2018/04/16/the-development-of-first-tool-steels-book/
From the article:
[M]olybdenum-alloyed, or combined molybdenum- and tungsten-alloyed high speed steels became the dominant alloys in the USA by the 50’s or 60’s, and this was due to several factors:

1. There were significant tungsten shortages during World War II and the Korean War because the majority of tungsten is imported [1].
2. Salt bath heat treating of high speed steels became much more common which offered protection against decarburization [1].
3. The realization that molybdenum-alloying led to a lower melting point, meaning the optimum processing temperatures are lower. Too high austenitization led to poor performance in earlier experimentation [1].
4. The operation of Climax mine by the Climax Molybdenum company, for increased availability of molybdenum [5].