A2 steel - History and Properties

[Nick Dunham]

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].

Well dang. I should have. Very cool, thanks!

 

[bikerector]

These articles always make me realize that toughness is a fickle characteristic and I have no idea how much I really need, but it does make me feel pretty good about my love for 52100 for anything non-stainless or when I don't care for really high edge retention. It's fun to read, but it reminds me that sometimes I just need to use the knife or buy based more on design and craftsmanship and less on the steel/materials as many are "perfectly adequate" for anything I would use it for.

Another good article Larrin . I enjoy reading about some of the older tried and true tool steels, how poorly some actually perform (1095 and O1 surprised me on toughness, or lack of), and how some of the advancements came about.

On some of the steels that at typically run in the mid-50's hardness, 5160 and 1095 come to mind as manufactures seem to like to run them soft, would you expect the toughness curves to be relatively linear if one were to extrapolate that out? I think 5160 had an odd curve at a certain point above 60, but I don't have the info handy (maybe it was the HT or tempering graph). I'm kind of curious if there is a rate of change of the lines/curves that eventually makes some of the steels tougher at lower hardness that makes one a better option at a lower hardness, like if 1095 becomes tougher than 52100 at 55 rockwell (unlikely based on your data, more for framing the question). On the toughness hardness charts, I really only see an intersection of AEB-L and NioMax that kind of shows this phenomenon; A2 and PSF27 kind of looking at the relative intersection around 64 or 64.5.

 

[Larrin]

These articles always make me realize that toughness is a fickle characteristic and I have no idea how much I really need, but it does make me feel pretty good about my love for 52100 for anything non-stainless or when I don't care for really high edge retention. It's fun to read, but it reminds me that sometimes I just need to use the knife or buy based more on design and craftsmanship and less on the steel/materials as many are "perfectly adequate" for anything I would use it for.

Another good article Larrin . I enjoy reading about some of the older tried and true tool steels, how poorly some actually perform (1095 and O1 surprised me on toughness, or lack of), and how some of the advancements came about.

On some of the steels that at typically run in the mid-50's hardness, 5160 and 1095 come to mind as manufactures seem to like to run them soft, would you expect the toughness curves to be relatively linear if one were to extrapolate that out? I think 5160 had an odd curve at a certain point above 60, but I don't have the info handy (maybe it was the HT or tempering graph). I'm kind of curious if there is a rate of change of the lines/curves that eventually makes some of the steels tougher at lower hardness that makes one a better option at a lower hardness, like if 1095 becomes tougher than 52100 at 55 rockwell (unlikely based on your data, more for framing the question). On the toughness hardness charts, I really only see an intersection of AEB-L and NioMax that kind of shows this phenomenon; A2 and PSF27 kind of looking at the relative intersection around 64 or 64.5.

We didn't see anything in the toughness data of 5160 to see an increase in toughness below about 59 Rc. Austenitizing lower than 1500°F led to no improvement in toughness and tempering at 450°F was already showing tempered martensite embrittlement. Bainite probably has the best shot at having higher toughness in the 56-57 Rc range.

High alloy steels in general seem to be able to handle a wider range of austenitizing-tempering combinations with real improvements in toughness. CruForgeV acted the most like a high alloy steel in terms of forging grades. The low alloy steels are seemingly more fickle and are optimal in a narrower range of hardness. Maybe that's why there is a 10XX steel for seemingly every possible carbon content.