I just registered for this forum, as google brought me to this thread when I looked up 52100 plane irons. I'm an amateur woodworker and planemaker who works almost entirely by hand (from rough lumber to finished work). I generally make a vintage english pattern wooden plane (out of solid quartered beech) or infills (with rosewood infills, mostly all steel bottom and sides dovetailed).
https://i.imgur.com/wqwrv0B.jpg
https://i.imgur.com/RnBIwC0.jpg
(as I said, amateur - I don't sell tools, but try to make them well enough that I will use them over purchased tools).
At any rate, I've got a fascination with plane irons and have an answer to some of the questions above. Last year, I durability tested to dull a group of plane irons. Part of the reason was to get data on feet planed in total (rather than accelerated tests, or torture tests, which don't match planing wood), and the other part was to get a relative result for V11, which the manufacturer was claiming to wear twice as long as what's typically available (O1 and A2). The answer is mixed - in clean smoothing work, the claim is actually true. But simpler older steels are probably better for work in rough wood and heavier planing as the edge takes damage (fine edge, not what knife people would call a working edge - a working edge is too dull in a plane as the plane won't stay in a cut without someone leaning on it, and if you try that woodworking, you'll be sucking wind in 10 minutes when you planned to work for half a day).
At any rate, in relative edge wear, this is what I found. I made the O1 iron, the A2 iron is Lie Nielsen (they make the best I've seen), the blue steel is tsunesaburo (And was partially defective - the edge looked as if it was letting go of carbides - I took pictures of the edges every 200 feet of planing), the HSS is chinese make (not quite M2, but close), and the 3v and M4 are CPM heat treated by paul bos before he retired (they don't belong to me, but were given to me for the test). The edge for the test was confirmed under a metallurgical scope and sharpened through 1 micron diamond so that no steel would be incompletely sharpened (no carbides/abrasives battling for superiority).
In general, you can multiply these ratios and assume that in most test pieces (maple and american beech), the 01 iron ran about 800 feet. So in relative ratios:
O1 - 1.0
A2 - 1.25 (but the 1.0-1.25 territory was an edge falling apart and one would sharpen as the shavings coming out of the plane didn't stay together - O1 wears more uniformly. LN's A2 is cryo treated - the other irons that are not and made of A2 generally are less uniform yet - I ran A2 irons as a separate test a few years ago and found this)
Blue steel - 1.0 (I think it would've been closer to A2 due to higher hardness had it held together better)
Chinese HSS - 1.65 (this iron was supposed to be 61 hardness, but a versitron averaged a little over 65 on the c scale - it actually doesn't seem to have a negative effect, but hand work on the irons is pretty tough if they don't arrive flat)
3V at 59 hardness - 1.65 (it probably would've gained 15-20% if it had been hardened to 61 as requested - I understand knife folks like 59 for 3v for toughness, but planing is an exercise of abrasion and the extra toughness isn't needed - it actually makes the wire edge a pain to deal with sharpening a plane).
V11 - 2.0
CPM - M4 - 2.05
As to more exotic steels, planing is about two things -wear - and no unexpected failures in an edge (they leave little lines all over the place and then you have to sand those out). All of the above planed well in clean wood, but the blue steel iron did leave a duller surface from the outset as it started letting go of bits right away - uniformly, not catastrophic, but not great).
here's a picture of the edge trouble on blue steel (I don't know if this would be solved by forging - these irons are just made of hitachi prelaminated steel)
https://i.imgur.com/dhmKa79.jpg
O1 wear at complete dullness looks like this:
https://i.imgur.com/J2OMH4M.jpg
(notice the edge uniformity - lovely - this counts in woodworking -not just the area of wear, but how clean the line is at the very tip)
3v (V11 and M4 looked similar - the PMs all were fairly uniform and wore long)
https://i.imgur.com/pWTMz7s.jpg
Heavy hand tool users may resharpen a plane four times in a work session, and sometimes just to remove damage to finish a surface. To that end, V11 (which is mostly chromium carbides) is easier to deal with than M4 and 3V and O1 takes about half the time to hone as V11. In an ideal setting where wood is already clean (maybe out of a machine planer) the V11 (which is nearly identical to XHP) is lovely. When the work gets rougher, O1 is a better choice. A2 is more or less obsoleted by XHP/V11.
I planed somewhere between 40,000 and 50,000 feet of wood testing irons for these results and ran a few tests several times to confirm relative comparisons. Chromium in V11 makes it really slick through wood. The 3V and M4 had quite a bit more friction at the same sharpness. Is it vanadium carbides grabbing wood? I don't know.
Sorry to lay out so much info on my first post (especially on an old thread).
(by the way, since the O1 iron is my make from good quality us O1, a few people complained that they can't buy it and requested I test a hock iron -a familiar name to people in woodworking. My iron ran about 5% further than the hock iron in a head to head test alternating the irons back and forth in the same board until both were dull, but 5% is probably not outside of the range of error in the test for one take, so about the same. Softer O1 irons, like lee valley sells, will not last as long on a relative basis as these two)
What brings me here is someone asked how long 52100 will last planing, and I should know that in a couple of weeks as I have some 52100 on the way. Fortunately, planing is more about hardness and metal composition than it is perfect microstructure (nobody is prying or hammering, etc).
Long story short, I wouldn't bother with 3V or M4 or anything, and I wouldn't bother with any really high carbide steel that wasn't PM (These were all PMs). The wear is more uniform and the planing more pleasant with the PMs due to uniformity. The reality with both of the 3v and M4 irons is that both were sent to me incompletely sharpened. My cycle time to sharpen O1 is around a minute for a plane iron. 3V is at least two, and then more of the cycle shows edge damage if you hit something unexpected, so it's just not a great tradeoff. People who are less competent sharpening just never completely sharpen all of the damage out of it.
(the pictures above are at 150x optical with a good indian metallurgical scope - which is good compared to a hand held scope. Maybe not good compared to a $20K american scope that includes specialty software to take layered images, but good enough for this test).
this picture shows about 4000 feet of shavings. The postal scale on the desk is to weigh shavings - when I ran the results, I weighted the shavings as well to make sure everything was fair, and the testing for all but one (larger iron - the 3v) was done using the same plane.
https://i.imgur.com/bjgFohA.jpg
I've also found out since starting to make some hobby knives/blades, that setting a knife edge up for rough use is a whole lot different than planing!
(one other side comment - there are a lot of knife tests on youtube, some less controlled or not quantified at all. In terms of finding what's good for a plane blade, a comparison of sharpenability/grindability for a knife and a test of something like cutting clean rope or clean cardboard is good. As soon as a working edge is acceptable (vs. a very fine edge) and the test mediums go to impact or really abrasive stuff (like sandy rope), the results don't transfer well to planing as it's essential that a plane is sharp enough that it will take a shaving under its own weight. Anything less will play the user out in short order and result in ripples on the surface of wood where a plane comes in and out of a cut.
