Thread: CPM M4 steel for razors

I have been a lurker here and have learned much from the forum in my short three years with a straight razor....thanks. After collecting many less than perfect vintage blades to test their shave-ability and spending more and more time with the hobby and of course honing, stropping, honing, stropping it occurred to me that none of these vintage blades ever benefited from the new "super" steels. In the last thirty years or so quantum leaps have been made in specialty steels with a lot of feedback from the knife forums but virtually nothing from the razor guys in typical searches. It piqued my interest to know how a "modern" steel from the hands of a custom maker, like Doug of Douglas Cutlery, would compare to the tried and true Filarmonica, Dbl Duck, Henckels, Boker, Wade, Torrey or other favorite?. How would those blades compare to what Doug was already making? Doug has agreed to satisfy my curiosity. He is currently making a pair of razors in the same style but with his preferred choice of steel to compare with the micro-powder processed CPM M4 which has won many extreme cutting competitions. How is it as a razor steel? Doug and I will let you know how this project progresses. I for one am very excited at the mere chance of getting my "perfect razor".

I have often wondered why the old blade makers didn't try some of the "harder" steels, i.e., tool steel, (50 Rockwell hardness +-), vs 4140/4130 steels with a Rockwell down around 32 Rc. Tool steel has been around for a long time. Maybe the lack of use comes from the greater effort that it takes to grind and hone, or possibly the cost. Interesting.

It sounds like an interesting test, but I wonder if you aren't starting from some wrong assumptions. As I understand it, steel hardness is dependent not only on composition but on the technique used in its shaping. A "soft" Iwasaki razor made from Swedish steel is HRV 740, which is roughly 60 Rockwell. A hard Tamahagane is HRV 780 if I recall correctly.

I don't know where the 32 Rockwell number comes from, but I doubt that many razors are that soft.

I'm conducting the test in such a way as to hopefully eliminate any effect during working. But just in case such effect is unavoidable, the M4 is being worked two different ways, 1 razor 'hot' worked (no quinching) the other worked as any other piece of steel. Heat treating is being done to the letter as publised on the net on both the M4 razors. Even though I'm taking these precautions, it wouldn't really matter if I wasn't, the test in the end is a carbon-chromium low alloy vs. CPM-M4, both are modern alloys. It's Low Alloy vs. Super Steel.

As for the Rockwell Hardness the M4 should end up 62-66RC, and the carbon-chromium alloy should end up 58-64RC, not a lot of difference, and in the end is not the subject of the test . The test is about wearabilityand shaveability, I will freely admit the CPM-M4 should have better wear characteristics, I don't however believe the difference will be as significant as one would think.

here's an artical on Low Alloys
Classification of Carbon and Low-Alloy Steels :: KEY to METALS Articles

Originally Posted by JimR

It sounds like an interesting test, but I wonder if you aren't starting from some wrong assumptions. As I understand it, steel hardness is dependent not only on composition but on the technique used in its shaping. A "soft" Iwasaki razor made from Swedish steel is HRV 740, which is roughly 60 Rockwell. A hard Tamahagane is HRV 780 if I recall correctly.

I don't know where the 32 Rockwell number comes from, but I doubt that many razors are that soft.

Originally Posted by JimR

It sounds like an interesting test, but I wonder if you aren't starting from some wrong assumptions. As I understand it, steel hardness is dependent not only on composition but on the technique used in its shaping.

Big +1... Steel hardness alone can often mean a chippy nature to the edge. The thing is to have an adequate amount of ductility & toughness.
This Iwasaki rated at 860 on the Vickers scale ie approx. 66HRC never chipped once throughout the whole honing process from bevel set to polish which included the use of diamond plates & sprays.
Yep, took a lot of trips back to the hones but not one of the 7 shave tests was uncomfortable. No offence but a good razor comes from the smith's hands as much as from the steel used.

I'll just roll this out on the floor for everyone to look at: Selecting Hi-Performance Tool Steels

In this end of the cutlery spectrum, take note of the fact that M4 has more vanadium carbides than M2 for the purpose of wear resistance. This should increase the frustration of anyone honing this type of steel because the blade will likely polish the stones unless the grit in the stones is harder than the steel.

I can testify that the High Speed Steels like M2 or M4 or the CPM variations of like kind will make a good enough blade to cut other blades. For cutting hair, I'm sure that it will be a case of over-engineering to get the job done. I enjoyed the experimentation when I did it, I hope you do too, that's what makes building a blade really fun.

Of traditional custom knife steels that were at one time exotic, I've had an ATS-34, and still have a couple of S30V straight razors. They shave well IME, but do require more time on the stones.

I went through a period of buying knives made with most of the super steels, and testing their edge longevity in all sorts of real-world applications.

Eventually, I found my "good steel" knives stayed sharp about 55-75% as long, but got 15% sharper, and could be resharpened in 10-25% of the amount of time as the super steels (S30V, M2, ZDP). VG-10 and 154CM turned out to be the best "good steels" for me. (VG-10 could be tweaked to slightly sharper/smoother of an edge). However, I got about as good a performance as 154CM out of C-75 (75% carbon, non-stainless), which is a LOT cheaper, and so easy to heat treat I don't have to worry about getting a bad one.

Personally, I suspect the main reason vintage razors didn't use tool steel, was that users wanted something soft enough that stropping had a noticeable effect on the edge. I notice that my Carbonsong C135 blade is so hard that I have to strop 2 times more strokes than I do for my "Swedish Steel" Dovo. It also takes 1.5x more stokes with my Naniwa 12K finishing stone (which may be similar to vintage barber hones).

This only seems to matter when I'm traveling and packing the strop &/or a barber hone is a pain. I can get about 1 extra shave out of the harder blade without stropping (before loosing comfort). For everyday use, it's not worth the hassle to strop me.

Honing a 66 HRc blade will be like whittling your hones: An exercise in frustration.
Btw, where does the number 32 come from? From what has been tested to our knowledge, old sheffields are all > 55 HRc, with 57-58 being the common value. Solingen blades go up to 61. Plenty hard enough.

Also, about the wonder steels: they are often designed for a purpose.
For example, take 12C27 which I have been looking into lately.
12C27 is a stainless steel with very good cutting properties.
12C27M has significantly lower carbon, which was apparently one of the trade-offs to make it even more stain resistant for kitchen and dishwasher use.
19C27 is the most wear resistant variation of that steel. However, it has bigger carbides. Because of this, it will never take a wicked edge.
And then there is 13C26, which they say is ideal for razors and surgical blades because of its edge retention and fine carbides, but it is not as tough.

Modern steels are all pretty much designed for a purpose.
For a razor you don't need high tensile strength, high toughness, or other mechanical properties. All that matters is that it doesn't microchip, has a decent hardness, and fine carbides. Tool steel has all of this.

It's like commuting to work in a car. Any decent car in good condition will do this just as well as a porche or ferrari. The Porche or ferrari might have a higher 'cool' factor, but they get you there in the same amount of time.

Btw, wear resistance is the big focus for supersteels for one reason. Ok 2 reasons. The first is that people always look (and pay) for the next big thing. The other is that most people still live with the assumption that knives never need sharpening. Most of my colleagues or friends buy a knife in the assumption that it will stay sharp. They even base their buying decision on factory edge sharpness. The first time I went buying a good kitchen knife in a knifeshop I felt like shouting at the proprietor who knew nothing about steel, and used factory edges as a sales pitch. And this is of course perfectly in line with a society in which people are not interested in maintenance or taking care of their tools.

Originally Posted by Bruno

Honing a 66 HRc blade will be like whittling your hones: An exercise in frustration.

Yes & no. Although the Iwasaki I honed took a lot of work there was never any doubt the stones were working, just very slowly
By contrast some old Sheffields I have honed squealed & skated on the stones like a blunt drill bit on case hardened steel. I was convinced they missed the tempering process altogether as they chipped at random intervals even 8k. I don't know what HRC old Sheffield steel would be at the quench but these were glass like.