M-2 Rockwell ?

jonearlt

June 29, 2014 18:31

58-60 I think.

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jonearlt

June 29, 2014 18:35

Yeah. This is from the BM site.

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fastjan

June 30, 2014 01:55

That's a handy chart with the Rockwell values right there on the end. What I'd like to know is if you could do additional heat-treating on a coated blade to enhance the Rockwell hardness. I'm guessing it might trash the coating, but it would be cool to step up the Rc.

I wonder if doing additional heat treating could warp the blades.

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zacn

June 30, 2014 02:32

Most likely Benchmade's M2 was closer to 62 than 60. It still has good toughness even when Rockwell Hardness exceeds 60.

No idea about if it could be heat treated for a higher hardness, but M2 itself is sometimes taken higher than 62. I'm not sure what level of toughness that would leave one with (brittleness could be an issue?). I think Benchmade is currently taking M4 higher because it's a tougher steel than M2 once the patented PM process is used, which M4 benefits from quite a lot.

http://www.buffaloprecision.co...ta_sheets/dsm2hs.htm

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lightning

June 30, 2014 03:38

The only way to increase the hardness would be to completely re-do the H.T. right from scratch.

Depending on the specific steel, the heat treat process can be simple to very complex, but the basiic process is the same:

1. Heat the blade up over above the upper critical temperature (aeound 2,100 Degree F), hold it there for a while, then quench it.

At this point the blade is at it's absolute hardest, but will be extremely brittle

2. heat it up in an oven to somewhere above the lower critical temp, the exact time and temperature is dictated by the hardness level you want to bring the blade down to. The higher the tempering temperature, the lower the hardness level. With M2 (and M4 is about the same temps) tempering temps are typically between 1,000 and 1,100 Deg. F. Which will give hardness levels between 58 and 64 Rc.

It is a very slim temperature margin between too hard and too soft for a knife.

After the first step, the maximum hardness is achieved, the second drops the hardness to point where the steel is actually usable as a knife.

So, can't just pop a blade back into a furnace heat it up a little more and make it just a bit harder. You can do that to make it softer though, but somehow I don't think that is the goal here...

And yes, either way it would completely bugger up the coating and markings on the blade.

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fastjan

June 30, 2014 04:18

Thanks for the info. I had no idea how they heat treated blades.

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lightning

June 30, 2014 18:16

np FJ, anytime

It actually is quite the process, especially when we get into the super steels.

We just take it for granted that a knife is properly heat treated, but don't really realize just how difficult it can actually be.

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dj

July 01, 2014 00:41

I used to work in a machine shop (2 yrs.) and used to take parts to the heat treat place .......... I saw where they put them and was told there process for the stuff we had.
Its quite surprising what they do ..........

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zacn

July 02, 2014 00:11

Awesome info!

Question: I have read that one of the downsides of some of the newer alloy steels (many called super steels) have a heat treatment window in which there is less room for variation and less forgiving and that this becomes an increasingly greater issue as one approaches the upper hardness levels of a steel when just 1/2 or so points higher and it becomes too brittle for practical cutting usage. Is this true?

Do some of the newer PM processes give the heat treatment stage a little more ease or leeway room, or does the increase in homogenous carbide distribution really not affect this aspect?

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po

July 11, 2014 15:16

There were some threads on the forum, several years ago, about a person who had Phil Wilson re-heat treat some M2 710 blades to full hardness, like 63-65, and the result was quite the success from his point of view.

There are a lot of knife smiths out there who will tell you that edge holding is not all about hardness, more about edge geometry and ductility. Busse, on their web site, say edges don't wear down on most knives, they actually chip away for the most part.

I've always liked the heat treat Benchmade did on the M2 blades. Very much tougher than ATS34 or 154CM at 60-62 RcH, more wear resistance, finer grain...Result is a much more durable edge. I do sometimes miss the toothy edge on 154CM though.

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mobilefirelord

August 08, 2014 01:40

Here is M2's data, assuming BKC used Crusible Rex M2. Hardness was ranging from 61-66 HRC, but I bet it is not as high as CPM-M4.

Same wear resistance at 62Hrc as D2(Airdi 150)@60Hrc. And a bit more than double in toughness. Until CPM-M4, it was formidable tool steel in those days.

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