BM's M4 steel....good and bad.

L

line6scott

Joined
Feb 22, 2015
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I got a Contego about 5 months ago. I usually love BM stuff. I have an Adamas in D2, and a Bone Collector, also in D2. The Bone Collector is uncoated, the Adamas has a DLC coating on it. I have never had rust issues with either, and I use these as work knives. I have to wear blue jeans as part on my uniform, and I work outside and sweat quite a bit. I also live on the Gulf Coast, so things get rusty. I've always heard that D2 was semi-stainless, but I've never had a problem with it.

So when BM came out with the Contego in M4, I thought I'd give it a try. Well, the cutting performance is great. Takes and holds an edge better than D2, I feel. Not that D2 is bad, but the cutting on M4 is that good.

However, I've noticed that the BM logo on the side that sits against my leg in my pocket, gets rust spots on it within an hour or 2. I can usually wipe them off, but sometimes I have to use a little steel wool. The blade has a gray DLC coating, so it stays pretty rust free, but the logo, which is exposed metal, and any scratches I might get, will rust it seems. And quickly too.

It's a shame, because I love the cutting performance of the M4, but I don't feel I can carry this one anymore at work, because I'm worried it will continue to have rust issues. I wish I'd have known this same knife came in M390, which is my favorite steel right now, but I was curious about the M4 steel.

Oh well. We live and we learn. Has anyone else noticed this with M4? I think I will still carry this knife, but not when I'm working outside, and probably not in the summer.
 
This has nothing to do with BM's M4 but M4 in general. D2 while not stainless is a semi-stainless. I'm sorry it's not working out though. Maybe try some tuffglide or vaseline?
 
You could try rubbing some oil or hot wax on the logo for protection. The logo is in an area where the oil/wax shouldn't get rubbed off during cutting.
 
I got mine around the same time as you and had the same problem! The good news is this problem is simple. I thought for a week the steel was not as rust prone as forums say. It was cool that week and I mostly worked inside. The next week I was outside in the 90 degree high humidity power washing stuff. The laser etches showed small rust spots all over. The edge bevel was pristine and stayed so for days. I got the rust off with a pencil. Then, I took some metal polish and lightly did the areas. This might smooth out whatever the laser did to that metal. I use Tri-Flo oil on my knives. I started using is to keep rust off my carbon swords. Just rub a bit on the etchings every week when you clean all the lint out. No rust for weeks and i got REALLY hot and moist today! ;)

May I ask about your lockup? Mine was great when new. I paid $20 over and got it as a retail store to inspect in person. This is the price of picky! After just a few days, especially weeks, the lockup went to about 95%. The axis bar sets deep into the cutout with maybe 1.5 mm more travel. It really cant wear much more before it goes in for a fix up. My blue class (grip, barrage, 940 and 940-1...) have way more room to wear in. This is my only black class. Honestly, it probably wont ever make it all the way and is only stronger the further it gets. I was just wondering if it yours was the same.
 
M4 is a (very) non stainless high speed tool steel. t is what it is.

It has a following and is constantly requested because of its performance. BM coats their M4 which many actually do not like. Imagine if it was uncoated like other brands' M4 models... Nature of the beast, it requires extra attention. I just coat mine in Ballistol occasionally and do not worry about the patina.
 
M4 is a great steel but WILL rust and stain if you're not careful with it!

A word on rustproofing. The BEST stuff I have found for high carbon steel is natural lanolin, the stuff that makes sheep's wool water resistant. It is totally superior to synthetic products because it doesnt evaporate! Put it there and it stays there... I even store my carbon blades in their leather sheaths without issues since I started using it. I tried everything and this stuff is leagues ahead.

You can get it in spray form from a company called Fluid Film. Trust me this stuff is the bomb! Also preserves leather and wood! I live in a sub-tropical climate and use it a bunch.
 
M4 is a very good knife steel, but not as good as the one it replaced.
It requires a bit more attention in highly corrosive environments, but well worth it.
 
Yeah, I still like the knife, and the steel is definitely a good performing steel, I just think it was a poor choice on my part. I should have researched the steel more. Living where I do, I should have realized it would be rust prone. I'm surprised I don't have more problems with my D2 knives.

Honed, as to the lock up, all 3 of my BM's lock up the same. I've had my Bone collector for about 3 years, and it hasn't changed. I think that is one of the advantages of the Axis Lock. It really doesn't wear the same as a lock bar type of knife. It still wears, but it doesn't seen to wear in any significant way. My experience at least... And I'm a fiddler. I flick my knives all day long. Your mileage may very though... All my knives are high impact tool steel. M4 and D2. I don't have any knives in a softer steel.
 
Glad I found this.. Just got the 810 this week and haven't noticed anything yet. I don't live in a humid area at all but still gets wet up here. Going to keep an eye on it since mine has the black coating but just mentioning about the laser etching.. When I took my h1 salt series it rusted on the etching.
 
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