Report on m4 corrosion resistance

[Joris Mo]

Interesting read, there's a GB on it's way now and a custom blade in M4 should be finished soon. Both where meant to see some real use.

[Phil Wilson]

I am somewhat surprised on the corrosion resistance of SurfGringo's knife. His blade is CPM M4, not M4 and Spyderco also uses the CPM version. There is only 4% chrome in this grade, less than A2 for example, so there is not going to be much chrome floating around in the matrix to resist corrosion no matter how it is heat treated. Most of it is going to be tied up in complex carbides, maybe a small amount but not enough to explain the results here. The chrome is there for other reasons than corrosion resistance. I think SGringo's lack of corrosion is due to his care of the knife, ambient conditions, some due to clean steel and a bit due to the finish on the blade. I would not normally advocate this grade for use around salt water or humid climates but Lance likes the steel and is what he requested. The feed back here on this knife with this grade under these conditions has been very informative. Thanks, Phil

[Surfingringo]

i would agree with you Phil that I have been very careful about keeping this one cleaned after use and I think that's a large factor in the results I've gotten. As a counter example I got a Spyderco Swick in s30v about the same time and I have had more corrosion issues with it than I have with the m4. Now that's ovviously not about steel properties. S30v is vastly more corrosion resistant than m4. The difference is just that I have been much more cavalier about how I care for the stainless Swick. The Swick might occasionally get left dirty/salty/bloody in the sink after a long day of fishing. The custom m4?? NEVER! :eek:

So m4 certainly isn't going to perform like a stainless steel when it comes to corrosion resistance but I can testify that even with daily exposure to salt, blood and a humid tropical environment, it can be kept rust free with the most basic of care. Rinse and dry after use and you should have zero problems with this steel other than normal staining.

[Johnnie1801]

i would agree with you Phil that I have been very careful about keeping this one cleaned after use and I think that's a large factor in the results I've gotten.

I always wipe down my blades after use but my Gayle Bradley for example more so. I guess it's just at the back of my mind and I want to look after the blades so I can continue to get the great performance.

btw, I hope you have all found time to vote for a ukpk sprint, I would be interested to read your thoughts on the 4 steels with m4 being one of them. (sorry for the shameless plug :p)

http://www.spyderco.com/forumII/viewtop ... =2&t=66807

[Cliff Stamp]

Most of it is going to be tied up in complex carbides, maybe a small amount but not enough to explain the results here.

Phil, as I noted in the above, the chromium in the carbides will actually dissolve during tempering in a specific temperature range and one which is commonly used in hardening. The main chromium rich carbide M23C6 will be totally dissolved at an austenization temperature of 1200C, tempering above 575 C will further dissolve M4C3 carbides which were not dissolved in the soak. In short, M4 after tempering could easily have more Chromium in solution than A2. The molybdenum in M4 also strongly acts to increase corrosion resistance.

[bearfacedkiller]

I use an M4 Mule in my kitchen all the time. It is definitely stained but rust has never been an issue with minimal care. I live in a very arid climate though.