CPM-CRUWEAR Military issues, need help

[Liquid Cobra]

Mine had the same when I first got it. I cleaned the blade with rubbing alcohol and it went away. I would try this before anything else as it can't hurt the blade.

 

[GatorFlash1]

I don't wax the internals. I only use it on the blade to

1) polish the steel very, very mildly

2) wax and seal the cleaned, and dried blades before storing them for a few weeks. Longer with periodic inspections.

When I buy a knife I always treat it with tuff glide and similar products which help the steel resist rust to an extent. I insure not to get acidic or corrosive stuff in areas I can't clean them out of too, which helps. Nothing is perfect and everything takes work, and follow up.



The amount of Chrome in the composition isn't what determines how stainless a particular steel is. It's the "free chrome" that isn't locked up in carbides etc. Carbon content, and heat treat are two of the things that help determine this. This is also one of the reasons that the same batch of steel cut into two matching pieces can have different levels of corrosion resistance, toughness, wear resistance, etc. The heat treat info gives you recommendations for max wear resistance, etc and recommends temps and times, and tempers. Check out some Data sheets. http://www.nsm-ny.com/index.cfm?fuseaction=page.display&page_id=35

Thanks for the good info. I didn't know there was such a thing as "free chrome". All the data sheets for stainless steel do not reference this, they do show a chromium content over 10.5% though.

http://en.wikipedia.org/wiki/Stainless_steel

 

[Skywalker31]

Thanks for the good info. I didn't know there was such a thing as "free chrome". All the data sheets for stainless steel do not reference this, they do show a chromium content over 10.5% though.

http://en.wikipedia.org/wiki/Stainless_steel

GatorFlash,

If you look at the link you posted, under Properties -> Oxidation, note that stainless steel's corrosion resistance comes from a passivation layer of chromium oxide that forms on the surface in the presence of oxygen. However, chromium can also be bound up in chromium carbides. If enough chromium is forming carbides with the carbon instead of remaining free, it will not be able to form that chromium oxide layer and corrosion resistance will suffer.

As Mastiff points out, the amount of chromium carbides formed depends on carbon content (the other, defining element in carbides), heat treat, and other alloying elements present. For example, compare ZDP-189 and M390. Both are 20% chromium steels, made of the same eight elements. But ZDP-189 is known to rust a bit under the right conditions while M390 is touted as having completely superior corrosion resistance.

This is partially attributable to their other alloying elements' percentages and carbon content. ZDP-189 has 50% more carbon than M390, a bit more than 1% molybdenum, and less than 1% of every other alloying element. So it has more carbon available to form carbides, which will necessarily be mostly with chromium in the absence of significant amounts of other carbide formers (yes, molybdenum and tungsten will form carbides - but there's very little of them present compared to the chromium).

M390 on the other hand, starts off with 33% less carbon than ZDP-198 - and it has 4% vanadium, another very competitive carbide former. The end result is that less of its chromium is tied up in carbides, more of it remains free, and its corrosion resistance is better as a result (I realize I'm assuming that HT has equal effect on carbide formation in my comparison here - just trying to look at one variable at a time).

Graph comparing M390/ZDP-189: http://zknives.com/knives/steels/steelgraph.php?nm=zdp-189,m390&hrn=1&gm=0

If you look at Cruwear and CPM-M4, notice that while CPM-M4 has less chromium and more carbon - it also has significantly more molybdenum, tungsten, and vanadium than Cruwear, leaving more chromium free to form that protective chromium oxide passivation layer.

Graph for CPM-M4/Cruwear: http://zknives.com/knives/steels/steelgraph.php?nm=cpm m4,Cru-Wear&ni=,272&hrn=1&gm=0


(this is my understanding based on my own [admittedly somewhat limited] knowledge of chemistry and discussions with metallurgists and a materials scientist; if anyone has any corrections or comments I'd be glad to hear them.)

 

[The Mastiff]

Skywalker, you explained it better than I could. I was going to use the example of 420J2 at between 12 to 14% chrome being way more stainless than ZDP at 20% chrome but you did it better. Plus, the heat treat can change the amount of chrome tied up in carbides in the same steel from the same batch in two different knives. Some steels can change quite a bit when heat treated and tempered at high, or low temps. 154cm is one known for this. It begins getting more complicated than I care to take the time to type out though with my lousy typing skills.

 

[PayneTrain]

Skywalker,
Awesome explanation indeed. But I question the Cruwear/M4 comparison. I have a GB and a Cruwear Military and carry them just about the same in just about the same conditions, most notably skiing (hey, you never know). One day skiing with the Cruwear in my waistband, and not a spot on it. One day with the M4 and it's covered in freckles. There may be more to it than steel, like maybe the finish, but so far in my experience the Cruwear is more stain resistant than the M4. Not that either should be in the first place, maybe I sweat more on the GB, but I do remember wiping sweat from the Military too...

Iunno. Just my thoughts. I don't know what to do with my days off anymore.

 

[shunsui]

I don't care for steels that rust if you look at them hard or pit, but I figured, what the heck, it's not like I don't have a spare or two around, and picked up a Cruwear Millie and a Superblue Endura.

Give them a try. You can always bead blast them and sell them on the exchange if they go south.

 

[Skywalker31]

Skywalker,
Awesome explanation indeed. But I question the Cruwear/M4 comparison. I have a GB and a Cruwear Military and carry them just about the same in just about the same conditions, most notably skiing (hey, you never know). One day skiing with the Cruwear in my waistband, and not a spot on it. One day with the M4 and it's covered in freckles. There may be more to it than steel, like maybe the finish, but so far in my experience the Cruwear is more stain resistant than the M4. Not that either should be in the first place, maybe I sweat more on the GB, but I do remember wiping sweat from the Military too...

Iunno. Just my thoughts. I don't know what to do with my days off anymore.

I don't have any personal experience with Cruwear (I'm one of the guys that would like a LH Millie sprint, hah), but I had kind of picked up the impression that it seems to maybe go a little faster than CPM-M4 from some of the folks on here. I've got an Air that I love and haven't had any issues with at all so far.

So, um... I guess what I'm saying is that y'all should start agitating for some runs of LH Millies in Cruwear, CPM-M4, M390, and figure out one in ZDP-189, too, so us southpaws can chip in our own anecdotal evidence, hahaha.

Skiing sounds like a pretty good off-day activity to me. :thumbup:

 

[Orion's Belt]

I learned a bit from reading this thread. I came in thinking it wasn't as rust resistant as it is.

 

[Marten]

I use "Museum Wax" which is obtainable from one of the local knife makers. Stops any oxidation and cleans at the same time.

 

[GatorFlash1]

GatorFlash,

If you look at the link you posted, under Properties -> Oxidation, note that stainless steel's corrosion resistance comes from a passivation layer of chromium oxide that forms on the surface in the presence of oxygen. However, chromium can also be bound up in chromium carbides. If enough chromium is forming carbides with the carbon instead of remaining free, it will not be able to form that chromium oxide layer and corrosion resistance will suffer.

As Mastiff points out, the amount of chromium carbides formed depends on carbon content (the other, defining element in carbides), heat treat, and other alloying elements present. For example, compare ZDP-189 and M390. Both are 20% chromium steels, made of the same eight elements. But ZDP-189 is known to rust a bit under the right conditions while M390 is touted as having completely superior corrosion resistance.

This is partially attributable to their other alloying elements' percentages and carbon content. ZDP-189 has 50% more carbon than M390, a bit more than 1% molybdenum, and less than 1% of every other alloying element. So it has more carbon available to form carbides, which will necessarily be mostly with chromium in the absence of significant amounts of other carbide formers (yes, molybdenum and tungsten will form carbides - but there's very little of them present compared to the chromium).

M390 on the other hand, starts off with 33% less carbon than ZDP-198 - and it has 4% vanadium, another very competitive carbide former. The end result is that less of its chromium is tied up in carbides, more of it remains free, and its corrosion resistance is better as a result (I realize I'm assuming that HT has equal effect on carbide formation in my comparison here - just trying to look at one variable at a time).

Graph comparing M390/ZDP-189: http://zknives.com/knives/steels/steelgraph.php?nm=zdp-189,m390&hrn=1&gm=0

If you look at Cruwear and CPM-M4, notice that while CPM-M4 has less chromium and more carbon - it also has significantly more molybdenum, tungsten, and vanadium than Cruwear, leaving more chromium free to form that protective chromium oxide passivation layer.

Graph for CPM-M4/Cruwear: http://zknives.com/knives/steels/steelgraph.php?nm=cpm m4,Cru-Wear&ni=,272&hrn=1&gm=0


(this is my understanding based on my own [admittedly somewhat limited] knowledge of chemistry and discussions with metallurgists and a materials scientist; if anyone has any corrections or comments I'd be glad to hear them.)

This was great, thanks so much. I know certain guns have chrome lined barrels. I need to do some studying on carbides and what forms them under certain conditions. From your comments that is the key to stainless.