Cpm m4 patina?

[american21]

Just got my first m4 knife the spyderco mantra 2. I know this is a carbon steel but I sort of tried to patina it the natural way of leaving it in an apple for half and hour the blade got stained with rust orange in some spots not a black patina like I've had with super blue and other carbon steel. What do you guys do? This is my new favorite edc so I'm trying to keep rust away with handling it a few times a day.

 

[knarfeng]

CPM M4 is not "a carbon steel". It is a high alloy powder metal steel that lacks sufficient chromium to be "stainless". It will darken and rust, but there is no real reason to expect it to behave exactly the same as an actual "carbon steel". I've had good luck just keeping CPM M4 lightly oiled with mineral oil.

 

[hhmoore]

I'm not sure sticking it in an apple for half an hour is "the natural way", lol.
I've never bothered trying to patina M4...but, in my experience with other knives, an apple doesn't do much in that regard. If you simply want to straight up force a patina, clean the blade thoroughly...then wrap it in a paper towel soaked in vinegar for a while.
If you want to speed up a working patina; cut up some stew beef, some tomatoes, an onion, your choice of peppers...you get chili and patina!
Maybe use it to peel and cut a potato or two.
You can also slice fruits - bananas, cherries, berries make a tasty snack; and they all contribute to patina (I've even gotten a mild patina on D2 this way). I'd guess that slicing a lemon, or lime, would do it as well.

I have done all of the above to patina 1095. CPM-M4 is an entirely different thing; but it discolors failry easily, so I'd expect those methods to work. If it gets too dark, or you don't like it, a dab of polish rubbed/scrubbed with foil will knock it back pretty well.

 

[Spyder59]

Try sticking it in a potato overnight.

 

[somber]

Properties:

C 1.42
Mn 0.30
Si 0.25
Cr 4.00
W 5.50
Mo 5.25
V 4.00

With less chromium and more carbon than A2, you can expect it to patina, but it may take a little bit of intent. Try dipping it in warmed vinegar for a length of time, it should promote the steel to develop a darkened patina.

(not my picture - photocredit LowCountryBurl)

 

[jbmonkey]

it well darken naturally just from using it and keeping it cleaned so no rust emerges. you don't have to force it unless you just want to do that. i prefer no patina on mine, so i use a wax....but too each their own.

 

[shinyedges]

With all due respect, I do believe it is still a carbon steel despite it having various alloying elements and being a powdered steel. Granted it is not a "simple carbon steel" I think of it as a higher end carbon steel.

CPM M4 is not "a carbon steel". It is a high alloy powder metal steel that lacks sufficient chromium to be "stainless". It will darken and rust, but there is no real reason to expect it to behave exactly the same as an actual "carbon steel". I've had good luck just keeping CPM M4 lightly oiled with mineral oil.

 

[knifeglide]

what kind of wax do you guys use to cover your M4 steel? or to clean patina? i tried rubbing foil, it works but soon as i apply oil to clean, the patina comes right back

 

[Smiling]

Well, 52100 on my Drop Forged Hunter develops black staining (patina) really often when I use it on food. It only develops near the edge itself, since rest of the blade is coated.
Patina also developed on uncoated part of the blade on my Recon Tanto multiple times. It comes on it's own with use.
But Recon Tanto is SK-5 and Forged Hunter is 52100. But I guess any steel will develop patina with use.

I also have a small knife in D2 but I didn't really use it so far...

 

[knifeglide]

for the most part my M4 blade is oiled with no patina, but the flicker and top of the blade is darkening due to constant opening and closing ( fidgeting ), wondering if there is a way to remove it, i dont us this blade on food

 

[Danke42]

what kind of wax do you guys use to cover your M4 steel? or to clean patina? i tried rubbing foil, it works but soon as i apply oil to clean, the patina comes right back

I use Boeshield. Not a wax exactly but made to deal with rust and stick onto metal without gumming it up.

for the most part my M4 blade is oiled with no patina, but the flicker and top of the blade is darkening due to constant opening and closing ( fidgeting ), wondering if there is a way to remove it, i dont us this blade on food

Flitz is a great polishing compound to remove marks from any blade material.

 

[Richard Coyle]

Maybe try putting it in between vinegar soaked towels and putting it in the oven @ 170 degrees for 20ish minutes. It will make the vinegar evaporate and leave a super cool patina.
You’ll have to scrub some very light rust off, but it comes off easy.

 

[tyyreaun]

what kind of wax do you guys use to cover your M4 steel? or to clean patina? i tried rubbing foil, it works but soon as i apply oil to clean, the patina comes right back

Try Aegis EDCi corrosion inhibitor. Works great for me. The Cedric and Ada channel on YouTube shows some testing with it, against control knives without it.

 

[knifeglide]

Maybe try putting it in between vinegar soaked towels and putting it in the oven @ 170 degrees for 20ish minutes. It will make the vinegar evaporate and leave a super cool patina. View attachment 1286380 View attachment 1286381 View attachment 1286382
You’ll have to scrub some very light rust off, but it comes off easy.

love that design, looks like a great idea with the towel, looks wicked cool, thanks for the replies, will look further into this

 

[Petunia D. Feeble]

With all due respect, I do believe it is still a carbon steel despite it having various alloying elements and being a powdered steel. Granted it is not a "simple carbon steel" I think of it as a higher end carbon steel.

I agree with you, but here's why you're wrong :

Steel is classified to be carbon steel when:

• no minimum content is specified or required for chromium, cobalt, molybdenum, nickel, niobium, titanium, tungsten, vanadium, zirconium, or any other element to be added to obtain a desired alloying effect;
• the specified minimum for copper does not exceed 0.40 percent;
• or the maximum content specified for any of the following elements does not exceed the percentages noted: manganese 1.65, silicon0.60, copper 0.60.[1]

Technically I think it's classified as an alloy steel and simply happens to not be stainless. We tend to use "carbon steel" in a more colloquial sense though and just mean that it's not stainless. I'll certainly continue to refer to it and other non-stainless alloys as carbon steels.

 

[Danke42]

I tend to call M4 and the like "Tool Steel" instead of a carbon or stainless.

 

[knifeglide]

so one would assume tool steel is not meant to prep food?

 

[Danke42]

so one would assume tool steel is not meant to prep food?

Tool steel or carbon steel is fine for food prep.

Everyone used to use carbon steel for food prep. Now I know most of those olden days people are now dead or dying but it wasn't related to bad juju from not using stainless steel.

One of the best ways to keep a knife clear of rust is to use it a lot and keep it clean. If you do live in a humid area and need to put oil on any knife you use for food use one of the safe ones. Don't go with new or used motor oil etc.

 

[jpm2]

I tend to call M4 and the like "Tool Steel" instead of a carbon or stainless.

And more specifically, “high speed tool steel”.

 

[Smiling]

Tool steel or carbon steel is fine for food prep.

Everyone used to use carbon steel for food prep. Now I know most of those olden days people are now dead or dying but it wasn't related to bad juju from not using stainless steel.

One of the best ways to keep a knife clear of rust is to use it a lot and keep it clean. If you do live in a humid area and need to put oil on any knife you use for food use one of the safe ones. Don't go with new or used motor oil etc.

I use coconut oil for my Tanto and lip balm for my EDC.

Never experienced rust on any of them. Perfectly food safe too.