Knife Care

[jimbo]

So I did lotso dives this weekend and forgot to dry my new Akona knife between dives.... By the time I unpacked it this morning, it was showing signs of rust. This is supposed to be 420 SS. Help! Do I use emery cloth and a bit of vaseline? Why is this knife showing signs of rust after 8-10 dives? What's up?

[jbd]

and the metal stayed wet too long. Also check to see where the knife was made. A lot of edged tools are made in developing countries and the metal is not of high quality. Even top of theline cutlery makers have introduced lines that are inferior to the products that brought them great reputation worldwide. These lesser lines will get rust spots unless dried immediately. The surface rust should come of easily with a SOS pad or a fine steel wool. Rinse well and dry thoroughly. Make sure the sheath is thoroughly dry before placing the knife back in it.

[blacknet]

Hello,

The best thing you can do is rince the knife IMMEDIATELY after the dive or as soon after as you can. Just because it's stainless steel does NOT mean it won't rust.

420 stainless the following properties:
carbon: .15 min.
nickel: 0
chromium: 12.0- 14.0
OTHER:
Mn 1.0MAX S .03MAX
P .04MAX Si 1.0MAX

AMS 5506
ASTM A-176
Density (lb/cu in) .28
RC 53/58

There is a trade off with all metals, you need carbon for it to hold an edge but the more carbon the more it will rust, the less carbon the more resistance it is but harder for it to hold an edge.

You can use an old tooth brush and hot soapy water and scrub it really good, hopefully it'll all come off. If it doesn't you may have to move up to the bigger toys (i've used a dremel tool to polish/clean one of my old dive knives) Your basicaly removing the surface rust so it won't spread.

Knives are somewhat high maintance but there's other dive gear that's even higher maintance. Some knives have removable parts like the handle. If this one can be removed then by all means remove it and start scrubing it.

Remember a wise man once said if you want to keep something in good condition then NEVER put it in saltwater.

Ed

[Iguana Don]

I keep all mine coated with a thin film of silicone grease, keeps the rust away.

ID

[kauai_diver]

Cost more but doens't rust and holds a great edge.

This is what I do to my stainless knife....

Freshwater rinse after each dive session(day)
Blow off/dry and spray with silicone....

Stainless is good but will rust, Titanium is the best bet but cost more.......

[joewr]

Jimbo,

All the above are true! All stainless steels are not created equal and, sadly, once the surface of the steel becomes pitted, it is nearly impossible to stop the rusting without constant maintainance. What IG says will work, though, for you if you clean and dry your knife off everyday and coat it with silicone oil or grease. If you do not have a ready supply of the grease, you can usually get it from a dive shop...use the Sea & Sea camera o-ring grease.

But, you need to remove the rust that is already there first. A Dremel tool will work, but a bench "grinder" with an appropriate buffing wheel and buffing compound works better. (Do not, I repeat, do not use the grinding wheel!)

If you have a buffing wheel, great! If you know someone with access to a machine shop, great. Unless you spend a lot of time with emery paper and crocus cloth, you will not remove the rust and you will have a badly "scarred" knife.

Good luck.

Joewr...who if he lived near you, would be happy to do it for you!

[blacknet]

hello,

Well a cheaper method is to epoxy the metal on the knife ;) Just like the non-military k-bars. This way the ONLY thing that CAN rust is the edge itself, if you keep it sharp you won't have to worry about that.

Ed

[joewr]

That is what I did! Ti is wonderful stuff...does not quite hold an edge the way steel does, but it is good enough and maintainance free! I was afraid that folks would think me a name dropper if I mentioned it, K-D! But you did and I am off the hook! We're gonna get along just fine, K-D, just fine!

And, blacknet, once the rust starts, epoxy will just not do the trick anymore. The epoxy will flake off because even the smallest amount of moisture + air will continue the corrosion process. It is nearly impossible under normal conditions to exclude them.

Joewr...with the foldable Ti knife always at the ready!

[blacknet]

Hello,

that's why you coat everything really good and when you sharpen the knife you remove part of the epoxy and metal. works really great for a durable rugged and extreme survival knife. Now the best thing for a 'dive knife' is a box cutter ;) When the blade gets rusty just throw it away and put a new one on it. The purpose of a 'dive knife' is to remove obstructions like fishing line and the like if you get entangled. Most dive knives on the market today fail to perform well in this task.

Ed

[NetDoc]

Hey all,

Hmnnn.... where to begin??? First off, carbon makes iron steel, and gives it strength, but not much hardness. Hardness works both ways. It makes a knife harder to sharpen, but more likely to retain its edge while working. Many people complain about a knife not holding its edge, when in actuality they have never put a proper edge on it to begin with. The Chromium that is used in the manufacture of most stainless steels, not only replaces some carbon which is how it inhibits rust, but it also adds hardness to the steel alloy as well. A hard steel is NOT a strong steel. Hard=Brittle!!! The angles for sharpening a stainless steel knife are also different and an aggressive stone must be first employed to get the shape just right. I use four diamond impregnated hones to accomplish all of my knife sharpening, and never ever leave them with a wire edge.

As for the treatment of a knife's surface, please be careful. Most knives are "case hardened" which means that just the outer layer of the steel (alloy) has been hardened by one of various processes (arsenic and heat being the most traditional). This usually means most of the blade has been hardened (where its thin), but not necessarily the underlying body (core) of the knife. If you polish/grind too much you will be exposing the softer alloy. BTW, as hardening makes an alloy more brittle, having the core of the knife not hardened preserves a good bit of its strength.

A better method is to use petroleum jelly per instructions, and then the "neutralizer" that actually bonds with the metal. This will preserve the metal of the knife, and will still inhibit the rusting process. Yes, your knife may have pits in it and not be a show piece. Oh well… you shoulda thought of that way before you took it in diving, Chester. IDs comment about slathering it with any silicone product is good.

As an aside, knives are about the only things that are case hardened. Bolts are NEVER hardened, much less Case Hardened (See the Hard=Brittle note above). Bolts come in various grades, denoted by a number on their head or a series of raised bars. Each grade denotes a certain strength (usually expressed in KIPs), with the higher grade meaning greater strength. Grade 5 bolts are the most common, and most of us have seen the familiar three bars on the head that indicate this grade (don't even ask). Bolts are designed and graded as to their shear strength. Tensile strength is hardly ever a factor.

And, uh Joe... here's that knife you stuck in my back earlier... :tease:

[NetDoc]

I heartily agree with Joewr on the composite knives issue. I have have seen two where the owners have asked me how to re-affix the edge. I merely told them to sharpen the carbon base, and use that... :tease:

[Grajan]

I have a Wenoka that I foolishly assumed would not rust so it is now in horrible condition - I will use a Dremel polisher to get it back.

For me a knife is a very rarely used emergency tool and I would dearly love it to be maintenance free - enough other stuff to do as it is. So how about dipping the whole blade in hot wax?

The wax will not interfere with cutting and should protect the blade the rest of the time. That way you should only need to clean/recoat it after you have used it (hopefully never).

Will this work?

[FredT]

420 SST is a good material that holds an edge well, but it will rust a bit, and that rust does stain the metal.

One method of cleaning is mechanical removal. This is relatively fast but takes elbow grease.

The easy way is to simply soak it in Phosphoric acid for a while. Coca Cola has a fair amount of Phosphoric in it. A couple hours in a non-metallic container of Coke will clean up most light rust on any stainlesss.

Rustproofing of old black powder guns used in wet environments was done with wax floating on a vat of boiling water. The boiling water heated the metal and caused rapid drying, the very thin hot wax coating applied as the metal was removed from the vat protected the metal until the next cleaning.

If you just have to do things the hard way the polish route works. I have other things to do besides polich metal so I use the chemical method.

FT

[Grajan]

I like the chemical approach. coke sounds good (if a little worrying - I tend not to routinely drink metal cleaners....).

I really like the hot waxing method - much more efficient than a bowl of wax. I will try it and let you know how it goes.

[Green_Manelishi]

Regardless of the cleaning method, alloy used, sheath
material, etc. it is NOT a good idea to store a knife in a sheath.

CARRY the knife in a sheath (or your hand)

STORE the knife on a shelf or somewhere OTHER than inside
the sheath.

[daylight]

A good set of 4 steakknives is about $4.00 at the dollar store. When they get too funky, toss away. My "good" knife has been on the shelf for two years. Gotta put it on Ebay one of these days.

[kevink]

Stainless steel does not rust. It gets surface stains from free iron on the surface, if this condition continues, due to repeated exposure to salt water, it can pit the surface.

Stainless comes in three broad categories - -

300 Stainless - - 303, 304, 316 are the most common. Some older forms are called 18-8. This is what the flatware in your kitchen cabinet is made out of. Great corrosion resistance because of the amount of nickel and chromium, but it wont take a sharp edge to save its life. 320 is the most salt resistant of the lot, mostly used for lab hardware and pipes.

400 Stainless - - Hardenable stainless. Not case hardened, but full hard the whole way through (at least in something as thin as a dive knife). This will hold an edge, but not the sort of razor sharp edge we would expect. These grades are very prone to 'corrosion' and 'staining' especially when near salt water.

Precipitation Hardening Stainless - - things like 17-4PH and the like. Full hard the whole way through. Corrosion resistance like the 300 series. A little pricey for dive knives, if anyone has seen one let me know.

FredT was on the right track with the Coke trick. Stainless won't rust, but if there is any 'free' iron left on the surface that is where your staining comes from. The Acid eats away the iron and leaves behind a layer of chrome or nickel oxide. I normally use a 1:5 mixture of white vinegar and water. I have to try coke. What you are doing is called 'passivation'. There is a diferent 'pickling' mixture for every grade of stainless, do a google search but most of the mixtures will be hell on earth to brew up at home. Stick with Coke or vinegar.

You need to do this when you pull the knife out of the package, and then after every couple of dives. After you let it soak for ~30 minutes, rinse it thoroughly. Don't worry about the acid eating the knife, once the free iron is removed the process stops itself. You then want to coat the surface with silicone gel or jelly, this is your added insurance. You also need to be very diligent about rinsing your knife after every dive!!

You should also acid soak the knife after it is sharpened. It can pick up iron from the last thing you sharpened. Try not to take a wire wheel or grinding stone to your knife becuase you run the risk of really coating it with free iron (and it will stain in a heartbeat). If it has started to pit a Dremel with a cloth wheel and a little rubbing compound should bring back the shine, be prepared to invest an hour.

Be especially careful anywhere there is metal to metal contact on the knife (i.e. hilt to handguard). Even if they are the same grade of stainless there is slight diferences in the exact composition. When dissimilar metals touch underwater they are prone to galvanic corrosion, which is a form of rusting. Look for a stainless knife that is just a metal blade with a plastic handle and nothing else, this will eliminate this problem.

The long and short, if you want a pretty dive knife, mount it above the mantle when you pull it out of the box. If you want a workable stainless knife, be prepared for maintenance after every dive. Are you thinking that the $70 for a titanium knife isn't that much now???

[KYDan]

I've been a cutlery nut since I was a young boy. Have always believed that a knife should be able to CUT to be worth carrying.

One of the best aspects of diving is the opportunity to buy a new type of kinfe!

Ever since I was able to master the craft well enough to do it, I've tried to keep at least one blade of my pocketknife sharp enough to shave with.

Some great info has been shared here. Thanks.

I'll have to try the Coke/vinegar trick on some Leatherman pliers that picked up some rust stains.

KYDan