440C Rusting.... Need help!

A

AK-Edge

Member
I know its not exactly a knife, but the principles are similar, way I make them is similar..they're similar in every way, except that they don't have a long cutting edge... So instead of trying to find some other metal working forum to join, I figured it would be ok to just ask here. I am making a line of sculpting tools to eb used in both oil, polymer, and water based clays. Think of them as spikes that taper into different fine flats and curves to work the clay with. Simple but for a hole and a set screw on one end, where a small piece of bent wire is inserted to create fine lines and other things. I polish to a shine about an inch from each end, and then sandblast lightly the center to give the tools a grip. I also etch the name of the tool. Hardening is done at 1850F, with a 30 min soak, and air cool. Tempering is done right away. Twice, for one hour, each time, at 450F. Tools performed amazingly! And hardness, which is a big concern of mine, as the tips of these tools are very thin, and will accidentally hit hard concrete floors 10 times a day, making me fear chipping, breaking, or bending.... Are holding on better than expected. But... I suddenly hear from a guy working on a project that the tools are rusting! And now I am confused. I put a lot of time, money... thought I did my homework.... Not sure yet were the rusting is happening, but he's sending me pics in the next couple of days. Any ideas as to what I did wrong? Hadn't had this happen till now... Could I maybe have Gotten a bad/different batch of steel, that I unknowingly used? I know he probably had the tools underwater, soaking, for days... Will that do it regardless of stainless grade? Could it be the area I am sandblasting? The pitting is rusting? Any thoughts would be truly appreciated. This is a small business idea I'm working, since I work as a sculptor for special effects for film and tv. (make all the big, rubber monsters:), and we don't have anything like a high end sculpting tool. So figured i would give it a shot but if they are rusting.... I am screwed.... Any thoughts would be truly appreciated.
Andy

I will post pics of the tools andthe rusting, as soon as I get them. Thanks!
 
Stainless steel is rust resistant but not rust proof. Even 440C will rust if left in contact with water long enough. If the tools are wiped dry after use this shouldn't be happening unless there are some other chemicals involved that are reacting with the steel.
 
Is there any chance that the steel has been exposed to acids, especially nitric acid? It doesn't have to be direct exposure nor does the acid have to be strong.

Doug
 
For what you described, my instincts say that the person is simply not taking care of them....and in my opinion, likely bordering on abusing them. Bead blasted areas of the steel will be more prone to rust simply because of the tiny topography that bead blasting causes.
 
Thanks for the comments guys.. Still waiting for pictures to see exactly where and what this rust looks like. Don't think any other chemicals were involved... Just weird...
 
No stainless steel is truly "stainless". Stainless just means that it "stains less" than a high carbon steel.

Now that being said, some stainless steels are more stain "resistant" than others. 440C is typically fairly maintenance free if taken care of half way decently in my experience.

If you want something that can be left damp and dirty for longer periods, you might try something like H1, or even go the other direction and use a "lower grade" stainless with a lower carbon content. Also, the higher the polish, typically the easier they are to keep dry and clean. Like Ed said, bead blasting typically encourage moisture and other corrosives to adhere to the bead blasted finish due to the "rough" surface.
 
Any deviation from a perfectly polished surface is a place where corrosion is likely to occur. You might look into electro-polishing the tools in order to get the most rust resistant finish.

ernie
 
440c is a good steel but you still have to take care of it .it needs wiped clean after use .when you modeling clay there is a lot of water used so the tools need wiped cleaned after every use..
 
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