Rust Problems

Only made about 15 knives so far but have sold a couple (to family friends), have given a few as gifts and have orders for a dozen.

I learned quickly that high carbon steels rust way too easily for the clientele around these parts so I moved to aeb-l but the chef knife I made for my mother has rust spot/stains already and I don’t expect anyone I sell a knife to to look after it any better than she would (she is pretty meticulous with it. It is possible that she didn’t dry it 100% perfect one time ((though she claims she always does and I believe her)) that resulted in these small spots. It also goes into a kydex sheath which may have allowed any minimal amounts of water to sit on the blade longer). The knife was finished on the bevel to 600grit and the flats were 800 hand sanded then to a grey very fine scotch brite belt and there were rust spots on both areas.

I’m kind of crushed because I’m loving this hobby but I know people around here will not be impressed to pay for a custom knife that rusts.

Is there other steels I should be considering that have better stainless properties but not a lot of down sides? I can read and research until I’m blue in the face but what I really value is actual input from real people.

Note: I have and will continue to send all stainless out for heat treating for the foreseeable future.

 

I do a lot with AEB-L and have never had an issue with rust. AEB-L is supposed to be pretty resistant.

You noted hand sanding to a scotchbrite finish. Did you use a scotchbrit belt? If so was it previously used on a carbon steel knife? If so the steel may have been contaminated. Refinishing the blade may help.

I also recently saw a post on another forum where someone was noting some imperfections in their AEB-L. Maybe a bad batch of AEB-L was recently released. It sometimes happens. Alpha Knife supply got into a pretty good pissing match a couple years ago with Niagara Specialty over inclusions within their S35VN. They don't carry CPM.

https://www.bladeforums.com/threads/aeb-l-steel-imperfection.1752610/

 

I have been using AEB-L for years and never experienced any rust. There will be some light patina that forms over time with use, but never the familiar brownish rust.

I'd be curious to see a photo of this. My first thought would be whether there is some galvanic activity going on in the sheath. Is it riveted? If so what are the rivets made of? Any other metals and water in contact? In my care instructions I state "hand wash, wipe dry and place in a wooden block or other holder where the knife is not in contact with other cutlery."

My knives we use at home are pretty abused. A nameless member of our household (hereafter known as "wife") leaves them in the sink of water overnight, jams them together with other spoons, forks and knives, chops things on a ceramic plate etc. Really good proving grounds. In my opinion, AEB-L does really well in a kitchen environment.

Dan

 

Scott mentioned the contamination issue. Try to never use the same belts for stainless and carbon steel. Bits of steel can get embedded in the belt and transferred to the other. The same applies to different grits. I keep my conditioning belts in a separate cabinet with a closed door. Nothing like getting a nice chunk of 36 grit ceramic stuck in your very fine conditioning belt.

 

I’d say cross contamination is a very good deduction. That said ‘rust spots’ on AEB-L have been posted about.

As for a look into ‘corrosion resistance’ tests on stainless (including AEB-L) it’s Knife Nerds to the rescue again. This is a must read.

https://knifesteelnerds.com/2019/10/14/corrosion-resistance-testing/

 

So when I first took up this hobby, I took a weekend workshop with Ed Storch (Storch Knives out of Mannville, AB) and he gave me a tip that I've used ever since. He recommended spraying some diluted gun blue on the finished blade and let it sit for a couple of hours. If there's any discolouration then sand some more (as fine a grit as you can). Eventually the blade will stay clean. I've never done any with/without testing on this but I haven't had any complaints so far.

Unfortunately I work exclusively with stainless steels so I can't speak to how it would work on non-stainless.

Good luck
Dave

 

Thank you all so much for the replies.
I will have to read this article (which so far looks very helpful) and get back to some of these individual questions and comments. I’m currently a stay at home dad so I don’t have the luxury of a lot of time on my hands lol.

 

After reading the article it does seem to imply that I should certainly not be getting rust on my aeb- so easily. I just had a knife I was working on develop rust overnight so there is an issue. I have some finishing belts (higher grit gator belts) that are brand new put away so I will use those ones from now on and keep them stored separate. Unfortunately I have grown found of the grey scotch brite finishing belt look and don’t have a new one so I guess I’ll be placing an order and try that.

If the HT (which I don’t do myself) wasn’t spot on or perhaps I heated the steel up too much post HT during grinding would you think that could cause it to rust? The article seemed to hint at this possibility but I don’t think I was heating it up that much, I mean, I’m using my bare hands and dunking in water.

 

It’s very unlikely overheating while grinding would effect corrosion resistance. You’d need higher temps to effect the amount of dissolved chromium. How large is the area rusting? Is it all over or just in tiny spots? If just tiny spots then it’s likely cross contamination, but if it’s all over it’s possibly a heat treat issue. if your austenitizing temp isn’t high enough not enough chromium will dissolve to give adequate stain resistance. This is also why when you work with stainless before hardening it’ll rust pretty easily. So if your whole batch is having problems maybe talk to your heat treater and confirm they heat treated for the right steel.

 

Thanks Joelsund.
It is in tiny spots which is leading me to think cross contamination. There is such a steep learning curve to knife making and I just never heard about this before. It is possible I used my finishing belt on high carbon knives when I first got it to test the look and never thought twice about it.
Waiting on new ones to arrive.

 

I use scraps of AEB-L for bolsters all the time. Never heat treated and have never seen or have had customers report any rust. AEB-L contains approximately 12% chromium. It's the chromium atoms on the surface of the steel that react with oxygen and form a protective film that resists rusting. The amount of chromium in the steel doesn't change with heat treatment. If it could, where would it go?

There is something called intergranular corrosion which can form in tiny areas where the chromium has been pushed out of the grain boundaries by heat. This is more likely to happen with Austenitic stainless like 304 or 316 during welding. Again, never seen any intergranular corrosion with any Martensitic stainless steel.

I'd say you have some tiny carbon steel swarf stuck on the surface. You can always do an experiment and leave some new AEB-L laying around water for a while. I am pretty confident you won't find any corrosion happening at all.

Dan

 

Never thought to ask...does your mother live near the sea?

 

I guess I shouldn’t speak on things With anecdotal evidence or without being able to back it up with an article. I messaged Larrin about having rust on nitro V and he mentioned that austenitizing temp not being high enough can lead to corrosion resistance problems from not enough chromium being put into solution (After testing my oven was 70F lower than I thought). His book also discusses corrosion resistance and why certain things reduce corrosion resistance like having chromium form carbides rather than being free. Heat treating doesn’t change the amount of chromium but it does change where it is in the steel structure and how it’s bound. I’ll test some hardened and annealed AEBL tomorrow.

 

Here’s another good article discussing some of the technicals of corrosion resistance.

https://knifesteelnerds.com/2018/06/11/how-much-more-chromium-does-d2-need-to-be-stainless/

 

Thanks for the response. All I got is anecdotal evidence. This makes sense. Some of the available chromium get locked up as carbides and isn't available for the passive film.

 

No, she does not live near the sea. We are in eastern Ontario.

I just got a batch of knives back from HT so I plan on cleaning up a patch on a couple and doing some testing. I might even use the same belts on one knife and see if I can get the same results just to confirm that it is cross contamination for sure.

 

Contamination of stainless steel from carbon steel is a significant issue in the welding trade.
Never use carbon steel belts on stainless steel. You can use stainless steel belts on carbon steel without issues.

Chlorine in water will bring out the rust problem faster than anything else and pool water or salt water in the air will cause a rust reaction in just a few days.

Solution is a solution when cross contamination happens the best and fastest way to remove it is with an acid that will dissolve the carbon steel.

 

I use my well water and baking soda for dunking.

In regards to the acid, can you elaborate a bit more on this or perhaps point my in the direction of a website or video that explains this.
Thanks!

 

This video should get you on the right path and the "Other" in the formula can be alcohol or water

 

Could you just acid Etch all your stainless blades before finishing hand sanding To dissolve the carbon steel? I assume the contamination’s is only on the very surface.