Can SS rust?

[Wade Lippman]

I have a steel hook that a magnet just barely sticks to, but there is some very light rust in a few places.
Is there a kind of SS that rusts a little, and a magnet sticks to it just a little?

[Lee Schierer]

Yes stainless steel can rust. Certain grades such as 300 series are more resistant than others. Some series of stainless are magnetic. But almost all of them will rust given the right conditions. Stainless also doesn't like long term exposure to such things as salt (Chlorides). Note that the name is stain Less, not stain proof.

[Larry Frank]

I think a better term is corrode. Depending on the environment, stainless can react with various acid, bases and other chemicals. It is always good to check the actual stainless grade against the environment. Of course, you can get grades that are more resistant but they cost goes up for increased nickel and chrome.

Most people want to select the most economic grade for their application.

[Lisa Starr]

Slightly magnetic and "rusting" is frequently an indicator of poorer quality "18-8" Stainless Steel. Grade 416 will be somewhat magnetic, but rarely corrodes.

[Wade Lippman]

I don't know where I got the hook or how it got corroded. But assuming it is poor quality 18-8, will it last a few years in fresh water? I am wanting a hook for a mooring to connect to my bow eye. It is a really nice heavy duty hook, but if it will rust out in a year I will keep looking. Thanks

My new SS refrigerator is as strongly magnetic as normal steel; go figure.

[Ben Helmich]

The way I understand it is the more stainless in the alloy makes it resistant to corrosion but soft, and the less stainless in the alloy is less resistant to corrosion but harder and more durable. It that about right?

[Dave Zellers]

My new SS refrigerator is as strongly magnetic as normal steel; go figure.

I have a hunch the SS on the doors is very thin and backed by regular steel to accommodate the peoples affinity for refrigerator magnets.

NOBODY with small children is going to buy a refrigerator that they can't attach fine art to with a banana magnet.

I mean, really!

[Kev Williams]

Practically any stainless will corrode given the right circumstances, but it's usually superfiicial...

Most stainless refrigerators, a magnet will not stick to the doors. To the SIDES, yes... sticking magnets on a pristine satin finish fridge door will make a mess of it in short order.

Wade, that hook will probably last 200 years in fresh water. And to clean up the rust, get some liquid Bar Keepers Friend cleanser and a Magic Eraser. Maybe a little vinegar if it's stubborn...

[Dave Zellers]

The magnets on my mid level SS Frigidaire fridge stick very well on the door. I know that the side is painted steel to mimic the door, but the difference in magnets sticking is minimal.

[John K Jordan]

NOBODY with small children is going to buy a refrigerator that they can't attach fine art to with a banana magnet.
I mean, really!

We have that problem with the grandkids! Ain't no magnet be a-stickin' to the front of the ice box here! I don't know if she knew that when she bought it and the other appliances years ago but it does give a clean look. PostIt notes take care of the occasional communication such as "get more coffee creamer or else." Magnets will stick to the sides of the fridge, the freezer in the next room, and the extra fridge in the garage.

We put up a white board that will accommodate magnets.

I agree with the Kev's guess of 200 years of use in fresh water. Maybe longer. After going through several steel burn barrels here on the farm I finally made one from a stainless steel 55-gal drum. The cycle of intense heat and moisture destroys ordinary steel very quickly - the steel rusts and falls off in big flakes. (The sides glow bright orange at times and the heat even at the bottom has been enough to soften and sag a grate I welded up from 1/2" rebar.) The stainless drum does have a very light patina of rust but it looks like it will outlast me and my grandkids.

409346

Hey, a well-made hook made from non-stainless might even last longer than a year away from salt water. I have some unpainted hooks welded to my tractor bucket and on chains that that are out in the weather all the time and are still in good condition after dozens of years. While scuba diving 30+ years ago I found one 3/8" chain at the bottom of the lake and who knows how long it was there. Still looks like new except for the light surface rust.

JKJ

[Ole Anderson]

I have a stainless steel anchor chain that has seen salt water over the last 20 years. It is as bright as if it were new.

[Perry Hilbert Jr]

I have had stainless cheap steel knives develop actual brown rust. Got some cheap stainless knives in a box of junk at an auction and kept the knives in the barn for cutting hay strings, ropes etc. One of the knives was knocked on the floor and when I found it, it had been laying a while on a moist damp floor in a stall with manure etc. There were spots of brown rust on it. My good kitchen knives are Wusthoff brand from Germany and they never show a hint of rust or corrosion or even of changing darker and I have had them 4 years.

[michael langman]

There are different series of stainless steel. 300 series and 400 series are typical. The 400 series has a higher carbon rate then the 300 and is heat treatable. It also will corrode or rust more. It still will last many years outside.
There are dozens of variety of SS to suit different needs and conditions.

[Steve Jenkins]

Taught scuba for over 30 years so have seen more than my share of stainless diving knives and invariably the first place corrosion shows up is in stamped letters “stainless steel “

[Ole Anderson]

Taught scuba for over 30 years so have seen more than my share of stainless diving knives and invariably the first place corrosion shows up is in stamped letters “stainless steel “

The die used to stamp the words is not stainless steel and some of it scuffs off on the knife during the process. This is typical with many stainless items.

[Steve Jenkins]

Learned something

[Malcolm McLeod]

The die used to stamp the words is not stainless steel and some of it scuffs off on the knife during the process. This is typical with many stainless items.


Learned something

I have heard the same thing about many SS fittings & fasteners used in industry. The corrosion resistance of most SS types can be compromised by the use of improper tools.

A high carbon tool (steel), when used to install/remove a SS part, can actually embed carbon into the SS - especially in high torque applications. I hear the term "carbon transfer" used. The carbon rich area becomes a hot-spot for corrosion to initiate - and I believe it will spread (caveat - been a long time since Metallurgy class). I haven't looked in many years, but some companies used to offer dedicated tool sets for use on SS.

Nothing like buying a new spendiferous-manufactiriffic-machitech-ROI-earning- ... thing, and have the resident wrench bender hurry over to fine tune it with the wrong tool box. :eek: Oops.

[Malcolm Schweizer]

"Stainless Steel" is a misnomer. All steel will rust. The addition of Nickle, Chromium, and Molybendum, depending on the alloy, causes the metal to react with oxygen in the air and form an oxidizing layer around the metal that causes it to inhibit rust. Here is a big catch: It requires exposure to air to work. Have you ever seen rust streaks coming from under the heads of stainless steel screws? That's because they didn't have sufficient exposure to oxygen to maintain the oxidizing layer.

There are too many alloys to discuss each one. I used 316 Stainless for my centerboard on the boat I'm building, which is very resistant to corrosion. Just below that would be 304, which is still resistant to corrosion, but has less resistance than 316. The difference would be that 316 has more nickel and also adds molybendum. One downside of stainless is that although it's tougher than carbon steel (believe me, I know, as I'm grinding a massive chunk of it for my centerboard) it can be more brittle. Many offshore sailors will not use stainless chain on their boats because although it's strong, it doesn't give like galvanized carbon steel will and will therefore snap before galvanized will.

[Malcolm McLeod]

... and form an oxidizing layer around the metal that causes it to inhibit rust...

I stand corrected, or at least reminded. For anyone who can't sleep...

I pulled out the handy research books and the oxide layer is the actual inhibitor (just like aluminum). I'd forgotten this detail.

And it also seems that my use of the term 'carbon transfer' is induced by my spending too much time in my wayward youth with evil and decadent machinists. :o In defense of them (OK - me), the use of 'carbon transfer' is due to most people seeing the effects of improper tool use on SS, rather than a manufacturing process error - like sandblasting SS with recycled iron-contaminated sand. So presumably to most, this IS a carbon steel transfer.

It is actually iron transfer that does the deed to SS. Iron particles from tools (i.e. dies) or other processes and fixtures damage the oxide layer, embed themselves, and provide the starting point for corrosion. Most quality suppliers of SS components should be able to eliminate the contamination during manufacture.

...Hello? Anybody still awake?

And hope the keel grind is going well, Mr Schweizer; still following your boat build. And don't use any grinding media that was used on carbon steels!!;)

[Lee Schierer]

Stainless steel should be passivated at the end of the manufacturing process to remove iron contamination for the welding, machining and bending processes. Iron contamination gives rust and corrosion a place to start.

[Malcolm McLeod]

I thought I might put everyone in a coma if I started in on pickling & passivation...:o. Nice to have another analytical around!

[lowell holmes]

Maybe you should wipe the steel to remove residue and hit it with Johnson floor wax. It worked for me on my Cal 34 sailboat.

[Bruce Page]

Any SS will corrode under the right conditions but some SS’s are much better resisting corrosion than others. 316L & 321 SS are often used in nuclear reactors and reactor test hardware.
I made 4 of these tie-down strap thingy’s for my gleaming new ‘95 Dodge Ram out of 17-4ph h900 stainless. The Ram has spent the last 23 years outdoors and isn’t very shiny anymore but aside from some dirt, the 17-4 tie-downs are as shiny as the day I made them.

[andrew whicker]

It's a chromium oxide layer that develops. The Moly and Nickel (and etc) are there for other properties. The chrome needs to be around 11% -12% minimum to create the oxide layer. 410 is the bottom of that limit, for example. But, as said above, you can heat treat it to strengthen it. This makes it a very useful type of stainless steel even if it does have less corrosion resistance. As someone else said above, "the more stainless, the softer". This is obviously way over simplified, but makes sense for the common stuff you'll find. The 300 series is softer because you can't heat treat it which means you can't strengthen it. It's a trade off between strength and corrosion resistance.

It gets all very nerdy, but the magnetism is basically used for everyday problems to let a person know if it is 400 series or 300 series (which is a huge oversimplification, but not everyone has to nerd about this stuff for work). My kitchen sink holds a magnet, so it is probably 400 series. I don't know what type exactly. I'm sure it's a common type (409 or 410). (The series number is actually a bit misleading if you know more, but it's a good simplification)

316 and generic structural steel have basically the same 'strength' (tensile), but 316 is harder (hardness). 316 also work hardens, which is why it is such a pain to machine.

Anyway, I have to nerd out about this stuff for work. Stainless steels and corrosion is SUPER interesting and I totally suggest going deeper into metals in general. It really is fascinating stuff. Lots of smart people figuring out difficult problems over a long period of time. Metals are very cool.

I personally don't think pickling is necessary unless you plan on using the stainless in an anaerobic (no oxygen) environment. You're not doing this if you put it in regular water. Pickling is basically a safety check to ensure that you have this magical Chromium Oxide layer before you put the thing into service. However, the layer self heals if loose oxygen is around. Lakes are aerobic, so you're fine.