WARNING: Possible stupid question

[Finalreminder]

Stainless steel. Is stainless steel a coating or is it the actual steel.
If, for instance, I cut a stainless steel bolt in half would it rust at the ends like a galvanised bolt?

Second question:
Stainless steel never rusts, corrodes?

 

[Drains]

Definitely a stupid question. Stainless is a group of steel alloys containing various other metals which prohibit corrosion, add other properties etc etc. It's not a coating.

Stainless can rust. It depends what type it is and the conditions it's in, also, if welded and left unclean, expect it to rust.

check it out here - http://en.wikipedia.org/wiki/Stainless_steel

 

[Wozzaaah]

Stainless is not a coating, it's the actual steel itself. Regarding it corroding, I think some types do discolour after a while, especially if it's in contact with carbon steel but I don't think they actually corrode as such. Stainless is used for marine stuff so it's pretty good. Someone will be able to tell you more about the grades and the different contents (martensitic, austenitic and ferritic (sp?) I think are the most common ones, afaik ferritic is the only magnetic one?)

 

[TechnicAl]

Its stainless all the way through.
It contains Chromium which oxidises in the atmosphere and forms a passive layer. Therefore, if you cut it it reform the Chromium Oxide layer, in other words its self healing.

 

[Finalreminder]

You were warned lol, but thanks for the answers anyway
How does stainless get on with Aluminium over time?
I notice on my landy where steel touches ally it corrodes (chalky).
Does stainless prevent this happening?

PS: The grade of stainless bolts I'm using is A2-70 grade
Good, bad, OK?

 

[Wozzaaah]

Some good reading there Si, good old wiki

 

[Sparkey]

martensitic is magnetic wozzie...

 

[TechnicAl]

If you read the books, Aluminium corrodes preferentially when in contact with steel / stainless steel, however, Aluminium also oxidises in atmosphere so its Al Oxide in contact with the steel. Al Oxide is very noble and will NOT corrode preferentially to mild steel. With stainless it depends on the grade but most common grades will corrode preferentially to Al Oxide but VERY slowly so it could take years to see much evidence of it.

I can never remember these A grades but I think A2 is 304L and A3 is 316L ( I think we have been over this before, was it Simondrains who had the info).

 

[Drains]

I can never remember these A grades but I think A2 is 304L and A3 is 316L ( I think we have been over this before, was it Simondrains who had the info).

I think (but i'm not sure), A4 is 316(L?)

In marine-land, A2 bolts tarnish easy, tending towards rust. A4 should stay clean. A3 is pretty unusual.

You're right Al, we've been here before. Like visiting old relatives, but without the smell.

 

[TechnicAl]

From the Wiki
Harry Brearley of the Brown-Firth research laboratory in Sheffield, England is commonly credited as the inventor of stainless steel. In 1913, while seeking an erosion-resistant alloy for gun barrels, he discovered and subsequently industrialized a martensitic stainless steel alloy. The discovery was announced two years later in a January 1915 newspaper article in The New York Times.[2] This was latter marketed under the "Staybrite" brand by Firth Vickers in England and was used for the new entrance canopy for the Savoy Hotel in 1929 in London.[5]

My Dad used to work for Harry Brearley and I did my training at Firth-Vickers.

I think the entry is wrong, Harry Brearley worked for Brown-Bayley Steels and he was also Technical Director of Welding Rods Ltd who later became Lincoln Electric UK Ltd.

Firth-Vickers were competitors and they did market their products as Staybrite.

 

[rtbcomp]

Stainless causes ally to corrode faster, which is why you shouldn't use SS bolts with aluminium panels unless you use a barrier (gasket or cream &c).

 

[TechnicAl]

Stainless causes ally to corrode faster, which is why you shouldn't use SS bolts with aluminium panels unless you use a barrier (gasket or cream &c).

Thats the theory but in practice its the stainless that actually corrodes but it takes a long time. Its more pronounced with mild steel.

Try bolting a piece of ms to a piece of ally and stand it in the rain. The ms will corrode.

 

[zardoz]

I was told that after stainless steel is made it needs immersing in a bath of hot chemicals (acids) for several hours, after its initial rolling and annealing process. Otherwise its passivation surface layer will not form.

No idea if its true, but i did wonder if thats what happened to my brothers new stainless steel cutlery set, that developed rusty spots after a month

 

[Hitch]

Its generaly good practice to isolate different layers with a fiber/plastic/rubber washer.
The termis galvanic or electrolytic corrosion iirc.
Its all about each piece acting as anodes and cathodes. There is a chart which puts them in order, the closer together on the chart, the less likely they will corrode.
The further away, the worse it will be.

I think Platinum is at one end, and magnesium or cadmium the other.

 

[English Steve]

Upto 1986 Landrover body cappings were galvanised to slow the galvanic corrosion. Subsequently, as a cost reduction, the cappings were plain steel which is why so many have rotted in that area.
My wife has a 1986 V8 90CSW which is showing absolutely no sign of corrosion around the body cappings. This is in spite of it being used for several years launching boats into the sea, and spending it's entire life outdoors. The rear crossmember and most of the outriggers have needed replacement, but the body cappings are fine.

For the non-Landrover people out there, the steel body cappings are on top of the aluminium sides of the rear tub and protect the body from knocks.

 

[jimmy shoes]

i think its chromium which make it "stainless", there is different types of stainless steels for example i made a stainless steel storage box which is really strong but gets rusty, and the other type of stainless i got ain't that strong but doesn't rust

 

[Finalreminder]

Thanks for all that info. I've got a good angle on it now

 

[TechnicAl]

I was told that after stainless steel is made it needs immersing in a bath of hot chemicals (acids) for several hours, after its initial rolling and annealing process. Otherwise its passivation surface layer will not form.

No idea if its true, but i did wonder if thats what happened to my brothers new stainless steel cutlery set, that developed rusty spots after a month

No thats to clean it / make it look nice. Its pickled in acid, otherwise the surface is all sorts of shades, the pickliong gives it that dull appearance. It can also be polished in acid by passing a current over it.

The passivation layer forms in air

 

[Knipex]

No thats to clean it / make it look nice. Its pickled in acid, otherwise the surface is all sorts of shades, the pickliong gives it that dull appearance. It can also be polished in acid by passing a current over it.

The passivation layer forms in air

Not quite 100% accurate.

The pickling process will generate a passive layer.

Certain grades of stainless are more prone to rusting than others and do require passivisation in Nitric, Nitric Dichromate or Citric acids. All stainless used in medial and pharmaceutical industries is passivated and in the food industry its becoming more and more common. The introduction of citric passivators ahas made it cheaper, safer and more environmentally friendly.

Any grade of stainless that has been handles poorly will rust unless passivated.

 

[TechnicAl]

Knipex

Dont take my word for it but you should read this.

http://www.euro-inox.org/pdf/map/Passivating_Pickling_EN.pdf