|Bill Phinn||08/02/2019 00:39:51|
|374 forum posts|
I recently bought some M36 studding and nuts, which were advertised as "stainless steel".
Can anyone tell me whether the coding B7 BP on the end of the bar indicates a kind of stainless steel, or at least whether this bar looks to you like stainless steel.
Thanks for any help.
P.S. Can anyone tell me how to get round the fact that when I insert images from my albums they often seem to flip top to bottom?
Edited By Bill Phinn on 08/02/2019 00:43:19
|Jeff Dayman||08/02/2019 00:51:14|
|1896 forum posts|
If it really is in fact B7 it is a carbon steel, not stainless, and is a construction grade similar to AISI 4140. Not sure about what the BP is, could be a mill ID mark.
(could mean Bloomin' Peculiar re calling this stuff stainless, maybe)
Quick check would be to cut off a tiny piece, grind it bare, place outside on a wet day and see if it's still silver colour or if it's orangey brown in the morning. Low tech but pretty accurate.
|Paul Lousick||08/02/2019 02:51:41|
|1554 forum posts|
Use a magnet to check. Stainless in non-magnetic. (some poorer grades may be slightly attracted).
|115 forum posts|
If it is carbon steel the BP may simply stand for Bright Plated. Given that there is no evidence of corrosion on the cut end I would think this a reasonable prospect.
I have never seen this type of coding on stainless steel. However all things are possible.
If it is stainless steel I would expect it to be marked 304 (or A2) or 316 (or A4) which are the usual grades for threaded studding.
Re the magnet test, 304 SS tends to become more magnetic as it is worked. That is, it leaves the mill as non-magnetic and becomes more so as it is worked into final shapes. Testing SS using a rare earth magnet yields some startling results. By way of contrast 316 does not appear similarly affected.
Stainless steels exhibiting magnetic qualities are not necessarily poorer grades it just reflects the differences in their composition and intended use.
|1277 forum posts|
|John Haine||08/02/2019 07:39:59|
|3356 forum posts|
All our stainless cooking knives live on a magnetic knife rack...
|Michael Gilligan||08/02/2019 08:24:06|
16422 forum posts
If you can afford to buy M36 then BP might be a personalisation
Seriously though ... look here for B7 : **LINK**
... and also follow the link to their 'microsite'
Edited By Michael Gilligan on 08/02/2019 08:28:52
|578 forum posts|
I bought a big lump of ground finish stainless bar 30mm dia x 3m long from a scrap yard.....
def stainless as stored out side for a long time (forgot about it)
because it was magnetic I got for the price of mild steel = peanuts.....hahaha.....
6346 forum posts
Whether B7 is a stainless steel or not depends on what your definition of 'stainless' is!
There is no such thing as stainless steel in the sense of it being a single material. Rather, stainless steels are a large family of different alloys each formulated to resist some sort of corrosion. Loosely, 'stainless' just means a steel that doesn't rust, ie a steel that resists the corrosive action of oxygen, 'Inox' as they say in Europe.
But 'stainless' is much more complicated than that. For example, cutlery is made of an alloy suited to rolling knives, forks and spoons. Not only does the alloy resist oxygen, it also takes a high polish, and resists acid and biological staining. Unfortunately cutlery stainless isn't much cop for anything else because priority is given to corrosion resistance and manufacturing properties - cutlery steel is weak.
Other stainless steels are much stronger, tougher, harder or able to hold an edge. In the kitchen a different stainless is used to make sharp knives rather than cutlery. And the stainless used in an aircraft probably won't be the same alloy used to make chemical plant, or in food processing, in a hospital or at sea. Where it matters the designer chooses the alloy best suited to the application. They don't always get it right! At least one posh make of kitchen sink turned out to be highly vulnerable to salt, especially dish-washer salt. It doesn't obviously damage the sink, instead the salt bores tiny holes through it by reacting with one component of the alloy. Even though the stainless used is expensive, it's the wrong type of stainless to use when there's salt about.
For many ordinary purposes the exact grade of stainless may not matter much, except that quite a few of them work-harden ferociously and are very difficult to machine. Avoid milling, drilling, tapping sawing or turning them!
Looking closely at B7 it's a member of a group of strong, tough, shock resistant steels all of which apart from B7 do claim to be stainless. The alloy family is popular in the oil industry for strong nuts and bolts etc in a hostile environment, ie they are much more highly specified than 'needs to be rust-proof in a shed'. B7 is favoured for use in components exposed to 'Sour Gas', that is natural gas contaminated with Hydrogen Sulphide. This is a good thing - many stainless steel alloys that would be rust-proof in a damp shed are attacked by Hydrogen Sulphide!
My guess is that B7, especially if it is 'Bright Plated', is sufficiently 'stainless' for most ordinary purposes. Leave it out in the rain for a week and see what happens.
|John Paton 1||08/02/2019 10:36:31|
283 forum posts
SoD reference to salt is correct - having experience of stainless steel in seaside locations developing a rust sheen where the builder had not used (or been able to obtain) the component in the grade of stainless specified. Perhaps the most dramatic cases of this fissile corrosion have been stainless fixings for suspended ceilings in the heavily chlorinated atmosphere of swimming pool roofs and use of domestic bleach to sterilise flexible hose connector to domestic handbasin taps. ( the hose corroded to a white dust and the rubber lining bulged and split causing major flood damage within the flat)
|Michael Gilligan||08/02/2019 10:41:45|
16422 forum posts
Surely that's the key point ... [my bold]
|Chris Trice||08/02/2019 12:21:01|
1362 forum posts
I have several stated "stainless steel" rulers that have got rust on them and from good makers too. They're probably forty plus years old but untarnished they ain't.
5492 forum posts
The chromium in the B7 is there as a strengthener but might be adding corrosion resistance as a side benefit. Mostly it is the nickel that reduces the corrosion and cutlery has high nickel and low chromium. As far as I can remember after 40 since my degree when Cr is added for more strength more Ni has to be added to keep the Cr in solution.
The non magnetic property comes from the fact that Nickel is magnetic too. However the Fe and Ni tend to align their minimagnets in opposite directions cancelling each other out. But the degree of cancellation depends on the ratio in the sample.
6346 forum posts
Yes, indeed. I'm being obscure again!
Bill's question was 'Can anyone tell me whether the coding B7 BP on the end of the bar indicates a kind of stainless steel'. The seller's description of the steel as 'stainless' is borderline. I think B7 is a 'kind of' stainless steel and it might well be good enough for his needs, or not. Leaving it out in the rain for a few days might answer Bill's concern.
What I was trying to say - and Bazyle says it better - is that B7 is a member of a group of steels that are stainless, but it's the one with the least claim to that status. Despite that, it's 'stainless' in the sense it resists Hydrogen Sulphide, and it's certainly a good steel in the sense that it's tough.
My general point about 'stainless' as a description is there are many different stainless alloys that might be fit for purpose in one application and rubbish in another. It depends on what the steel is exposed too. Most hobby applications aren't demanding and many items can be made no problem with junk box metal. But sometimes you have to be more careful. Not sure what category of job Bill needs his studding for.
|Michael Gilligan||08/02/2019 16:29:30|
16422 forum posts
No argument against your logic, Dave ... I was just highlighting that B7 is not claimed to be a Stainless Steel.
... and neither is 4140/4142 when sold as a raw material : **LINK**
It may however, as Bazyle deduces, stain less than many other steels.
|Bill Phinn||08/02/2019 19:44:42|
|374 forum posts|
Many thanks to everyone for the great answers!
My question was prompted chiefly by a desire to know whether the seller was justified in describing the bars etc. as "stainless". It looks like the answer is "in a way".
Anyway, since the bars are not intended for outdoor use (I vaguely intend to make a bookbinding press out of them, or maybe just one of them) the degree of corrosion-resistance they appear to have (they came to me as new old stock and there was no evidence of rust on them) will do me.
Posted by Michael Gilligan on 08/02/2019 08:24:06:
For the curious, the two 22 inch lengths with eight nuts and washers cost me under £20, and they are quite noticeably magnetic, which I know doesn't in itself necessarily preclude them from being a variety of "stainless steel".
That's good to know because only a few weeks ago I looked at a six inch rule of mine marked "stainless" that I've had for over twenty years and found a few rust spots on it. I was assuming I'd been had. Maybe we have been.
Contrary to what I implied initially, I see that the image was flipped automatically when it entered the album, not when I inserted it from the album into the text box on this page. I don't know how to counteract this flipping problem.
|Michael Gilligan||08/02/2019 20:18:14|
16422 forum posts
Regardless of its stainlessness quotient, I would say that's a very good price for high spec. material.
|Chris Trice||08/02/2019 22:25:38|
1362 forum posts
It highlights the misconception that the words "Stainless Steel" mean corrosion proof rather than corrosion resistant. It depends entirely on the grade employed. The other often quoted misconception is that SS's are non magnetic and that's not always true either. If certain features are important including machinability and/or cost then the appropriate grade to meet all criteria has to be selected.
Please login to post a reply.
Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!
You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.
Click THIS LINK for full contact details.
For subscription issues please see THIS LINK.