Metallurgy Q

Cross post from UK.D-I-Y
Hi all
Something cropped up at work that is not altogether obvious! Looking at steel for keys - the type of keys that fit in shafts and drive
sprockets (rather than doors).
The material specified for my application is an American designation 1018, which appears to be pretty low grade stuff around British Equivalent 080A17. Key steel suppliers in the UK quote higher specs for their general stocks - typically 080M40.
That's just the background, the question is, why do the two grade references exist? If the fourth character in the string is an "A" then the steel is supplied "with close limits of chemical composition". If the fourth character in the string is an "M" then the steel is supplies "with mechanical property requirements". The above definitions taken from a British Steel reference book on Iron and Steel Specifications.
I can see the requirement for buying steel that has been tested and therefore has guaranteed mechanical properties, but why would you buy (essentially the same stuff) steel with supposedly "closes limits of chemical composition". The stated chemical composition for "A" grade materials doesn't seem radically different from the equivalent "M" grade - so why would anyone ever by the "A" grade?
Hope this all makes sense.
Phil
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On Thu, 22 Oct 2009 11:38:16 +0100, "TheScullster"

Something wrong in your book there perhaps? The last two numbers always indicate the mean carbon content, so the 080A17 is 0.17% carbon, and 080M40 is 0.40% carbon. The 080M40 btw is a standard EN8 medium carbon steel, whilst the other is obviously just a mild steel, but with more carbon than a 'dead mild' steel.
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On Thu, 22 Oct 2009 11:38:16 +0100, "TheScullster"

Just re-read that and realised you're not comparing 080A17 to 080M40, so ignore my previous post. Other than that, I don't know why the 2 grades exist, but I could possibly hazard a guess.
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Phil,
No metallurgy expert, but I wonder if the reason may be that some things are more influenced by composition. Possible list includes: weldability, hardenability (and all the associated heat treatment things), corrosion resistance, and toxicity (for food processing).
David
--
David Littlewood

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They exist only because there are so many steel specs been issued over the years. Try to find someone producing all the different specs would be a different story. For example I think you would struggle to find someone actually producing 080A17,as in that range 080A15 is the preferred grade and that is basically the lowest grade of bright mild steel available. These specs and similar ones with an M in them were adopted ISO standards.The British ones were EN numbers. Although there are all these grades there is only so many that are actually produced commercially.And a lot of the non preferred grades will cease to be listed as times go by. I don`t agree that keysteel is EN8 which as Peter says is a 0.4% carbon steel and which I would class as the lowest grade of engineering steels.Keysteel in Europe is made to either of two specs depending on whether it is metric or imperial sized and is not an EN8 spec.
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Thanks Mark Can you elaborate on/clarify the last paragraph please? My understanding of your statement is that metric keys are supplied to a different "material" spec to imperial keys. If so do you know what those specs are?
Phil
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The following info is from Macreadys Orange book. Imperial sized keysteel is sized to BS 46,Part 1,1958. Main chemical composition is 0.45% carbon max. Note that is max,there is no lower limit. 0.6-1.00% Manganese.
Metric keysteel is produced to BS4235,Pt 1,1972 and German keysteel standard DIN 6880. Chemical composition is 0.42-0.50 % carbon and 0.5-0.8 % Manganese
Doesn`t look much difference but in the world of steel specs quite a bit. I recently supplied a part which was a bit of 20mm dia x 40 long,black, 50D steel.One end had a 10mm radius machined on it and that was it finished.Supplied two of them to an oil company.They were locating studs for a cover. Material certs were supplied with the job and the client would not accept them (the certs).When asked why,they said the certs were not correct.There then followed several days of emails and phone calls between myself,the customer,the steel stockholder and the mill where the steel was cast.At the end of the day they accepted the certs and I still don`t know what they didn`t like about them.That carry-on lasted for several weeks,all for 70.
Mark.
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1018 plain mild steel with .18 carbon
Steve R.
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