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