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Because of its genesis and the era in which it occurred, ALL the steels used in a Mklll / lll* are carbon steels. I'm still looking through a pile of stuff for more details of each brew.
As late as 1938, the No1 Mk111 specifications contained references to the various steels AND their heat-treatment / finish condition. Alloy steels like 4140 and 8620 were pretty much excluded. Component suppliers wishing to use alloy steels had to submit sample billets to the ordnance boffins for approval.
I'd say there is a fair chance that if you run the steel numbers through the old search engine, you may find what you seek.
Unfortunately, I have not yet got my sticky paws on similar data for the Ishapore production or for the No4 / 5 series.
What is apparent is that the "system" changed over the years and a lot more text was to be found on later drawings for later products.
For instance:
On the drawing for the No4 Body, part No. CR 503, last amended / checked 20 Feb 1961!, it notes:
Material - Steel BS 970 En19R OR BS 970 En21R.
One quick search will take you here: BS 970,Â*forÂ*Mechanical and Allied Engineering Steel
Before the days of precision pyrometers and X-Ray crystallography, alloy composition and heat treatment procedures were a bit of a crap-shoot. Because of this, components were "over-engineered" from mostly "predictable" materials.
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Badger has these files, they will appear when he's ready.
I could have displayed them piece meal, but they would soon get lost into the archives and eventually disappear as pic files often do.
This way they will be saved as a sticky or tech. bulletin for the use of all users...….just give him time, he's a busy boy.
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File is now up as a sticky.:thup:
