It is a standard steel basically it is EN8 in BS970 (1955) or 80M40 in the newer definitions of BS970.
It is medium strength unalloyed steel.
It is usually used for stressed pins and shafts
It ain’t as easy to turn/machine as EN1 by a long way – if one looks at machinability indexes EN1 is 100 whilst EN8 is something like 45.
A good round tool – loads of suds etc and it turns OK
With milling, lots of small cuts and a carbide tool is best.
The big issue is that it is very heat treatable, so if you generate too much heat at the cutting surface it ends up hardened! – even a slight bit of heat and rapid cooling (such as the mass of the workpiece) and it is harder than the rest.
Julie