Hi fella's, was doing a search for something else and found this Q and forum.
Having looked into this, bars can vary a bit in composition.
GB use, or at least used to use Australian Bisalloy Bisplate 500 in their top of the range bars.
It's a through hardened low/mid carbon/silicon/manganese/nickel/moly and relatively high levels of chrome type steel, originally developed for mining applications (gougers, buckets, dump truck liners, etc)
It has a UTS of around 1640mPa
Tsumura from Japan who make excellent bars every bit as good or better than anyone else use Japanese SKS51 tool steel, which has a much higher carbon content than Bisplate 500 (0.75-0.85% vs 0.29% for BP500) and mid levels of silicon/manganese/copper, very high nickel levels and no moly.
It's primarily developed for knives, tools and handsaws. Bisplate500.pdf
