A bit late, but I think it may be in DIN 17.007 T1 (4.59), T2(9.61),
I only have a partial excerpt from another source (unknown)
Roughly, the first digit left of 1st decimal is the Main Material Group
1 being steel
The middle 4 digits are "Sortennumer or Sortenklasse + Zaehlnumer
which is roughly type class + count number.
Number(s) to the right of the 2nd decimal are "AnhaengeZahlen" or
"attached numbers" These latter numbers depend, for steel, on how the
steel was made, e.g.
1st digit: 0=undefined, 1= un Killed ThomasStahl, 2= killed ThomasStahl etc
2nd digit: 0=no or any treatment; others are temper type, hardened, coldformed etc.
Its a bit long to reproduce here. Best to get the standard.