according to ISO 898, part 5
1) Free-cutting steel may be used, with lead content 0,35 % maximum, phosphorus content 0,11 % maximum and sulphur content 0,34 % maximum.
2) Case hardening is allowed in the case of square-head set screws.
3) Steel with lead content 0,35 % maximum may be used.
4) The alloying steel must contain an alloying element or several alloying elements like chromium, nickel, molybdenum, vanadium or bor.
5) For thread pins with property class 45H other steels may be used if the conditions of the torque test is conform to ISO 898, part 5. Boron alloyed steels shall content boron between 0,0008 and 0,005. Hard steel is permitted with min. 0,45 % C if alloying elements contains at least 50 % according to ISO 8981, part 1.
6) To ≤ M16 boron alloyed carbon steel contents min. 0,35 % C.