It is typically measured on the Brinell hardness scale, with values ranging between 150 and 241 HB (Brinell hardness).
Unfortunately, I couldn’t find specific mechanic properties for P355NH and P355GH. They are both grades of pressure vessel steel that are used in the manufacturing of boilers, storage tanks, and pressure vessels. These grades are known for their high temperature and corrosion resistance, as well as their good mechanical properties such as tensile strength and yield strength. It is advisable to consult the material data sheets or technical specifications provided by the manufacturer for more detailed information on the mechanical properties of these grades.