Gr. Materials Features P1 Free cutting steel and structural steel Rm < 500 N/mm² ISO Code P2 Carbon steel and low alloy steel Rm 500-700 N/mm² P3 Medium alloy steel and heat treated steel Rm 600-800 N/mm² P4 High alloy steel Rm 800-1000 N/mm² P5 Tool steel Rm 900-1200 N/mm² P6 High tensile strength steel Rm 1200-1600 N/mm² M1 Ferritic stainless steel Rm 400-700 N/mm² M2 Austenitic stainless steel (good machinability) Rm 500-750 N/mm² M3 Austenitic stainless steel (medium machinability) Rm 550-850 N/mm² M4 Martensitic stainless steel Rm 650-950 N/mm² M5 PH stainless steel Rm 800-1250 N/mm² K1 Grey cast iron HB 150-250 K2 Nodular cast iron HB 150-350 K3 Austenitic cast iron HB 120-260 K4 ADI cast iron HB 250-500 N1 Aluminium alloys < 12% Si N2 Aluminium alloys > 12% Si N3 Copper alloys N4 Brass alloys and bronze alloys N5 Plastic materials N6 Fiber and composites S1 Heat resistant super alloys (HRSA) (good machinability) HRC < 25 S2 Heat resistant super alloys (HRSA) (medium machinability) HRC 25-35 S3 Heat resistant super alloys (HRSA) (low machinability) HRC 35-45 S4 Low alloy Titanium (good machinability) S5 High alloy Titanium (medium machinability) H1 Hardened general steel HRC 50-56 H2 Hardened bearing steel HRC 54-62 H3 Hardened tool steel HRC 60-65 H4 Hardened martensitic stainless steel HRC 50-56 H5 Hardened white cast iron HRC 48-55 11