Nitriding in vacuum P6M5 steel

The nitriding of high–speed steel P6M5 is studied in the present paper in two ways: 1) nitriding at 750°C 15 min and pressure of the NH3–120 Torr, followed by quench hardening at 1220°C in lubricating triple oil and triple tempering at 560°C and duration of 1 h. The preceding nitriding makes a very fine corn in the diffusion layer. The nitrogen converts, when heated, in austenite and after the quench hardening, in martensite and retained austenite. 2) A preceding quench hardening at 1220°C in lubricating oil and during the triple tempering at 560°C, 1 h nitriding in vacuum at pressure of the ammonia of 100 Torr. Nitrides of the V, W, Mo and Cr alloying elements occur in the diffusion layer. The hardness of the nitride layer reaches 1000–1100 MHV100, after each of the two procedures is carried out while the hardness of the core is 800 MVH100. The nitriding in vacuum of puncheons with diameter 6–10mm, made of the P6M5 steel, increases their durability 2 to 8 times.