LAUSR

Abstract The paper presents the investigation of conical blades made of unalloyed steel C20 gas-nitrided by the Nitreg method. On the surface of steel blades (with tip angles in the range of 20–170°) an approx. 15 mm-thick nitride layer of was fabricated, which had a bizonal structure of: ɛ (Fe2–3N and Fe3(N,C)1–x) and ɛ + γ′(Fe4N) with a hardness of 1310 HV and 910 HV, respectively. Hardness tests carried out on blade cross-section showed that a 0.7–1 mm thick diffusion layer occurred under the nitride layer. By applying the criterion of effective nitrided layer thickness, gc+50, it was demonstrated that blades with a tip angle of 20° and 30° had been through-nitrided (i.e. nitrided through and through). A static compression test showed that, as a result of nitriding, the compressive strength of the blades had increased by a factor of two.