SUMMARY
Thickness of the ε+γ′ nitride zone and the total thickness of the nitrided layer (including the ε+γ′ and the α-base precipitation zones) on hot-work WCL steel and on dies made of the same material, were measured using eddy current method. Two types of istruments were used, Wirotest 301 with a shielded sensor (frequency 0.5 and 1.0 MHz) and Wirotest 03 with an unshielded sensor (3.4 MHz). Specimens were gas nitrided for 4 - 40 hours at 540 0C and nitriding potential of 3.6 atm-1/2 and for 22 - 76 hours at 500 0C and potential 14.2 atm-1/2. Forging dies of WCL were plasma nitrided at 500 ÷ 520 0C for 10 hours. It has been demonstrated that the Wirotest devices allow a relatively precise estimation of ε+γ′ zone and nitrided layer thicknrss. The relationship between instrument indications and layer thickness was linear or close to linear. In the investigations of nitrided layer thickness a good correlation was obtained betweeen the Wirotest 03 indications for dies and control specimens. The described method can be used for quality control of nitrided parts.

Keywords
Gas nitriding, plasma nitriding, nitrided layer, diffusion layer, iron nitrides zone, eddy currents.

¹ Instytut Obróbki Plastycznej, Poznań
²Politechnika Poznańska