Tytuł pozycji:
Effect of laser heat treatment parameters on the microstructure and hardness of gas-nitrided layers
Nitriding is commonly used method of thermochemical treatment in order to produce surface layers of improved hardness and wear resistance. Using a gas nitriding with changeable nitriding potential, a nitrogen concentration at the surface could be controlled, influencing the phase composition and the growth kinetics of the layer. In this study, the hybrid surface treatment was applied. It consisted in gas nitriding and laser heat treatment (LHT) of 42CrMo4 steel. Two nitriding processes were carried out using changeable nitriding potential. Parameters on first process were as follows: temperature 570°C (843 K), time 4 h. The second process was performed at lower temperature 520°C (793 K) and longer duration 10 h. This resulted in various depths of the compound zone at the surface (20 and 8 μm, respectively). Next, the nitrided layers were laser heat-treated using TRUMPF TLF 2600 Turbo CO2 laser. Laser tracks were arranged as the single tracks with various scanning rates (vl = 2.88 m/min and vl = 3.84 m/min). The laser beam power (P) ranged from 0.26 to 0.91 kW. The effects of the depth of compound zone as well as LHT parameters on the microstructure, dimensions and microhardness of laser tracks were analysed. In the majority of the produced laser tracks, remelted (MZ) and heat-affected (HAZ) zones were easily identified. Different microstructure was visible at low laser beam power (0.26 kW). The dimensions of MZ were limited, whereas the HAZ was clearly observed. The compound zone was still visible at the surface. Only the porous ε nitrides were slightly melted. Hardness increased significantly after LHT with complete and partial remelting of compound zone. Laser beam power and scanning rate influenced the depth and width of MZ and HAZ, so the thickness of hardened zone. The greater laser beam power or the smaller scanning rate, the larger hardened zone was observed.
Azotowanie jest jedną z najpopularniejszych metod obróbki cieplno- chemicznej prowadzącą do wytwarzania warstw powierzchniowych o dużej twardości i odporności na zużycie. Stosując odpowiedni proces azotowania gazowego (ze zmiennym potencjałem azotowym), można kontrolować stężenie azotu na powierzchni, wpływając na kinetykę wzrostu strefy związków (azotków) oraz strefy dyfuzyjnej. Celem pracy była modyfikacja warstwy azotowanej za pomocą laserowej obróbki cieplnej. Badano wpływ parametrów laserowej obróbki cieplnej (mocy wiązki laserowej i szybkości skanowania) oraz grubości wytworzonej w wyniku azotowania strefy związków (azotków żelaza) na mikrostrukturę i twardość.
Opracowanie ze środków MNiSW w ramach umowy 812/P-DUN/2016 na działalność upowszechniającą naukę.
