Abstract
A tempered martensitic gear steel (18CrNiMo7-6) sample was nitrided on two sides using a 5 atm pressurized gas at 530 °C for five hours. The nitrided sample was characterized by means of microhardness, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. A microhardness gradient was identified over a distance of 1000 µm with hardness values from 900 HV0.1 at the surface to 300 HV0.1 in the center matrix. The gradient microstructure was mainly divided into three zones: (i) a nitride compound layer at the top surface (~20 µm thick), (ii) a diffusion zone with containing precipitates (~350 µm thick), and (iii) the center matrix of the tempered martensite. Compared with carburized sample, the harder surface of the nitrided one ensures a better performance of the present pressured gas nitrided gears.
Highlights
IntroductionThe efficiency of wind turbines can be improved by having gears with better performance, e.g., an increased life time
Wind energy is an important source of electrical power
The base materials were tempered martensitic plates, which were obtained by the following heat treatments: (i) a solid solution treatment at 825 ◦ C for 1 h followed by oil cooling and (ii) tempering at 180 ◦ C for 2 h followed by air cooling
Summary
The efficiency of wind turbines can be improved by having gears with better performance, e.g., an increased life time. Increasing the life time of gears requires precise dimensions and a better surface finish of the gears [1,2,3,4,5,6]. Surface hardening treatments are usually used to harden the surface while leaving the interior untreated. Examples of such surface hardening processes widely used are nitriding [9,10], carburizing [11,12] and shot peening [13,14]
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