Abstract: The 42CrMo steel has been successfully used for small-power (2 MW or below) wind turbine yaw bearing rings, but it could not match the demand of the high-power wind turbine yaw bearing rings resulting from its limited hardenability. The 40CrNiMo steel and the boron microalloyed 42CrMnMoB steel are studied for comparison. The hardenability of the 42CrMnMoB steel, the 40CrNiMo steel and the 42CrMo steel are studied. The cooling rate at the 1/4 of the wall thickness of 5 MW wind turbine yaw bearing rings, in oil quenching process, is simulated using DEFORM3D software. A thermal simulation furnace is used for heat treatment process, and the mechanical properties have been tested. The results show that the hardness value of the 42CrMnMoB steel in the end quenching distance of 85 mm is 46 HRC and the relatively ideal critical diameter after oil quenching is about 160 mm, much higher than the ideal critical diameter of 43 mm and 29 HRC at 85 mm position of the 42CrMo steel. The average cooling rate at the 1/4 of the wall thickness in oil quenching is about 0.7 ℃/s that obtained by simulation of DFFORM3D software. Mechanical properties of the 42CrMnMoB steel can match the demand of 5 MW wind yaw bearing rings requirements for performance after simulated oil cooling and tempering at 590 ℃ for 1 hour, indicating that it has the potential to used for the high-power wind turbine yaw bearing rings.

Key words: bearing steels, hardenability, heat treatment, simulation, wind power