Main bearings for wind turbine generator sets are a key component for a new power generation. Highest reliability and availability are mandatory in order to assure beneficial power production. These bearings have to withstand numerous load cycles for more than 20 years under extreme conditions. This results in a high degree of material utilization. The environmental conditions of offshore applications amplify these requirements. The increase in power rating of these kinds of machines leads to expanding bearing dimensions. These large diameters can hardly be produced in a classic way like through hardening or by means of case carburizing. A rather new manufacturing process has been developed based on the principle of induction hardening, as this is a key technology for manufacturing of large bearings without soft zones. However, this process requires a different steel grade than the classical manufacturing processes, i.e., medium carbon steel in quenched and tempered condition, which is commonly used for slewing applications, was further qualified for large bearings without soft zones. Only this technology enables the wind energy turbine (WET) producers to design highly efficient large size wind power generators applying direct drive technology. The complete manufacturing process chain has been analyzed with regard to an enhancement of the final product quality. The material cleanliness is an essential factor for availability and reliability. ThyssenKrupp Rothe Erde, in close cooperation with steel manufacturers, qualified a new material grade for rotor main bearings with highest demands on material cleanliness with special focus on large ring diameters and industrial sourceability on a high volume. Enhanced quality processes within the total production chain are applied in order to assure highest bearing reliability and availability.