Characterisation of case-hardened gear steel by multiparameter Barkhausen noise measurements

Renewable energy sources have become nowadays very popular. Wind energy is one of the most promising renewable energy sources of the future. Due to the booming energy markets and increasing production of wind turbines, the requirement for long-lasting and reliably working windmills has emerged. The Barkhausen noise (BN) method is a world-leading technique in the quality control of industrial grinding processes, for example in windmill gear production. The main goal for this study is to create a profound approach to the multiparameter Barkhausen noise measured and to compare the measured values to the absolute values obtained with other research methods such as residual stress measurements by X-ray diffraction, hardness measurements and microstructural studies. A test bar series was made from a case-hardened steel used in wind turbine gears. Different tempering parameters were used to vary the surface hardness of the test bars. A stepwise loading was done simultaneously with the BN measurements to obtain relevant multiparameter BN data and to investigate the effect of applied stress on the BN signal. The results indicate clearly that the response of the studied material is mainly consistent with the known BN relations, but there exist some unequal BN stress correlations in the tempered test bars.