Microstructural evolution of martensitic 100Cr6 bearing steel during tempering: From thermoelectric power measurements to the prediction of dimensional changes

Tempering of a martensitic 100Cr6 (AISI52100) bearing steel during isothermal treatments is studied using thermoelectric power, transmission electron microscopy (TEM), X-ray diffraction and dimensional analysis. Dimensional changes occurring during tempering are due to: (i) the precipitation of e-carbides, (ii) the decomposition of retained austenite, (iii) the precipitation of cementite and (iv) the recovery of the dislocation structure and coarsening of martensite lathes. Analysis of thermoelectric power evolutions, measured during isothermal ageing treatments, and assisted by TEM characterization, leads to a quantitative estimation of austenite and precipitate volume fraction. These data are used to predict dimensional changes, and these are in very good agreement with dimensional measurements.