Ageing of Medium-C Martensite and High-C Metastable Austenite: A Neutron Diffraction Study

摘要

Neutron diffraction measurements were used to obtain a better understanding of the ageing behaviour in dual phase ferrite-martensite and TRIP-aided steels. In order to understand the tempering of the high-C phases present in these steels, a high carbon FeCMnSi metastable austenitic steel and a FeCMnCrMo martensitic steel were used. The influence of deformation and undercooling of the metastable austenitic phase, leading to respectively strain-induced and athermal martensite, was investigated. Additionally, different ageing treatments were performed which resulted in the sequential precipitation of η- and θ-carbides and in the loss of tetragonality of the martensite phase. Tempering of the FeCMnCrMo martensites at 100℃ only caused a small decrease of the tetragonality of the martensite. After tempering at 170℃ the tetragonality decreased rapidly and clear η-carbide diffraction peaks were observed.