Ageing effects on α′ precipitation and resistance to corrosion of a novel Cr–Mo stainless steel with high Mo content

The consequences of ageing at 400 and 475 °C on α′ precipitation and corrosion resistance of a novel Cr–Mo ferritic SS with high Mo content were investigated. Combination of X-ray diffraction and Mossbauer spectroscopy results indicates the appearance of a small amount of a paramagnetic phase as a result of the ageing. This phase is iso-structural with the α phase and is thus associated with a Cr-rich α′ phase. The appearance of this phase is related to a decrease of the resistance to corrosion as studied by DL-EPR because the presence of this paramagnetic phase leads to discontinuities in the oxide layer thus reducing corrosion protection and exposing the steel to the action of the corrosive solution.