Xiuyan Li

Anomalous Phase Transformation from Martensite to Austenite in Fe-13%Cr-4%Ni-Mo Martensitic Stainless Steel

The thermal stability of the reversed austenite in a low carbon Fe-13%Cr-4%Ni-Mo (in wt pct) martensitic stainless steel was investigated by X-ray diffraction (XRD) and superconducting quantum interference device (SQUID) magnetometer. Different amount of the reversed austenite was obtained by controlling tempered temperature. It was found that the amount of the reversed austenite increased after keeping the specimens at liquid nitrogen temperature for 72 h. The mechanism of the anomalous phase transformation from martensite to austenite was discussed.

Effect of precipitations on the damping capacity of Fe-13Cr-2.5Mo alloy

The influence of precipitations on the damping capacity of Fe-13Cr-2.5Mo (mass %) based alloys has been investigated in this paper. The damping behaviors were examined by dynamic mechanical analyzer (DMA) at temperature t = 35 °C, vibrate frequency f = 1 Hz and strain amplitude ε of 10-6 and 10-3. Field-emission scanning electron microscope (FESEM) with X-ray energy dispersive spectrometer (EDS) was used to observe microstructure and determine the composition of precipitations. The results show that damping capacity of Fe-13Cr-2.5Mo based alloys is more strongly correlated with intragranular precipitation than with grain boundary (GB) precipitation. Fe-Cr-Mo alloy annealed at 1100 °C for 1 h followed by furnace cooling (FC) with relatively fewer intergranular precipitations, exhibits higher damping behavior. With the increase of annealing temperature, the amount of intragranular precipitations increases while damping capacity of Fe-Cr-Mo alloy decreases. Addition of 1.0% Ti obviously inhibits precipitation of GB precipitations, but promotes the intragranular precipitations in the alloy distinctly, so the damping capacity of Fe-Cr-Mo- 1Ti is slightly lower than that of Fe-Cr-Mo alloy. Addition of 1.0% Nb can significantly decrease damping capacity of Fe-Cr-Mo-1Nb at low strain amplitude. But at higher strain amplitude, damping capacity increases more rapidly and Fe- Cr-Mo-1Nb possesses the highest damping capacity. This result reveals that larger amount of precipitations in Fe-Cr-Mo based alloys can interact with dislocations and generate an amplitude-dependent dislocation damping Q-1dis at high strain amplitude.