Man Wang

Effect of Thermomechanical Parameters on Σ3n Grain Boundaries and Grain Boundary Networks of a New Superaustenitic Stainless Steel

Hot compression tests were conducted in a temperature range of 800 – 1100 °C and strain rate range of 0. 1 – 10 s−1 using a Gleeble 3500 thermomechanical simulator to investigate the influence of hot deformation parameters (temperatures, strain rates and strains) on the grain boundary network evolution of a new grade Fe-Cr-Ni superaustenitic stainless steel. The results showed that a dominant effect of deformed temperature is Σ3n (n=0, 1, 2, 3) boundaries population increased with decreasing temperature, while they first increased and then reduced with in-creasing strain and strain rate. Interestingly, besides Σ3n (n=0, 1, 2, 3) twin grain boundaries, some Σ1 boundaries could interrupt grain boundaries network effectively, which enhance material performances. But they are scarcely reported. The misorientation of some segments LAGBs in the deformed microstructure (pancaked grains) increased and slid to high angle grain boundaries with increasing the fraction of recrystallized grains during hot deformation.

Microstructure and mechanical properties of 16 Cr-ODS ferritic steel for advanced nuclear energy system

A 16Cr-0.5Ti-lW-0.35Y2O3 oxide dispersion strengthened (ODS) ferritic steel was fabricated by mechanically alloying and hot isostatic pressing (HIP). Subsequent thermo-mechanical treatments were performed to improve the microstructure homogeneous and service properties of the HIPed 16Cr-ODS steel. Nano-oxide particles were observed by TEM, which can be identified to be (Y, Ti) complex oxide by EDS and SAED. The mechanical property was measured by tensile test, and the oxidation behaviour of the ODS steel was performed at high temperature in a muffle.

Effects of Solution Depletion and Segregation Oxidation on Morphology of Modified 310 Austenitic Stainless Steel

The oxidation morphologies of modified 310 steel exposed in 900 and 1100 °C air were investigated. A double layer morphology consisting of a (Cr, Mn)-rich outer layer and a fine Cr-rich inner layer was formed at 900 °C. It was related to the breakaway oxidation induced by the Cr-depletion and the Mn-segregation in inner layer. Some Cr-rich oxides with amorphous state were formed along grain boundaries. And some new finer oxide grains, voids and Cr-rich precipitates were observed in spallation areas at 1100 °C. Correspondingly, the oxidation kinetic curve dropped with the spallation of scale and increased with the formation of some new oxide grains. It was caused by segregation of Cr and the transformation of oxides from Cr2O3 to the volatile oxides at elevated temperature. XRD analysis showed that the precipitates were mainly composed of CrO3. Segregation and depletion for solutions were also discussed by oxidation diffusion mechanisms.

Fabrication and mechanical properties of a 14Cr-ODS steel

In this paper, the fabrication method and the mechanical properties of a 14Cr-ODS steel are investigated. The pre-alloyed steel powders and oxide powders were mechanical alloyed after milling for 30 h under a rotation of 300 rpm. Y-Ti-O phase was obtained after annealing the MA powders at 1100 °C. The tensile strength of the HIPed 14Cr-ODS steels at room temperature was about 1120 MPa. Micro structure observation showed that there were amount of nano dispersion particles in the base alloy which resulted in the high hardness and tensile strength.

Microstructural evolution and mechanical properties of an Fe–18Ni–16Cr–4Al base alloy during aging at 950°C

The development of Gen-IV nuclear systems and ultra-supercritical power plants proposes greater demands on structural materials used for key components. An Fe–18Ni–16Cr–4Al (316-base) alumina-forming austenitic steel was developed in our laboratory. Its microstructural evolution and mechanical properties during aging at 950°C were investigated subsequently. Micro-structural changes were characterized by scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy. Needle-shaped NiAl particles begin to precipitate in austenite after ageing for 10 h, whereas round NiAl particles in ferrite are coarsened during aging. Precipitates of NiAl with different shapes in different matrices result from differences in lattice misfits. The tensile plasticity increases by 32.4% after aging because of the improvement in the percentage of coincidence site lattice grain boundaries, whereas the tensile strength remains relatively high at approximately 790 MPa.