Transmission Electron Microscopy Study on the Grain Boundary Precipitation of an Fe-Ni-Mn Maraging Steel

Abstract

Transmission electron microscopy was used to study grain boundary precipitation of an Fe-10Ni-7Mn (wt pct) maraging steel during isothermal aging at 753 K. Precipitation of a facecentered tetragonal (fct) h-NiMn phase in association with solute-depleted precipitate free zone (PFZ) was found at prior austenite grain boundaries. Precipitation-induced puckering of grain boundaries in the early stages of aging initiates grain boundary displacement, creating PFZs behind the displaced grain boundary. Further grain boundary migration is driven by the manganese and nickel concentration gradients across the migrating boundary and the elastic strain energy and interphase boundary energy of fine fct h-NiMn particles in the grain that is to be swept by the migrating boundary. Consequently, coarsening of the fct h-NiMn particles occurs via grain boundary diffusion as they are passed by the migrating boundary. As rationale, the reaction is defined as discontinuous coarsening of grain boundary precipitates, featuring a nodular morphology of discontinuous coarsening aggregate. Continuous precipitation within the grain facing reaction front decreases overall reaction driving force at later stages, which leads to a decelerated reaction rate.

Effect of Severe Plastic Deformation on Mechanical Properties of Fe-Ni-Mn High Strength Steel

“…Hossein Nedjad et al [9] reported preliminarily an improvement in the tensile properties of an Fe-10Ni-7Mn maraging steel after cold rolling for 85% and subsequent aging at 753 K. Nevertheless, effect of cold rolling for a wide range of thickness reduction in combination with isothermal aging treatment needs to be more clarified. Further, it has been demonstrated that cold rolling and aging of the Fe-Ni-Mn steel realizes ultrafine grain formation [10]. Therefore, the aim of this paper is to determine the tensile properties and microstructure evolution of an Fe-10Ni-7Mn steel after sever plastic deformation by cold rolling and ECAP processes.…”

On the microstructure and mechanical properties of an Fe-10Ni-7Mn martensitic steel processed by high-pressure torsion

“…The Fe-10Ni-7Mn (wt.%) low carbon martensitic steel is classified as an ultra-high strength steel which exhibits adequate ductility in the solution annealed (SA) condition. However, this excellent age-hardenable steel suffers from post-aging intergranular embrittlement along prior austenite grain boundaries [1,2]. Recent efforts have focused on the effects of adding alloying elements [3,4], intercritical annealing [5,6] and also employing various severe plastic deformation methods to improve the alloy ductility after aging [7,8].…”

Investigation on the Fatigue Behaviors of Maraging Steel at Different Stress Ratios

“…As the ageing temperature increases to 600 °C (see Figure 1d), the dimensions of Ni 3 Ti precipitates become larger, and the length of Ni 3 Ti is 78.8 ± 10.2 nm. [ 12 ] To some degree, it can be detected that there is coarsening of boundaries, and the boundaries coarsening would result in the generation of precipitation‐free zones (PFZs) at the boundaries, [ 32,33 ] as shown in Figure 1d. As the ageing temperature further upgrades to 630 °C, it can be observed from Figure 1e and f that the sizes of Ni 3 Ti, boundaries, and PFZs would further improve, and the distribution of Ni 3 Ti becomes sparse.…”

“…Chemical compositions of the experimental maraging steel (wt%). [12] Ti Cr (PFZs) at the boundaries, [32,33] as shown in Figure 1d. As the ageing temperature further upgrades to 630 °C, it can be observed from Figure 1e and f that the sizes of Ni 3 Ti, boundaries, and PFZs would further improve, and the distribution of Ni 3 Ti becomes sparse.…”