[en] The experiment provides a method for rapidly preparing a lamellar structure via processing a homogenous material with electropulsing. Treatments initially formed microstructure with residual ferrite along the current direction and produced the macroscopic soft and hard alternating layers after austenitization. The difference in elemental content was thought to be responsible for the observed phenomenon.

[en] The microstructure and tensile properties at 973 K in 9CrODS steels were investigated with respect to various fractions of the residual ferrite from zero to 47 vol.%. The formation of the residual ferrite was discussed from a balance between a chemical driving force for α to γ reverse transformation and the oxide particle pinning force, while 0.04 mass% carbon sample could contain an equilibrium δ-ferrite. With increasing volume fraction of the residual ferrite, strength at 973 K increases but ductility decreases, which is attributed to the fact that the residual ferrite is harder than the tempered martensite

[en] Highlights: • Typical microstructure of F82H–ODS steel is observed. • The existence of a meta-stable ferrite phase in F82H–ODS steel is confirmed. • The microstructure can be modified by the coarsening of the oxide particles. • The relationship between the phase formation and oxide particles is revealed. - Abstract: For the reduced activation F82H–ODS ferritic steel developed as the advanced fusion blanket material, the structure control and phase formation mechanisms were investigated. The area fraction of the ferrite phase was reduced, when the specimens were annealed at 1250 °C for long enough time inducing oxide particle coarsening. The effect of oxide particles on α–γ transformation was investigated, and ferrite formation is ascribed to pinning of α–γ interfacial boundaries by the dispersed oxide particles. This ferrite is meta-stable, and designated as residual-ferrite

[en] Stretch-flangeability as a parameter of formability is measured on dual-phase (DP) and complex-phase (CP) steels by the hole-expansion ratio (HER), and nanoindentation is introduced to assess the hardness of constituent phases before and after HER testing. Hole-expansion ratios of two dual-phase (DP1, DP2) and one complex-phase (CP1) steels are measured as 51%, 126% and 136%, respectively. The primary site of void formation is found to be the interfacial boundary for DP1, the ferrite phase close to the martensite phase where numerous geometrically necessary dislocations (GNDs) are formed for DP2, and the martensite phase for CP1. The hardness ratio of the hard to soft phase is a key indicator of formability, and this introduces the stress concentration from strain disparity at the interfacial boundaries between the hard and soft phases. Here, it is founded that strain-hardenability of constituent phases depends on the hardness of the GND layer, and the strain disparity under deformation is determined by the GND layer hardness as well as the hardness ratio of the hard to soft phase. This study suggests the GND layer as a stress-dispersion layer and the hardness of GND layers in soft phases as a critical role in formability.

[en] The process of residual ferrite formation and resultant high-temperature strengthening in 9Cr-ODS ferritic steel was investigated by TEM observation, dilatometric measurement and thermodynamic analysis. Formation of the residual ferrite is dominated by a balance between pinning of α-γ interfaces and the α-γ reverse transformation, and α-γ reverse transformation is affected by dissolution of carbides into the γ-matrix at the A_C1 and A_C3 points. The fine size of oxide particles is responsible for the higher strength of the residual ferrite containing ODS steels.

[en] Highlights: → Mn-Zn ferrite wastes were recycled through wet chemical route. → The Mn-Zn ferrite takes advantage over A102 made in Acme Electronics Corporation. → The novel recycling technology attained environmental, social and economic benefits. - Abstract: A novel recycling route using acid leaching, reduction, purification, co-precipitation and traditional ceramic process was applied to process the Mn-Zn ferrite wastes and prepare the corresponding high permeability soft magnetic product. Above 95% of Fe, Mn, Zn in the waste materials could be recycled in the form of Mn-Zn ferrite products through the hydrometallurgical route. The comprehensive properties of Mn-Zn ferrite prepared from wastes by this route have broader frequency characteristics, higher resistivity, lower loss coefficient and temperature coefficient as compared to the A102 product (Acme Electronics Corporation, Taiwan). Moreover, the cost of this recycling technology has economical advantage over the traditional ceramic process, which holds a promising industrial application.

[en] Heterogeneous materials are ubiquitous in nature and synthetic situations and have a wide range of important engineering applications. Accurate modeling and reconstructing three-dimensional (3D) microstructure of topologically complex materials from limited morphological information such as a two-dimensional (2D) micrograph is crucial to the assessment and prediction of effective material properties and performance under extreme conditions. Here, we extend a recently developed dilation–erosion method and employ the Yeong–Torquato stochastic reconstruction procedure to model and generate 3D austenitic–ferritic cast duplex stainless steel microstructure containing percolating filamentary ferrite phase from 2D optical micrographs of the material sample. Specifically, the ferrite phase is dilated to produce a modified target 2D microstructure and the resulting 3D reconstruction is eroded to recover the percolating ferrite filaments. The dilation–erosion reconstruction is compared with the actual 3D microstructure, obtained from serial sectioning (polishing), as well as the standard stochastic reconstructions incorporating topological connectedness information. The fact that the former can achieve the same level of accuracy as the latter suggests that the dilation–erosion procedure is tantamount to incorporating appreciably more topological and geometrical information into the reconstruction while being much more computationally efficient. - Highlights: • Spatial correlation functions used to characterize filamentary ferrite phase • Clustering information assessed from 3D experimental structure via serial sectioning • Stochastic reconstruction used to generate 3D virtual structure 2D micrograph • Dilation–erosion method to improve accuracy of 3D reconstruction

[en] The article discusses factors determining the reproducibility of measurement results for a banded microstructure in sheet steels St3sp and 09G2s using computerized procedures.

[en] 9CrODS steel, a candidate fission and fusion structural material, was subjected to hot-rolling with varying parameters of surface temperature and cooling rate just after hot-rolling. The deformation-induced dynamic ferrite transformation was confirmed at the rolling temperature 805 °C above Ar₃ (780 °C). This transformation exhibits three characteristic features: transformation for extremely short duration (0.044 second), retaining carbon content equal to the original without long-distance carbon diffusion, and elongated coarse ferrite grains (10 μm). The massive transformation was proposed for the dynamic ferrite transformation from the hot-rolled austenite. The driving force for massive transformation was quantitatively estimated considering dislocations accumulated by hot-rolling. It was also shown that the oxide particles in 9CrODS steel play a critical role for dynamic ferrite transformation by suppressing the dynamic recrystallization at hot-rolling.

[en] Effect of the initial as-cast structure on the microstructure–texture evolution during thermomechanical processing of 409L grade ferritic stainless steel was studied. Samples from the regions of cast slab having ‘columnar,’ ‘equiaxed,’ and a mixture of ‘columnar’ and ‘equiaxed’ grains were subjected to two different processing schedules: one with intermediate hot-band annealing before cold-rolling followed by final annealing, and another without any hot-band annealing. EBSD study reveals that large columnar crystals with cube orientation are very difficult to deform and recrystallize uniformly. Resultant variations in ferrite grain structure and retention of cube-textured band in cold-rolled and annealed sheet contribute to ridging behavior during stretch forming. Initial equiaxed grain structure is certainly beneficial to reduce or even eliminate ridging defect by producing uniform ferrite grain structure, free from any texture banding. Application of hot-band annealing treatment is also advantageous as it can maximize the evolution of beneficial gamma-fiber texture and eliminate the ridging defect in case of completely ‘equiaxed’ starting structure. Such treatment reduces the severity of ridging even if the initial structure contains typically mixed ‘columnar-equiaxed’ grains.