Elke Leunis

EBSD study of angular deviations from the Goss component in grain-oriented electrical steels

The magnetic properties of grain-oriented (GO) electrical steels strongly depend on the distribution of the α and β angles, i.e., the deviations of the easy magnetisation <100> from the rolling direction (RD) in the rolling plane and out of the rolling plane, respectively. However, most Electron Backscatter Diffraction (EBSD) studies consider the standard Goss deviation angle, which includes the rotation of the (110) plane about the RD. Therefore, in the present work, a new procedure is demonstrated for deriving the α and β angles from EBSD mappings to obtain a quantitative texture characterisation in line with the magnetic properties. This procedure is later applied to 37 GO steels after secondary recrystallisation that exhibit a wide range of permeability levels. The relation between the texture and the polarisation at 800A/m (J800) that is measured in the present study by EBSD is compared to the one that has been determined in previous papers with optical goniometers and X-ray diffraction techniques, and this relation is subsequently used to define a relevant parameter to describe the orientation quality of the grains. The results indicate that the average angle of the α and β deviations is a relevant deviation parameter for the characterisation of grain orientations. Finally, it is demonstrated that the combination of the quantitative correlation between polarisation and texture with the orientation imaging of EBSD offers the possibilities of both studying the crystallographic environment of highly oriented grains in the primary recrystallised matrix for the production of high-permeability steels and evaluating the spatial distribution of the angular deviations in GO steels after secondary recrystallisation.

Texture Control in Non-Oriented Electrical Steels by Severe Plastic Deformation

Although plenty of research has already been carried out on the issue of texture control in non-oriented electrical steels, there is not yet a universally applied industrial process to obtain an optimized {001} fibre texture. Among the various laboratory processes that have been studied so far, cross rolling seems to be one of the most promising approaches. For evident reasons cross-rolling cannot be implemented on a conventional continuous rolling line of an industrial plant. In the present study a potential interesting alternative is presented which may deliver a similar texture evolution as the cross rolling process, but can be applied in a continuous line of hot and cold rolling operations followed by recrystallization annealing. By applying severe rolling reductions a very strong rotated cube texture is obtained very much similar to the one that is observed after cross rolling. After annealing, the rotated cube texture changes to a {h11}<1/h,21> fibre texture with a maximum on the {311}<136> component which implies the potential to develop a {001} fibre texture after further processing. It is argued that the appearance of the {311}<136> recrystallization texture component can be attributed to oriented nucleation in the vicinity of grain boundaries between slightly misoriented rotated cube grains.

Effect of Mn on the Nanoprecipitation in Binary Fe-Cu alloys

Effect of the third alloying element Mn on Cu-precipitation was studied in a binary Fe-1.3% Cu alloy. Precipitation in both the alloys was investigated after homogenization treatment and subsequent artificial aging. Advanced characterization techniques such as Positron Annihilation Spectroscopy (PAS) and Tomographic Atom Probe (TAP) were used to establish the chemical composition, morphology, size and number density of the Cu-rich phases. Combined results of PAS and TAP were particularly useful in order to follow the Cu precipitation in the binary alloy. At short aging times, addition of Mn significantly increased the kinetics of hardening while its effect on the magnitude of precipitation strengthening is only marginal. It further increases the over-aging kinetics.

Microstructure and Texture Optimization in Fe-Si Ferritic Steels

The ferromagnetic properties of ferritic steels are known to strongly depend on the direction of magnetization. The <100> are the axes of spontaneous magnetic moments and hence the directions of easy magnetization. Materials displaying a <100>//ND texture are ideal not only for transformer but also for rotating machines due to their isotropic magnetic character. In the present study the potential of severe plastic rolling deformation is investigated. The cold rolling and annealing microstructures and textures are identified with increasing rolling strains to a maximum vM equivalent of 8.0. It is shown that excessive rolling reduction is capable of producing non-conventional texture components with promising potential for magnetic applications.

Nucleation and Growth of Surface Texture during α-γ-α Transformation in Ultra Low Carbon Steel Alloyed with Mn, Al and Si

. It is well known that surface energy anisotropy is one of the driving forces for the orientation selection at the metal-vapour interface. This affects the microstructure and texture evolution at the surface during phase transformation, which is an inherent feature of low-alloyed low-carbon steels. This paper investigates the nucleation and growth of the surface texture by orientation contrast microscopy. It has been found that the surface texture is dominated by {001} oriented grains, which exhibit a remarkable orientation gradient from the centre of the grain towards the edge. The {001} oriented grain centre gradually rotates around a <110> axis in small incre¬mental steps when nearing the edge of the grain. Towards the edge the accumulated rotation angle has commonly reached a value of 30°. Underneath the surface grains (~30 µm) the bulk texture consists of a strong -fibre.

Influence of initial heating during final high temperature annealing on the offset of primary and secondary recrystallization in Cu-bearing grain oriented electrical steels

The industrial production route of Grain Oriented Electrical Steels (GOES) is complex and fine-tuned for each grade. Its metallurgical process requires in all cases the abnormal grain growth (AGG) of the Goss orientation during the final high temperature annealing (HTA). The exact mechanism of AGG is not yet fully understood, but is controlled by the different inhibition systems, namely MnS, AlN and CuxS, their size and distribution, and the initial primary recrystallized grain size. Therefore, among other parameters, the initial heating stage during the HTA is crucial for the proper development of primary and secondary recrystallized microstructures. Cold rolled 0.3 mm Cu-bearing Grain Oriented Electrical Steel has been submitted to interrupted annealing experiments in a lab tubular furnace. Two different annealing cycles were applied:• Constant heating at 30°C/h up to 1000°C. Two step cycle with initial heating at 100°C/h up to 600°C, followed by 18 h soaking at 600°C and then heating at 30°C/h up to 10...

Strain induced inward grain growth during recrystallisation in steel sheets with BCC crystal structure

The present paper investigates the potential application of Strain Induced Boundary Migration mechanism on the two different types of surface textures developed after α-γ-α phase transformation annealing, one with preferred cube and Goss orientation at the surface and the other with random surface texture without preferred orientations. It has been demonstrated that these surface texture components grow in across the thickness of the sheet after an appropriate combinations of a critical amount of rolling reductions and an annealing treatment at the recrystallisation temperature.

Surface Microstructure Evolution during Phase Transformation on Mn, Al and Si Alloyed Ultra Low Carbon Steel

This paper investigates the surface texture evolution after a short phase transformation annealing in low vacuum on ultra low carbon steel sheets alloyed with high Mn and Al and the cold rolled steel sheets of industrial composition alloyed with silicon. The ultra low carbon steel sheets with high Mn and Al show surface monolayer which has a characteristic surface texture components <100>//ND texture and microstructure with special grain morphology. Contrastingly, the industrial composition alloyed with silicon does not show specific surface texture components inspired by surface energy anisotropy at the surface. The composition depth profiling investigations performed on the all steel sheet surface shows that oxidation characteristics of alloying elements at the metal vapour interface have played a decisive influence on surface texture evolution. Further, transformation annealing in higher vacuum reveals that surface texture can be obtained in an industrial composition alloyed with silicon.

Surface Microstructure and Texture Evolution during Interrupted Annealing in Ultra Low Carbon Steels

The austenite-to-ferrite phase transformation, which is an inherent feature of low-alloyed ultra low carbon steels, has scarcely been investigated to control surface texture and microstructure evolution. This paper investigates the systematic evolution of texture and microstructure at the metal-vapour interface during interrupted annealing in vacuum. Interrupted annealing experiments were carried out on three ultra low carbon steel sheets alloyed with Mn, Al and Si. The texture and microstructures have been investigated by X-ray diffraction and SEM-EBSD techniques. These results reveal a very clear variation in the surface texture components as well as in the surface microstructure after BCC recrystallisation and double  transformation interrupted annealing. The recrystallisation texture consists mainly of a <111>//ND fibre, while the transformation texture at the surface exhibits a <100>// ND fibre in combination with components of the <110> //ND fibre. It has been revealed that the latter specific surface texture was present in a monolayer of outer surface grains which were in direct contact with the vapour atmosphere. This observed phenomenon could be explained by considering the role of surface energy anisotropy occurring during phase transformation annealing.