Papers by Keyword: Misorientation Angle

Abstract: Measurements over fractured surfaces of samples obtained from impact Charpy tests and four-point double-notch bend tests, carried out at-60°C and-196°C were performed in the present work. This in order to quantify cleavage facets misorientation for the resistance of cleavage fracture propagation. The material used for the analyses was a ferritic Grade A ship plate steel. The grains misorientation angle was quantified by measuring the orientation of single cleavage facets with respect to its neighbors, of a number of cleavage facets, and the misorientation angle was measured. The misorientation angle of cleavage facets was analyze in four groups: all facets, small-small, small-large and large-large facets in order to identify how this classification can affect the misorientation angle of cleavage facets. The results showed that high misorientation angles between neighboring grains, can act as barriers for cleavage propagation, and offer more resistance for brittle fracture propagation or may arrest potential microcracks of critical size in the ductile-brittle transition of ferritic steels. Therefore, the analysis revealed arrest of microcracks when the fracture path found high misoriented grains in the lower shelf of a Grade A ship plate steel. The effect of the misorientation of the ferrite grains in terms of the cleavage facets misorientation on fracture propagation was also discussed in the present work. Keywords: Cleavage fracture, Misorientation angle, Charpy tests, Four-point double-notch bend tests, Cleavage facets.

Abstract: Grain growth and grain boundary character distribution relationships in Fe-Ga rolled sheet is investigated to study the influence of H₂S gas content in argon on the development of selective grain growth through secondary recrystallization. Abnormal growth of (011) grains was predominant at the low content of H₂S gas, while (113) grain growth was well developed at contents higher than 1.33% H₂S. On the other hand, the development of (001) grains was challenging to produce because it is very sensitive to the anneal environment and has a relatively low fraction of high energy grain boundaries associated with misorientation angles that determine the mobility of boundaries.

Abstract: The strengthening mechanisms which are operative in bainite are very well known: small bainite packet, small width of the laths, dislocation density and size and number of carbide particles (Fe₃C), among others. Bainite packet size has been traditionally considered as the value measured by optical microscopy (OM), as electron back scattered diffraction (EBSD) technique is relatively recent. In a V-microalloyed steel with bainitic microstructure of C=0.38%, V=0.12% and N= 0.0214% the average length and width of ferrite laths and of cementite carbides were measured. On the other hand, the bainite packet size was measured by OM and EBSD with a misorientation of 15o. These values of the microstructural units have been taken in account to calculate the effective surface energy γ_p given by Griffith’s model for cleavage fracture. It was concluded that bainite packet size determined by EBSD with a misorientation angle criterion of 15o was the microstructural parameter that controls cleavage crack propagation. Given the relationship between the average unit crack path (UCP) and the bainite packet size, it was concluded that the effective surface energy of cleavage fracture (γ_p) would be between 71.6 and 82.6 J m^-2.

Abstract: Behavior of the selective growth of Goss grains in grain-oriented electrical steel was investigated by controlling the heating rate in secondary recrystallization annealing．It was clarified that the important factors on the selective growth of Goss grains were the frequency and the mobility of grain boundary. It was demonstrated that boundaries having misorientation angle between 30 degree and 35 degree had the greatest influence on the selective growth, and the change of crystal orientation of secondary recrystallized grains expected by analyzing the change of primary recrystallized texture during secondary recrystallization annealing showed good agreement with the experimental result.

Abstract: Recrystallization texture in grain oriented silicon steel at different annealing temperature is investigated. Normalized x-ray intensities of various orientation components observed in Orientation Distribution Function are used for comparison. The computed CSL boundary distributions about Goss component with annealing condition were calculated. The misorientation angle distribution is also measured in order to find the importance of high-energy boundary with misorientation 20~45° range for the secondary recrystallization of Goss grain. From the analysis of CSL boundary distribution and misorienation angle distribution, the distribution of CSL boundaries does not evidently show any preferred difference between Goss and other texture components. Whereas, the misorientation angle analysis shows that the number of 20°~45° misoriented boundaries is higher around the Goss grains than around other texture components.

Abstract: The magnetic properties of nonoriented electrical steels are influenced by grain size and texture of final products. The key technology in the commercial production of nonoriented electrical steels is to grow grains with {hk0}<001> texture up to the optimum size in the final annealing process. The problems related to grain size control have been extensively investigated, while texture control has received much less attention. Therefore, there is enough room to improve the magnetic properties through the control of texture. In this study, systematic investigations on the texture evolution during both recrystallization and grain growth have been made. The formation of recrystallization texture is explained by oriented nucleation. This is supported by the fact that the area fraction of nuclei or recrystallized grains with specific orientation to all new grains remains almost constant during the progress of recrystallization. Most nuclei have a high misorientation angle of 25∼55° with the surrounding deformed matrices. During the progress of grain growth, the Goss texture component continues to decrease because the Goss grains have a high percentage of low angle, low mobility grain boundaries. The grains of Goss orientation have a smaller grain size than those of random orientation.

Abstract: Electron backscattered diffraction analysis has been used to investigate the effect of shear deformation on microstructural evolution of a Ni-30Fe alloy during hot deformation. The alloy was compressed by 50% or 75% in thickness at a strain rate of 1/s in a single pass at 1023K using a hot compression simulator. Three-dimensional finite element analysis was carried out to evaluate inhomogeneous strain distribution introduced in the specimens by the simulator. As the equivalent strain increased, the fraction of high angle grain boundaries (HAGBs) with misorientaions between 15o and 30o increased almost in the similar way regardless of the presence of shear strain. The fraction of HAGBs having misorientations in excess of 30o increased mainly at the expense of low angle grain boundaries with misorientations smaller than 15o. Such the expense occurred at much higher rate with shear strain than without shear strain. The shear component is effective to develop HAGBs in austenite grain interiors.

Abstract: Nonoriented electrical steels have been widely used as core materials in motors and generators. For these applications low core loss and high permeability are required. The magnetic properties of these steels depend on the grain size and crystallographic texture of the annealed final products. The problems related to grain size control have been extensively investigated, while texture control has received much less attention. The technologies used to control the grain size in nonoriented electrical steels have approached to their limits. However, there is still some possibility for improvement of the magnetic properties through texture control. In order to explore this possibility, the evolution of recrystallization texture for nonoriented electrical steels with 2% Si was systematically studied. Texture change during grain growth was additionally analyzed. The formation of recrystallization texture is explained by oriented nucleation. This is supported by the fact that the area fraction of nuclei or recrystallized grains with specific orientation to all new grains remains almost constant during the progress of recrystallization. Most nuclei have a high misorientation angle of 25~55° with the surrounding deformed matrices. During the progress of grain growth, Goss and {111}<112> components are weakened and the random texture is strengthened. The grains of the Goss and {111}<112> orientations have smaller grain size than those of random orientation.