EBSD characterisation of grain size distribution and grain sub-structures for ferritic steel weld metals

Abstract

Microstructural characterisation of engineering materials is required for understanding the relationships between microstructure and mechanical properties. Conventionally grain size is measured from grain boundary maps obtained using optical or electron microscopy. This paper implements EBSD-based linear intercept measurement of spatial grain size variation for ferritic steel weld metals, making analysis flexible and robust. While grain size has been shown to correlate with the strength of the material according to the Hall–Petch relationship, similar grain sizes in weld metals with different phase volume fractions can have significantly different mechanical properties. Furthermore, the solidification of the weld pool induces the formation of grain sub-structures that can alter mechanical properties. The recently developed domain misorientation approach is used in this study to provide a more comprehensive characterisation of the grain sub-structures for ferritic steel weld metals. The studied weld metals consist of varying mixtures of primary ferrite, acicular ferrite, and bainite/martensite, with large differences observed in hardness, grain size, grain morphology, and dislocation cell size. For the studied weld metals, the average dislocation cell size varied between 0.68 and 1.41 µm, with bainitic/martensitic weld metals showing the smallest sub-structures and primary ferrite the largest. In contrast, the volume-weighted average grain size was largest for the bainitic/martensitic weld metal. Results indicate that a Hall–Petch-type relationship exists between hardness and average dislocation cell size and that it partially corrects the significantly different grain size—hardness relationship observed for ferritic and bainitic/martensitic weld metals. The methods and datasets are provided as open access.

Study of cyclic crack‐tip opening displacement of microstructurally small fatigue crack using digital image correlation

“…The analyses were conducted with a step size of 2–5 μm. EBSD data were post‐processed using the MTEX toolbox 56,57 . The Vickers micro‐indentations were used to correct the drift‐induced trapezoidal distortion in the EBSD data by skewing and scaling the orientation and grain boundary images 58 …”

“…EBSD data were post-processed using the MTEX toolbox. 56,57 The Vickers micro-indentations were used to correct the drift-induced trapezoidal distortion in the EBSD data by skewing and scaling the orientation and grain boundary images. 58 A silicon stamp was used to apply an optimized speckle pattern for high-resolution DIC analyses with a characteristic speckle size of 10 μm.…”

Microstructure and Mechanical Properties of Laser Narrow-Gap Multi-Pass Weld 20 mm-Thick Ti-6Al-4V Alloy with Different Filling Layers

“…It can be considered that due to the layer-by-layer weld process, the welding thermal cycle during the post-weld welding made the solidified gion receive heat treatment, so the dislocation density of grains in this region decreas and the grains also grew to a certain extent. According to the Hall-Petch formula, at ro temperature, the smaller the grain size, the more grain boundaries contained in the u volume, and the better the strengthening effect [21,22], so the bottom of the filling la exhibited lower hardness. The hardness of the filling layer with a large range decreased from the surface (370 HV) to the bottom (345 HV).…”

“…Combined with the analysis of the microstructure characteristics, it can be considered that when the number of filling layers was large with a low line energy, the lower peak temperature and high-temperature residence time led to a larger cooling rate, so the final microstructure of the weld area was finer. In the tensile test, the dense grain boundary had a strong ability to resist deformation [21,22], thus exhibiting higher strength. With the increase in line energy, the size of solidified grain in the weld zone became larger and the grain boundary density decreased, so it became more easily deformed under tensile load and exhibited lower tensile strength.…”

Misorientation Angle Study on Cleavage Fracture Propagation Surfaces of a Grade a Ship Steel, through Charpy and Four-Point Double-Notch Bend Tests

“…The misorientation angle between adjacent grains of steels, has become one of the major concerns for the study of some mechanical and toughness properties of irons [1][2][3][4][5], carbon steel [3,6], stainless steel [7][8], other types of steels [8][9][10] and different alloys [11][12]. The misorientation angle play a big role for the propagation of cleavage fracture in steels and on the fracture surface appearance.…”