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4 Crystalline arrangement: (a) an array of atoms in space, (b) construction of space lattice (a network of lines), (c) a representative volume element (unit cell), and (d) parameters of a unit cell.
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The perpetual flow of understanding between phase transformation that controls grain/microstructures and heat treatment which decides the size of grains/microstructures of steels is not well articulated in the perspective of undergraduate students. In Phase Transformations and Heat Treatments of Steels, theories of phase transformation have been us...
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... Since normalization is a heat treatment on which cooling rates assume higher values than annealing, the austenitic transformation occurs out of thermodynamic equilibrium, placing an adverse condition for atomic diffusion of carbon atoms [65]. Then, the pearlite formation is only assured by the decrease in the mean interlamellar spacing, which results in higher perlite volume fraction and higher ferrite content in the perlite, therefore, resulting in higher mechanical strength [65,66]. Specifically, concerning fracture toughness, this increase is justified by higher ferrite content in the perlite, making it more tough, and also by the decrease in the mean interlamellar spacing itself [65], which would result in more pearlite bands acting as mechanical reinforcements ahead of the crack front. ...
Fracture toughness determination is crucial for the design phase of pressure vessels, and, although ASTM E1820 and ISO 12135 fracture toughness standards have existed for some time, some differences have been reported in the determination of this property. This study investigates the ductile fracture behavior of ASTM A516 Gr.70 pressure vessel steel and assesses the differences in estimating both standards. The steel’s tensile properties and initiation fracture toughness (JIC) were evaluated, taking into account the parallel and perpendicular orientations to the rolling direction. The results reveal the properties’ dependence on the rolling direction, mainly attributed to perlite banding. Additionally, as for the JIC determination, the differences were associated with the different blunting line slope estimations on each standard, reinforcing the necessity of a work-hardening-based blunting line for each material assessed.
This research discusses the machine component distortion problem after the hardening process. This research focuses on the inside diameter of the hole and gap width dimension changes in components. Austenite temperature, quench medium, and material thickness were examined to determine their effect on distortion. The components are made of AISI 4140 machinery steel group. Another idea in this study is to substitute the material with AISI 4340 to minimize the risk of distortion. This study used a Navy C-Ring specimen. This study applies the Design of Experiment, followed by statistical analysis with ANOVA and Response Surface optimization. The austenite temperature of 895.2°C, oil quench medium, and 8 mm thickness are the best hardening parameters for AISI 4140, which reduce inside diameter distortion up to 82.51% and reduce gap width distortion up to 78.16%. Austenite temperature of 900°C, oil cooling medium, and 8 mm thickness is the best hardening parameter for AISI 4340, which reduces inside diameter distortion by up to 62.23% and reduces gap width distortion by up to 86.61%. Material substitution of AISI 4140 with AISI 4340 can be done by considering the risk of warping.
