This study investigated the mechanical properties of steel in flanges, with the goal of obtaining high strength and high toughness. Quenching was applied alone or in combination with tempering at one of nine combinations of three temperatures TTEM and durations tTEM. Cooling rates at various flange locations during quenching were first estimated using finite element method simulation, and the three locations were selected for mechanical testing in terms of cooling rate. Microstructures of specimens were observed at each condition. Tensile test and hardness test were performed at room temperature, and a Charpy impact test was performed at −46 °C. All specimens had a multiphase microstructure composed of matrix and secondary phases, which decomposed under the various tempering conditions. Decrease in cooling rate (CR) during quenching caused reduction in hardness and strength but did not affect low-temperature toughness significantly. After tempering, hardness and strength were reduced and low-temperature toughness was increased. Microstructures and mechanical properties under the various tempering conditions and CRs during quenching were discussed. This work was based on the properties directly obtained from flanges under industrial processes and is thus expected to be useful for practical applications.
To date, extensive studies have been conducted to assess diverse types of sutures. But there is a paucity of data regarding biomechanical properties of commonly used suture materials. In the current experiment, we compared biomechanical properties and biocompatibility, such as tensile strength and elongation, the degree of bovine serum albumin (BSA) release, in vitro cytotoxicity and ex vivo frictional properties, between a non-absorbable elastic thread (NAT; HansBiomed Co. Ltd., Seoul, Korea) (NAT-R: NAT with a rough surface, NAT-S: NAT with a smooth surface) and the Elasticum® (Korpo SRL, Genova, Italy). The degree of tensile strength and elongation of Si threads was significantly higher in both the NAT-R and -S as compared with the Elasticum® (p < 0.05). Moreover, the degree of tensile strength and elongation of PET threads was significantly lower in both NAT-R and -S as compared with the Elasticum® (p < 0.05). Furthermore, the degree of tensile strength and elongation of braided Si/PET threads was significantly lower in NAT-S as compared with NAT-R and Elasticum® (p < 0.05). The degree of BSA release was significantly higher in the NAT-R as compared with Elasticum® and NAT-S throughout a 2-h period in the descending order (p < 0.05). The degree of cell viability was significantly higher in both NAT-R and -S as compared with Elasticum® (p < 0.05). The degree of coefficient of friction as well as the frictional force and strength was significantly higher in NAT-R as compared with NAT-S and Elasticum® (p < 0.05). NAT had a higher degree of biomechanical properties and biocompatibility as compared with Elasticum®. But further experimental and clinical studies are warranted to compare the efficacy, safety, and potential role as a carrier for drug delivery between NAT and Elasticum®.
High-strength steel is widely used in hot forging products for application to the oil and gas industry because it has good mechanical properties under severe environment. In order to apply to the extreme environment industry requiring high temperature and high pressure, heat treatments such as austenitizing, quenching and tempering are required. The microstructure of high-strength steel after heat treatment has various microstructures such as Granular Bainite (GB), Acicular Ferrite (AF), Bainitic Ferrite (BF), and Martensite (M) depending on the heat treatment conditions and cooling rate. Especially in large forged products, the difference in microstructure occurs due to the difference in the forging ratio depending on the location and the temperature gradient according to the thickness during post-heat treatment. Therefore, this study attempted to quantitatively analyze various phases of F70 high-strength steel according to the austenitizing temperature and hot forging ratio using the existing EBSD analysis method. In addition, the correlation between microstructure and mechanical properties was investigated through various phase analysis and fracture behavior of high-strength steel. We found that various microstructures of strength steel depend on the austenitizing temperature and hot forging ratio, and influence the mechanical properties and fracture behavior.
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