Mechanical Characteristics of Structural Thick Plates Depending on Vacuum Time of RH Process

The structural thick plates were manufactured by varying the vacuum time at a constant argon gas flow rate and degree of vacuum during the Ruhrstahl Heraeus (RH) refining process. The inclusion and mechanical properties of the structural thick-plate specimens were evaluated according to vacuum time. The nitrogen in the converter had an effect after the RH process, and as the vacuum time of the RH process increased, the nitrogen content also increased. The nitrogen in the continuous casting (CC) decreased more than that in the converter, and as the vacuum time increased, the hydrogen decreased. Al2O3·CaO, MnS and Al2O3·MgO inclusions were observed in the structural thick plate. The average size of the oxides was (6.1 to 33.46) μm, while the average size of the Al-O-based inclusions was (4.26 - 6.3) μm. The mechanical properties, such as tensile strength, yield strength, and elongation, were affected by the vacuum time of the RH process with 10 min being the best. The micro-Vickers hardness showed dispersion regardless of the vacuum time of the RH process, which can be explained by the Weibull probability distribution. From the shape and scale parameters, although the specimen with the vacuum time of the RH process of 10 min showed a large dispersion in the micro-Vickers hardness, the characteristic value of 63.2 % was the best.