The final solidification position in continuous casting is a very important index for productivity and product quality, and continuous measurement is required. An apparatus to measure solidification completion position by electromagnetic ultrasonic method was developed. High sensitivity electromagnetic ultrasonic sensor using digital signal processing and Halbach array, and calibration method using longitudinal and transverse waves of ultrasonic wave enabled high sensitivity and continuous measurement of final solidification position. As a result of the application to the operation improvement, the following effects were obtained: productivity improvement by the improvement of casting speed, and improvement of center segregation in the steel plate for pipeline.

Copper bearing steel is hard to recycle because it shows severe surface cracking in hot working due to the formation of copper liquid phase on the interface between scale and steel, i.e. hot shortness. Suppression of the hot shortness is a critical issue to attain sustainable society. In order to clarify the mechanism of the surface cracking in hot rolling, in this study, 0.30%Cu with/without 0.15%Ni bearing square steel bars with controlled oxide scale were hot rolled in a laboratory. The height was reduced 5%, 25% or 40% at 1273 K, 1373 K or 1473 K. After the hot rolling at 1273 K, few cracks were found on both upper and side surface where no copper liquid phase appear. After the hot rolling at 1373 K or 1473 K, surface cracks shallower than 50 µm were found on upper surface, while surface cracks deeper than 100 µm were found on side surface of the rolled bars. Depth and width of cracks increased with an increase in height reduction. On the upper surface, cracks were suppressed by temperature drop due to heat transfer to the cold roll. The copper liquid phase on the interface between scale and steel was transformed to solid. On the other hand, edge cracks were formed on side surface (free surface).

Creep testing is time-consuming and costly, leading institutions to limit the number of tests conducted to the minimum necessary for their specific objectives. By pooling data from each institution, it is anticipated that predictive models can be developed for a wide range of materials, including welded joints and degraded materials exposed to service conditions. However, the data obtained by each institution is often highly confidential, making it challenging to share with others. Federated learning, a type of privacy-preserving computation technology, allows for learning while keeping data confidential. Utilizing this approach, it is possible to develop creep life prediction models by leveraging data from various institutions. In this paper, we constructed global deep neural network models for predicting the creep rupture life of heat-resistant ferritic steels in collaboration with eight institutions using the federated learning system we developed for this purpose. Each institution built a local model using only its own data for comparison. While these local models demonstrated good predictive accuracy for their respective datasets, their predictive performance declined when applied to data from other institutions. In contrast, the global model constructed using federated learning showed reasonably good predictive performance across all institutions. The distance between each institution's data was defined in the space of explanatory variables, with the NIMS data, which had the largest dataset, serving as the reference point. The global model maintained high predictive accuracy regardless of the distance from the NIMS data, whereas the predictive accuracy of the NIMS local model significantly decreased as the distance increased.

Steel slag, a by-product of the steelmaking process, contains free-lime which can expand upon hydration. This expansion characteristic necessitates pre-aging when used as a subbase material. Various countries regulate the expansion characteristics of steel slag through different test methods and standards. However, the temperature conditions of these tests and their correlation to actual environments are not clearly defined. This study aimed to evaluate the temperature dependence of the immersion expansion ratio of steel slag for road construction through expansion tests. The results identified the rate-limiting step in the hydration process and calculated the reaction rate constant. The study compared the immersion expansion test method with actual environments to quantitatively assess the degree of acceleration in the tests. It was found that the hydration of steel slag follows a pseudo-first-order surface reaction. By analyzing the temperature changes in the water tank, the study estimated the continuous immersion expansion test period corresponding to the JIS method. The 80°C continuous immersion expansion test period of 4.1–4.6 days was equivalent to the 10-day JIS immersion expansion test. The JIS immersion expansion standard was found to correspond to a legal service life of 10 years or more.