A study of superplasticity in Fe-Mn-(Al-Si)-C low density steels

Junyeong Jeong･Jaeyoon Hwang･Minwoo kang (Hyundai Motor)･Jeongho Han (Hanyang University)

Low density steel sheets can exhibit super-plasticity properties under characteristic composition and process conditions, so they can be applied to large-sized plate parts with high forming difficulty based on high elongation in a single press process, which has the advantages of process simplification (welding deletion, etc.) and mold reduction. We designed various compositions of Fe-Mn-(Al-Si)-C low-specific-weight steel sheets, evaluated super-plasticity properties, analyzed the cause of its occurrence, and verified the properties at room temperature in consideration of future part applicability

Development of Hydrogen Embrittlement Cracking Prevention Technology for High-Strength Steel Sheet Parts

Masaya Yagura･Yusuke Tsunemi･Naoki Kimoto･Masahiro Kubo (Nippon Steel)

In general, hydrogen embrittlement cracking can be a concern in high-strength materials. In this study, assuming automotive components as the application, we focused on the influence of deformation and residual stress on hydrogen embrittlement cracking at sheared edges. Our group investigated methods to reduce residual stress at the sheared edge and, as one example, verified that compressing the sheared edge effectively decreases the residual stress.

oxidation Behavior of Ferritic Stainless Steels under a Simulated Hydrogen Combustion Atmosphere

Yoshitomo Fujimura･Atsutaka Hayashi･Naoki Hirakawa･Junichi Hamada (Nipponsteel)

The steam oxidation behavior of various ferritic stainless steels was investigated under a simulated hydrogen combustion atmosphere consisting of 30% H₂O–N₂ at 400-700 ℃ for 100 hours. For pickled surface, steels showed the greatest weight gain at 600 ℃ in these conditions, and oxidation resistance improved with increasing Cr and Si content. Furthermore, even steels with low Cr and Si showed significantly suppressed oxidation when their surfaces were polished.

Prediction of Abnormal Grain Growth in Hot-forged carburized drivetrain parts

Yasuo Itou･Gou Katou･Makoto Maeda (JATCO)･Tsubasa Yamashita･Naoki Wada･Shuhei Kojima (MI-6 Ltd)･Junya Inoue (The University of Tokyo)

Abnormal grain growth that causes strength reduction occurs in hot-forged carburized drivetrain parts. Predicting this phenomenon is difficult due to its complex occurrence mechanism. In this study, we developed a method to predict the occurrence of abnormal grain growth from controllable factors during part manufacturing by analyzing test results that simulate hot forging using machine learning.

Development of molten flame-retardant magnesium alloys for die casting

Yasumasa Chino (AIST)･Hiroshi Komai (The Japan Magnesium Association)

In the Japan Magnesium Association's “Automotive Magnesium Application Expansion Committee” (2014–2018), efforts were directed toward enhancing safety and eliminating the need for protective cover gases by developing molten flame-retardant magnesium alloys for die-casting, which exhibits significantly reduced flammability during the melting process. In the presentation, we show the flame-resistant behavior of the developed alloy, along with its mechanical and corrosion properties, and further report on the characteristics of prototype components fabricated using the material.

On the Fatigue Limit Diagram and Fatigue Life Prediction Models

Gyoko Oh (Tokyo Roki)

The fatigue limit and lifespan vary depending on the loading mode and are also greatly affected by stress concentration. The effect of mean stress has been mathematically expressed using several models, but based on experimental data, the Walker model has been shown to be the most appropriate and to have high predictive accuracy. The same was true for the effect of assembly stress due to welding on the fatigue limit and the threshold stress intensity range.