Tohoku University · Engineering
Professor Tomohiko Hojo's research lab specializes in the development and characterization of ultra-high-strength low-alloy steels, with a primary focus on hydrogen embrittlement resistance and delayed fracture behavior in advanced TRIP-aided steels. The lab investigates the effects of alloying elements—particularly aluminum, chromium, and vanadium—on hydrogen trapping mechanisms, phase transformation behavior, and mechanical properties in steels with bainitic ferrite and martensite matrices. Key research directions include optimizing microstructure design to enhance hydrogen tolerance and improving the reliability of high-strength steels for automotive applications through advanced testing techniques such as thermal desorption spectroscopy and four-point bending tests.
Figures are computed from collected data and may differ slightly.
To improve the delayed fracture strength of ultra high-strength low alloy TRIP-aided steels with bainitic ferrite matrix (TBF steels), the effects of aluminum content on hydrogen absorption behavior and delayed fracture properties of 0.2%C–0.2–1.5%Si–1.5%Mn TBF steel were investigated. When aluminum was added to the TBF steel, the diffusible hydrogen increased. It was expected that the hydrogen was charged not only in retained austenite films but also on lath boundary. Delayed fracture strength
The effect of strain rate on the hydrogen embrittlement property of an ultra high-strength TRIP-aided bainitic ferrite (TBF) steel with bainitic ferrite matrix was investigated to clarify the correlation between the transformation behavior of retained austenite and the hydrogen embrittlement fracture behavior of the TBF steel. Tensile tests were carried out at the strain rates between 5.56 × 10−6 and 2.78 × 10−2/s without and with hydrogen charging. Hydrogen analysis after tensile tests was cond
To develop ultra high-strength cold stamping steels for automobile frame parts, the effects of alloying elements on hydrogen embrittlement properties of ultra high-strength low alloy transformation induced plasticity (TRIP)-aided steels with a martensite matrix (TM steels) were investigated using the four-point bending test and conventional strain rate tensile test (CSRT). Hydrogen embrittlement properties of the TM steels were improved by the alloying addition. Particularly, 1.0 mass% chromium
The amount of charged hydrogen and its effect on ductility in three kinds of ultra high strength low alloy TRIP-aided steels with different matrix structure were investigated. These TRIP-aided steels, especially the TRIP-aided steels with bainitic ferrite matrix, were charged hydrogen more than the conventional tempered martensitic steel. This was principally associated with retained austenite trapped so much hydrogen in solute. Hydrogen embrittlement was considerably suppressed in the TRIP-aide
Hydrogen absorption behavior and hydrogen embrittlement properties of 1000-1800 MPa grade ultra high-strength low alloy TRIP-aided steels with bainitic ferrite matrix were investigated. The TRIP-aided steels absorbed a large amount of hydrogen, compared with the conventional tempered martensitic and bainitic steels. It was expected that the absorbed hydrogen was principally trapped in interlath retained austenite films and along bainitic ferrite lath boundary. Superior hydrogen embrittlement per
To standardize the evaluation technique of hydrogen embrittlement properties of ultra high-strength steel sheets, hydrogen embrittlement properties of SCM435 and V added steel sheets with tempered martensitic matrix were investigated and compared by using 4-Point Bending Cathode Charging Technique, 4-point Bending Constant Displacement Compression Technique and Conventional Strain Rate Technique which was tensile tests. In the SCM435 and the V added steels, it was confirmed that little deteriora
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