Noboru Wade

Precipitation behavior of laves phase and its effect on toughness of 9Cr-2Mo Ferritic-martensitic steel

This study clarified the ralationship between the toughness of a 9Cr-2Mo dual phase steel and precipitates formed during aging, with special attention to the Laves phase (Fe 2 Mo). The ductile-brittle transition temperature (DBTT) is increased and the upper shelf energy decreased when the Laves phase begins to precipitate during aging. Electron microscopy and X-ray diffraction indicate that elimination of Si in the steel reduces the precipitation of the Laves phase and results in maintaining good toughness. It is also noted that the toughness of the steel is controlled by the total amount of precipitates (Laves + carbides) in the aging at 873 K for more than 3.6 × 10 3 ks. A time-temperature-precipitation diagram for the Laves phase is established and it clearly shows that the precipitation of the Laves phase is markedly retarded by the decrease of Si content. In Si-free steel, no Laves phase is observed in the temperature and time range investigated.

Change in microstructure and toughness of ferritic-martensitic stainless steels during long-term aging

A study has been made on the improvement of toughness of ferritic-martensitic (9Cr-2Mo) steel during long-term aging in the temperature range from 773 to 873 K. It was found that an increase in Mn and elimination of Si give a very beneficial effect on the toughness, whereas a relatively large loss of the toughness was found in conventional 9Cr-2Mo steel. P in the steel is also shown to be harmful to the touchness. Microstructural observations reveal that intermetallic compounds containing Si and P precipitate massively in ferrite grains, and relatively large carbides (M23C6 and M6C) are observed in martensite grains and at grain boundaries in the aged materials containing Si. On the other hand, in the aged Si-free high Mn steel, no such intermetallic compounds are detected. It is believed that intermetallic compounds as well as carbides play an important role in changes of toughness by aging and that the loss of toughness by aging may be prevented by the addition of Mn without Si. which probably suppresses the precipitation of intermetallic compounds and carbide growth.

Phase stability and high-temperature strengths of high manganese-chromium-iron base alloys as reduced radio-activation materials

Abstract The Fe-Cr-Mn alloy system has been proposed to replace the Fe-Cr-Ni alloy system in the construction of components for fusion energy devices. The present work is to investigate the potential properties of high Mn-Cr austenitic steels. Especially, the focus is placed on the microstructural stability and high-temperature mechanical properties of Fe-12% Cr-15% Mn-C-N alloys. By the combined addition of 0.2% C and 0.2% N to the Fe-12% Cr-15% Mn alloy, a good microstructural stability of austenitic phase and high-temperature tensile strengths comparable with those of Type 316 austenitic stainless steel are obtained.

Effect of variation of microstructure on the creep and rupture strengths of a Sn-3.5 % Ag lead-free solder alloy

The present authors [1] and Ochoa et al. [2, 3] indicated that the creep and rupture strengths of a Sn-3.5 % Ag lead-free solder alloy are very much affected by the variation of the microstructure formed under different solidification and cooling rates after casting. In the present research, the cooling effect and microstructural effect on the creep and rupture strengths of the Sn-3.5 % Ag alloy is further investigated. The effect of the reflow and flow joining process on the rupture life is also discussed.