ENVIRONMENTAL STRENGTH OF TRIP STEELS WITH RETAINED AUSTENITE POSSESSING HIGH DUCTILITY AND HYDROGEN-EMBRITTLEMENT RESISTANCE.

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The small specimen test technique (SSTT) using miniaturized specimens has been performed for high strength sheets of retained-austenite transformation induced plasticity, martensitic and austenitic steels and laser weld joint to evaluate ductile-brittle transition behavior and hydrogen embrittlement resistance, in comparison with the intermetallics having high susceptibility to hydrogen embrittlement. The small punch (SP) test using a small specimen in the form of 10 x 1 0 x 0.5 mm demonstrated different behavior of ductile-brittle transition, low lemperature ductility and the temperature-dependence Weibull distribution shape parameter and dispersion in SP fracture energies, for two different contents of retained austenitic TRIP steels. An impact testing for the toughness evaluation of local microstructures in laser weld joint using miniaturized v-notch specimens of 0.7,1.0,1.0 mm^2 in square and 20 mm in long has been successfully constructed and a linear correlation between the DBTT … More measured by standard Charpy-impact test and that by the small specimen test has been clarified.The resistance to hydrogen embrittlement of prestressed concrete steels has been largely improved by the addition of Si and Ni with quench-tempered heat treatment. The hydrogen induced ductility loss in the sensitized Type 316 stainless steels has been accompanied by the brittle intergranular cracking and enhanced ductile rapture along grain boundaries at below and above room temperature, respectively. High susceptibility to hydrogen embrittlement in the sensitized Type 316 SS has been attributed to the grain boundary precipitation relating phenomena such as the weakening of interface bonding between carbides and matrix and the martensitic transformation in the Cr-depleted zone near grain boundaries. Behavior and suppression of hydrogen environmental embrittlement in Co_3Ti intermetallic compound have been inbestigated by means of the SP test, electrochemical measurements and tritium autoradiography. The mechanism of the suppression by the additionof Fe is to reduce a supply of hydrogen from the surface to the interior of Co_3Ti due to the increase of hydrogen desorption rate resulting from the enhancement of hydrogen recombination. Less