Influence of step austenitizing treatment on the toughness and tensile ductility of hydrogen charged HT-9

The goal of this study was to evaluate the hydrogen compatibility of the 12Cr-1Mo ferritic/martensitic steel HT-9 for use in first wall and blanket structures. This report summarizes data on the effect of internal hydrogen on the room temperature tensile properties of this ESR processed 12Cr-1Mo steel. Prior research on the tensile behavior of the quenched and tempered steel HT-9 has shown that the steel exhibits marked susceptibility to hydrogen embrittlement and hydrogen induced intergranular fracture. The severity of the embrittlement can be significantly reduced and the intergranular fracture mode entirely eliminated by swaging and retempering the steel. The swaging results suggest that the hydrogen compatibility of HT-9 could be increased by reducing the grain size. To assess the role of grain size, two different austenitizing treatments were employed. The first employed reductions in austenitizing temperature to refine the prior austenite grain size. The second austenitizing temperature will redistribute the carbides and grain boundary segregants. The major effects of lowering the austenitizing temperature from 10500C are to increase the hydrogen charged tensile ductility and to reduce the yield strength. Decreasing the austenitizing temperature from 10500 to 9000C increases the hydrogen charged tensile ductility from 13% to 47% and decreases the yield strength from 110 ksi to 72 ksi. Decreasing the second austenitizing temperature in the step treatment does not lower the yield strength as much as lowering the austenitizing temperature