Effect of Thermal Charging of Hydrogen on the Microstructure of Metastable Austenitic Stainless Steel

The tensile behavior of hydrogen-charged 304-type austenitic stainless steel, with and without prestrain, is investigated. The specimens are thermally charged with hydrogen in 15MPa hydrogen gas at 300 degrees C for 72h. Tensile behavior of the specimen is compared with the specimen aged in vacuum at 300 degrees C. The effect of the charging condition on the stability of microstructure is determined by characterizing prestrained specimens before and after charging. The hydrogen content in the specimens is determined using thermal desorption spectroscopy (TDS). Analysis of X-ray diffraction (XRD) data and electron backscattered diffraction (EBSD) shows that the fraction of martensite increases after charging in hydrogen by 5-10%. The fracture surfaces of the uncharged and charged specimens are examined for characteristic features. Flow stress and ductility of the charged and prestrained and charged specimens are discussed in terms of the martensite fraction and hydrogen content.