Hydrogen trapping in high strength martensitic steel after austenitized at different temperatures

• Hydrogen trapping was investigated by TDS for a steel austenitized at 880–1250 °C.
• Hydrogen concentration varies non-monotonically with austenitizing temperature.
• Hydrogen concentration in the steel is the lowest at 1050 °C austenitizing.
• The variation is related to the prior austenite grain size and solute Nb content.
• Grain boundary and Nb solute atom may act as shallow hydrogen traps in the steel.

Hydrogen trapping behavior has been investigated by means of thermal desorption spectrometry (TDS) for a high strength steel after it is austenitized at the temperature range of 880–1250 °C, oil quenched, and tempered at 200 °C. Results show that with increasing austenitizing temperature, the pre-charged hydrogen concentration in the steel first decreases and then increases, being the lowest value at the austenitizing temperature of 1050 °C. The variation of hydrogen concentration with austenitizing temperature is related to the differences in the prior austenite grain size and solute Nb content, which may act as shallow hydrogen traps in the steel. The difference in the pre-charged hydrogen concentration can account for the previously reported result on delayed fracture resistance of the steel after austenitized at different temperatures.