Thermal Desorption Analysis of Hydrogen in High Strength Martensitic Steels

Thermal desorption analyses (TDA) were conducted in high strength martensitic steels containing carbon from 0.33 to 1.0 mass pct, which were charged with hydrogen at 1223 K (950 A degrees C) under hydrogen of one atmospheric pressure and quenched to room temperature. In 0.33C steel, which had the highest M (s) temperature, only one desorption peak was observed around 373 K (100 A degrees C), whereas two peaks, one at a similar temperature and the other around and above 573 K (300 A degrees C), were observed in the other steels, the height of the second peak increasing with carbon content. In 0.82C steel, both peaks disappeared during exposure at room temperature in 1 week, whereas the peak heights decreased gradually over 2 weeks in specimens electrolytically charged with hydrogen and aged for varying times at room temperature. From computer simulation, by means of the McNabb-Foster theory coupled with theories of carbon segregation, these peaks are likely to be due to trapping of hydrogen in the strain fields and cores of dislocations, and presumably to a lesser extent in prior austenite grain boundaries. The results also indicate that carbon atoms prevent and even expel hydrogen from trapping sites during quenching and aging in these steels.