Kinetics and Mechanism of Hydrogen Attack of Steel

The kinetics of hydrogen attack of a killed steel have been studied in the temperature range 800 to 1200 F and in the pressure range 450 to 950 psi hydrogen. A quantitative relationship between incubation of attack and temperature and pressure has been obtained. Based on these results and those from a series of iron alloys, a model is presented in which (1) incubation is controlled by the reduction of grain boundary iron oxides forming water vapor which acts to inhibit the accumulation of methane in the boundaries by reacting with it; (2) grain boundary methane pressure forming a network of fissures and/or stress concentrators acts as the embrittling agent; (3) when the carbides are stabilized by spheroidization or alloying, resistance to attack is increased since carbide dissolution controls both incubation and embrittlement. 3.2.2, 6.2.1