Hydrogen Absorption and Desorption during Heat Treatment of AISI 4140 Steel

Hydrogen plays an important role in the formation of quench cracks of structural steels. To clarify hydrogen absorption and desorption during heat treatment of AISI 4140 steel, thermal desorption spectrometry (TDS) analysis was carried out for the specimens in the as-rolled, as-quenched, and quenched and tempered conditions. Results show that hydrogen content increased from 0.127×10−6 in the as-rolled specimen to 0.316×10−6 in the as-oil-quenched specimen. After tempering at 200 °C, the hydrogen content in the oil-quenched specimen decreased to 0.155×10−6, and the peak temperature of hydrogen desorption increased from 200 to 360 °C. From the dependence of hydrogen content in the as-quenched specimens on austenitizing time, it can be deduced that hydrogen absorption occurs during austenitizing. The simulation of hydrogen absorption contributes to a better understanding on the distribution of hydrogen during the heat treatment in structural steels.