Influence of microstructure on yield stress and cleavage fracture stress at −196°C of SA 508 Class 2 pressure vessel steel

AbstractTests have been performed to examine the yield stress and the cleavage fracture stress at −196°C of SA 508 Class 2 pressure vessel steel in a range of heat treatment conditions. The heat treatments either varied the austenitization temperature before isothermal transformation at 450°C or varied the tempering treatment after austenitizing at 900°C and transforming at 450°C. The resultant microstructures have been characterized by metallographic and fractographic examination. Austenitization at temperatures below about 1000°C produced a polygonal ferritic structure, whereas an upper bainite was produced following austenitization above this temperature. Increasing the austenitizing temperature caused first the ferrite grain size and then the bainitic packet size to increase. However, the lath width of the bainitic microstructures decreased, which is consistent with an increase in hardenability accompanying the increased prior austenite grain size. Tempering caused the precipitation of rodlike carbide...