Effect of Normalizing Cooling Rate on Impact Toughness of ASME SA – 350 LF2 CL1 Forgings

This paper intends to contribute to a better understanding of how normalizing cooling rate affects toughness of SA – 350 LF2 Class 1 forgings. This is a sensitive material widely used in pressure vessels fabrication when toughness requirements are applicable. Three pieces from the same forging were normalized at 870°C for two hours. Each of them was subjected to a different cooling rate from normalizing to room temperature, being the temperature in the center of the piece registered by thermocouples every two seconds. Test specimens were extracted for impact testing at −46°C and metallographic examination. Subsequently, the normalized samples were cut out in two and subjected to two simulated post weld heat treatment at 630°C. Further specimens for metallographic characterization and impact testing were taken. It can be concluded that normalizing cooling rate has a pivotal role in the morphology of pearlite, and hence in its ability to offset the deterioration of toughness in the post weld heat treatment due to iron carbide precipitation by means of pearlite spheroidization.