Effects of Heat Treatment Conditions on SOHIC in Normalized Steel Plates for Pressure Vessel Use

Abstract

The resistance to SOHIC (stress oriented hydrogen induced cracking) has been examined in ASTM A516 Grade 70 steel plate, a popular steel plate for pressure vessls of oil refinery. The results have been discussed with the possible dominating factors, viz, hardness values of ferrite and pearlite, that were proposed in the previous paper.
Increase of cooling rate from ausutenizing resulted the improvement of the SOHIC resistance through both increasing ferrite hardness and decreasing pearlite hardness, until MA (Martensite-Austenite) constituent appears around 100°C/ min. The resistance was imporved by PWHT (Post-Weld Heat Treatment) through the favorable change in the hardness of ferrite and pearlite. This is not always true; it is dependent on the contents of precipitation hardening elements or the amount of MA constituent.