Effects of PWHT Time on Pitting Behavior in Modified 9Cr-1Mo Steel Welds

摘要

The effect of PWHT time on the pitting behavior in NaCl solution was evaluated in the weld of Mod. 9Cr-1Mo steels. Specimens were fabricated using autogeneous gas tungsten arc welding (GTAW) and tested using various post weld heat treatment (PWHT) times (i.e., 30 min, 1 h, and 2 h). More retained delta-ferrite was produced adjacent to the fusion line than the weld center. The polarization curves shifted to low E-corr, and large I-corr, therefore decreasing the pitting corrosion resistance of the weld as the PWHT holding time increased. The 'as-welded' specimens showed random pitting at the martensite lath. With increasing PWHT time, pitting was also found at the delta-ferrite/tempered martensite (delta/TM) interface. This is because more coarse and dense Cr-rich M23C6 carbides were formed along the delta/TM interface than at the TM/TM interface as the PWHT holding time increased.