Abstract: In this paper,weld thermal cycle simulation technique was used to reveal the structures in the HAZ.Weld thermal cycle heating-water quenching method was employed to fix the structures in the high temperature regions of the HAZ.It has been found that austenite can be totally dissolved in ferrite when subjected to rapid weld heating.The ferrite→austenite transformation,however,can not reach an equilibrium during the subsequenent rapid cooling.The test results revealed that pure ferrite-grain boundaries in the high temperature regions of the HAZ have a tendency to intergranular corrosion,while the austenite-ferrite boundaries are corrosion resistant and act as barriers to corrosion development.It is an effective way to enhance the intergranular corrosion resistance of this steel by adopting metallurgical and technological measure to obtain a secondary austenite network to enclose the ferrite grain,constituting a "closed-boundary" mode bi-phase structure in the HAZ.