A Study on the Post-Weld Heat Treatment Effect to Mechanical Properties and Hydrogen Embrittlement for Heating Affected Zone of a RE 36 Steel

Abstract

The cathodic protection method is being widely used in marine structural steel, however a high tensile steel like RE 36 steel for marine structural steel is easy to get hydrogen embrittlement due to over protection during cathodic protection as well as preferential corrosion of HAZ(Heating Affected Zone) part. In this paper, corrosion resistance and mechanical properties such as elongation and hydrogen embrittlement were investigated with not only in terms of electrochemical view but also SSRT(Slow Strain Rate Test) method with applied constant cathodic potential, analysis of SEM fractography in case of both As-welded and PWHT(Post-Weld Heat Treatment) of 550℃. The best effect for corrosion resistance was apparently indicated at PWHT of 550℃ and elongation was increased with PWHT of 550℃ than that of As-welded condition. On the other hand. Elongation was decreased with applied potential shifting to low potential direction which may be caused by hydrogen embrittlement, however the susceptibility of hydrogen embrittlement was decreased with PWHT of 550℃ than that of As-welded condition and Q.C(quasi cleavage) fracture mode was also observed significantly according to increasing of susceptibility of hydrogen embrittlement. Eventually it is suggested that an optimum cathodic protection potential range not causing hydrogen embrittlement is from -770 ㎷(SCE) to -850 ㎷(SCE) in As-welded condition while is from -770 ㎷(SCE) to -875 ㎷(SCE) in PWHT of 550℃.