Measurement of degree of sensitization in post-weld heat treated 13Cr-4Ni martensitic stainless steel clad using double loop electrochemical potentiokinetic technique

•Preferred site for precipitation varies with changing in PWHT temperature.•Presence of δ-ferrite dramatically affect localized corrosion behavior.•The highest value of the DOS was observed at 500 °C.•Prolonging the PWHT facilitates Cr diffusion to recover depleted regions.•An inverse relation between the DOS and pitting potential was observed. In this paper, the susceptibility to intergranular corrosion (IGC) of 13Cr-4Ni martensitic stainless steel clad deposited by submerged arc welding was studied in the as-welded condition and after post-weld heat treats (PWHT) at 420, 500, 540, and 580 °C. Microstructural studies showed a martensitic matrix, about 20% δ-ferrite and carbide precipitates in the microstructure under the as-welded condition. The results of the double loop electrochemical potentiokinetic technique revealed that the PWHT process significantly increased the degree of sensitization (DOS). The highest DOS corresponded was 87.9% in the sample treated at 500 °C. PWHT at temperatures higher than 500 °C returned the DOS to lower values. PWHT at 500 °C and below promoted the decomposition of δ-ferrite, and hence some new chromium carbides precipitated at δ-ferrite and martensite interfaces, whereas tempering at temperatures higher than 500 °C accounted for carbides precipitation at martensite lath boundaries owing to the formation of tempered martensite. The DOS value decreased with increasing PWHT time due to chromium diffusion to chromium-depleted regions. Also, the potentiodynamic studies showed an inverse relationship between the DOS and pitting potential; the higher DOS, the lower the pitting potential.