College of Engineering

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    INVESTIGATION OF POST-WELD HEAT TREATMENT EFFECTS ON SIMILAR AND DISSIMILAR LOW-CARBON AND STAINLESS-STEEL WELDMENTS
    (Covenant University, Ota, 2025-05) FASUYI, AKINBAYONLE AYOMIDE; Covenant University, Thesis
    This study investigated the effect of post-weld heat treatment (PWHT) on the mechanical properties and corrosion behaviour of dissimilar metal (DM) weldments of carbon steel and AISI 304 austenitic stainless steel, as well as similar metal (SM) stainless steel-to-stainless steel weldments. PWHT of the specimens was performed at three temperatures (900⁰C, 1000⁰C, and 1100⁰C), along with an as-welded control. Tensile testing, weight-loss corrosion measurement, corrosion-rate determination, and Vickers microhardness profiling were conducted, and a two-way analysis of variance (ANOVA) was used to determine the statistical significance of the effects of material type and treatment temperature. The findings showed that the tensile strength of the two types of welds was similar, at about 240 MPa in the as-welded condition. Following PWHT, SM welds exhibited a significantly greater improvement, with a maximum ultimate tensile strength of 466 MPa at 1000⁰C, compared to 321 MPa in DM welds at the same temperature. ANOVA confirmed highly significant effects of material type, temperature, and their interaction on tensile performance. The corrosion analysis showed that DM welds had much higher weight loss and corrosion rates than SM welds in all conditions, with material type identified as the dominant controlling factor. Raising the PWHT temperature progressively reduced corrosion in DM welds, with 1100⁰C yielding the greatest effect. Hardness profiling showed that PWHT reduced peak fusion-zone hardness and enhanced distribution uniformity in both weld types, but DM welds consistently exhibited asymmetric softening attributable to compositional mismatch at the weld interface. The results indicate that 1000⁰C is the optimum PWHT temperature for tensile performance and that SM weldments outperform DM weldments under all tested treatment conditions.