STRUCTURAL AND MECHANICAL ANALYSIS OF FRACTURE IN PLASMA-WELDED JOINTS OF S235JRE-N STEEL

Abstract

A comparative structural and mechanical analysis was performed on two autogenous plasma-welded joints of S235JRE-N steel, one without a visible crack and the other containing a developed crack in the weld metal. The investigation included macrostructural and microstructural examinations, tensile testing, HV0.05 microhardness profiling, and HV5 hardness measurements. The sound joint exhibited continuous fusion, a relatively homogeneous fine-grained microstructure, and a ferrite-pearlite matrix. The cracked joint showed localized lack of fusion, an intergranular fracture morphology, microstructural heterogeneity, and a coarser-grained base metal with areas identified as cementite along the grain boundaries. The tensile strength and elongation of specimen 2 were 9.51% and 11.76% lower, respectively, than those of specimen 1, whereas its mean HV5 hardness was approximately 2.30% higher. The combined results indicate that cracking should not be attributed to a single factor but rather to the combined effects of an unfavorable initial microstructure, localized lack of fusion, and thermal shrinkage stresses. The limitations of the available data are specified, together with the additional investigations required to establish causality.