Fracture toughness characterization of a weldment in a microalloyed steel using resistance curves

Abstract

Various weldment regions, e.g. the weld zone, heat-affected zone (HAZ) and parent metal, are characterized in terms of strength and fracture toughness parameters, J integral and crack-tip-opening displacement (CTOD) δ after manual metal arc weld to a microalloyed steel plate. The critical J values are obtained by three methods, namely the ASTM Standard E 813-81, the stretched-zone width measurement with superposition on the R curve and the proposed method based on the experimental data. On the contrary the critical δ values are determined by four methods: (i) British Standard 5762; (ii) superposition of the blunting line on the R curve; (iii) stretched-zone width measurement and superposition on the R curve; (iv) the proposed method. A linear relationship between the CTOD and stretched-zone width with a slope of 0.43 is obtained in the present study. The crack growth toughness values are also obtained from the R curves. The crack initiation toughness values obtained by the above methods are compared. The study focuses on the J- δ relationship for the weld metal and the HAZ. Quantitative microstructural analysis and fractographic studies have also been conducted to rationalize the observed toughness values in the weld metal, HAZ and the parent metal.