No abstract

No abstract

For investigating the impact of ferritic morphology on yield strength (YS) of the high-heat-input welding induced coarse-grained heat-affected zone (CGHAZ) of a low carbon Mo-V-N-Ti-B steel, a group of particular welding heat inputs were designed to obtain different ferritic microstructures in CGHAZ. The tensile properties were estimated from typical samples with ferritic microstructures. The mixed microstructures dominated by the intragranular polygonal ferrite (IGPF), the intragranular acicular ferrite (IGAF), and the granular bainite (GB) were obtained at the heat inputs of 35, 65, 85 and 120 kJ/cm, respectively. When the main microstructure changed from IGPF to IGAF and GB, YS increased first and then decreased. The microstructure consisting mainly of IGAF possessed the maximum YS. As the main microstructure changed from IGPF to IGAF and GB, the contribution of grain refinement strengthening to YS was estimated to be elevated remarkably. This means the strength of CGHAZ in a low-carbon steel subjected to the high-heat-input welding could be enhanced by promoting the fine-grained AF and GB formation.

Welding heat input greatly influences the microstructure and impacts the affected zone's toughness. To interpret the relationships between the welding heat input, microstructure, and low-temperature toughness of the coarse-grained heat-affected zone (CGHAZ) of Mo-V-Ti-N-B steels, welding heat cycles with different heat inputs (25–75 kJ/cm) were performed on a Gleeble 3500 simulator. Intragranular ferrite in the simulated samples subjected to different thermal cycles was characterized and quantified, and the impact energies of simulated samples were evaluated at -20 °C. Upon increasing the heat input, the intragranular ferrite content rose sharply from 4.3% to 76.0%. The V(C,N) enrichment on the precipitate surface increased the size of precipitates, providing favourable nucleation conditions for intragranular ferrite. The prior austenite grain (PAG) and martensite/austenite (M/A) constituents became rough, and the content of the M/A constituent increased while the impact energy of the CGHAZ increased. This behaviour occurred due to the formation of intragranular acicular ferrite (IGAF), which refined the microstructure of the CGHAZ. Grain refinement eliminated the negative influence of higher M/A content on the impact toughness of the CGHAZ.

No abstract