Effect of Line-Heating on the Microstructural and Mechanical Characteristics of 320-MPa-Grade High-Strength Hull Plates

Abstract

This study examined the effect of the line-heating process on the microstructure and mechanical properties of 320-MPa-grade high-strength steel designed for low-temperature applications. The samples were heated thrice to the maximum temperature condition of 900 ℃ prior to air cooling or water quenching. Tensile strength and Charpy impact toughness tests were performed to understand the variation in the mechanical characteristics across the thermal histories. The decrease in the tensile strength of the air-cooled specimen was attributed to grain growth and phase transformation caused by slow cooling, while the water quenched specimen exhibited grain refinement. The experimental results indicated that the line-heating process was suitable because all the specimens with various thermal histories satisfied the international classification standard.