Super High HAZ Toughness Technology with Fine Microstructure Imparted by Fine Particles

Abstract

In order to produce high HAZ toughness steel plates with tensile strength of 490MPa to 590MPa class, the innovative technology for HAZ microstructure refinement, HTUFF ® , has been developed. Fine dispersion of oxides and/or sulfides in steel has been tried to retard γ grain growth in the HAZ near a weld fusion line. It has been discovered that very small oxides and/or sulfides with sizes of several 10nm to several 100nm can be dispersed in steel by the appropriate addition of Mg and/or Ca into steel. Utilizing these fine particles containing Mg or Ca, the strong pinning technology to retard γ grain growth in a HAZ has been commercially established. Based on the concept of HTUFF providing excellent HAZ toughness, high-performance structural steel plates have been mass-produced.