Development of offshore steel for high heat input welding

To reduce the construction cost and period of steel structure, high-efficiency welding methods applying high heat input have been widely employed. However, deterioration of the strength and toughness, especially low-temperature impact toughness, due to the coarse grains in the heat-affected zone (HAZ) of weld steels often comes along with high heat input welding. Thick offshore steel has been developed by Ti deoxidization for the use of high heat input welding. The inclusions of the steel were analysed by EPMA and SEM, and the major inclusions were identified to be Al O -(MgO) and Al O -CaO-(TiO ) types. The steel plates with different thickness over 40 mm were welded with heat input over 100 kJ/cm, and Charpy impact energies of the welding joints at −40 °C were over 75 J. The nano-sized TiN particles in HAZ were observed and were considered to retard the grain coarsening in the HAZ during high heat input welding

Casting Simulation of Calcium Titanate and Calcium Zirconate Nozzles for Continuous Casting of Aluminum-Killed Steels

The clogging of submerged entry nozzles (SENs) and tundish well nozzles is a common problem in the continuous casting of aluminum-killed steels. Clogging occurs when alumina attaches to the inside of the nozzle restricting the flow. This article explores the use of new nozzle materials that could prevent accretion growth through the formation of liquid phases at the inclusion-refractory interface. Casting simulation experiments were conducted using three nozzle refractory formulations: calcium titanate, calcium zirconate, and a 2:1 calcium titanate to calcium zirconate molar mixture. Nozzles fabricated from these materials cast more aluminum-killed steel without clogging than typical industrial alumina graphite nozzles. However, the nozzles constructed of calcium titanate dramatically outperformed alumina graphite, calcium zirconate, and the mixed nozzles. Microscopy investigation of spent nozzles found no accretion formation in the calcium titanate nozzles. The performance difference was due to the formation of a liquid calcium aluminum titanate phase, which prevented alumina accretions