Relation between Hot Rolling Conditions and Mechanical Properties of Heavy Plates Produced from Thin Continuously-cast Slabs

Abstract

Continuously-cast slabs with thickness of 80, 100, 150 and 210 mm have been hot rolled to heavy plates of 31 mm in thickness after the austenitization at 1000 °C, and the effect of reduction ratio on mechanical properties of plates has been evaluated. It is demonstrated that center porosities are annihilated by hot rolling even with smaller reduction ratio than usual under the conditions that high rolling shape factor is employed for individual rolling pass. Increase in reduction ratio deteriorates the toughness of material in the short-transverse direction whereas it has no adverse effects in the longitudinal direction. Statistical analysis shows that scattering of data on absorbed energy measured by Charpy test has no positive relations with reduction ratio. As far as weldability is concerned, increase in reduction ratio markedly increases susceptibility of plates to cracking which occurs in the heat affected zone after submerged arc welding with heat input of 200 kJ/cm was applied. It is confirmed that the rolling conditions made up of high rolling shape factor and low reduction ratio, together with refinement of initial austenite grain, are appropriate for continuously cast slabs in order to improve the properties of plate which are affected by solidification structure.