Experimental Simulation of Thermally Induced Stresses during Cooling of Continuously Cast Steel Slabs

Abstract

Continuous casting is an established production route for steel slabs. The solidifying slab suffers a combination of internal stresses caused by thermal gradients, phase transformation, and external bending. The complex superimposed stress condition may produce local concentrations of tensile stresses that initiate cracks during cooling and deformation. Samples prepared from low-carbon steel slabs with and without Ni-content are compared and transformation stress phenomena are analyzed. In situ neutron diffraction experiments are carried out to reveal the stress condition within sections of cast steel slabs during cooling while passing the austenite–ferrite transformation temperature. The austenite–ferrite phase transformation is accompanied by an increase of volume of ≈1% between austenite-f.c.c. and ferrite-b.c.c., which causes internal stresses within the thermal stress gradients by cooling from the surface. The superposition of these thermal and transformation stresses is determined during cooling by an additional in situ diffraction experiment at constant macroscopic strain. The crack sensitivity of the Ni-containing slab is attributed to higher internal stresses within the austenite caused by the lower transition temperature than for the Ni-free steel.