Stress Development During Cooling of Continuously Cast Boron-Containing Steel Slabs

Boron-containing steels have good hardenability in wide applications, but may exhibit defects such as transverse corner cracks in slabs after continuous casting. These problems can arise during the post-casting cooling process because boron addition changes the phase transformation behavior of steel. A 3D thermomechanical finite volume model with coupled heat transfer, stress, and phase transformation calculations was developed in the OpenFOAM platform to investigate the temperature history, phase evolution, and stress development during cooling. The model was used to simulate the air cooling process in slabs of two similar steel grades, one with and the other without boron. The simulation results show the slab with boron consists of mostly bainite, in contrast to the non-boron grade which is mostly ferrite and pearlite after cooling. Higher tensile stresses, both peak and residual, and plastic strains, which could lead to cracking, are observed at the edge of slab in the boron-containing grade. The effect of slowing the cooling rate by using a radiation shield was also studied for the boron-containing steel. The reduced thermal gradient and the increased ferrite formation reduced the stresses in the slab.