Controlling centre segregation and shrinkage cavities without internal crack in as-cast bloom of steel GCr15 induced by soft reduction technologies

Abstract

To investigate the alleviation technology of internal cracks, center shrinkage cavities and center segregation of as-cast bloom simultaneously, a three-dimensional finite element model was developed to calculate and analyze the strain fields and deformation behavior of as-cast bloom induced by soft reduction process. In the present work, a multi-stage mechanical soft reduction (MSR) has been developed to simultaneously alleviate center segregation and shrinkage cavities without internal cracks, which aims to provide theoretical basis for improving the internal quality of high carbon as-cast blooms induced by soft reduction technologies. According to the experimental results, the internal cracks were effectively alleviated and center shrinkage cavities were nearly eliminated by optimum designed experiments, the homogeneity and compactness of as-cast bloom can been remarkably improved in comparison with that induced by the conventional soft reduction process. The carbide size and bandwidth of the carbides in the hotrolled wire were both decreased.

Influence of differential reduction rate in adjacent roll reduction zone on internal cracks of high carbon bloom induced by mechanical soft reduction

“…To accurately describe the deformation behavior of the GCr15 bloom between the reduction rolls and bloom surface, the properties of steel material have been taken from our previous work, 11,17 such as density, thermal conductivity, specific heat capacity and thermal expansion coefficient. In addition, an Arrhenius-type constitutive equation of high carbon steel 11,17,18 has been adopted in the 3D thermalmechanical coupled model.…”

“…To accurately describe the deformation behavior of the GCr15 bloom between the reduction rolls and bloom surface, the properties of steel material have been taken from our previous work, 11,17 such as density, thermal conductivity, specific heat capacity and thermal expansion coefficient. In addition, an Arrhenius-type constitutive equation of high carbon steel 11,17,18 has been adopted in the 3D thermalmechanical coupled model. With this model, the effect of differential reduction amount of the first and the end reduction rolls on evolution of stress and displacement in as-cast bloom was systematically investigated under different process parameters.…”

“…A multi-stage MSR technology has been developed to provide theoretical basis for improving the internal quality of high carbon as-cast bloom induced by MSR in the present authors' previous work. 17 In order to decrease center segregation and porosity of as-cast bloom, the total reduction zone has been divided into two sequential reduction zones. In the control center segregation stage, the reduction amount was enhanced to improve the homogeneity of as-cast bloom (withdrawal units 1#, 2# and 3#), and avoid to form internal crack.…”

“…The results of industrial application make experimental analysis and verify the effectiveness of the MSR. 17 In addition, the centre solid fraction of as-cast bloom should not be too large to effectively compress the mushy zone to alleviate center segregation without internal cracks. The risk of internal cracks can decrease as the centre solid fraction of as-cast bloom increasing, cracking area of bloom cross section under withdrawal units 1 # is larger than cracking area of bloom cross section under withdrawal units 2# and 3# along the continuous casting direction.…”

Effect of Dynamic Soft Reduction Range and Amount on Central Segregation in Bloom and the Resulting Microstructure in the Rod of GCr15‐Bearing Steel

“…For GCr15 steel, due to high carbon content, wide mushy zone, and long solidification time, carbon segregation usually occurs during the phase change in continuous casting, resulting in an inhomogeneous distribution of carbon content, where central segregation is the fundamental cause of carbide formation. [8][9][10] Carbide could destroy the continuity of metal, cause stress concentrations, and reduce machinability. Many studies have shown that a rods' internal elements and microstructure homogeneity could be adjusted by controlling the heating and hot-rolling parameters.…”