Industrial Application of Mechanical Reduction on Continuous Casting of Bearing Steel Bloom

Industrial experiments of mechanical soft reduction in continuous casting were conducted in the present study aiming to improve the internal quality of the bearing steel blooms. Two methods were developed to verify the solidification model for a reliable crater end in the caster, which is provided by SMS CONCAST. The verified solidification model was applied to determine the solidification status of the bloom and provides theoretical reduction region. Several trials were conducted to study the optimization of the reduction rate regarding the V-shaped and centerline segregation of the bloom. The results show an obvious improvement of internal quality in the bearing steel bloom by applying appropriate reduction during casting.

Expansion and Reduction of Soft Sets and their Applications in Decision Making

In this study, we first define expansion and reduction of the soft sets that are based on the linguistic modifiers. By using these new notions we then construct a decision making method called soft reduction method, which selects a set of optimum alternatives. We finally present an example which shows that the methods can be successfully applied to many problems containing uncertainties.

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

To comprehensively investigate and alleviate internal cracks in high carbon bloom induced by mechanical soft reduction (MSR), a 3D thermal-mechanical coupled model, containing two adjacent pairs of reduction rolls, was developed to investigate the influence of differential reduction rate on evolution of stress concentration and displacement in as-cast bloom. In order to effectively provide theoretical basis for actual production, the reduction rate was calculated according to the appropriate reduction amount of each pair of reduction rolls, which can be adopted in the MSR to determinate the appropriate roll reduction amount in adjacent roll reduction zone. With the differential reduction rate of MSR increasing from −2.67 mm/m to 5.33 mm/m, the maximum equivalent stress of cracking area in as-cast bloom significantly decreased under first roll reduction position, the maximal displacement along the bloom width direction is significantly decreased with increasing of the differential reduction rate of MSR under end roll reduction position. According to the results of industrial experiment, the internal cracks were effectively alleviated and center shrinkage cavities were nearly eliminated by optimum designed experiments.

Influence of External Action on the Internal Structure of Continuously Cast Slab Produced from Tube Steel

The paper compares the internal structure of two continuously cast slabs with a section of 300 × 2600 mm from a tube steel of the strength class K60, one of which is molded with a soft reduction, and the other is without external influence. A comparative analysis of the structure of two templates showed that the location of areas with an increased metal pickle ness in the axial part of the templates varies. On the template from a slab cast without reduction, this section is below the geometric center of the work-piece in thickness, at a distance of 49.2% from the underside, that is, the "lower" asymmetry of the slab structure is observed. On the template from the slab cast off with soft reduction, the area with an increased pickle-ness is located above the middle of the work-piece: at a distance of 51.7% of the side of the large radius, an "upper" asymmetry of the slab structure is formed. Consequently, as a result of the external action on the cast work-piece, the location of the axial sponginess, relative to the geometric centre of the slab, is changed by moving from the lower to the upper half of the work-piece. The metal of the axial part of the reduced slab has a denser structure, the degree of development of axial looseness in the metallographic evaluation is reduced by an average of 0.5 points. The work shows the change in the content of chemical elements along the thickness of slabs. In the reduced metal, the maximum value of the degree of zonal inhomogeneity of the most impurities is higher than in the metal without external influence. This is explained by the fact that, as a result of reduction, the zone of location of the axial chemical heterogeneity in the slab becomes smaller in width.

A new method for determination of the theoretical reduction amount for wide-thick slab during the mechanical reduction process

Mechanical soft reduction (MSR) is an effective method for elimination of the centerline segregation and porosity of the continuous casting steel slab, and the reduction amount is a key parameter that determines whether the MSR could be applied successfully. In the present work, a 2D heat transfer model was developed for predicting the non-uniform solidification of the wide-thick slab. The measured shell thickness by nail shooting experiment and the measured slab surface temperature by infrared camera were applied to validate the 2D heat transfer model. A new calculation method of theoretical reduction amount that could consider the influence of non-uniform solidification of the wide-thick slab was then derived. Based on the predicted temperature field by the 2D heat transfer model and the newly-proposed calculation method, the required theoretical reduction amount and reduction gradient/rate for the wide-thick slab were calculated and discussed. The difference between the newly-proposed method and the previous method, the influence of the casting speed and slab thickness on the required theoretical reduction amount and reduction gradient/rate were also investigated.