Analysis and Response of Steel Stacking Accidents in Hot Rolling Coilers

Through long-term production and maintenance practice,various types of stacking steel in the 2250mm hot rolling coiler of Ma Steel were tracked and analyzed,and the causes of stacking steel were summarized.Cor-responding measures were formulated to effectively reduce the probability of stacking steel.

Instrumented oscillographic study on impact toughness of an axle steel DZ2 with different tempering temperatures

Compared with the conventional Charpy impact test method,the oscillographic impact test can help in the behavioral analysis of materials during the fracture process.In this study,the trade-off relationship between the strength and toughness of a DZ2 axle steel at various tempering temperatures and the cause of the improvement in impact toughness was evaluated.The tempering process dramatically influenced carbide precipitation behavior,which resulted in different aspect ratios of carbides.Impact toughness improved along with the rise in tempering temperature mainly due to the increase in energy required in impact crack propagation.The characteristics of the impact crack propagation process were studied through a comprehensive analysis of stress distribution,oscilloscopic impact statistics,fracture morphology,and carbide morphology.The poor impact toughness of low-tempering-temperature specimens was attributed to the increased number of stress concentration points caused by carbide morphology in the small plastic zone during the propagation process,which resulted in a mixed distribution of brittle and ductile fractures on the fracture surface.

Microstructures and Properties of 550 MPa Grade High Strength Thin-walled H-beam Steel

The microstructures and mechanical properties of 550 MPa grade lightweight high strength thin-walled H-beam steel were experimentally studied. The experimental results show that the microstructure of the air-cooled H-beam steel sample is consisted of ferrite, pearlite and a small amount of granular bainites as well as fine and dispersive V（C,N） precipitates. The microstructure of the water-cooled steel sample is consisted of ferrite and bainite as well as a small amount of fine pearlites. The microstructure of the water-cooled sample is finer than that of the air-cooled sample with the average intercept size of the surface grains reaching to 3.5 gna. The finish rolling temperature of the thin-walled high strength H-beam steel is in the range of 750 ~C-850 ~C. The lower the finish rolling temperature and the faster the cooling rate, the finer the ferrite grains, the volume fraction of bainite is increased through water cooling process. Grain refinement strengthening and precipitation strengthening are used as major strengthening means to develop 550 MPa grade lightweight high strength thin- walled H-beam steel. Vanadium partially soluted in the matrix and contributes to the solution strengthening. The 550 MPa grade high-strength thin-walled H-beam steel could be developed by direct air cooling after hot rolling to fully meet the requirements of the target properties.

Hot working process optimization of Fe-20Mn-19Cr-0.5C-0.6N steel by activation energy, power dissipation and microstructural evolution

Hot deformation behavior of an Fe-20Mn-19Cr-0.5C-0.6N high-nitrogen austenitic steel has been studied by isothermal compression tests in deformation temperature range of 800-1200℃ and strain rate range of 0.01-10 s^-1. Results indicate that the Fe-20Mn-19Cr-0.5C-0.6N steel has high deformation resistance due to strong hindering effect on dislocation moving by nitrogen-induced lattice misfit. The twinning-induced plasticity effect is gradually suppressed with the increase in deformation temperature, and high-temperature plastic deformation mechanism by twinning is gradually replaced by dislocation planar slip. The deformation resistance is up to 343 MPa at deformation conditions of (1000 ℃, 0.01 s^-1), which is over 100 MPa higher than that in martensitic steel and 50 MPa higher than that in austenitic steel. Besides, value of deformation activation energy for the Fe-20Mn-19Cr-0.6N steel is up to 784 kJ mol^-1. Power dissipation efficiency is lower than 0.13, while hot processing map exhibits a very wide range of working area. The optimum hot working process obtains at deformation temperature range of 950-1200℃ and strain rate range of 0.01-10 s^-1, when deformation acti-vation energy is less than 662.6 kJ mol^-1, power dissipation efficiency exceeds 0.22, dynamic recrystallization fraction is over 46.1% and microstructures are without instable characteristics.

Numerical Simulation of Influence of Casting Speed Variation on Surface Fluctuation of Molten Steel in Mold

The influences of casting speed variation on surface fluctuation of the molten steel in mold during continuous casting were investigated with numerical simulation method.It was found that when the casting speed was evenly decreased from 1.4 m·min-1 to 0.6 m·min-1,the increase of the surface fluctuation of the molten steel in mold was observed only on time that was at the start of casting speed change.While,in experiment of increasing casting speed evenly from 0.6 m·min-1 to 1.4 m·min-1,the increase of the surface fluctuation of the molten steel in mold was observed only at the time when the casting speed was stopped to increase after it had been increased to 1.4 m·min-1.For surface fluctuation of the molten steel in mold which was produced during the casting speed evenly increasing or decreasing period and at the time when increasing or decreasing the casting speed at low casting speed level（0.6 m·min-1）,the influence of casting speed change is very small.In addition,it is found that,at high casting speed level（1.4 m·min-1）,even a little change of casting speed could result in remarkable increase of the surface fluctuation.Thus,at high casting speed,changing casting speed should be avoided or much slower speed changing rate should be used.

Experiment and Simulation of Metal Flow in Multi-stage Forming Process of Railway Wheel

To investigate the metal flow during the railway wheel forming process, experiments and finite element method （FEM） simulation were carried out. An axisymmetric modeling for the wheel rolling process was proposed to predict the metal flow in radial direction, by which the whole multi-stage forming process could be simulated in axisymmetric and integral way. The result shows that the axisymmetric simulation method was an effective method to explore the metal flow in radial direction and to analyze the relationships of tools motion during the wheel rolling. The detail information about metal flow in railway wheel forming process was obtained. The metal in the wheel web was from the area near the half radius of the original billet; the chill zone of the billet became an envelope of the rim and part of the web with a maximum thickness of about 6 mm below the tread. At the wheel rolling stage, the metal in the rim flowed towards the web; the metal near the surfaces of the conjunction region between the web and rim suffered severe shear deformation.

Analysis of Thermal Behavior for Beam Blank Continuous Casting Mold

Finite element models of steady heat conduction for cross section of beam blank mold were developed by using ABAQUS software. The effect of mold grinding thickness, cooling water velocity, diameter of restrietor rods and water channel design on hot face temperature was analyzed in detail. Attention was focused on the peak temperature and temperature uniformity along hot face. The results showed that the peak temperature of existing mold, about 337.2 ℃, is located in the fillet, and two valleys of hot face temperature are found in flange corner and junction of wide face and narrow face, respectively. Decreasing mold thickness, increasing cooling water velocity and increasing diameter of restrictor rods can all reduce peak temperature and improve temperature uniformity along hot race at the expense of lower overall temperature. Redesigning the water channel can decrease peak temperature and thermal gradient of mold without lowering overall temperature of hot face. In particular, the small hole design can improve temperature uniformity across hot face and obtain the best advantage.

Research and Application of Flat Roll Technology in the Downstream Stands for CSP

CVC mills are generally used in the whole stands of CSP（Compact Strip Product）.Their special ＂s＂ curve of work roll contour and shifting strategy aimed at controlling strip shape,and the characteristics of continuous casting and rolling production,which make the work roll wear in downstream stands seriously uneven,and easily form abnormal transverse profile at the rolling end.As a result,CVC mill configuration in the downstream stands can not meet the profile and flatness control requirement for schedule free rolling,and bring some difficulties in profile and flatness control for the subsequent cold rolling.Based on the characteristics of the shape control system of CSP production line,and combined with the theory of flat roll technology,a kind of technology solution of using flat roll in the downsteam stands for CSP hot strip mills was proposed.At last,industrial test was carried out in the last stand of Masteel CSP,and good results were obtained.

Austenite Grain Size Evolution in Railway Wheel During Multi-Stage Forging Processes

The knowledge of microstructure evolution of railway wheel during hot forming process is the prerequisite of improving mechanical properties of the final product.In order to investigate the austenite grain size evolution of railway wheel during multi-stage forging process,mathematical models of recrystallization and austenite grain growth were derived firstly by hot compression tests for railway wheel steel CL50D,which then were integrated with a thermal-mechanical finite element model by the developed subroutines.The information about kinetics of recrystallization and grain size distribution during the forging process was obtained by simulation.The predicted results were validated by experiments in an industrial scale,and the average error between the predicted grain sizes and the measured ones is about 5%.The result shows that,under the current railway wheel forging process,the grain size distribution after final forging is inhomogeneous extremely.There is a narrow coarse grain zone between the external part and center of the hub caused by static recrystallization after final forging.With cooling of 60 s after final forging,the grain size is about 85 μm for the areas near the web surface and 175 μm for center areas of the hub and rim.