Papers by Keyword: IF Steel

Abstract: The source of inclusion in IF steel end slabs after reducing the casting remnant were studied by means of total oxygen and nitrogen content analysis, original position analyzer for metal (OPA), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Slims. The results show that: reducing the casting remnant have little influence on reoxidation in continuous casting process, the size of micro-inclusions are mostly smaller than 5 μm. The size of large-sized inclusions in end slab are mainly trapped in mold, they are mostly from 140 μm to 300 μm and over 300 μm, which accounted individually for 19.94% and 73.21% of total large-sized inclusions. In the end of a cast, decreasing the casting speed with slower speed changing rate can decrease the slag entrainment index of hot rolled coils from end slabs.

Abstract: One kind of high strength interstitial free steel sheets are annealed in a salt bath at 810 C for different times (1-30 s). The microstructure and recrystallized texture evolution during annealing are investigated using the optical microscopy and the Electron Back Scattered Diffraction technique. The results show that beginning and finishing of recrystallization are observed in the sample annealed at 810 C for 8 and for 20 s, respectively. The recrystallized grains nucleate in the order of ‹111›//ND, ‹110›//ND and ‹100›//ND. Recrystallized grains with ‹111›//ND orientation nucleate firstly in the ‹111›//ND deformed grains as well as at their boundaries and grow up by consuming the ‹111›//ND deformed grains at the initial stage of recrystallization. The ‹111›//ND recrystallized grains grow up by depleting the remained formed ‹100›//ND grains after the full consumption of the ‹111›//ND deformed grains. The overall recrystallization texture is mainly the ‹111›//ND component in the steel.

Abstract: Combining with the production experience in steel making and rolling plant, the oxide inclusions of IF steel were investigated. In the operation process, the inclusions of IF steel are main Al₂O₃-TiN. They are granular and dispersed in the steel, and most of sizes are 1~5μm. In the inclusion center, the Al₂O₃ plays the role of TiN heterogeneous nucleation center. So reducing the Al₂O₃ inclusion is essential to stabilize the Ti content and strengthen the fixtation to C and N in steel. The quantity of Al₂O₃ inclusion was closely relation to the operation process. The Al₂O₃ inclusions can be significantly reduced by taking some measure.

Abstract: In the present study, the effects of kinematic and geometric asymmetries in rolling during multi-pass processing of IF steel are examined. The theoretical investigation by final element simulations and experimental investigations by means of electron-backscatter diffraction analysis and tensile tests suggest that asymmetric rolling increases the total imposed strain compared to symmetric rolling, and largely re-distributes the strain components due to additional shear. This enhances the intensity of grain refinement, strengthens and tilts crystallographic orientations, and increases mechanical strength. The effect is highest in the asymmetric rolling with differential roll diameters.

Abstract: Specimens cut from a cold-rolled IF steel sheet of 1 mm thickness were respectively annealed at 750°C for 20min under a range of DC electric fields (1kV/cm~4kV/cm). The Effect of electric field strength on recrystallization texture of IF steel sheet was studied by mean of X-ray diffraction ODF analysis. It was found that γ-fiber textures were notably enhanced as electric field strength increased. The strength of γ-fiber textures got their peak values as the applied electric field reached to 4kV/cm. The possible reason for such phenomena was discussed in the viewpoint of interaction between the applied electric field and the orientation-dependent stored-energy in deformed metals which is known as the driving force for recrystallization during annealing.

Abstract: In a recent work, the present authors developed a new formal kinetics methodology suitablefor the situation in which transformations take place simultaneously or sequentially. In this work themain results of such a methodology are briefly presented in a simplified form. It is shown here howthis new methodology may be used for obtaining expressions for simultaneous or sequential reactionsfrom models of the kinetics of each reaction in isolation. It is also shown how one may extract theo-retical information from the experimentally measured quantities. Moreover, the methodology is usedto analyse published data on the recrystallization kinetics of IF steels.

Abstract: Based on the experimental materials of hot rolled Ti+Nb-IF steels and Ti-IF steels produced in the industry, the effects of cold reduction ratios on its microstructures, mechanical properties and textures were investigated. The results show that experimental samples with different cold reduction ratios have been finished recrystallization by batch annealing at 720°C and soaking with 5h. As the cold reduction ratio increases, the grains will be refined and uniform, and the textures trends to be {111} texture. The {223}<110>, {111}, and {114}<110> textures appeared after cold rolling are inherited followed by annealing, whose intensities would be higher as the cold rolling ratio increased. And the textures will transform to the {223}<110>, {111}<110> and {114}<110> textures. With the increasing cold reduction ratio, the values of the yield strength R_p0.2 and tension strength R_m increase, but the R_p0.2 is almost about 100MPa. However, the strain hardening index n₉₀ gradually decreases. The plastic strain ratio r₉₀ which reaches the maximum with cold reduction ratio of 70% increases firstly and then decreases. Thus, the optimal cold reduction ratio of 70% to 80% is determined, which can obtain good deep drawing performances.

Abstract: In this paper, the ultra-low carbon IF steel was studied by dynamic baking and the influence of dynamic baking process parameters on bake-hardening performance was analysed .The result is: The maximum bake-hardening value occur at 5 min. After 5 min ,the bake-hardening value gradually decreased and stabilized finally. The BH value gradually increases along with the increase of temperature. The BH value reaches to the maximum with the stretch rate of 5.64*10-4mm/s and 0.00169mm/s.The BH value decreases along with the increase of pre-strain increases.

Abstract: From an EBSD map made on a polycrystal one can define a set of grains using a criterion of misorientation between the adjacent pixels. Once such a list of grains is obtained, various quantities can be associated to each grain such as its size, (mean) orientation, GOS (Grain Orientation Spread) etc... The GOS associated to one grain is the mean value of the misorientations between all the pixels of the grain and the mean orientation of the grain. This value is quite sensitive to the state of the material (degree of plastic deformation, degree of recrystallization for example). Therefore it can help in interpreting the evolution of a microstructure during thermomechanical treatments. It is the purpose of this presentation to provide GOS values for an IF steel after several degrees of plastic deformation as well as after several annealing treatments which lead to partially or totally recrystallized states. The sources of influence on GOS values (as grain detection limit or grain size) are analyzed. The link between the values and the state of the material will be discussed at a global stage for a given population of grains.

Abstract: One-pass hot rolling in the ferrite region was conducted at higher temperatures, using various rolling temperatures and rolling reductions, with two types of ULC steels, 0.016% Nb and 0.023% Ti, and recrystallization behaviors immediately after hot rolling were investigated. The γ-fiber strength reached its maximum at around 50% rolling reduction at 1273K with the Nb-added steel and 1323K with the Ti-added steel. On the other hand, in high temperature rolling of the Ti-added steel, the γ-fiber did not develop, independent of rolling reduction. These changes corresponded to the recrystallized fraction, in that the strength of the γ-fiber decreased when recrystallization occurred immediately after rolling. New recrystallized-like grains were produced in the domain where distortions were particularly concentrated. Recrystallization seemed to be the result of various mechanisms, as some recrystallized grains were formed by a bulging mechanism, whilst others were surrounded by high angle grain boundaries.