The Influence of Friction on the Texture Formation of a IF Steel during Hot Rolling in the Ferrite Region

The effect of friction on evolution of the microstructure and texture during hot rolling in the ferrite region was studied with secondary electromicroscopy (SEM), X‐ray diffractometer, and FEM simulation. The friction between a roll and a steel sheet surface leads to the formation of notable through‐thickness texture gradients. The finite element method (FEM) simulation shows that the large friction coefficient between a roll and sample results in a pronounced variation of ${\dot {\varepsilon }}_{13} $ (shear strain rate) and large ε₁₃/ε₁₁ value which accounts for strong {110}<001> texture components and weak γ‐fiber components at rolled sheet surface; whereas the friction condition do not exert notable effect on texture formation at the sheet center.     

Effect of Processing Condition on Texture and Drawability of a Ferritic Rolled and Annealed Interstitial-Free Steel

The processing conditions of the texture formation and deep drawability of a Ti-IF steel strip hot-rolled in ferritic region and subsequently annealed were investigated. The r-value increases with the decrease of reheating temperature, and finish rolling temperature and the increase of reductions in ferritic region. For lubricated ferritic rolling and annealing, the r-value is raised up to 1.75, and elongation rate is over 50% at the finish rolling temperature of 650 ℃, which is suitable for DDQ grade products. However, the r-value is below 1.0 in the case of unlubricated rolling. The X-ray diffraction was used to analyze the textural characteristic of samples. For samples subjected to lubricated rolling and annealing, the strong { 111 }//ND recrystallization texture is distributed homogeneously along the thickness direction, and the intensity of { 110} recrystallization texture is very low even in surface. However, for unlubricated samples, the {111} texture is distributed inhomogeneously and is weak along the thickness direction, and （110}//ND recrystallization texture is strong, which deteriorates the formability.     

摩擦对IF钢铁素体区热轧和退火织构的影响

采用X射线衍射仪分析IF钢铁素体区热轧织构以及退火织构的演化,在实验室热轧机上进行了IF钢的铁素体区热轧,研究了摩擦对IF钢铁素体区热轧、退火织构的影响。结果表明：无润滑轧制时,钢板表层形成强高斯织构组分{110}〈001〉,弱γ纤维织构,导致再结晶织构中高斯组分强度高,γ纤维织构强度低;润滑轧制时,钢板表层高斯织构组分强度降低,{100}〈011〉、γ纤维织构强度提高,退火后γ纤维织构强度提高。钢板中心受摩擦作用影响较小,轧制过程中发展为较强的α和γ纤维织构,退火后γ纤维织构成为主要织构组分。     

Simulation of Hot Strip-Rolling Process Based on Dislocation Density Variation

Based on the variation of dislocation density, which is influenced by rolling variables in hot strip-rolling process, a yield stress model was constructed. An integrated model was built to predict the temperature variation and microstructure evolution, in which the Orowan formula was used to calculate the stress and strain, and the finite difference method was adopted to determine the temperature field. This model was applied to predict the temperature variation, austenite grain size and phase transformation in hot strip-rolling process, and the prediction results are in good agreement with the measured ones on 2 050 mm continuous hot striprolling mill.     

Effects of Magnetic Field Direction on γ‐fiber Texture Evolution in Cold‐rolled Interstitial‐free Steel Sheet during Annealing

The effects of magnetic field direction on γ‐fiber texture evolution in as‐annealed interstitial‐free (IF) steel sheet were investigated by means of X‐ray diffraction ODF analysis. Specimens cut from cold‐rolled IF steel sheets were placed at the center of a 12‐T magnetic field, tilted by different angles to the magnetic field direction respectively, and annealed at 750 °C for 30 min. The results show that altering the specimen orientation to the magnetic field direction during annealing does not change the final annealing textures. The average intensity of the γ‐fiber texture of specimens annealed under the magnetic field is higher compared to conventionally annealed specimens. The intensity of the main γ‐fiber texture components presents a similar periodic variation with respect to the specimen orientation to the magnetic field, i.e., it is weakened as the tilt angle increases from 0°, and subsequently strengthened to a maximum value at 45°, and then weakened again as the tilt angle continues to increase. When the magnetic field is applied in the direction perpendicular to the specimen's rolling plane, the intensity of the main γ‐fiber texture components of specimens annealed in the magnetic field is close to that of the specimen annealed without field. This phenomenon might be attributed to the demagnetic effect.     

Effect of Through‐Thickness Macro and Micro‐Texture Gradients on Ridging of 17%Cr Ferritic Stainless Steel Sheet

In order to study the formation of ridging in ferritic stainless steel (FSS) sheets, the evolution of the crystallographic texture was investigated by macro and micro‐texture measurements throughout the thickness of the sheets. The as‐received hot band material displayed a pronounced through‐thickness texture gradient with a strong rotated cube orientation in the sheet center layer. The initial texture of the hot band had a high impact on the formation of the cold rolling texture and on the final recrystallization texture. Modification of the cold rolling texture by means of cross‐rolling led to an improvement of the macro and micro‐textures after final recrystallization annealing, which gave rise to an enhanced sheet formability in FSS. Tensile tests of specimens with half thickness revealed that ridging formed in the sheet center was much stronger than that in the surface. This observation was attributed to the more frequent formation of orientation colonies in the sheet center when compared to the sheet surface.     

Model of Mean Flow Stress of Ti‐IF Steel Considering Effect of Phase Transformations

The aim of this work was to describe the deformation resistance of austenitized Ti‐IF steel in the temperature range of 650 to 1100°C by a complex equation. The mean flow stress was determined by an original procedure, based on laboratory rolling of flat samples. Deformation resistance was described by a single formula, using a cumulative function in which particular terms are multiplied by a coefficient of 1 or 0, in dependence on a specific temperature. Calculation of specific coefficients had to be proposed in such a way that they could react to exceeding temperature boundaries between individual phase regions. The developed model can be used for off‐line predictions of power/force parameters in the forming of Ti‐IF steel, in a wide range of conditions of hot and warm deformation.     

退火工艺对冷轧高强IF钢组织及织构的影响

为了观察高强IF钢退火处理后的显微组织和再结晶织构的变化规律,采用两种不同退火工艺对高强IF钢进行热处理。结果表明,IF钢在两种退火方式下均形成了γ-{111}纤维织构,快速升温(350℃/min)退火时,再结晶新核呈等轴状,由变形带内的亚晶合并形成,与冷轧变形基体保持相同取向。慢速升温(2℃/min)退火时,新核在晶界弓出形成,且沿轧制方向呈饼形分布,与基体没有明显取向关系。慢速升温退火样品的γ-{111}取向密度强于快速升温的。对进一步改善薄板钢深冲性能具有指导作用。     

Influence of Texture on Magnetic Aging of Cold Rolling Non‐oriented Silicon Steel Sheets

The relationship between magnetic aging and texture of 50W800 non‐oriented silicon steel (0.002~0.003 % C) was investigated. The Young's modulus of cementite is very close to that of {100} planes in ferrite and obviously lower than those of other crystallographic planes in ferrite. Therefore, cementite particles would precipitate in the form of disks along the {100} planes of the ferrite matrix during aging. The magnetic properties after aging at 200°C for 24 hours showed that the aging precipitation of cementite particles increased the core loss. The driving force for the wall movement of 180° stripe domains depends on the sheet texture. The texture, in which the <100> direction is parallel to the magnetizing field, is the most favourable texture component to reduce the core loss increment induced by aging.