Cold Rolled Interstitial Free Steel Sheets Research Articles

Effect of Equivalent Stress-Strain Relation and Differential Hardening on Accuracy of Forming Limit Analyses

Multiaxial tube expansion tests (MTETs) were performed to measure the multiaxial plastic deformation behavior of a cold rolled interstitial-free (IF) steel sheet for a range of strain from initial yield to fracture. The testing machine is capable of applying arbitrary principal stress or strain paths to tubular specimens using an electrical, closed-loop servo-control system for an axial force and an internal pressure. Tubular specimens with an inner diameter of 44.6 mm were fabricated from a cold rolled IF steel sheet with a thickness of 0.7 mm by roller bending and laser welding. Many linear stress paths in the first quadrant of stress space were applied to the tubular specimens to measure the forming limit strains and forming limit stresses of the as-received sheet sample, in addition to the contours of plastic work and the directions of the plastic strain rates. It was found that the shapes of the measured work contours changed with increasing plastic work. The observed differential hardening behavior was approximated by changing the material parameters and the exponent of the Yld2000-2d yield function (Barlat et al, 2003) as functions of the reference plastic strain. The hydraulic bulge tests were also conducted to measure the forming limit strain and forming limit stress for equibiaxial tension and to determine the equivalent stress-equivalent plastic strain relation for a larger strain range. The forming limit curve and forming limit stress curve were calculated using the Marciniak-Kuczyński-type approach. The calculated results were in fair agreement with the measurement.

Observation of co-segregation of titanium and boron at the interface between recrystallized and unrecrystallized grains in cold-rolled interstitial-free steel sheets

It has been reported that the addition of ppm levels of B strongly retarded the growth of recrystallized grain into unrecrystallized grains in the process of cold-rolling and annealing of Ti-added interstitial-free (IF) ferritic steels. This phenomenon was explained by solute drag effect based on the assumption that, during annealing, B atoms segregate at the interface between recrystallized and unrecrystallized grains where they interact with Ti atoms. To verify this, atom probe tomography analysis of the interface was performed in Ti-added IF steels with and without B addition. Needle tips containing the interface identified from electron backscattering diffraction analysis, were produced by focused ion beam milling with the lift-out method. To increase the experiment reliability, the misorientation angle of the aimed interface was compared with that estimated by field ion microscopy analysis. Considerable amount of Ti segregation was observed at the interface in the steel without B addition, which increased with increasing amount of B segregation in the steel with B addition. The results suggest that the retardation of the interface migration was caused by solute drag effect based on the simultaneous co-segregation of Ti and B due to their attractive interaction.

Effect of Micro-Alloying Elements of Ti, Nb and B on Recrystallization Behavior of Cold-Rolled Interstitial-Free Steel Sheets

The effect of micro-alloying elements of niobium and boron and titanium on recrystallization behavior is researched after the cold rolled IF steels are annealed at high temperature. The results show that there is high density dislocation in the cold rolled steel and the microstructure is fibrous tissue. The recrystallization grains appear when the cold steel annealed at 655 °C and then the grains grow up with the annealing temperature increased to 840 °C. The recrystallization temperature and time of B-Ti-IF steel is lower than that of Nb-Ti-IF and Ti-IF steels. The recrystallization activation energy of Nb-Ti-IF steel is 181.7KJ/mol which is 56.6KJ/mol larger than that of B-Ti-IF steel.

Designing cold rolled IF steel sheets with optimized tensile properties using ANN and GA

Artificial neural network (ANN) models, correlating the mechanical properties (yield strength, tensile strength, %elongation and r ¯ ) of the cold rolled interstitial free (IF) steel sheets with compositional and processing parameters, are used to find the importance of different variables. Further the above models are used as objective functions for the evolutionary multi-objective optimization algorithms by evolving tradeoffs, which gives a range of combination of strength and ductility. The optimal solutions are also analysed to extract further knowledge on the role of various parameters, which could be used for designing the chemistry of the alloy as well as process parameters for producing cold rolled strips of IF steel with tailor made property.

Microstructure and Texture Evolution in Cold Rolled Interstitial Free (IF) Steel Sheet during Annealing under AC Magnetic Field

An AC magnetic field (0.5Tesla) is applied with the field direction perpendicular to the rolling direction during annealing of a 76% cold-rolled IF steel sheet. Microstructure and texture evolution in the as-annealed specimens were determined using SEM based OIM technique. It is found that the recrystallization is noticeably retarded by AC magnetic field annealing. At the early stage of recrystallization (annealing at 650°C for 30min), the development of (111) <123> orientations was favored by the AC magnetic field. With progress of recrystallization (annealing at 700°C and 750°C for 30min), the applied AC magnetic field suppressed the development of γ-fiber recrystallization textures to some extent.

Effects of High Magnetic Field Annealing on the Nucleation Sites for Recrystallized Nuclei with {111} <112> Orientation in Cold-Rolled IF Steel Sheet

The effect of high magnetic field annealing on the nucleation sites for recrystallized nuclei with {111}<112> orientation in the initial stage of recrystallization in as-annealed interstitial-free (IF) steel sheet were investigated by the SEM-EBSD analysis. Specimens of cold rolled IF steel sheet were annealed at 650°C for 0min and 10min respectively with a 12-tesla magnetic field to obtain a partially recrystallized microstructure. During the magnetic field annealing, they were respectively placed at the center of the applied field with their rolling planes parallel to the magnetic field direction (MD), and with their rolling direction (RD) parallel and normal to the MD, respectively. It was found that different to the non-field annealed specimen, in the field annealed specimens, the {111}<112> oriented recrystallized nulei favored to nucleate in the {111}<112> deformed matrix and not in the {111}<110> deformed matrix. This phenomenon may be attributed to the magnetic ordered state induced by the magnetic field, which might suppress the formation of high-energy grain boundaries between the newly formed nuclei and the deformed matrix.

Composition–Processing–Property Correlation of Cold-Rolled IF Steel Sheets Using Neural Network

Artificial neural network (ANN) models have been developed to establish relationships between the mechanical properties of the cold-rolled sheets of interstitial free (IF) as a function of the chemical composition of the steel, the rolling and the batch annealing parameters. The mechanical properties studied include yield and . The technology of rolling mill automation necessarily embraces a broad spectrum of interests, ranging from fundamental process analysis to the solution of special control-theoretic problems. Determining the relationship between various compositional and processing parameters and the mechanical properties of cold-rolled sheets is important but not easy to establish. The complex and highly nonlinear interactions between the variables make the system difficult to assess from the prediction point of view. ANN model is found to be capable of developing the inherent relationship between the variables and could be successfully used to develop better understanding on the metallurgical principles of cold rolled IF steel.

Study of recrystallisation in interstitial free (IF) steel by ultrasonic measurements

The purpose of understanding recrystallisation in interstitial free (IF) steel through non-destructive ultrasonic measurements was to develop an online system to monitor specific grain conditions, textures and mechanical properties during annealing of such steels. Ultrasonic measurements for microstructure and property evaluation samples had larger volumes of the material when compared with other conventional methods. In order to make it an alternative to the conventional destructive methods using microscopes, X-ray diffraction, mechanical testing, hardness testing, etc., correlation between the ultrasonic surface wave velocities in 45° to rolling direction and average velocity v-Bar and those of materials parameters like plastic strain ratio r-Bar, hardness, texture, in cold rolled IF steel sheets with 79% thickness reduction and annealed at 650°C for different soaking times were developed. The ultrasonic surface wave velocity measurements at 45° to rolling direction and average velocity v-Bar were found to be the ultrasonic parameters to be monitored to control recrystallisation in IF steels.

Effects of High Magnetic Field and Field Direction on Recrystallization and Recrystallization Texture in Cold-Rolled IF Steel Sheet

The effects of magnetic annealing on recrystallization and texture evolution in asannealed interstitial-free (IF) steel sheet were investigated by means of X-ray diffraction ODF analysis, SEM-EBSD analysis, and optical microstructure observation. During the magnetic annealing, specimens were placed at the center of the applied magnetic field, with their rolling planes parallel to the field direction (MD) and their rolling direction (RD) normal to the field direction (MD). It was found that the magnetic annealing retards the recrystallization process, but promotes the nucleation at the initial stage of recrystallization. Magnetic annealing did not change the mechanism of recrystallization texture evolution but improved the development of γ-fiber texture during the process of recrystallization, and the magnetically annealed specimen had stronger γ-fiber texture compared with the conventionally annealed specimen; this interesting finding is quite different from the previous work on magnetically annealed IF steel.

Effect of Processing Parameters on Properties and Microstructures of Warm-Rolled Interstitial-Free (IF) Steel Sheets

In order to simplify production processes and to lower production cost of thicker coldrolled IF steel sheets for deep drawing applications, a new warm-rolled IF steel sheet was developed in our lab through hot-rolling in high-temperature ferrite range. In this paper, effect of processing parameters on properties, microstructures and precipitate morphology of warm-rolled IF steel sheets was investigated. It is found that firstly, good deep drawing properties and favorable textures were achieved as steels were warm-rolled in good lubricant condition. Secondly, most precipitates in steels were TiS, TiC, TiN and Ti4C2S2.

Analysis of Texture Formation and Microstructure Characteristics of Cold Rolled IF Steel Sheets

The aim of this work is to investigate the relationship between the deformation microstructure and texture in cold rolled Interstitial Free (IF) steel sheets. In the present research, the cold rolled IF steel sheets with 10%-50% reductions are used to observe the characteristic microstructure and individual orientations by transmission electron microscopy (TEM) and SAED patterns. The experimental results on inter-granular strain homogeneity and dislocation wall formation are given in details in this paper. The results are explained by the analysis of crystallographic gliding and are helpful to improve the prediction of cold rolling textures.

Study on the Micro Mechanism of Recrystallization Texture Formation in Cold-Rolled IF Steel Sheet

An experimental setup was designed to study the recrystallization kinetics of Interstitial Free (IF) steel in this work. The 80% cold rolled IF steel foils are heated rapidly to 680°C, 730°C and 780°C by a salt bath. The recrystallization kinetic curves were obtained by the quantitative analysis of texture components, microstructures and EBSP (electron back-scattering patterns) measurements. With the help of EBSD, the orientations of the recrystallization nuclei are determined. The growth rule of the recrystallization nuclei was analyzed statistically. The effect of nucleus orientation on the formation of the recrystallization texture was investigated.

Characteristics of Recrystallization Texture Evolution in High Magnetic Field for Interstitial Free (IF) Steel Sheet

High magnetic field is applied with the field direction parallel to the rolling direction during annealing of a cold rolled IF steel sheet. Results of X-ray ODF analysis show that, magnetic field annealing retards the normal recrystallization texture evolution for the IF steel sheet. It is worth noting that an abnormal increase of orientation intensity at {100}<110> is found after magnetic annealing for 25min at 650°C. When the magnetic field strength is increased from 10 Tesla to 14 Tesla, the a-fiber is further strengthened, especially the {100}<110> component. Combined with EBSD analysis results, it is considered that the magnetic field does not change the mechanism of recrystallization texture evolution for the IF steel sheet in the present case.

Texture and microstructure development in cold-rolled interstitial free (IF) steel sheet during electric field annealing

The effects of electric field annealing on the development of recrystallization texture and microstructure in a cold-rolled IF steel sheet were studied by means of ODF analysis and optical microscopy. Results showed that the applied external electric field might retard recrystallization, and enhance the γ-fiber recrystallization texture that is beneficial to the deep-drawability.