Papers by Keyword: Interstitial Free Steel

Abstract: The investigation was focused on the detailed description of precipitation/formation processes of TiN, TixSy, Ti4C2S2, TiC, and (Fe,Ti)P particles occurring in the production of thin sheets of titanium-bearing interstitial-free steels. The knowledge concerning this reactions was gained based on the thermodynamic calculation and physical simulations conducted on Gleeble 3800 thermal – mechanical simulator. The formation process of titanium carbosufide of Ti4C2S2 is the crucial reaction for the thin sheets properties. The investigation confirmed the in-situ mechanism of this phase formation, involving carbon diffusion in the TiS and TixSy sulfides’ crystal lattice. Thus, the precipitation of the substantial fraction of these sulfides is a prerequisite for further intense carbosulfide formation. Titanium sulfides are formed at the rough rolling stage of the transfer bar rolling process. The most intense precipitation of the sulfides occurs at around 1000°C. Besides the effect on the carbosulfide formation, it was found out that the sulfides substantially retard the recrystallization and grain growth in the IF steels. The most favourable Ti4C2S2 formation conditions prevail in the temperature range of approximately 950 - 920°C, which corresponds to the plate finish rolling stage. Both reactions, i.e. sulfides and carbosulfide formation, are deformationinduced processes.

Abstract: The recovery and recrystallization kinetics of a cold rolled interstitial free (IF) steel were studied during isothermal annealing. Magnetic methods based on coercive field measurements, hardness tests and metallography were applied so as to follow the kinetics experimentally. The coercive field measurement technique reveals a higher degree of resolution for monitoring recovery than conventional hardness determination and also allows the recrystallization progress to be monitored. The results obtained are compared to those previously determined for a non-stabilized extra low carbon (ELC) steel. The observed differences are discussed in terms of the presence of microalloying elements, Ti and Nb, which slow down recovery and delay recrystallization.

Abstract: The effect of five ideal texture components ({001}<110>, {112}<110>, {111}<110>, {111}<112> and {554}<225>) typical in interstitial free (IF) steels on the development of ears was investigated using crystal plasticity finite element method (CPFEM). For the polycrystal model, the material behavior is described using crystal plasticity theory where each integration point in the element is considered to be a single grain of polycrystalline IF steel. The experimental earing profile for a IF steel was also compared to the earing profile predicted by CPFEM.

Abstract: This paper examines an effect of boron (B) on dynamic softening behavior, mechanical properties and microstructures for Nb-Ti added high strength interstitial free (IF) steel. For this purpose, IF steels containing 0ppm B, 5ppm B and 30ppm B were chosen. Continuous cooling compression test was performed to investigate dynamic softening behavior. Mechanical properties and microstructures of pilot hot-rolled IF steel sheet were analyzed by uni-axial tensile test and electron back-scattered diffraction (EBSD). It was found that no-dynamic recrystallization temperature (Tndrx) which can be determined from the relationship between flow stress and temperature is a constant of 955oC for all IF steels. However, an addition of B into IF steels increases work hardening rate at the temperature below Tndrx. It was also verified that B retards phase transformation of austenite into ferrite. EBSD analysis revealed that absence of B induces fine ferrite grain size and many high angle grain boundaries.

Abstract: We have investigated the static and metadynamic behaviour of the interstitial free steels and in particular the effects of the steeling elements (phosphorous and boron) on kinetics of recrystallisation. The results showed that the strain for the initiation of strain independent softening (often referred to as metadynamic recrystallisation) varies with the Zener-Hollomon parameter and steel composition. Strain rate had a strong influence on kinetics of metadynamic recrystallisation. An increase in temperature from 930oC to 1100oC led to a decrease in time for 50% softening (about one order of magnitude) in the SRX region. However, for the same temperature range, the time for 50% MDRX did not change significantly.

Abstract: IF steel processed by equal channel angular pressing to an equivalent strain of 9.2 via route BA was annealed for different times at 500°C and 600°C. At both temperatures the microstructural evolution shows continuous recrystallization followed by grain growth, in absence of primary recrystallization. At 600°C a slightly bimodal grain size distribution develops.