Papers by Keyword: IF Steel

Abstract: Tensile tests have been carried out in the rolling and transverse directions of 'interstitialfree' (IF) steel cold rolled to a strain of εh= -0.18. Tests in the transverse direction showed the characteristic features of the orthogonal strain path change effect, with an initially increased flow stress- compared to tests in the rolling direction- followed by a transient regime of very low strain hardening. Tests were also carried out following recovery annealing of the prestrained sheet at 500°C and 600°C. Static recovery had a marked effect on the strain-induced anisotropy, but this was not eliminated even when the cell structure generated by prestraining haD condensed to one consisting of low-angle boundaries. This supports the view that the length scale, with respect to active slip systems, between boundary obstacles is a significant factor in the orthogonal path change effect.

Abstract: New type of IF cold-rolled high strength steels (HSSs) with the strength level of 390 and 440MPa have been developed under the chemistry of the extra-low carbon steel containing around 60ppm C with an intentional addition of niobium by hybridizing the precipitation hardening with niobium carbides and the supplemental solid-solution hardening. In this steel, Precipitation Free Zone (PFZ) nearby recrystallized grain boundaries forms during continuous annealing. This structure leads to unique mechanical properties such as lower yielding and superior anti-secondary-work embrittlement under fine grain structure strictly required for the exposed panels in Body-in-White. Principles of the unique mechanical properties of the steel are introduced related with the formation of PFZ during annealing, and the results of further approach to improve them as the state-of-the-art product, which is widely used for the exposed panels in Body in White, are introduced in the paper.

Abstract: The oxidation behaviors of several commercial low and ultra low carbon steels in air at 700-950°C were studied. Under isothermal oxidation conditions, the oxidation kinetics, scale structure and scale-steel interface adherence were significantly affected by the steel composition.

Abstract: Interstitial free (IF) steels are widely used as thin sheet in the automobile industries because of their many favorable properties. Although, fatigue properties of IF steels do not have significant importance to auto body makers, however, they are very concerned about the tensile and fatigue strength of the steels used for structural purposes to ensure safety of passengers. So, fatigue results of this steel might help researchers to understand the behaviors of high strength steels. In this study cyclic and static properties have been studied at room temperature in the air. Initiative has also been taken to observe the fatigue fracture morphology of this steel. Experimental results show that the fatigue limit is corresponding to about 40% of tensile strength and 80% of the yield strength of this steel. Fractographic observations reveal a mixed type of fracture mode (intergranular and transgranular cracking) fractures.

Abstract: The effect of near surface-ultrafine grain (NSUFG) layer with grain size of about 90nm on the solid reaction between Ti-added ultra-low carbon interstitial free steel sheet and electroplated zinc layer (ZP) was basically investigated at 473K and 573K, in comparison with the reactions of the coarse grains IF steel sheet (CG-IF) and the ZP. The NSUFG structure dramatically changes the reactions between ZP and IF steel, as follows; (1) the incubation times for the formation of reaction layers, pseudo-z-phase, are quite shorter for the NSUFG/ZP reactions than the CG/ZP ones, (2) in the early stage of annealing the former has the smooth interfaces of pseudo-z-phase layers but the latter has wavier ones like a stone wall, (3) the thickness of the pseudo-z-phase layer of the former is thicker than that of the latter, (4) some cracks are observed in NSUFG layers while no crack in coarse grain IF steel, and (5) the subsequent layer appears in the reaction between pseudo-z-phase and NSUFG layers former after long annealing by the blast-like break of the interface.

Abstract: The effect of microstructure and texture on the flow stress anisotropy in aluminium and IF steel has been investigated. The samples are recrystallized commercial purity aluminium (AA1050) cold rolled to prestrains of 0.05, 0.11 and 0.2, and recrystallized IF steel cold rolled to a prestrain of 0.28. The flow stress anisotropy was measured by tensile testing of specimens cut along different directions in the rolling plane. Pronounced anisotropy was found in both materials in spite of weak textures. The yield stress increases with increasing angle between the tensile direction and the rolling direction at all prestrains. The effect of microstructure and texture on the flow stress anisotropy was modelled by incorporating into a full-constraint Taylor model the strengthening effect of dislocation boundaries. The modelling and experimental results agree well, leading to a discussion of effect of the microstructure and texture on the flow stress anisotropy.

Abstract: An explicit integration algorithm using a texture-based plastic potential and isotropic hardening has been developed and implemented into a commercial explicit finite-element software program through a user material subroutine (VUMAT in ABAQUS/Explicit). Simulations of cup drawing of an IF-steel are presented and compared to both experimental data and calculation results obtained with a previously developed fully implicit approach (UMAT in ABAQUS/Standard). The explicit formulation has the advantage of being more stable, but local sheet thickness variations cannot be reproduced with the same accuracy.

Abstract: The influence of Mn on the surface texture formation through a®g®a transformation was investigated. After the a®g®a transformation, a weak texture was formed at the surface of ultra low carbon cold-rolled sheet steel without Mn. In contrast, a sharp <100>//ND cube texture was observed in Mn alloyed ultra low carbon steel. In order to interpret the effect of Mn two alternative mechanisms were considered : (i) one assumption attributes the occurrence of the specific surface texture to the effect of outer-surface energy (ii) and according to an alternative hypothesis the release of elastic work parallel to ND in the surface area is responsible for the observed <100>//ND surface texture.

Abstract: 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.