Properties Of Interstitial Free Steel Research Articles

Hall-Petch relationship of interstitial-free steel with a wide grain size range processed by asymmetric rolling and subsequent annealing

Asymmetric rolling (ASR) is an efficient processing for fabricating ultrafine-grained (UFG) materials. In the present investigation, interstitial-free (IF) steels with the grain size ranged from 500 nm to 500 μm were obtained by asymmetric rolling and subsequent annealing. The evolution of microstructures and mechanical properties of IF steel were studied. Accordingly, the Hall-Petch relationship of IF steel with a wide grain size range was established. It was found that ultimate tensile strength (UTS) corresponds well to the Hall-Petch relationship over the whole grain size range. However, the yield strength (YS) and hardness deviated from the Hall-Petch relationship as the grain size is larger than 100 μm, which is mainly attributed to the slight effect of grain boundary as obstacle on the dislocation movement and/or pile-up under small deformation in coarse grain (CG).

Effect of Heterogeneous Surface Structure on Mechanical Properties of Interstitial-Free Steel Subjected to Laser Surface Treatment

To investigate the effect of heterogeneous gradient surface structure on mechanical properties of metals, a Ti-added interstitial-free steel with coarse-grained matrix and ultrafine-grained matrix were applied and were treated by laser surface treatment using liner-scanning. The distances between the scanning lines were modified to alter the space between the hard-treated zone and soft matrix. The laser-treated zone contains a melting zone, comprised of fine grains, and a heat-affected zone featured by coarse columnar grains grown radically from the laser beam center. For coarse-grained matrix sample, after proper laser surface treatment significant improvement (about 100%) in yield strength and moderate improvement (22.8%) in ultimate tensile strength were achieved with little loss in elongation. For ultrafine-grained matrix sample, gradual decrease in strength together with recovering of elongation was realized. Electron channeling contrast imaging was applied to investigate the structure of the sample which was then compared with the untreated one to reveal the origin of the mechanical behavior of the laser surface-treated steel.

Effect of heterogeneous laser surface treatment on mechanical properties of interstitial free steel

Laser surface treatment was applied to a Ti-added interstitial-free steel by linear-scanning. The distance between each linear scan was 1.5 mm and the width of the laser-modified zone for each scan was 1 mm. These process parameters result in a heterogeneous surface, containing hard laser-modified lamella separated by non-treated material. It is found that after the treatment, higher strength and good ductility can be obtained. Electron channelling contrast imaging was used to investigate the structure of the sample, which was then compared with the untreated one to reveal the origin of the improved mechanical behaviour of the laser surface-treated steel.

Structural evolutions and mechanical properties of IF steel deformed by differential speed rolling at various per-pass-thickness reductions

In the present work, the effects of thickness reduction per pass introduced by differential speed rolling (DSR) on microstructure and texture evolutions and related mechanical properties of interstitial-free (IF) steel samples were investigated. For this purpose, the samples were subjected to DSR deformation at various per-pass-thickness reductions; 10% (14 passes), 30% (4 passes), and 50% (2 passes). The results showed that the DSR deformation at a high thickness reduction per pass (50%) leads to ultrafine grained structure (∼0.5 μm) with significant fractions of high angle grain boundaries (HAGBs). This structure was conjugated with a high strength and low ductility as compared to those in the non-deformed sample.

Effect of Isothermal Treatment on Microstructure and Mechanical Properties of Cold-Deformed IF Steel

In this study, we investigated the recrystallisation kinetics of Ti-stabilised interstitial-free (IF) steel manufactured by the Mexican steel industry through the route of electric arc furnace with vacuum degassing, secondary refining, and subsequent continuous casting. The IF steel was hot-rolled at 950°C and then cold-rolled until deformation of 94% was attained, followed by recrystallisation at different times at a constant temperature of 780°C. In addition, the mechanical properties of the IF steel were assessed as a function of recrystallisation time. The results obtained from the mechanical property tests were presented in the form of plots of microhardness, yield strength, ultimate tensile stress, and deformation percent as functions of the recrystallised fraction with an indirect dependence on recrystallisation time. A graphical model of the recrystallisation behaviour showed the evolution of the microstructure, including phase transformations, hardness, and the mechanical properties determined from the tensile tests. In view of subsequent recovery and recrystallisation, stored energy analysis derived from the strain induced by deformation was presented. Furthermore, we determined the precipitates formed in the different processing stages of IF steel.

Material Selection for a Fuel Tank and its FE Simulation in deep drawing

Deep drawing is a sheet metal forming process in which deformation forces are oriented in the plane of the sheet, and the surface pressures in the tool are generally lower than the yield stress of the sheet material. The present work discusses the selection of sheet material suitable for a fuel tank by experimental evaluation of tensile properties of interstitial free steel and deep draw quality steel sheets of the same thickness of 0.8mm. The tensile specimens are laser cut from a blank with a known rolling direction and are tested for tensile properties and anisotropy. These tensile properties of the sheets are used in the material model in FE simulation of the deep draw process using HyperWorks. It is observed that an optimum blank holder force is necessary to remove the wrinkling defects. It is concluded that higher ductility and normal anisotropy are the key factors for higher thinning resistance in deep drawing and hence, interstitial free steel sheet qualifies as the better material for the fuel tank.

Effect of Deformation on the Structure and Properties of Interstitial Free Steels

As received interstitial free steel of composition 0.0029C – 0.15 Mn – 0.054 Ti – 0.011 Nb was heated to various temperatures ranging from 740°C to 930°C, held for 20 minutes and were quenched in water. The microstructure of water quenched samples were observed and taken as reference to map the changes in structure due to application of deformation. The samples from same steel are deformed at the above mentioned temperatures; the deformation percentages at each temperature are 30% and 50%. Transmission electron microscopy was carried out for microstructural study. Electron backscattered diffraction (EBSD) studies were done to understand the effect of deformation on the transformation behaviour of austenite. In order to gather information about the elastoplastic behaviour of the ferrite formed due to deformation, nanoindentation technique was used for a few selected samples. The transformation kinetics was also studied by DSC analysis.

Evaluation of Residual Stresses and Mechanical Properties of IF Steel Welded Joints by Laser and Plasma Processes

Interstitial free (IF) steel has an extensive application in the automotive industry where the Laser Beam Welding (LBW) process is widely used due to its high productivity. Similarly, the other used process, Plasma Arc Welding (PAW), is characterized by a greater energy concentration and current density and therefore lower distortion, higher welding speeds and higher penetration may be obtained. However, while the traditional welding processes have been extensively studied with regard to the generation of residual stresses, there are few studies about residual stresses analysis and characterization of LBW and PAW joints. Therefore, the aim of the present work is to analyse the residual stresses resulting from LBW and PAW processes by X-ray diffraction technique with sin2ψ method in IF steel butt joints. For both joints, macro and microstructure were characterized and mechanical properties were determined. Tensile residual stresses in the heat-affected zone (HAZ) and in the fusion zone (FZ) were verified for both welding processes.

Effect of rolling temperature on the microstructure and mechanical properties of interstitial free steel

Effect of rolling temperature on the microstructure and mechanical properties of interstitial free steel

Effect of rolling temperature on the microstructure and mechanical properties of interstitial free steel

In the present research, to improve the mechanical of interstitial free steel, the hot rolling process has performed for 50% reduction in area at three different phase regions (below the lower critical point, above the upper critical point and intermediate region) of interstitial free steel. Samples were cooled down to room temperature by normal air cooling in the room temperature. The microstructure and mechanical properties of control rolled steel have been investigated by an optical microscope, Vickers hardness tester and tensile test. It has found that yield strength and ultimate tensile strength of sample rolled at a lower critical temperature (600°C) improved significantly without much significant change in ductility, due to ferrite grain refinement and an increase of dislocation density. Scanning electron microscope fractography analysis shows cup and cone fracture. Finally, it is suggested that a controlled rolling process of interstitial free steel in pure ferritic region conferred optimum properties.

Modification of Initial Blank Shape to Minimize Earing in Deep Drawing Process

Earing is a common defect that occurs in deep drawing process due to non-uniform material properties within the plane of the sheet that is planar anisotropy. In this study, efforts were made to study the earing problem in deep drawing of cylindrical cups by finite element modeling using HYPERWORKS6.10. Interstitial Free (IF) steel sheet of 1.0 mm thickness has been considered as it has wide application in fabricating critical automobile components. Mechanical properties of IF steel along with tool design parameters were incorporated in the finite element modeling of deep drawing process.Significant earing was observed at rolling and transverse direction in the deformed cup from a circular blank. The cup heights were measured at several points with respect to the rolling direction of the sheet. To minimize earing, flow of material was observed at various steps during the simulation and accordingly initial blank shape had been modified. Modified blanks showed significant reduction in earing and improvement in thickness distribution in simulation.

Ratcheting strain in interstitial free steel

This investigation illustrates ratcheting phenomenon, in-situ substructural variations during ratcheting and post-ratcheting tensile properties of interstitial free steel at ambient temperature (≈300K). The results highlight that the nature of strain accumulation is dependent on the magnitude of the employed combinations of mean stress (σm) and stress amplitude (σa); this phenomenon has been explained considering the asymmetry of loading cycles and substructural variations as delineated by TEM. Tensile strength increases while ductility decreases for ratcheted samples with increasing σm and/or σa and these variations in tensile properties are correlated with the induced cyclic hardening.

Effect of Processing Parameters on the Mechanical Properties of Interstitial Free Steel Subjected to Friction Stir Processing

In the present work, the effect of friction stir processing parameters on the mechanical properties of an interstitial free steel was studied. Four rotating speeds (800, 1250, 1600, 2000 rpm) and two traverse speeds (31.5 and 63 mm/min) were employed. On both sides of specimens, a nanograin layer with the thickness and nanograins of 150 μm and 50-100 nm were formed, respectively. For the specimen processed at rotating speed of 1600 rpm and the traverse speed of 31.5 mm/min, the maximum strength was achieved, which was about 80% increase in the strength comparing to that of base material. For constant traverse speed, the increase in the rotation speed from 800 to 1600 rpm led to a decrease in uniform and total elongation of friction stir processed samples. By contrast, when the rotating speed exceeded 1600 rpm, the uniform and total elongation was increased again, while there was a drop in strength. The results of microhardness indicate more than threefold increase in the hardness of the stirred zone comparing to that of base material.

Effect of strain ageing on the mechanical properties of interstitial-free steels under as-received, heat-treated, and spot-welded conditions for automotive applications

In this study, the artificial ageing behaviour of interstitial-free steels is investigated under as-received, heat-treated, and spot-welded conditions. All the test specimens except those in the as-received condition were austenitized at 950°C for 15min followed by water cooling. Both as-received test pieces and heat-treated test pieces were prestrained by 8 per cent in tension, and then aged at 170°C for 10min, 20min, 40min, 60min, 80min, and 120min. The experimental work revealed that strain ageing takes place in as-received, heat-treated, and spot-welded test pieces. However, strain ageing is more pronounced in heat-treated test pieces and spot-welded heat-treated test pieces, compared with the as-received test pieces and spot-welded as-received test pieces. This is due to the nature of heat treatment and spot welding.

Microstructural evolution of equal-channel angular pressed interstitial-free steel

Abstract Equal-channel angular pressing (ECAP) belongs to advanced technologies for improving mechanical properties of materials. In the present work, the influence of the number of ECAP passes using route BC on both grain size and mechanical properties of interstitial-free steel was investigated by means of transmission electron microscopy, electron back-scattering diffraction, and microhardness testing. It was found that the grain size decreases with the increasing number of passes. At the same time, an increase in microhardness was observed. The evolution of microstructure with increasing strain imposed through ECAP, in particular the process of grain fragmentation and the formation of high-angle boundaries were also examined.

Fatigue Strength and Fracture Mechanisms of IF28 Steels

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.

Effect of Ti on Formability of IF Steels

The influence of the texture development in Ti-added (0.03, 0.05 and 0.07wt%) IF (Interstitial Free) steels on physical properties, especially ř -value was investigated. It was intended to determine the proper Ti content for the promotion of deep drawability as well as mechanical properties of IF steels. The precipitation behavior in the IF steels was clarified with the aid of computer simulation. The quantitative X-ray analysis on the texture development of IF steels was performed using pole figure and orientation distribution function measurement. For the IF steel with the composition of 0.025C, 0.070Mn, 0.002N and 0.007S, the optimum Ti content was found to be 0.05wt%.

Microstructure and Mechanical Properties of Interstitial Free Steel Subjected to Equal Channel Angular Extrusion

The development of fine-grained microstructure and mechanical properties of interstitial free steel during equal channel angular extrusion was studied. The tests were performed in air at room temperature with the angle between channels of the die of 90 and 120° and up to 2 and 4 passes, respectively. Repetitive passes were conducted using designated processing routes A and C. Anisotropy of microstructure and mechanical properties in three planes (perpendicular to the longitudinal axis of the sample, side-viewed and top-viewed planes along the longitudinal axis of the sample) as a function of processing route has been assessed.