IF Steel Research Articles

Wear Friction and Corrosion Performance Assessment on IF, HSLA and DP600 Steels Subjected to Severe Vibratory Peening

Wear Friction and Corrosion Performance Assessment on IF, HSLA and DP600 Steels Subjected to Severe Vibratory Peening

Corrosion characteristics of PPY/GO/CuO nano-composite powder reinforced epoxy coatings on IF steel

Corrosion characteristics of PPY/GO/CuO nano-composite powder reinforced epoxy coatings on IF steel

Orientation dependence of dynamic compared to static recovery in Interstitial Free steel

This study investigates the sub-structure of IF steel in three conditions: cold rolled, statically recovered, and warm rolled. After both cold and warm rolling, the steel exhibits the typical 〈110〉//RD and 〈111〉//ND fiber textures. Considering the short-range misorientation gradient ∆θ/∆x to assess locally stored energy variations, it was observed that 〈111〉//ND grains exhibit significantly higher gradients than 〈001〉//ND grains in all conditions. In the statically recovered conditions, the ∆θ/∆x values are significantly reduced compared to the cold rolled condition, but these values are significantly higher than those of the dynamically recovered after warm rolling. The strongly reduced orientation gradients in the 〈111〉//ND grains after warm rolling may reduce the nucleation potency of these orientations in the ensuing recrystallization. This study enhances our knowledge of deformation microstructure as a function of rolling temperature and is relevant in explaining reported differences in annealing textures during static recrystallization after cold vs warm rolling.

Microstructural Features Intimated in Automotive Grade IF Steel Subjected to Conventional and Severe Shot Peening

Microstructural Features Intimated in Automotive Grade IF Steel Subjected to Conventional and Severe Shot Peening

Investigation of Mold Flux Entrapment in Deep Oscillation Mark of Interstitial-Free Steel Shell Using Mold Simulator.

The slag entrapment defect has become a big issue for the IF steel casting process. In this study, the mechanism of mold flux entrapment in deep oscillation mark of an IF steel shell was studied by a high-temperature mold simulator. Results show that both temperature and heat flux in a copper mold become lower when mold flux B with lower melting and viscosity is used, compared with these when mold flux A with higher melting and viscosity is used. The average thickness of the slag film for mold fluxes A and B is 1.31 mm and 1.63 mm, and the consumption of them is 0.33 kg/m2 and 0.35 kg/m2, respectively. The shell for mold flux A exhibits sharper oscillation marks, while the shell for mold flux B has shallower oscillation marks. These deeper oscillation marks capture the mold flux by overflow of molten steel at the meniscus, which finally produces the slag entrapment defect in the shell.

Effect of Al-Ti complex deoxidation mode on steel cleanliness during RH refining of IF steels

The deoxidation in Ti containing Al killed IF steels is a vital parameter that directly influences the steel cleanliness. In this study, the evolution of steel compositions and inclusion characteristics during RH refining of IF steels were investigated by industrial trials involving three Al-Ti deoxidation modes, which were adding Ti-Fe 2 min after Al deoxidation in Mode I, adding Al and Ti-Fe simultaneously in Mode II, and adding Ti alloys with two equal batches at 3.2 min and 5 min after Al deoxidation in Mode III. The results showed that nitrogen pickup of several ppm was observed with Ti-Fe alloy addition. Therefore, nitrogen content in alloys should be strictly controlled. The main inclusions were single alumina particles, alumina clusters, alumina cluster with Al-Ti oxides, and Al-Ti complex oxides. Mode III had less amount of Al-Ti oxides compared with Mode I, and Mode II had a much higher proportion of Ti bearing inclusions than Mode I and Mode III at RH end. For Mode I & Mode III, the inclusion removal rate was 0.33–0.35 min−1 before adding Ti, and slowed down to 0.14 min−1 for Mode I and 0.22 min−1 for Mode III after Ti-Fe addition. While for Mode II, the rate was only 0.18 min−1. Mode III was the recommended mode for its excellent steel cleanliness and high Ti yield with slight elongation of RH treating time.

Removal behavior of Al–Ti–O inclusions in aluminum deoxidized molten steel containing titanium by microporous magnesium foam ceramic filters

Al–Ti–O inclusions in aluminum deoxidized and titanium (Ti)-alloyed steel aggravate the submerged nozzle clogging and instability of the continuous casting process, lowering the cleanliness of casting billet. In the present investigation, the removal behavior of the oxide inclusions in aluminum deoxidized IF steel and Ti-alloyed welding wire steel by microporous/fused MgO foam ceramic filter (PMF/FMF) and the improvement of the steel cleanliness were comparatively investigated. It is found that MgO foam ceramic filters immersed in Al deoxidized steel effectively reduced its number density of Al2O3 inclusions and total oxygen (TO) content, by use of forming Al–Mg–O spinel interface reaction layer between the filters and tested steel. Furthermore, the cleanliness increase of Ti-alloyed steel immersed by the filters, due to formation of a more complete and continuous Al–Mg–Ti–O spinel layer on their surface, was bigger compared with that in Ti-free steel, with sporadically distributed Al–Mg–O spinel of interface layer on the surface of filters immersed in Ti-free steel. This is ascribed to the higher Ti content and some liquid inclusion of MgO–Al2O3-TiOX in Ti-alloyed steel, enhancing the reaction of the MgO of aggregates in the filters with Al, Ti, and O and deposition of other solid MgO–Al2O3-TiOX on the surface of the filter, respectively. In addition, the better purification efficiency of the PMF on tested steel compared with the FMF, was due to its higher porosity, roughness and more liquid phase components of the matrix in PMF, which improve the reaction of filter with liquid steel, and raise its adsorption capacity with Al2O3-based inclusions in the steel, forming Al–Mg–O spinel interface layer to removal the oxide inclusions.

Microstructural Influence on Fracture Toughness of IF Steel and DP Steel

Interstitial free steels (IF) and Dual-phase (DP) steels are widely used in the automotive industry, their specific application is driven by requirements to optimize the strength-to-weight ratio. Utilizing the full capacity of their plasticity and strain hardenability requires an assessment of edge fracture susceptibility and flangeability. In this work, the ability of the mentioned steels to spreading of deformation along initiated cracks is evaluated by structural and fractographic analyzes. Microstructural restrictions of plasticity are correlated with fracture toughness results, adopting the essential work of fracture (EWF) methodology. Crystallographic analyzes (EBSD) are focused on the role of anisotropy and the deformation texture evolution, affecting the development of plasticity and thus the energy consumption to the fracture.

Tempering mechanism of lath martensite induced in IF steel under high pressure

In this paper, low- and high-strength lath martensite (350 and 640 HV) was fabricated in an IF steel via high pressure martensitic transformation. The microstructure and the softening during their tempering from 200 °C to 800 °C for 1 h were systematically investigated. A carbon-irrelevant tempering process was proposed, exhibiting a three-stage structural evolution pattern depending upon the tempering degree (1-(HV-HVFP)/(HVNP-HVFP), where the HV is the instant hardness, HVNP is the non-tempered hardness and HVFP is the fully tempered hardness): (1) low tempered (<10%), removing the loose dislocations and dislocation boundaries within martensitic variants; (2) medium tempered (10%-50%), eliminating the martensitic variant laths via the migration of their terminal tips; (3) highly tempered (>50%), clearing up the remained variant laths via the migration of the triple junctions. Martensite-type microstructure is tailored by low-index lamellar variant boundaries and is thus intrinsically thermally stable, whereas the mobile terminal tips decrease the tempering resistance. The underlying mechanism for such carbon-irrelevant process was discussed and the potential effect on the tempering behavior of carbon-contained martensite was highlighted.

Effects of the adjustable ring-mode laser on intermetallic formation and mechanical properties of steel to aluminium laser welded lap joints

Research has confirmed a positive effect of laser beam shaping on controlling weld profiles and keyhole stabilisation, with significant reductions of porosity in weldments. However, few attempts with scattered results have studied the impact of laser beam shaping on intermetallicphase formation. This paper implements the adjustable-ring mode (ARM) laser and studies the impact of the core/ring power ratio to explore the impact on intermetallic phase formation and mechanical properties during remote laser welding of IF steel to 1050 aluminium. It was found that in conduction mode, the core/ring power ratio of 0.2 provided a larger surface area for bonding at the weld interface, and this was translated through the maximum lap-shear strength of 97.6 N/mm2 (joint efficiency 71%). Furthermore, this significantly reduced the Fe2Al5 intermetallic compound (IMC) thickness by 62% and total IMC thickness by 40% in contrast to a core-dominant beam (power ratio greater than one). In keyhole mode, cracking and lower lap-shear strengths were observed compared to the conduction mode. Notably, with a core/ring power ratio of 0.5 a significant grain refinement in the steel side of the weld was observed.

Analysis of stamping cracking of laser tailor-welded IF steel door inner plate

The parts produced by laser tailor welded steel plates are more and more widely used in automobiles, due to their advantages of high strength, low weight, and low comprehensive cost. However, the welding seam of the laser tailor welded steel plate is prone to cracking during the stamping process. Based on solving the problem of stamping cracking of the IF steel door inner plate supplied by our company, the mechanical properties and friction coefficient were tested on the base metal. In addition, the cupping experiment was carried out on the weld seam of the tailor-welded blanks, and the hardness and microstructure of the weld seam were also tested and analyzed. The results showed that the lap height difference was the main reason for cracking. By optimizing the height difference of tailor-welded blanks, the incidence of cracking was greatly reduced.

Recrystallization Behavior of IF Steel at the Interface of Aluminum Junction

Recrystallization Behavior of IF Steel at the Interface of Aluminum Junction

STUDY ON DEEP DRAWING BEHAVIOR OF THE INTERSTITIAL FREE STEEL IN CORRELATION WITH THE MICROSTRUCTURE

The objective of this paper was to present results obtained about the behaviour of the IF steel associated with high deformation. To evaluate the deep drawing aptitude, samples were subjected to tensile test, n and r values determination, hole expansion and Erichsen tests. The results were correlated with a microstructural study. Through thermodynamic simulation, the phase transformation temperature (Tg®a) and the precipitates formation were estimated. The Tg®a value was also determined by dilatometry test. The failure of the material during deep drawing or stamping process is evidenced through the formation of cracks in areas with critical angles changes. It was relevant to understand the mechanisms of fracture nucleation and propagation of the IF steel. A fractography study was carried out and was possible to verify the presence of cavitation mechanism as results of the superplastic flow at high deformation conditions, promoting necking and fracture after a high plastic deformation achieved.

The influence of silicon on the formation of phosphate coatings for low-carbon IF steels

It is essential to clarify the influence of silicon on the phosphating process for low-carbon IF steels. In the present work, the formation of phosphate coatings for the IF steels with 0.01 wt%, 0.1 wt% and 0.5 wt% silicon was experimental determined by the combination of electrochemical characterization with X-rays photoelectron spectroscopy (XPS), focused Ion beam and transmission electron microscope (FIB-TEM), X-ray diffraction (XRD) and scanning electron microscope (SEM) analysis. It was confirmed that the silicon layer formed on the IF steels surface was mainly composed by Si, SiO2, SiC, Si3+ and oxides of Fe. Thicker silicon layers were formed with the increase of silicon concentrations, which inhibited the electrochemical reaction on the steels surface during the phosphating process. The diffusion of the ions including Me2+, PO43− and H+ to the surface of the substrate was severely restricted by the thick silicon layer, leading to the deterioration of the phosphating performance. The influence mechanism of silicon was finally proposed for a deep understanding of the phosphating process for IF steels.

A comparative study on laser bending process with linear and curved irradiating schemes

A comparison is made between linear and curved irradiating schemes in laser bending process of ultra-thin IF sheet. In order to comprise the linear and curved irradiating schemes, Y-displacements and curvature uniformity of bent edge are examined. In addition, the effects of laser output power and laser scanning speed on the average value of Y-displacements (A-Y) of laser-bent edge of ultra-thin IF steel sheets are studied and compared. The results showed that the obtained Y-displacements of bent edge for linear irradiating scheme are noticeably more than the Y-displacements for curved irradiating scheme. Also, curvature uniformity of bent edge obtained by linear irradiating scheme is greater than the curved irradiating scheme. It is concluded that with increasing the laser power, obtained A-Y for both linear and curved irradiating schemes are increased. In addition, with increasing the laser scanning speed, evaluated A-Y for both linear and curved paths are decreased. It is proved that the A-Y of bent edge is increased for both linear and curved schemes with increasing the number of irradiation passes.

Improved In-Mold Metallurgical Behavior for Slab Casting of IF Steels by a Novel Multi-poles Electromagnetic Stirring

Improved In-Mold Metallurgical Behavior for Slab Casting of IF Steels by a Novel Multi-poles Electromagnetic Stirring

Evolution of Inclusions and Cleanliness in Ti-Bearing IF Steel Produced via the BOF–LF–RH–CC Process

Owing to the insufficient converter heat, IF steel is produced via the BOF–LF–RH–CC process in Pangang Group Xichang Steel and Vanadium Co., Ltd. To clarify the evolution of inclusions and the control strategy to improve the cleanliness of molten steel in Ti-bearing IF steel produced via the long process, scanning electron microscopy with energy spectroscopy analysis and automatic scanning electron microscopy were employed to analyze the number, size, type and morphology of inclusions in IF steel from RH to tundish. The results show that the characteristics of inclusions are similar in two heats during RH treatment. In the tundish sample of Heat 2, the number density (ND) and area fraction (AF) of Al2O3 and Al2O3·TiOx inclusions increase significantly, and the size of Al2O3 inclusions decreases obviously, which is closely related to the serious reoxidation of molten steel caused by the slag with high oxidability during the holding process. Meanwhile, a new method of determining the number of cluster inclusions is used to evaluate the cleanliness of IF steel in this paper, and the obtained number of inclusion clusters is consistent with the trend of ND and AF of inclusions. The effects of reoxidation on the morphology, number and other indexes of Al2O3 and Al2O3·TiOx inclusions are discussed in detail, and there are two ways of forming Al2O3·TiOx inclusions in the case of serious reoxidation. To weaken the reoxidation process and enhance the cleanliness of IF steel produced via the long process, reducing the oxygen content in molten steel before Al deoxidation, minimizing the holding time and reducing the oxidability of slag after RH are helpful.

Electromagnetic sensors for in-situ dynamic microstructure monitoring of recovery and recrystallisation in interstitial free steels

An in-situ high temperature EM sensor was used to detect changes in the microstructural state caused by recovery and recrystallisation for IF steel samples during heat treatment. The relative permeability values determined from the sensor measurements at the different heat treatment temperatures showed the expected strong influence of temperature on the magnetic measurement. The relative permeability values determined at each temperature increased during the recovery and recrystallisation processes and correlated well with the different microstructural states determined by EBSD. The results show that the EM sensor measurement approach shows significant potential for in-situ microstructure monitoring during the annealing process of IF steels, with larger magnetic parameter changes between microstructural states at the higher temperatures typical of commercial annealing practice. In addition it is seen that the magnetic, and EM sensor, measurements show more sensitivity to recovery than hardness measurements, and can also monitor recrystallisation.

Evaluating the performance of sputter-deposited Aluminium alloy-based coatings on steel in the light of grain orientation, surface roughness, and corrosion behaviour

ABSTRACT Magnetron sputtering has been one of the significant processes for developing defect-free uniform coatings for a wide range of materials. Increasing Magnesium (Mg) content in Aluminium (Al)–Mg sputtered coats has been strongly linked to a heightened sacrificial nature. This has directed researchers towards investigating different combinations or compositions of Al-based coats. Sputtered Al coats having minute proportions of Zinc (Zn) and Mg could be promising in terms of offering a corrosion-resistant coating on steel substrates. This has prompted a detailed analysis of three different coatings deposited on 4130 grade IF steel substrates using pure Al, Al–Mg and Al–Zn–Mg as targets by magnetron sputtering. For a fixed deposition time of 10 h, thickness of the coatings were in the order: Al–Zn–Mg > Al > Al–Mg. The coatings were investigated in terms of the microstructure, corrosion behaviour, surface roughness and coating adhesiveness. XRD was conducted to study the evolution of phases with increasing coating thickness. Al–Zn–Mg coating was found to be the most durable one, in terms of corrosion resistance, through EIS and SST and role of surface roughness was identified as a critical controlling factor, which was outweighed by the coating compositions. Although this ternary coating exhibited unsatisfactory performance during bend test, it has been hypothesized that tailoring texture coefficients could be a promising way to attain an optimum combination of oxidation resistance and adhesion.

Grain Boundary Segregation of Boron and Microstructure Evolution in IF Steel at Different Strain Rates

Grain Boundary Segregation of Boron and Microstructure Evolution in IF Steel at Different Strain Rates