Steels For Automotive Applications Research Articles

An Enhanced Approach for High-Strain Plasticity in Flat Anisotropic Specimens with Progressively Distorting Neck Sections

An Enhanced Approach for High-Strain Plasticity in Flat Anisotropic Specimens with Progressively Distorting Neck Sections

Effect of austenite stability on the fracture micromechanisms and ductile-to-brittle transition in a medium-Mn, ultra-fine-grained steel for automotive applications

This work reports on the tensile and Charpy impact behaviour of a high-strength, ultra-fine-grained, medium-manganese steel with a ferrite + austenite microstructure. The mechanical stability of austenite was varied by varying the test temperature, while keeping all other microstructural features constant. By lowering the tensile test temperature, austenite decomposition into martensite occurred earlier, inducing strong work hardening, decreasing tensile elongation and triggering ferrite–martensite interfacial decohesion. Under impact testing, the material exhibited a broad transition in absorbed energy and in thickness reduction at fracture initiation. A continuous transition in fracture mechanism, from fully ductile to fully interfacial fracture, occurred with lowering the test temperature. Besides chemically induced weakening of ferrite–austenite interfaces, the temperature-dependent mechanical stability of retained austenite, as well as the strength of the ferrite phase, is thought to control local stresses at interfaces between ferrite and freshly formed martensite. It thus drives the extent of interfacial microcrack initiation and propagation before blunting and development into voids.

Development of 3rd generation Medium Mn duplex steels for automotive applications

ABSTRACTThe mechanical behaviour and fracture were studied in a Fe–5Mn–2.5Al–0.2C (in wt-%) Medium Mn steel. Metallographic and magnetic measurements confirm the significant influence of the transformation kinetics of the strain-induced martensite on the mechanical properties and strain heterogeneities (Lüders and Portevin-Le Chatelier-like phenomena). An accurate study of isothermal evolutions of the microstructure, associated with atomistic calculations, complements current thermodynamic databases to quantify the nature and volume fraction of phases at different temperatures. A kinetic approach then predicts the influence of annealing conditions on the composition of retained austenite, key parameter for the martensitic transformation kinetics. This supports quantitative modelling of the influence of the intercritical annealing temperature on the ultimate tensile strength for industrial developments of these new grades.

Weldability and Monitoring of Resistance Spot Welding of Q&P and TRIP Steels

This work aims at investigating the spot weldability of a new advanced Quenching and Partitioning (Q&P) steel and a Transformation Induced Plasticity (TRIP) steel for automotive applications by evaluating the effects of the main welding parameters on the mechanical performance of their dissimilar spot welds. The welding current, the electrode tip voltage and the electrical resistance of sheet stack were monitored in order to detect any metal expulsion and to evaluate its severity, as well as to clarify its effect on spot strength. The joint strength was assessed by means of shear and cross tension tests. The corresponding fracture modes were determined through optical microscopy. The welding current is the main process parameter that affects the weld strength, followed by the clamping force and welding time. Metal expulsion can occur through a single large expulsion or multiple expulsions, whose effects on the shear and cross tension strength have been assessed. Longer welding times can limit the negative effect of an expulsion if it occurs in the first part of the joining process. The spot welds exhibit different fracture modes according to their strengths. Overall, a proper weldability window for the selected process parameters has been determined to obtain sound joints.

Experimental investigation of the mechanical response of laser-welded dissimilar blanks from advanced- and ultra-high-strength steels

We report experimental results on the mechanical response of dissimilar tailor-welded blanks (TWB) from an advanced- and an ultra-high-strength steel for automotive applications. These are the dual-phase steels DP 780 and DP 1180, respectively. First, we present the tensile and anisotropic properties of the two base-materials. During testing, the full-fields of strain and temperature are acquired, using the Digital Image Correlation (DIC) and Infrared Thermography (IR) techniques. The latter is critical, since both materials are prone to deformation-induced heating, which establishes a temperature gradient along the test-section, and which in turn limits the ductility observed. We then describe the laser-welding apparatus, and microstructural observations and measurements around the weld-seam. Subsequently, we test tensile coupons from the TWBs, with the weld-seam oriented transversely, 45° and parallel to the longitudinal direction of the loading. We detail the failure modes and the macroscopic load–displacement responses. Furthermore, with the aid of the DIC and IR images, we probe the local strain and temperature fields and their evolution, and correlate these to the overall response and failure of the TWB tensile coupons.

Cold metal transfer spot plug welding of AA6061-T6-to-galvanized steel for automotive applications

In this study, cold metal transfer (CMT) spot plug joining of 1 mm thick Al AA6061-T6 to 1 mm thick galvanized steel (i.e., Q235) was studied. Welding variables were optimized for a plug weld in the center of a 25 mm overlap region with aluminum 4043 wire and 100% argon shielding gas. Microstructures and elemental distributions were characterized by scanning electron microscopy with energy dispersive X-ray spectrometer. Mechanical testing of CMT spot plug welded joints was conducted. It was found that it is feasible to join Al AA6061T6-to-galvanized steel by CMT spot plug welding method. The process variables for two joints with Al AA6061T6-to-galvanized mild steel and galvanized mild steel-to-Al AA6061T6 are optimized. The strength of CMT spot welded Al AA6061T6-to-galvanized mild steel is determined primarily by the strength and area of the brazed interface. While, the strength of the galvanized mild steel-to-Al AA6061T6 joint is mainly dependent upon the area of the weld metal.

Controlled Forging of a Nb Containing Microalloyed Steel for Automotive Applications

Controlled forging of microalloyed steels is a viable economical process for the manufacture of automotive parts. Ferrite grain refinement and precipitation hardening are the major microstructural parameters to enhance the mechanical properties of the forged components. In the current study, a modified thermomechanical treatment for additional ferrite grain refinement is developed by exploiting the effect of Nb in increasing the T NR (no recrystallization temperature) and via phase transformation from a pancaked austenite. This is accomplished by performing the final passes of forging below the T NR temperature followed by a controlled cooling stage to produce a mixture of fine grained ferrite, small scaled acicular ferrite as well as a limited amount of martensite. The effect of processing parameters in terms of forging strain, cooling rate and aging condition on the microstructure and mechanical properties of a medium carbon, Nb containing microalloyed steel is investigated. An attempt is made to identify a suitable microstructure that provides a proper combination of high strength and good impact toughness. The processing-microstructure relationships for the proposed novel forging procedure are discussed, and directions for further improvements are outlined.

Characterization of Partial Interfacial Fracture on Resistance Spot-Welded TRIP Steels for Automotive Applications

Characterization of Partial Interfacial Fracture on Resistance Spot-Welded TRIP Steels for Automotive Applications

Strain rate behaviour of multi-phase and complex-phase steels for automotive applications

A combined study on the mechanical behaviour of multi-phase 800 high yield strength steel (MP800HY) and complex-phase 800 steel (CP800) is carried out under tensile loads in the strain rate range from 0.001s −1 to 750s −1 . Quasi-static (0.001s −1 ) tests are performed on electromechanical machine, whereas, medium (5s −1 and 25s −1 ) and high strain rate (250s −1 , 500s −1 and 750s −1 ) experiments are conducted on hydro-pneumatic machine (HPM) and modified Hopkinson bar (MHB) setup respectively. The thermal softening behaviors of the materials are investigated at quasi-static condition and the materials’ m -parameters of the existing Johnson-Cook model are imposed in authors’ previous work. Thereafter, the predicted flow stress by Johnson-Cook model has been compared with the experimental results.

Corrosion resistance of a new high strength interstitial free steel

Potentiostatic polarisation studies have been carried out on a new high strength copper containing interstitial free steel for automotive applications under various industrially important processing conditions in 0·1M H2SO4 solution at room temperature. It is revealed that corrosion rate in the new steel is lower than that in the conventional mild and high strength interstitial free steels.

Stress Corrosion Cracking of Novel Steel for Automotive Applications

In the present study, susceptibility of a high manganese TWIP steel to stress corrosion cracking (SCC) in a 3.5% NaCl solution was investigated using slow strain rate tests (SSRT), constant load (CL) tests and fractography. Strain rates employed for SSRT were in the range of 10-06 - 10-08 s-1. The specimens tested in air revealed a ductile type of failure, whereas those tested in the corrosive solution exhibited a brittle feature that is attributed to stress corrosion cracking. SCC was observed at a relatively low strain rate of 10-07s-1.

Development of Cold-Rolled High-Strength Formable Steel for Automotive Applications

Higher fuel consumption and increased CO2 emission due to increasing number of automobiles are the global concern. Weight reduction of automobile is one of the ways to overcome this problem, and hence the automakers need a stronger and formable material for advanced vehicle applications. Interstitial free high strength (IFHS) steel has been developed with the addition of solid solution strengthening element, P and Mn, but it generally exhibits low -value ≤1.6. The present article deals with an effort in developing a new cold-rolled batch annealed high strength steel with improved drawability (). Reduction in P and B in Nb +Ti steel resulted in an improvement in -value to 1.8, but the strength becomes lower. A commercial trial with an optimum amount of P, Ti, Nb, and B in ultra low carbon steel resulted in excellent combination of strength (YS > 220 MPa, UTS > 350 MPa) and formability ( and n = 0.22). In addition, this steel showed lower planar anisotropy (Δr = 0.14) as compared to conventional steels.

Crevice Corrosion and Cracking Behavior of Cold Rolled Type 304 Stainless Steel in Chloride Environment

AbstractThe salt damage such as the snow melting salts in winter or the sea salt particle flying in the coast region has significant effect on the corrosive environment of the automobile. Moreover, the corrosive environment of the automobile become more severe by the wet/dry cyclic condition, for example, a car gets wet with the splash water and dryness by the thermal loading while driving. On the other hand, the further application of the high strength stainless steel to the automobile parts is expected because it can contribute durability and lightening. Then, it is important to clarify the corrosion characteristic of this material under the salt damage environment. In this study cold rolled type304 stainless steel pipe with shot peening were used to investigate the corrosion property of high strength type304 stainless steel for automotive applications in a salt damage environment. The hardness of the pipe was about HV450, and a clear difference was not admitted in the thickness direction. A crevice was created between the outside of the pipe and an O-ring, and the pipe was applied stress by press fitting of another part. The corrosion property of the sample was evaluated in an automotive field test in Okinawa. Cracking from a corrosion pit was observed in the crevice. The Electron Prove Micro Analysis（EPMA） indicated that pitting corrosion was caused by chloride (from sea salt) concentrated in the crevice. The crack occurred in the residual compressive stress layer created by shot peening. In this regard, it was confirmed by the XRD analysis that about 85% of the metallographic structure had been transformed into the martensite. And the observation of the metallographic structure by the Electron Back Scatter Diffraction（EBSD） clarified the crystal grain was greatly transformed by the strong processing. It means that the accumulation of strain occurred. These two factors are considered to raise the receptivity to the crack generation of this sample. A crack generated at a corrosion pit was reproduced in a wet/dry cyclic corrosion test after one flash of artificial seawater. To investigate the crack generating mechanism, a corrosion pit was previously generated on the sample by cyclic corrosion test, after which a cathodic charge test in artificial sea water was done. Similar cracking from a corrosion pit was observed on the sample after this test. Therefore, the cracking is presumed to be Hydrogen Embrittlement-Stress Corrosion Cracking（HE-SCC）

Bonding evolution with sintering temperature in low alloyed steels with chromium

At present, high performance PM steels for automotive applications follow a processing route that comprises die compaction of water-atomized powder, followed by sintering and secondary treatments, and finishing operations. This study examines Cr-alloyed sintered steels with two level of alloying. In chromium-alloyed steels, the surface oxide on the powder is of critical importance for developing the bonding between the particles during sintering. Reduction of this oxide depends mainly on three factors: temperature, dew point of the atmosphere, and carbothermic reduction provided by the added graphite. The transformation of the initial surface oxide evolves sequence as temperature increases during sintering, depending on the oxide composition. Carbothermic reduction is supposed to be the controlling mechanism, even when sintering in hydrogen-containing atmospheres. The effect of carbothermic reduction can be monitored by investigating the behavior of the specimens under tensile testing, and studying the resultant fracture surfaces.

Aging response and strength formability parameters of hot rolled copper alloyed interstitial free steel

Laboratory investigations have been carried out on a copper alloyed interstitial free steel to develop a high strength steel for automotive applications in hot rolled conditions. The aging characteristics for a wide range of temperature and time have been documented and discussed in terms of diffusivity and solubility of copper in α iron. Coiling temperature, in general, influences the strength formability parameters of the hot rolled steel owing to its effect on copper precipitation. A high strength hot rolled steel for automotives with high strain hardening rate can be developed by adopting low temperature coiling at 550°C, without using any additional step in the normal processing schedule of interstitial free steels. Deep drawability or the Lankford parameter appears not to be influenced much by the coiling temperature.

Steels for Automotive Applications

Steels for Automotive Applications

Crashworthiness characterization and modelling of high-strength steels for automotive applications

In recent years significant advances have been made in the field of multiphase steels for automotive applications. Complex steel grades have been developed with exceptional mechanical properties: they combine high strength values with an excellent ductility. Transformation-induced plasticity (TRIP) steels show these properties pre-eminently. The high ductility makes TRIP steels well suited for use in energy-absorbing devices. To guarantee a controlled dissipation of the energy released during a crash, knowledge and understanding of the impact-dynamic material properties are essential. An extensive experimental programme to investigate the strain rate dependent mechanical properties was set up, and the results for two CMnAl TRIP steels and a CMnSi TRIP steel are presented in this paper. A split Hopkinson tensile bar set-up was used for the experiments. Microstructural observation techniques were used to reveal the mechanisms governing the observed high strain rate behaviour. From the results it is clear that the excellent mechanical properties not only are preserved at higher strain rates but even improve. Several phenomenological material models were investigated to describe the strain rate and temperature dependent behaviour of TRIP steels. Both the Johnson—Cook model and an extended version of the Ludwig model were found to give good agreement with the experimental data.

Gears and Springs in Niobium Microalloyed Steels for Automotive Applications

The tensile strength levels required for spring and gear applications are far higher than those commonly associated with other uses of microalloyed steels. In addition, springs and gears are manufactured using highly specific processes. This is why we present first of all a brief overview of the context and objectives of these developments, in order to assess their scope. The work presented here confirms that the effects of Niobium are not simply those usually associated with the precipitation of Nb(CN) carbonitrides: inhibition of recrystallisation, control of austenitic grain coarsening and precipitation hardening . Account must also be taken of the interactions between the Nb and other elements, as well as the slowing down of g => a + carbides transformation observed in certain cases. The number of mechanisms (or interactions) identified clearly shows why there is still a broad range of choices for optimising steel products and processes according to the target application, the production characteristics and the desired value for money ratios.

Parameters Influencing the Bake Hardenability of Microalloyed ULC Steels

Ti-V and Ti-Nb bake hardenable Ultra Low Carbon (ULC) steels are used to produce hot dip zinc coated steels for automotive applications. An important factor influencing the bake hardenability in such microalloyed ULC steels is the level of solute carbon available to diffuse for pinning dislocations during baking. The level of solute carbon must be controlled carefully during annealing of the steel in the ferritic region. Therefore, this paper summarizes highlights of research conducted to study the effects of chemical composition and annealing temperature (in the ferrite region) on the precipitation (or dissolution) of NbC and VC using a variety of Ti-Nb and Ti-V ULC steels. Carbon diffusivity is another factor that could also influence the bake hardenability through controlling the aging and baking kinetics. Therefore, the paper presents highlights of internal friction measurements performed to assess effects of microalloying elements (Nb,V) and some commonly used solid solution strengthening elements (Mn, P) on carbon diffusivity measured using the internal friction technique.

IISI Continues Collaborative Research on New Steels for Automotive Applications

steel research internationalVolume 76, Issue 6 p. 471-472 News IISI Continues Collaborative Research on New Steels for Automotive Applications First published: 13 December 2016 https://doi.org/10.1002/srin.200506041AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URLThe site is currently under maintenance and this functionality is not available right now. Please try later. Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume76, Issue6June 2005Pages 471-472 RelatedInformation