Properties Of Dual Phase Steel Research Articles

Effects of spatial microstructure characteristics on mechanical properties of dual phase steel by inverse analysis and machine learning approach

This work aims to investigate complex relationship between microstructure characteristics and mechanical properties of dual phase (DP) steel through an inverse analysis based on Markov chain Monte Carlo (MCMC) method combined with meso-scale material modelling. In this framework, a machine learning approach as surrogate model was developed, in which support vector regression (SVR) and artificial neural network (ANN) were trained using results from representative volume element (RVE) simulations coupled with damage model, which were previously calibrated with experimental data of commercial DP steel grades. Moreover, specific microstructure descriptors including Moran’s index, martensite band index and martensite orientation were proposed for representing effects of spatial distributions of martensitic phase. As a result, inverse predictions of microstructure characteristics of DP steels for achieving defined yield strength, tensile strength, uniform elongation and toughness were presented. The inverse analysis could solve the non-uniqueness of structure–property relationships of steel, whereby significances of dispersed structures and aligned martensite bands were highlighted in details. The approach fairly dealt with multi-target optimization and high dimensional problem, which can be further applied as a guideline for designing DP microstructures with enhanced mechanical properties.

Effect of Intercritical Annealing on the Properties of Dual Phase Steel via Finite Element Method

Dual phase (DP) steels are rapidly becoming more and more popular for automotive applications. They offer a weight reduction with a combination of energy absorption for crash zones. Rails, reinforcements, back panels, cross members, and pillars can be given as application examples. DP steels microstructure consists of a soft ferrite matrix with hard martensite islands. The hard martensite islands provide strength while the ductile ferrite provides formability. The strength level of DP steel is related to the amount of martensite in the microstructure, and the martensite amount can be arranged via intercritical annealing. In this work, thermodynamic analysis of St52 steel was carried out with Thermo-Calc software. A1 and A3 temperatures were determined by calculating the temperature-dependent phase fractions. Intercritical annealing temperatures were determined according to the calculated critical temperatures (A1 and A3). The intercritical annealing process was modelled by using Simheat NxT software. In this modelling and simulation work, the effect of intercritical annealing temperature on the final microstructure and hardness of DP steel was investigated.

Comparison of welding temperature fields, residual stress distributions and deformations of Gas Tungsten Arc (GTA) and ultrasonic–wave–assisted gas tungsten pulsed arc (U–GTPA) welded DP780 steel joints

Considering the excellent anti-corrosion property in chlorinated mediums and comprehensive mechanical properties of dual phase steel, this kind of steel plate will be widely used in the future. However, when ordinary welding methods are used to weld these steel sheets, large deformation usually occurs during local heating due to the lower stiffness of sheet joints. Based on a thermo-elastic-plastic Finite Element Analysis (FEA) method, considering both material non-linearity and geometric non-linearity, the temperature field and deformation of DP780 steel thin-plate welded joints using Gas Tungsten Arc (GTA) welding and Ultrasonic-wave-assisted Gas Tungsten Pulsed Arc (U-GTPA) welding is simulated. Through the combination of experiment and numerical simulation, the difference in the simulation process for the weld deformation of sheet joints caused by GTA welding with and without acoustic-controlled arc is clarified. In particular, the effects of acoustic-controlled arc and external confining positions on the weld deformation, and residual stress distribution of duplex phase steel joints welded by two welding methods are compared. The research results indicate that the welding heat source of U-GTPA has a smaller acting range on the workpiece and a higher peak temperature (up about 200 °C) than that of GTA. Replacing the traditional GTA with U-GTPA can reduce weld deformation, the maximum buckling deformation of welded sheet is only 4.2 mm and the rate of deformation is reduced by 60%. The numerical simulation confirmed that the high longitudinal tensile stress ranges in U-GTPA-welded joints are narrower than that in GTA-welded joints, but the maximum longitudinal residual stress generated by U-GTPA welding is greater than that generated by GTA welding. Furthermore, the stress distribution in the fusion zone and its surroundings, as well as the out-of-plane deformation of the steel sheet can be further controlled by optimizing the confining positions. The selection of the appropriate restraint positions is also an important factor to the optimization of the U-GTPA welding process.

Development of Desirable Fine Ferrite Grain Size and Random Second Phase Dual-Phase Steel Microstructures Using Composition and/or Processing Modifications

Microstructural morphology is known to have a significant impact on the mechanical properties of dual-phase steels. A fine ferrite grain size and random distribution of small second phase islands are desirable to provide superior isotropic properties compared to the banded second phase distribution that is typical for this type of steel. A rapid alloy prototyping (RAP) facility has been used to investigate three different DP 800 variants by systematically varying the compositions and/or process parameters compared to the ‘standard’ DP800 composition and processing that gives a banded microstructure. For Variant 1, the heating rate during the annealing cycle after cold rolling varied between 0.65 and 30 °C/s for the 45%, 60% and 75% cold reduction samples. It was found that a cold reduction of 75% and heating rate of 15 °C/s resulted in the microstructure that can give the best combination of strength and ductility because of the fine grain size and high martensite volume fraction. For Variant 2, the effect of changing the hot rolled (HR) microstructure (ferrite–pearlite, ferrite–bainite or martensite) on the final microstructure was investigated. Both the ferrite–50% bainite and fully martensite/bainite HR materials for all cold reductions resulted in annealed microstructures with necklace martensite morphology and finer ferrite grains compared to the ferrite–pearlite HR material, which gave a typical banded ferrite–martensite microstructure with a coarser ferrite grain size. For Variant 3, the Mn content was reduced, and increased Nb was used to achieve higher pancaking during the hot rolling stage, which refined ferrite grains in the HR condition with the same hardness. After annealing with the standard parameters only the 45% cold-reduced material produced a finer ferrite grain size than the standard material, whereas the 60% and 75% cold-reduced samples required a higher heating rate to achieve finer ferrite grain sizes due to rapid recrystallisation and growth kinetics.

The effect of cold-rolling prior to the inter-critical heat treatment on microstructure and mechanical properties of 4340 steel with ferrite – Martensite microstructure

This study investigates the effect of cold rolling prior to inter-critical annealing on microstructure and mechanical properties of ferrite-martensite dual phase steel. Samples were heated to 850 °C for 1 h followed by oil quenching, then the steel sheet were cold rolled by 0%,10%,15% and 20% reduction in thickness. The inter-critical annealing treatment (750 °C, 120min) was performed to generate a ferrite-martensite microstructure. Microstructural studies showed that increasing the applied cold rolling, leading to increase in volume fraction of martensite and decrease in ferrite grain size. Mechanical properties of dual phase steel were measured by tensile, impact and hardness tests. Results showed that ultimate tensile strength, yield strength, micro-hardness and toughness (e.g. total elongation, uniform elongation and impact energy) increased with increasing the applied cold rolling. Improvement of mechanical properties were related to increase in martensite volume fraction and ferrite grain refinement. Analysis of strain hardening behavior of DP steels, by Hollomon analysis, showed two stages of strain hardening corresponding to ferrite deformation and co-deformation of ferrite and martensite, respectively. The strain hardening exponent of first stage (nI) increased with increasing volume fraction of martensite. The energy absorption capacity (UE × UTS) increased with increasing cold rolling deformation.

Numerical simulation of dual-phase steel based on real and virtual three-dimensional microstructures

Dual-phase steel shows a strong connection between its microstructure and its mechanical properties. This structure–property correlation is caused by the composition of the microstructure of a soft ferritic matrix with embedded hard martensite areas, leading to a simultaneous increase in strength and ductility. As a result, dual-phase steels are widely used especially for strength-relevant and energy-absorbing sheet metal structures. However, their use as heavy plate steel is also desirable. Therefore, a better understanding of the structure–property correlation is of great interest. Microstructure-based simulation is essential for a realistic simulation of the mechanical properties of dual-phase steel. This paper describes the entire process route of such a simulation, from the extraction of the microstructure by 3D tomography and the determination of the properties of the individual phases by nanoindentation, to the implementation of a simulation model and its validation by experiments. In addition to simulations based on real microstructures, simulations based on virtual microstructures are also of great importance. Thus, a model for the generation of virtual microstructures is presented, allowing for the same statistical properties as real microstructures. With the help of these structures and the aforementioned simulation model, it is then possible to predict the mechanical properties of a dual-phase steel, whose three-dimensional (3D) microstructure is not yet known with high accuracy. This will enable future investigations of new dual-phase steel microstructures within a virtual laboratory even before their production.

Enhanced mechanical properties of dual phase steel via cross rolling and intercritical annealing

Cross rolling followed by intercritical annealing was proposed as an alternative route for processing of dual phase (DP) steels, which led to fine recrystallized ferrite grain size and uniformly distributed martensite islands. Accordingly, the processed low-carbon steel showed better strength-ductility trade off, higher hardness, and greater work-hardening exponent.

Effect of MAG welding on microstructure and mechanical properties of dual phase steel

Effect of MAG welding on microstructure and mechanical properties of dual phase steel

Microstructural and Mechanical Characterization of Shielded Metal Arc Welded Dual Phase Steel Joints

Dual Phase steels are widely used in industry for various reasons for their improved mechanical properties owing to their ferrite and martensite contents in microstructure and good formability at industrial scale to achieve final shape with good ductility. In this study, shielded metal arc welding experiments were performed in order to evaluate the metallurgically and mechanically the properties of Dual Phase steels obtained from plain carbon steel AISI 1010 by water quenching at intercritical temperatures. Martensite volume fraction (MVF) was related to the intercritical quenching temperature which defines the mechanical properties of Dual Phase steel. All the welding parameters were kept constant in order to get a value of heat input equals 1.37 KJ/mm for all weldments. Martensite was found to be predominated in the fusion zone and its hardness was the highest compared to base metal (BM) and heat affected zone (HAZ). The extent of ductile zone was found to be dependent on the MVF and reached over 1.2 mm wide. Tensile properties of weldments were deteriorated by 35% in ultimate tensile strength (UTS) and by 15% in elongation. The failure of all the welded joints was occurred in the SC zone, with the fractured surfaces of a dimple feature.

Improved properties of dual-phase steel via pre-intercritical annealing treatment and thermal cycling

The synergistic effects of pre-intercritical annealing treatments and multiple heating to the two-phase region (followed by quenching) on the microstructure and mechanical properties of dual-phase (DP) steel were studied. Intercritical annealing of ferritic-pearlitic, martensitic, and cold-rolled martensitic microstructures was investigated. The effects of tempering, austenitisation, grain growth, and recrystallisation were unravelled and an optimum holding time was characterised for each initial microstructure. Grain refinement by recrystallisation of cold-rolled martensitic microstructure resulted in the enhancement of tensile properties. Thermal cycling through multi-step intercritical annealing resulted in grain refinement and enhanced mechanical response. It was revealed that thermal cycling combined with the carefully controlled pre-intercritical microstructure could be simply used for the improvement of mechanical properties of DP steel.

Evaluation of mechanical properties of ferrite-martensite DP steels produced through intermediate quenching technique

The objective of the present work is to investigate the mechanical properties of the dual phase (DP) steels produced by the intermediate quenching (IQ) technique. To produce the ferrite-martensite microstructure in the dual phase (DP) steel, low carbon micro alloyed steel is intercritically heat treated followed by short intercritical annealing and intermediate quenching using various intercritical temperatures. By varying the intercritical temperature (740, 760, 780, 800, 820 °C) different volume fraction of the ferrite and martensite phases of DP steel samples are produced. These series of dual phase (DP) steel samples were further analyzed through scanning electron and optical microscopy. The experimental investigations have been carried out to find the mechanical properties as per the ASTM testing standards. From the outcomes it is observed that DP780 steel have excellent tensile strength, better hardness and toughness which may be due to the fine distribution and equal volume fraction of ferrite and martensite phases. The enhancement in the mechanical properties of dual phase steel was the effect of intermediate quenching technique. Equal volume fraction of ferrite and martensite phases obtained, at temperature of 780 °C, converted low carbon micro alloyed steel into dual phase steel and also improves its mechanical properties.

A review of recent progress in mechanical and corrosion properties of dual phase steels

New concepts proposed for processing of dual phase (DP) steels as one of the main classes of advanced high-strength steels (AHSSs) to enhance their mechanical properties (strength–ductility combination) and corrosion resistance were introduced. The current review covers (I) the processing routes to obtain the ferritic–martensitic microstructures, (II) parameters of intercritical annealing (IA) treatment, (III) primary thermomechanical treatments, and (IV) post processing. First, the principal heat treatment methods, i.e., step quenching, intermediate quenching, and intercritical annealing of ferritic–pearlitic steel, as well as the partitioning of manganese were critically discussed. Then, the effects of holding time at the intercritical annealing temperature on the austenitization, grain coarsening kinetics, abnormal grain growth, and volume fraction of martensite were summarized. Next, the importance of cold deformation (notably rolling) and heating rate for the development of fine-grained DP microstructures (with chain-networked martensitic islands) through recrystallization and modification of the preferred nucleation sites for the austenite phase was discussed. Moreover, the applications of severe plastic deformation techniques (such as constrained groove pressing), thermal cycling (multi-step or repetitive intercritical annealing), and spheroidization heat treatment were discussed. Finally, the impacts of tempering, quench aging, and bake hardening on the properties of DP steel were reviewed. This short overview shows the opportunities that the conventional and innovative processing routes can offer for the potential industrial applications of DP steels, especially in the lightweight car body for the automotive industry to address the safety, fuel consumption, and air pollution issues.

Effect of post-weld heat treatment on microstructure and mechanical properties of DP800 and DP1200 high-strength steel butt-welded joints using diode laser beam welding

Among the available high-strength steels, there is growing demand for dual phase (DP) steels for wide application in the automotive industry owing to their good combination of high strength, ductility and formability. Also, the use of innovative welding technologies like laser beam welding (LBW) has growing importance in the field of high-strength steel because of its excellence in providing high-quality welds, high welding speed, high power density, low heat input, a narrow heat-affected zone and low heat distortions as compared to the conventional gas metal arc welding process. However, the hardening and softening in the heat-affected zone is a major issue when welding high-strength steel, i.e. DP steel grades, greatly affecting the strength, formability and plasticity of the whole-welded joint and thus affecting service performance and reliability. Based on preliminary experiments, the optimal welding condition was a nominal laser power of 1.0 kW and a welding speed of 8 mm/s. The aim of this work is to analyse and compare the weld and heat-affected zone characteristics, microstructure and mechanical properties of DP steels with 1-mm thick butt joints of DP800 and DP1200 high-strength steel (HSS) by diode laser beam welding. The effects of post-weld heat treatment (PWHT) on the strengthening of the laser-welded joints were evaluated by microstructural examinations under optical microscope and scanning electron microscope, and mechanical properties were examined by microhardness test, three-point bending tests and tensile tests.

Effects of tempering on the mechanical and corrosion properties of dual phase steel

The mechanical and corrosion behaviors of low carbon dual phase (DP) steel were studied based on different tempering conditions. By increasing the time and temperature of tempering, the ultimate tensile strength (UTS), the hardness, and the corrosion current density (icorr) in the polarization curves decrease while the total elongation and the diameter of the semicircular arc in the Nyquist plots increase. Tempering treatment resulted in the appearance of the yield point phenomenon and an initial rise in the yield stress (YS). While the UTS values were related to hardness through a single relationship for both tempered and DP steels, two separate trends were observed for the relation of the YS and hardness. The latter was related to the high work-hardening rate of DP steels that increased the hardness during indentation. The tempering kinetics were also studied and the average value of the Avrami exponent (n) was determined as 0.65, which was interpreted as precipitation on dislocations (theoretical n-value of 0.667). The tempering activation energy was determined as ∼ 40 kJ/mol, which was indicative of the rapid diffusion of carbon atoms along the dislocation core (pipe diffusion), and hence, it was concluded that the kinetics of tempering is essentially controlled by carbon atom diffusion.

Processing Route Effects on the Mechanical and Corrosion Properties of Dual Phase Steel

The mechanical and corrosion behaviors of low carbon DP steel were studied based on different processing routes: (1) intercritical annealing (IA), (2) step quenching (SQ) via austenitization and quick transferring of the sample to the second furnace, and (3) Slow SQ via furnace cooling to the desired temperature. The properties were found to be highly dependent on the volume fraction of martensite (VM) and the density of ferrite/martensite interfaces. However, at the same martensite content, the mechanical properties of Slow SQ sheet were inferior than those of SQ and IA sheets, which were related to the relatively poor work-hardening behavior due to the severe partitioning of Mn between ferrite and martensite phases. The latter was also responsible for an increase in the corrosion current density (icorr) via galvanic corrosion. These results were analyzed based on the polarization curves and Nyquist plots obtained from the electrochemical impedance spectroscopy test. This study revealed that the SQ route can result in both better mechanical performance and higher corrosion resistance.

Fine tuning the mechanical properties of dual phase steel via thermomechanical processing of cold rolling and intercritical annealing

Abstract The simultaneous effects of cold rolling reduction and intercritical annealing time on the microstructure and tensile properties of St12 steel were studied. It was revealed that by increasing the rolling reduction, the ferrite grain size of the dual phase (DP) microstructure is refined and a chain-like morphology of martensite develops, which results in improvement of work-hardening capacity and the tensile properties. Such a microstructure can be obtained via applying an optimum holding time at the intercritical annealing temperature. Beyond that optimum, grain coarsening occurs with the resulting deterioration of tensile properties. It was also shown that by consideration of quenched sheet or by applying low reductions in thickness, secondary recrystallization or abnormal grain growth (AGG) takes place during intercritical annealing, which is characterized by small grains and some large ferrite grains containing martensite islands. This study clarified that applying high reduction in thickness for grain refinement and also controlling the holding time in the two-phase austenite-ferrite region are the essential prerequisites to achieve the desired tensile strength, ductility, and toughness.

Synergistic effects of holding time at intercritical annealing temperature and initial microstructure on the mechanical properties of dual phase steel

The synergistic effects of the initial microstructure and the intercritical annealing time on the microstructure and tensile properties of low carbon steel were studied. It was found that by refining the pre-intercritical annealing microstructure, the resulting duplex DP microstructure becomes finer, which results in the enhancement of the tensile properties and work-hardening behavior. Based on the hardness measurements, three stages were identified for intercritical annealing: initial rise or fall, reaching a plateau, and final fall to a low value. The pre-intercritical annealing microstructure did not show any pronounced effects on these stages, with the exception of the short-lived initial stage. It was shown that the DP steel obtained right after reaching the abovementioned plateau can exhibit improved mechanical properties and work-hardening behavior. During the third stage, the enrichment of manganese in austenite and the concurrent grain growth were found to be the main factors taking part in the change of hardness and tensile strength and reappearance of the yield-point elongation. The impact of the microstructural features (austenite and ferrite) on the grain growth behavior during intercritical annealing and the effect of the grain size on the Lüders strain were also discussed.

Effect of multi-pass friction stir processing on the microstructure and mechanical properties of dual phase steel

Effect of multi-pass friction stir processing on the microstructure and mechanical properties of dual phase steel

Влияние многопроходной обработки трением с перемешиванием на микроструктуру и механические свойства двухфазной стали

Влияние многопроходной обработки трением с перемешиванием на микроструктуру и механические свойства двухфазной стали

Enhancement of work‐hardening behavior of dual phase steel by heat treatment

AbstractThe work‐hardening response and mechanical properties of dual phase steels originated from different initial microstructures under low and high martensite volume fractions were investigated using a typical carbon‐manganese steel. The modified Crussard‐Jaoul analysis was used for studying the work‐hardening stages and the deformation behavior of ferrite and martensite. It was revealed that the initial martensitic microstructure before intercritical annealing is much better than the full annealed banded ferritic‐pearlitic and spheroidized microstructures in terms of work‐hardening capacity and strength‐ductility trade off. By increasing the amount of martensite, via intercritical annealing at higher temperatures, the ductility decreased but the tensile toughness of dual phase steels increased toward reaching the domain of extra‐advanced high‐strength steels due to the enhancement of work‐hardening rate.