Behavior Of Dual-phase Steels Research Articles

Unraveling the effect of Al2O3-MnS complex inclusion on the pitting corrosion behavior of dual phase steel

Pitting corrosion behavior of dual phase steel triggered by Al2O3-MnS complex inclusion in NaCl solution was investigated. Results indicated that neither micro-defects nor strain fields existed around the insulating Al2O3-MnS inclusion, but an open circular pit was immediately initiated around the inclusion and grew in diameter approaching 200 μm in several minutes. The preferential dissolution of unstable MnS part created local acidic electrolytes promoting the dissolution of Al2O3 part and adjacent matrix. The radial diffusion and hydrolysis of Al3+ acidified the pit solution, resulting in the propagation of circular pit. Finally, the pitting propagation decelerated with the depletion of inclusion.

Effect of Friction Stir Process on Hole Expansion Behavior of Dual Phase Steel

Effect of Friction Stir Process on Hole Expansion Behavior of Dual Phase Steel

Use of miniaturized tensile specimens to evaluate the ductility and formability of dual phased steels for Rapid Alloy Prototyping

This work aims to investigate feasibility of using non-standard miniaturized tensile specimens (MTS) to characterize total elongation and formability behaviour of dual phase steels: to establish the scaling rules for MTS to predict a range of mechanical properties of steels obtained through rapid alloy prototyping (RAP) in the laboratory. Accurate measurement of these properties using miniature specimens allows the formability behaviour of materials produced using RAP, a process which can produce lab scale samples of < 100 grams. This allows the effects of multiple compositions and thermomechanical processing parameters on formability to be evaluated. For this study, the ability of miniature tensile specimens to characterize ductility, forming limits and r-values has been compared to properties measured using standard sized tensile specimens for the dual phase steels, DP600 and DP800. 5 different tensile specimens were investigated, with gauge lengths varying from 80 mm to 5 mm and samples were taken at different orientations to the rolling direction. Total elongation was evaluated against slimness ratio for each tensile sample using the Bertelle–Oliver method and good correlations were obtained, despite specimen thicknesses being below the critical value, and the tensile strength of DP800 exceeding the limit stated for the method. Forming limit curves (FLC) were predicted using the Keeler–Brazier method, based on tensile data obtained using the standard and non-standard tensile specimens These curves compared favourably to experimentally obtained FLCs, however the curve predicted using the miniaturized tensile specimen over-predicted the major strain. The anisotropy of the rolled sheet steels was characterized from r-values obtained from tensile tests performed at different orientations to the rolling direction. Values obtained from the miniature tensile test were comparable to those obtained from standard tests within the range of scatter. The results obtained through this study provide confidence in using the miniature tensile specimens to predict the formability of heterogeneous alloys such as DP steels, manufactured using the RAP process.

Mechanical Behaviour of Dual Phase Steels under Different Strain Rates

Mechanical Behaviour of Dual Phase Steels under Different Strain Rates

Finite Element Modeling of Indentation Behavior of Dual Phase Steels: Role of Plastic Zone Size in Property Mapping

Finite Element Modeling of Indentation Behavior of Dual Phase Steels: Role of Plastic Zone Size in Property Mapping

Effect of microstructural constituents and morphological characteristics on low cycle fatigue behaviour of inter-critically annealed 20MnMoNi55 steel

The effect of varying microstructural parameters on the cyclic behaviour of dual-phase steels was studied on the basis of experimental and micromechanical finite-element simulated results. The initial bainitic morphology of as-received 20MnMoNi55 steel was transformed into ferrite and martensite through proper inter-critical heat treatment procedures. Strain-controlled low cycle fatigue tests were conducted at room temperature with different strain amplitudes at a specific strain rate of 10−3/s. The cyclic stress–strain curve, obtained through joining the peak stresses of hysteresis loops corresponding to different strain amplitude, shows an increase in strain hardening with an increase in volume fraction of martensite. Whereas the rate of cyclic softening, considering the decrease in stress amplitude with respect to elapsed cycles, increases with increasing strain amplitude. Inclusive of all affecting microstructural parameters, an original microstructure-based representative volume element associated with a crystal plasticity-based material model was adopted for conducting micromechanical finite-element simulation. In addition to several parameters associated with a crystal plasticity model, consideration of initial geometrically necessary dislocation density in constituent phases resulted in the accurate prediction of a hysteresis loop at low strain amplitude as compared with the experimental results. A variation of stress triaxiality built up in ferrite matrix with martensite fraction along with deformation inhomogeneity between ferrite and martensite was also observed through a strain partitioning phenomenon obtained from finite-element simulated results.

Micromechanical Simulation Approach of Dual Phase Steel Artificial Microstructure Using Random Field Model

In this study, a random field (RF) model with a Gaussian kernel was applied to generate an artificial microstructure of dual phase (DP) steels. Micrographs obtained from Scanning Electron Microscopy (SEM) were analyzed using image processing software to extract the grain size and the volume fraction of each phase. Based on watershed (Ws) segmentation and quantitative analysis, the real and artificial microstructures were compared by analyzing grain features related the solidity, grain size and aspect ratio (the proportional relationship between its width and its height). Consequently, this approach allows to simulate the overall stress-strain behavior of the analyzed microstructures. As a result, it was shown that the strain localization starts to develop at the ferrite/martensite interface and that the RF model could replicate the micromechanical behavior of DP steels.

Modeling and optimization of operating parameters using RSM for mechanical behaviour of dual phase steels

In this study, the influence of operating parameters on the mechanical properties of Dual Phase (DP) steels was investigated, using response surface methodology (RSM) to develop a prediction model. In developing the model, temperature and holding time were considered as the model variables. To establish this fact, an experiment based on statistical four-level two factorial design method was carried out. Based on the statistical analysis, surface hardness (SH) shows a correlation coefficient of R2 = 0.9607 while Ultimate Tensile strength (UTS) gave R2 = 0.9297, this suggests that the proposed quadratic model is suitable for use. The optimum operating parameters were predicted using the user-defined design (UDD) under RSM and the result was confirmed through experiments, which predict at a temperature (T) of 800 °C and holding time (HT) of 60 min, hardness value was given as 157.798 HV and UTS as 553.648 Mpa. This result indicates that RSM is a suitable method to optimize the process variables for mechanical properties of DP steels.

Strain-Hardening Behavior of Dual-Phase Steel under Multistress States

The complexity and nonuniformity of microdeformation in high-strength dual-phase (DP) steels make it difficult to accurately predict the deformation processes in stamping. Here, in situ experiments under three kinds of stress states and a crystal plasticity finite element (CPFE) model were used to predict the strain-hardening behavior of DP steel. The microdeformation in various deformation stages was extracted from metallographs captured during in situ experiments to calculate the strain partitioning functions of each phase. Then, the multistress state mechanical behavior of DP steel was calculated based on the CPFE model combined with the strain partitioning functions of ferrite and martensite. The calculation results showed that (1) the CPFE model could accurately describe the load–stroke curves of the three experiments and that (2) the stress state had a significant effect on the strain partition ratio and the initial critical resolved shear stress of the material. In addition, the stress–strain curves of DP800 steel were predicted under six stress states; these curves did not coincide and had obvious deviations. Finally, the activity of the grain slip systems and the dislocation evolution were analyzed and discussed to predict the microdeformation and stress state effects on strain-hardening behavior.

Finite element and experimental method for analyzing the effects of martensite morphologies on the formability of DP steels

In this article, we investigated the effect of martensite morphology on the mechanical properties and formability of dual phase steels. At first, three heat treatment cycles were subjected to a low-carbon steel to produce ferrite–martensite microstructure with martensite morphology of blocky-shaped, continuous, and fibrous. Tensile tests were then carried out so as to study mechanical properties, particularly the strength and strain hardening behavior of dual phase steels. In order to study the formability of dual phase samples, Forming Limit Diagram was obtained experimentally and numerically. Experimental forming limit diagram was obtained using Nakazima forming test, while Finite Element Method was utilized to numerically predict the forming limit diagram. The results indicated that the dual phase samples with fibrous martensite morphology had the highest tensile properties and strain rate hardening out of the three different microstructures. Blocky-shaped martensite morphology, on the other hand, had the worst mechanical properties. The study of the strain hardening behavior of dual phase sample by Kocks–Mecking-type plots, evinced two stages of strain hardening for all specimens with different microstructures: stages III and IV. The forming limit diagram of dual phase steels also proved that samples with fibrous martensite morphology had the best formability compared to other two microstructures. The simulated forming limit diagram manifested that there is a good agreement between experimental results and those obtained by FEM.

Effect of martensite volume fraction on cyclic plastic deformation behavior of dual phase steel: micromechanics simulation study

The cyclic plastic deformation of an archetypal microstructure dual phase steels has been examined via micromechanics modelling based on representative volume elements technique. The dual phase steel has soft ferrite – matrix with hard martensite – islands, which are distributed in a discrete manner. In the field of automobile industries, the suitable combination of strain hardening, strength and ductility, and their lean combination represent them as an economically desire option for huge multiple lightweight options. In this numerical approach, different microstructures for micromechanical modelling were constructed to detailed examination and analysis for the tensile and cyclic deformation response of dual phase steels. Due to the distinct difference in the stress–strain responses of ferrite and martensite phases, incompatibility of strain between matrix-softer ferrite and island-harder martensite phase arises during tensile straining. The effect of strain partitioning in cyclic plastic deformation response of dual phase steel has been studied in the present investigation. Apart from this, effect of martensite volume fraction on cyclic stress–strain response of dual phase steels, cyclic plastic deformation distribution in individual phases and cyclic deformation inhomogeneity at microstructural level have been systematically investigated.

Influence of microstructure and strain rate on the strain partitioning behaviour of dual phase steels

Two dual phase steels with varying martensite content (∼ 10 and 33%) have been deformed in tensile mode at various strain rates (0.001–800/s). The microstructural parameters after deformation have been studied in detail using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The minute details of deformation features within the ferrite matrix have been investigated using EBSD based misorientation analysis. The influence of metallurgical parameters like ferrite grain size and its spatial distribution, the size and fraction of martensite on the deformation at different strain rates have also been investigated along with evolution of crystallographic texture. It has been found that strain rate influences the gradient in deformation in the ferrite grains between the interface and the grain interiors. Increase in martensite although enhances the dislocation density in the ferrite grains, but it also restricts the rotational ability of ferrite, which led to restricted sub-structural recovery at high strain rates. By observing the misorientation development ahead of the interphase boundaries, the failure mechanisms of these dual phase steels have been explained.

Corrosion Inhibition Behavior of Dual Phase Steel in 3.5 wt % NaCl Solution by Carica Papaya Peel Extracts

Abstract Corrosion behavior of dual phase steel was studied in 3.5 wt % NaCl solution and carica papaya peel extracts. Different concentrations of carica papaya peel extract were added to the salt solution to perceive the inhibition effect on corrosion of dual phase steel. Concentration of peel extract was varied from 50 -100 %. It is observed that with the increase in concentration of peel extract, the corrosion rate is decreasing. The rate of corrosion in salt solution is found to be more as compared to the corrosion rate obtained from 100 % peel extract solution. Therefore, carica papaya peel extract is a good corrosion inhibitor for dual phase steel. The inhibition efficiency increases from 66.31 to 98.67 %. Shift of Ecorr value in positive direction indicates that peel extract is an anodic type inhibitor. Impendence study was carried out to acquire knowledge about the solution resistance and charge transfer resistance offered by the film.

The Effects of Friction Coefficient on Formability Behaviour of Dual Phase Steel

The effects of friction coefficient on formability behavior of advanced high-strength steel sheets have been examined in this study. For this purpose, forming analysis has been conducted by stretching the three different steel sheets such as DP600, DP800 and DP1000. Forming processes have been done by using punch that has different friction coefficients (0.05, 0.15, 0.3, 0.6 µ) in nakajima forming die. As a result of the analysis, it has been observed that thinning amount and forming force have increased by the increasing in the friction coefficient. When major and minor deformations on the sheet have been examined, it has been determined that the increasing friction coefficient makes plastic deformation amount increase.

Micromechanical Modeling and Investigating the Effect of Particle Size and the Interface of Phases on the Mechanical Behavior of Dual-Phase Steels

Dual-phase (DP) ferrite–martensite steels have a fine microstructure that consist of martensite islands, dispersed in a ferrite matrix. In the present work, a micromechanical-based finite element (FE) analysis is carried out in order to investigate the mechanical properties of this type of steels, such as yield stress and tensile strength. The step forward contribution of the present study is to insert the effect of the presence of the interface of the constituting phases in the FE model. In order to do so, a micromechanical FE model is developed in which the effect of the interface of the constituting phases is taken into account by means of cohesive elements. The required parameters of the cohesive elements are determined by a trial and error procedure which compares the numerical results to the experimental ones. Experimental data is used to verify the created FE model. This model is then used to investigate the effect of martensite volume fraction and small-to-large particle size ratio of martensite on the deformation behavior of the DP steel. This study shows that considering the interface of the constituting phases greatly affects the numerical results on stress and strain distributions and produces more realistic findings in agreement with experiments. The results show that applying cohesive elements between two phases have reduced tensile strength, yield stress, and the amount of uniform elongation.

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.

New insights into martensite strength and the damage behaviour of dual phase steels

A detailed investigation of martensite islands in ultra-high strength dual phase (DP) steels using TEM EELS carbon measurements, nano-indentation studies and micro-mechanical modelling has been carried out. EELS analysis showed that the dispersion in the martensite island-to-island carbon content increases at lower intercritical annealing temperatures due to the influence of undissolved cementite. In a coarse-grained DP alloy, the median martensite island nano-hardness values and those calculated from EELS carbon data were in excellent agreement. However, in a fine-grained (microalloyed) DP alloy significant and unexplained softening occurred that is not consistent with the measured martensite carbon content. In both steels, the dispersion in martensite nano-hardness was greater than that expected from the measured carbon variations. Micro-mechanical modelling using the continuous composite approach (CCA) method was employed to calculate the martensite flow stress distribution required to fit the bulk tensile response of the two materials. The median martensite nano-hardness values derived from the fitted CCA stress spectra were in good agreement with those measured by nano-indentation, corroborating the observed martensite softening. These results provide experimental support for the CCA approach and suggest that the physical origins of the martensite stress spectrum can be strongly influenced by mechanisms other than carbon segregation. Finally, these data explain why the beneficial effect of reducing the α'/α phase strength ratio (PSR) on DP damage properties is highly asymmetrical, depending on whether the ferrite is strengthened or the martensite is softened (by tempering).

Effect of Martensite Volume Fraction on Strain Partitioning Behavior of Dual Phase Steel

Monotonic deformation behavior of ferrite-martensite dual phase steels with martensite volume of 13-43% have been analyzed in the current investigation using micromechanics based finite element simulation on representative volume elements. The effects of martensite volume fraction on the strain partitioning behavior between soft ferrite matrix and hard martensite islands in dual phase steels during tensile deformation have been investigated. As a consequence of strain incompatibility between hard martensite and soft ferrite phases, inhomogeneous deformation and finally deformation localization occur during tensile deformation. Restricted local deformation in ferrite phase caused by the adjacent martensite islands triggers the local stress triaxiality development. As the martensite volume fraction increases, the local deformation restrictions in ferrite phase also increases and which results in higher stress triaxiality development. Similarly the strain partitioning behavior between ferrite matrix and martensite island is also influenced by the volume fraction of martensite. The strain partitioning coefficient increases with increasing martensite volume fraction.

Dissolution Behavior of Dual Phase Steel during Pickling

Dual phase steels have been widely used in the automotive industry to produce lighter weight vehicles to meet stringent safety and fuel economy regulations. While the phenomenon of steel dissolution in acidic solution has been reported on carbon steel and stainless steel, little is known about the dissolution behavior of dual phase steel. Moreover, the resulting surface morphology after pickling could compromise the adhesion performance of Zn coating at the electrogalvanizing line (EGL). A fundamental study was undertaken to understand the dissolution behavior of dual phase steel in acid. The results show that the dissolution kinetics are strongly influenced by pickling conditions and steel microstructure. The study suggests a different dissolution mechanism for dual phase steel in hydrochloric acid (HCl) and sulfuric acid (H2SO4). Non-uniform dissolution in HCl was observed for dual phase steel in which the ferrite phase dissolved faster than the martensite phase. The preferential dissolution of the ferrite phase in dual phase steel could be attributed to the higher dissolution rate of the ferrite phase than the martensite phase due to its lower activation energy for dissolution, and the galvanic couplings formed between the ferrite phases and adjacent martensite phases.

Dissolution Behaviors of Dual Phase Steel during Pickling

Dual phase steels have been widely used in the automotive industry to produce lighter weight vehicles to meet stringent safety and fuel economy regulations. While the phenomena of steel dissolution in the acidic solution have been reported on carbon steel and stainless steel, little is known about the dissolution behavior of dual phase steel, which could compromise the coating adhesion performance in the subsequent electrogalvanzing line (EGL) or continuous galvanizing line (CGL). A fundamental study was undertaken to understand variables that could affect dissolution of dual phase steel in the acidic solution. The results show that the dissolution kinetics is strongly influenced by temperature, acid concentration and the steel microstructure. Different dissolution mechanism is observed in HCl and H2SO4. Dual phase steel displays a non-uniform dissolution behavior of which the ferrite phase dissolves faster than martensite phase. This selective dissolution phenomenon could be attributed to galvanic corrosion between ferrite and adjacent martensite phase and a higher resistance of martensite phase to dissolution than ferrite phase.