DP600 Steel Research Articles

Effect of internal pressure and loading path on deformation behavior during low pressure tube hydro-pressing

To overcome the limitations of hydro-pressing process with either linear increasing pressure loading path or constant pressure loading path, a hydro-pressing process with two steps pressure loading path was proposed and an experiment was conducted on hydro-pressing process of DP590 steel tubular part with varied rectangular-section perimeters. The effects of internal pressure and loading path on cross-sectional shape and stress distribution were discussed. An analysis was conducted to give the critical punch stroke of the first step, and an optimal loading path was put forward. The pressure loading path was divided into two steps, the result indicates no buckling happens even no internal pressure adopted in the first step. The wall thickness distribution of the tubular part formed under two steps pressure loading path is more uniform than that with constant pressure loading path. Mechanical analysis proves that the flexural modulus of the tube wall in the earlier stage of deformation is high enough due to the short length of the straight side, which is no need for supporting pressure. Under a reasonable loading path, a rectangular-section tubular part with a compression ratio of 5 % was obtained with lower pressure 13.5 MPa. Its relative corner radius is only 1.5, which exceeds the limiting value of that formed by conventional tube hydroforming.

Experimental Investigation on Bending Properties of DP780 Dual-Phase Steel Strengthened by Hybrid Polymer Composite with Aramid and Carbon Fibers

Lowering passenger vehicle weight is a major contributor to improving fuel consumption and reducing greenhouse gas emissions. One fundamental method to achieving lighter cars is to replace heavy materials with lighter ones while still ensuring the required strength, durability, and ride comfort. Currently, there is increasing interest in hybrid structures obtained through adhesive bonding of high-performance fiber-reinforced polymers (FRPs) to high-strength steel sheets. The high weight reduction potential of steel/FRP hybrid structures is obtained by the thickness reduction of the steel sheet with the use of a lightweight FRP. The result is a lighter structure, but it is challenging to retain the stiffness and load-carrying capacity of an unreduced-thickness steel sheet. This work investigates the bending properties of a non-reinforced DP780 steel sheet that has a thickness of 1.45 mm (S1.45) and a hybrid structure (S1.15/ACFRP), and its mechanical properties are examined. The proposed hybrid structure is composed of a DP780 steel sheet with a thickness of 1.15 mm (S1.15) and a hybrid composite (ACFRP) made from two plies of woven hybrid fabric of aramid and carbon fibers and an epoxy resin matrix. The hybridization effect of S1.15 with ACFRP is investigated, and the results are compared with those available in the literature. S1.15/ACFRP is only 5.71% heavier than S1.15, but its bending properties, including bending stiffness, maximum bending load capacity, and absorbed energy, are higher by 29.7, 49.8, and 41.2%, respectively. The results show that debonding at the interface between S1.15 and ACFRP is the primary mode of fracture in S1.15/ACFRP. Importantly, S1.15 is permanently deformed because it reaches its peak plastic strain. It is found that the reinforcement layers of ACFRP remain undamaged during the entire loading process. In the case of S1.45, typical ductile behavior and a two-stage bending response are observed. S1.15/ACFRP and S1.45 are also compared in terms of their weight and bending properties. It is observed that S1.15/ACFRP is 16.47% lighter than S1.45. However, the bending stiffness, maximum bending load capacity, and absorbed energy of S1.15/ACFRP remain 34.4, 11.5, and 21.1% lower compared to S1.45, respectively. Therefore, several modifications to the hybrid structure are suggested to improve its mechanical properties. The results of this study provide valuable conclusions and useful data to continue further research on the application of S1.15/ACFRP in the design of lightweight and durable thin-walled structures.

Effect of Different Heat Treatment Processes on Microstructures and Mechanical Properties of DP Steels

Effect of Different Heat Treatment Processes on Microstructures and Mechanical Properties of DP Steels

Size and microstructural factors affecting the micro-hole expansion ratio and fracture toughness of dual phase steel sheets

The microscopic hole expansion ratio (μHER) of a ferritic-martensitic (∼10 %) dual phase steel was measured using a novel in-situ scanning electron microscope based miniature hole expansion setup. The effect of extrinsic parameters such as specimen thickness and machining conditions, and intrinsic parameters such as hardness differential (ΔH =Hα'-Hα) between the soft ferrite matrix and hard martensite islands on μHER values was studied. The miniature HER setup allowed site-specific measurement of microscopic strain localizations in the DP microstructure through high resolution digital image correlation under the triaxial state of stress. The results from these experiments were juxtaposed against another triaxial state of stress ahead of a crack tip, in a fracture toughness (JIc) test using the single edge notched tensile (SENT) geometry for the same thickness and microstructural conditions of DP steel. It was found that the tempered DP specimen with lower ΔH resulted in a ∼45 % higher μHER as compared to the as-received DP600, although both specimens exhibited similar JIc values. This apparent discrepancy between the trends in μHER and JIc values was explained in terms of the differences in failure modes, triaxiality and plastic zone evolution in the two conditions.

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

Annealing temperature-dependent microstructure, mechanical, and tribological properties of intercritically heat-treated dual-phase steel

Abstract This study investigates the role of intercritical annealing temperature on microstructural characteristics, mechanical performance, and wear resistance of DP1000 steel. As-received DP1000 steel samples in cold-rolled conditions were subjected to intercritical annealing between 730 and 880 °C with an interval of 30 °C, followed by water quenching. After heat treatment, the specimens were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), mechanical tests consisting of hardness, impact, and tensile tests, and dry sliding wear tests. The findings revealed that equiaxed ferrite grains replaced elongated ones, and the martensite ratio increased from 21% up to 64% with increasing annealing temperature. Due to the formation of equiaxed grains, the impact strength was at least doubled for each specimen by heat treatment, reaching a peak value (9.55 J cm−2) at 760 °C. The hardness (311 HB) and tensile strength (1007 MPa) of the as-received sample were higher than that of the annealed steels up to 820 °C. The mechanical strength of the samples improved at 850 and 880 °C by approximately 10%, and accordingly, the lowest wear rate was obtained at the specimen annealed at 850 °C. The increase in temperature up to 880 °C caused a decrease in wear resistance due to excessive brittleness.

Novel method to assess anisotropy in formability using DIC

In this study, a novel technique was developed to identify localized neck of a tensile sample based on the curvature of the surface that is expected to work with any metal in which a localized neck forms prior to fracture. Moreover, a MATLAB-based computational tool has been developed to conduct advanced mathematical computations and numerical analysis on data generated from uniaxial tensile test of DP980 steel coupled with Digital Image Correlation (DIC) based on the novel curvature method. The presented curvature technique is a geometry-based approach that uses the specimen's surface profile and groove geometry to detect localized necking, avoiding the limitations of strain-based methods in distinguishing between localized and diffuse necking. A detailed analysis was conducted on the accuracy of the onset and anisotropy of localized neck. The results of the study revealed that specimens fabricated with 30-degree orientation with respect to the Rolling Direction (RD) of the sheet metal, exhibit a higher level of total strain at the onset of the localized necking, indicating the influence of anisotropy on the material's behavior for DP980. Moreover, consistent R-values were observed among specimens with the same orientation with respect to the RD, exhibiting a rising trend of R-value for orientations from zero to 60-degree, followed by a decrease from 60 to 90-degree. Furthermore, the results exhibited a negative linear relationship between R-values and the magnitude of thinning strain.

Study on the fatigue properties of SPR-bonded aluminum-steel sheet joints

This study deals mainly with the influence of adhesive layer on the fatigue behavior and fretting of self-piercing riveted (SPR) joint joining differing thicknesses of AlSi10MnMg aluminum and DP590 steel sheets in lap shear geometry. Fatigue life, failure modes, crack propagation and fretting behaviors of the SPR and SPR-bonded joints were investigated and compared. The results showed that the static strength and fatigue life of SPR-bonded joints were significantly enhanced than that of SPR joints, but the fatigue failure mode of SPR-bonded and SPR joints differed. The SPR-bonded joints all failed in a rivet tail pull-out mode at all tested loads, which accompanied with small cracking in the aluminum sheet in contact with the rivet tail at lower test load. However, the failure mode of the SPR joints shifted from the aluminum sheet cracking to rivet tail pull-out as the fatigue test load increased. And during the aluminum sheet cracking failure, the fatigue crack originated from the faying interface of aluminum and steel sheet at the vicinity of the rivet shank and propagated along the width direction of aluminum sheet. Fretting wear analysis showed that the overall extent of fretting decreased and the location of fretting areas varied due to the adhesive bonding. Fretting of SPR joints mostly existed at the faying interface between aluminum and steel about 1.5mm away from the rivet shank and resulted in fatigue crack initiation, while the fretting region of SPR-bonded joints shifted to the faying interface between rivet tail and aluminum sheet.

A generalized, computationally versatile plasticity model framework - Part II: Theory and verification focusing on shear anisotropy

Shear-dominated deformation (SHDD) is pivotal in sheet metal forming; however, comprehensive modeling of plastic anisotropy in SHDD, specifically shear anisotropy considering both yield stress and plastic flow, has been inadequately addressed in existing literature. In this work, a generalized constitutive framework is introduced on the basis of stress triaxiality-dependent state variable to accurately emulate plastic anisotropy and the physics-based shear constraint in SHDD. The framework is capable to seamlessly integrate with existing yield criteria, preserving computational efficiency and versatility. Notably, the yield function, anisotropic parameters, and their optimization or analytical determination for the non-shear deformation state remain unaltered. When integrated with the Hill48 yield function, featuring either one or two anisotropic parameters within the generalized constitutive framework, precise characterization of yield strength and plastic flow in SHDD is achieved. The applicability of the framework extends to various anisotropic yield functions such as the widely employed Yld2k-2d and the sixth-order polynomial (Poly6) function as a class of associated flow rule-based yield functions, and one non-quadratic yield function for non-associated flow rule scenarios. Experimental validation with two engineering sheet metals, high-strength dual-phase steel DP980 and high-strength aluminum alloy AA7075-T6, was conducted. Comparative analyses with several recently proposed yield criteria, especially Poly6-18p, highlighted the efficiency of the proposed constitutive framework. Furthermore, this study explores intrinsic shear constraints, particularly the absence of through-thickness strains under in-plane shear stress. Additionally, it offers an enhanced description of plastic anisotropy in shear yield stress within the general framework, providing valuable insights into the complexities of SHDD.

Correlation between individual phase constitutive properties and plastic heterogeneities in advanced-high strength dual-phase steels

The present study comprehensively investigates the individual phase constitutive properties and plastic heterogeneities in advanced high-strength steels (AHSS), particularly DP590 and DP780 dual-phase (DP) steels. A machine learning-based model is implemented to identify the ferrite and martensite phases in the microstructures of DP590 and DP780. Then, the constitutive properties of ferrite and martensite phases are successfully obtained through a hybrid approach of in-situ neutron diffraction coupled with the crystal plasticity finite element method (CPFEM). The distinct microstructures between DP590 and DP780 result in different macroscopic and microscopic properties among the two materials. Owing to different martensite volume fractions (Vm) in DP590 (Vm = 8.3 %) and DP780 (Vm = 35.4 %), a noticeable dependency of plastic heterogeneities during deformation on martensite fraction and its spatial distribution is revealed. Compared to DP590, the deformed microstructure of DP780 exhibits a more heterogeneous distribution of stress and strain fields, along with significant formation of plastic strain localization leading to a remarkable increase in strain partitioning index. It shows that a lower fraction of martensite with its discrete distribution decreases martensite ability to hinder the ferrite deformation, thus strain localization is primarily concentrated within the ferrite phase as the predominant failure mode in DP590. In contrast, a higher martensite fraction in DP780 causes more pronounced strain localization which occurs in the ferrite and at the ferrite/martensite interface. In addition, interconnect distribution between martensite islands enhances the inhibition of martensite to ferrite deformation, thereby high strain gradient at their interface leads to prevalence of ferrite/martensite interface decohesion in DP780.

Microscale modeling of damage mechanisms in dual‐phase steel DP800

Microscale modeling of damage mechanisms in dual‐phase steel DP800

Role of Si element in the IMC formation and tensile-shear property of the laser welding-brazing steel-Al dissimilar joints

A comparative investigation was conducted to explore the role of Si in the intermetallic compound (IMC) formation and tensile-shear property of steel-Al joints fabricated via laser welding-brazing (LWB) technique. Three filler wires including ER5356, ER4043 and ER4047 were employed to join the DP780 steel and 5754 Al alloy. The results exhibited that the presence of Si could improve the tensile-shear property of steel-Al joints. With increasing the Si addition, the failure locations of the joints changed from the interface, weld metal to Al alloy base metal. For the joints fabricated with ER5356 filler, the IMCs consisted of Fe2Al5 and Fe4Al13. On the contrary, Fe4(Al, Si)13 and Al8Fe2Si was detected for the joints prepared with ER4043 and ER4047 filler wires. The Si could suppress the generation of brittle Fe2Al5. In addition, Fe4(Al, Si)13 and Al8Fe2Si could resist the crack propagation, guaranteeing the qualified tensile-shear strength of the joints.

The calibration of the MMC damage model under various hardening models and yielding criterions for DP800 steel

The calibration of the MMC damage model under various hardening models and yielding criterions for DP800 steel

Research of microstructure and properties of resistance spot welded joints of galvanized DP steel for automobile

Research of microstructure and properties of resistance spot welded joints of galvanized DP steel for automobile

Optimizing sheet metal edge quality with laser-polishing: surface characterization and performance evaluation

Dual-phase (DP) steels are widely used in the automotive industry due to their exceptional performance. It offers excellent strength, ductility, formability, and weldability. However, there is a high risk of edge cracking, particularly in materials like DP1000 steel, caused by residual damage from blanking, such as microcracks and burrs, which needs further investigation. In this study, the transformative potential of laser-polishing on DP1000 steel was investigated. The goal was to reduce edge crack sensitivity and enhance edge formability. In this work, laser-polished samples produced by various pre-manufacturing techniques such as sawing, punching, and waterjet cutting were examined. Various evaluations were performed on laser-polished samples. Those included white-light-confocal microscopy, scanning electron microscopy, and Electron Backscatter Diffraction (EBSD) analysis. Those evaluations aimed to analyze the microstructural transformation, surface roughness, and micro grain size distribution resulting from laser-polishing. Laser-polishing is a process in which the edge of the sample is remelted locally. Hence, residual damage vanishes, and surface defects disappear, which should be beneficial for edge formability. On the other hand, the cooling rate during re-solidification is high, leading to high strength and reduced ductility compared to the initial DP steel. Therefore, hole expansion tests were conducted to evaluate the edge formability of the steel. The results indicated a significant improvement in the hole expansion ratio of the laser-polished samples compared to samples with conventional manufactured edges. These findings will help to assess the advantages and limitations of laser-polishing in sheet material manufacturing.

Characterization of Microstructure–Mechanical Properties Relationship in Dissimilar Resistance Spot Welding of the Advanced High-Strength Steel DP590 Steel to the Interstitial-Free Steel DC 06: EBSD Study

Characterization of Microstructure–Mechanical Properties Relationship in Dissimilar Resistance Spot Welding of the Advanced High-Strength Steel DP590 Steel to the Interstitial-Free Steel DC 06: EBSD Study

Analysis of the Microstructure and Mechanical Performance of Resistance Spot-Welding of Ti6Al4V to DP600 Steel Using Copper/Gold Cold-Sprayed Interlayers.

In this article, an attempt was made to join DP600 steel and Ti6Al4V titanium alloy sheets by resistance spot-welding (RSW) using an interlayer in the form of Cu and Au layers fabricated through the cold-spraying process. The welded joints obtained by RSW without an interlayer were also considered. The influence of Cu and Au as an interlayer on the resulting microstructure as well as mechanical properties (shear force and microhardness) of the joints were determined. A typical type of failure of Ti6Al4V/DP600 joints produced without the use of an interlayer is brittle fracture. The microstructure of the resulting joint consisted mainly of the intermetallic phases FeTi and Fe2Ti. The microstructure of the Ti6Al4V/Au/DP600 joint contained the intermetallic phases Ti3Au, TiAu, and TiAu4. The intermetallic phases TiCu and FeCu were found in the microstructure of the Ti6Al4V/Cu/DP600 joint. The maximum tensile/shear stress was 109.46 MPa, which is more than three times higher than for a welded joint fabricated without the use of Cu or Au interlayers. It has been observed that some alloying elements, such as Fe, can lower the martensitic transformation temperature, and some, such as Au, can increase the martensitic transformation temperature.

Damage parameters identification of dual-phase 800 steel based on microvoids analysis and response surface methodology

Accurately identifying the unknown parameters of the Gurson-Tvergaard-Needleman (GTN) damage model is essential to better understand the damage behavior of materials and improve the simulation accuracy. In order to solve the problem that traditional parameter identification methods are cumbersome and inefficient, this paper proposed an efficient damage parameter identification strategy with the combination of microscopic analysis, finite element simulation, and response surface analysis. The relationship between the evolution of microvoids and plastic strain in DP800 steel was quantified through the in-depth analysis of the microstructure of tensile specimens. Response surface method and Box-Behnken experimental design were adopted to efficiently identify and optimize the crucial damage parameters (fN, fC, fF) with the difference ratio of fracture strain as the response variable. Through analysis of variance, the factors that have significant influence on the damage parameters were further confirmed. Through the experimental comparison with the simulation results based on the GTN damage model, the effectiveness of the identified damage parameters was verified, and the influence of these parameters on the stress-strain curve was deeply revealed. The results show that the damage parameter identification strategy has achieved remarkable results in accuracy and efficiency, and has important engineering significance for the accurate prediction of the actual dual-phase steel sheet forming process.

Manufacturing of new dual phase steel with a combination of macro-laminated and micro-laminated morphology

ABSTRACT In this study, a new dual phase steel with a combination of macro-laminated and micro-laminated morphology was fabricated for the first time. Friction stir welding, heat treatment, and cold rolling were employed to produce the new laminated DP steel. The microstructure of produced DP steels consisted of elongated ferrite and martensite phases in the St52 layers. The microhardness profiles and stress–strain curves of produced laminated DP steels showed that the best mechanical properties corresponded to the traverse speed of 70 mm/min due to less hardness gradient. The failure morphology indicated good interfacial bonding that prevented delamination during the tensile deformation.

Damage mechanisms analyses in DP steels using SEM images, FEM, and nonlocal peridynamics methods

An investigation is performed to study the damage mechanisms of dual phase steels using experimental analysis, local finite element simulation, and nonlocal peridynamics (PDs) method. The uniaxial tensile tests and preparation of metallography and SEM images have been used to peruse the pattern of deformation and voids in different phases. Understanding of the relationship between real microstructure and damage mechanisms can often not be obtained from microstructural investigation using experiments only. Here, a novel numerical approach is presented to investigate damage mechanisms in multiphase materials at micro scale level using both local and nonlocal numerical analyses and microstructural images from a scanning electron microscope (SEM). The nonlocal PDs method is capable to overcome many challenges associated with convergence problems in other numerical methods and to detail-oriented study of damage initiation and propagation autonomously. In this study, images of real microstructure are used as RVEs and imported to the FEM software and PD-developed code. Moreover, the effects of different constitutive models for the interface of ferrite and martensite phases on the bond breakage and damage patterns have been also investigated.