Two-phase Steel Research Articles

Computational Model for Predicting Precipitation Evolution in Two-Phase Steel: First Application to Grain-Oriented Electrical Steel

Computational Model for Predicting Precipitation Evolution in Two-Phase Steel: First Application to Grain-Oriented Electrical Steel

Study of Electroless Nickel Plating on Super Duplex Stainless Steel for Lithium-Ion Battery Cases: Electrochemical Behaviour and Effects of Plating Time

With increasing demand for Li-ion batteries, studies are focusing on enhancing battery performance and safety. However, studies on battery cases remain scarce. Herein, we propose the use of super duplex stainless steel SAF2507, which is a two-phase (austenite + ferrite) steel, for battery casings. Unlike conventional AISI304, SAF2507 maintains its corrosion resistance and strength at high temperatures and precipitates a secondary phase at approximately 975 °C. However, the effects of Ni plating on this secondary phase are not well documented. Therefore, the electroless Ni plating of SAF2507 after secondary-phase precipitation was studied. Briefly, heat treatment at 1000 °C was used to induce precipitation, and the electroless Ni plating behaviour over varying plating periods was analysed using open-circuit potential, potentiodynamic polarisation, and electrochemical impedance spectroscopy measurements. The plating state and corrosion behaviour were examined using scanning electron microscopy. Heat-treated SAF2507 steel with a secondary phase exhibited excellent electroless Ni plating behaviour, which enhances the safety and durability of Li-ion batteries. Furthermore, uniform plating and electrochemical behaviour were achieved after 180 s, suggesting that SAF2507 is superior to AISI304. These findings contribute to the development of safer and more efficient batteries and address the growing demand for Li-ion battery case materials.

Analysis of the springback effect of laser welded DP600 high-strength steel thin sheets

Steel sheets are produced with increasingly smaller thicknesses, without compromising the properties of the steel, maintaining ductility, strength, and energy absorption after impact can total depth enhance vehicle energy efficiency, lower manufacturing costs, and address the springback effect. The springback effect of laser-welded DP600 two-phase steel sheets was studied in this research. Parameters such as punching speed, initial bending angle, and time were varied. Tests including tensile tests, Vickers hardness, and optical microscopy analysis were conducted to correlate results with material properties. Autogenous laser welding joined DP600 steel plates at the bending position. Controlling springback ensures better quality in vehicle manufacturing and assembly. The results revealed that increasing the punch descent speed from 4 to 12 mm/min, for an internal angle of 90°, on the first day of observation, led to higher springback values (0.58°–3.3°, respectively), while increasing the initial curvature angle (30°–90°), maintaining a constant speed of 4 mm/min on the first day of observation, and impacting the elastic return (6.74°–0.58°, respectively). Furthermore, the observation time demonstrated a continuous increase in the springback variation during 6 days after the flexural test before stabilization (6.89°– 8.7°), maintaining a constant value of 8 mm/min and the internal angle of doubles of 30°.

INVESTIGATION OF THE DEGREE DEFORMATION INFLUENCE DURING TENSILE TESTS ON THE TEXTURE, PHASE COMPOSITION AND RESIDUAL STRESSES IN THE α- AND ɣ-PHASES OF STEEL VNS9-SH

X-ray diffraction methods were used to study the influence of the degree of deformation during tensile testing on the phase composition, texture and stress state of the α- and ɣ-phases of the VNS9-SH alloy. It is shown that during testing to failure, the amount of the α-phase increases on the surface from 75 to 91% and from 45-50 to ~70% in the subsurface layers. To assess the susceptibility of two-phase steels to the trip effect, a parameter of austenite metastability is proposed in the form of the relative fraction of decomposed austenite at individual stages of tensile deformation. It has been established that in the initial steel strip 0.3 mm thick, as a result of the positive volumetric effect of the transformation ɣ = α, compressive stresses are formed in austenite, reaching a value of –1000 MPa on the surface, in contrast to tensile stresses in martensite. Their presence is associated with heating of the metal, the cooling of which leads to tensile stresses in martensite due to its significantly lower temperature coefficient of linear expansion value compared to austenite.

Tribological characteristics, phase composition and microhardness of subsurface regions of WC – (Fe – Mn – C) composites after high-speed sliding on steel

The authors investigated tribological characteristics, phase composition of friction surfaces and microhardness of near-surface regions of WC – (Fe – Mn – C) composites with a two-phase (γ + α′) matrix containing 4 % wt. Mn (WC – 80G4), and a single-phase matrix of γ-iron containing 20 % wt. Mn (WC – 80G20) after friction on a disk of high-speed steel at a contact pressure of 5 MPa and sliding speeds in the range from 10 to 37 m/s. The wear intensity of WC – 80G4 and WC – 80G20 increased with increasing sliding speed, while the wear rate of WC – 80G20 at fixed sliding speeds was approximately three times higher than that of WC – 80G4. The values of the friction coefficient decrease with increasing sliding speed in such a way that at fixed sliding speeds the values of the friction coefficient of WC – 80G4 were lower than those of WC – 80G20. The amount of complex oxide FeWO4 formed during tribo-oxidation of the composites’ worn surface increased with the sliding speed and was directly proportional to the wear intensity and inversely proportional to the friction coefficient values. At fixed sliding speeds, tribooxidation of WC – 80G4 leads to the formation of a larger amount of FeWO4 on the friction surface, compared to the WC – 80G20 composite. Indentation of worn surfaces with a Vickers pyramid showed that the nature of indentation resistance of tribolayers formed at high sliding speeds (30 m/s and 37 m/s) differs from that for tribolayers obtained at relatively low sliding speeds (10 and 20 m/s), namely, the friction surfaces after high sliding speeds were characterized by a more tough behavior. Measurement of microhardness values of the WC – 80G4 and WC – 80G20 composites obtained after indentation from the friction surface into the depth of the material recorded the fact of hardening of the near-surface regions of the WC – 80G4 composites and, on the contrary, softening in the case of WC – 80G20. Thus, under conditions of strong heating and severe plastic deformation of the surface, structural-phase state of the substrate of WC – (Fe – Mn – C) composites, on which this viscous protective tribolayer is formed, turns out to be a very important factor. It is the two-phase (γ + α′) steel matrix that, under conditions of strong frictional heating, provides the conditions for effective formation of a heterophase composite layer that reduces the friction coefficient and has a high resistance to fracture upon indentation.

Tribological Characteristics, Phase Composition and Microhardness of Subsurface Regions of WC–(Fe–Mn–C) Composites after High-Speed Sliding on Steel

The authors investigated tribological characteristics, phase composition of worn surfaces and microhardness of subsurface regions of WC–(Fe–Mn–C) composites with a two-phase (γ + α′) matrix containing 4 wt % Mn (WC–80G4), and a single-phase matrix of γ-iron containing 20 wt % Mn (WC–80G20) after sliding against a disk of high-speed steel at a contact pressure of 5 MPa and sliding speeds in the range from 10 to 37 m/s. The wear intensity of WC–80G4 and WC–80G20 increased with increasing sliding speed, while the wear rate of WC–80G20 at fixed sliding speeds was approximately three times higher than that of WC–80G4. The values of the friction coefficient decrease with increasing sliding speed in such a way that at fixed sliding speeds the values of the friction coefficient of WC–80G4 were lower than those of WC–80G20. The amount of mixed oxide FeWO4 formed during tribo-oxidation of the composites’ worn surface increased with the sliding speed and was directly proportional to the wear intensity and inversely proportional to the friction coefficient values. At fixed sliding speeds tribooxidation of WC–80G4 leads to the formation of a larger amount of FeWO4 on the friction surface compared to the WC–80G20 composite. Indentation of worn surfaces with a Vickers pyramid showed that the nature of indentation resistance of tribolayers formed at high sliding speeds (30 m/s and 37 m/s) differs from that for tribolayers obtained at relatively low sliding speeds (10 and 20 m/s), namely, the friction surfaces after high sliding speeds were characterized by a more tough behavior. Measurement of microhardness values of the WC–80G4 and WC–80G20 composites obtained after indentation below tha worn surfaces recorded the fact of hardening of the near-surface regions of the WC–80G4 composites and, on the contrary, softening in the case of WC–80G20. Thus, under conditions of intensive heating and severe plastic deformation of the surface, structural-phase state of the substrate of WC–(Fe–Mn–C) composites, on which this viscous protective tribolayer is formed, turns out to be a very important factor. It is the two-phase (γ + α′) steel matrix that, under conditions of intensive frictional heating, provides the conditions for effective formation of a heterophase composite layer that reduces the friction coefficient and has a high resistance to fracture upon indentation.

Estimation of the Effective Magnetic Properties of Two-Phase Steels

We investigate the predictive performance of specific analytical and numerical methods to determine the effective magnetic properties of two-phase steels at the macroscale. We utilize various mixture rules reported in the literature for the former, some of which correspond to rigorous bounds, e.g., Voigt (arithmetic) and Reuss (harmonic) averages. For the latter, we employ asymptotic homogenization together with the finite element method (FEM) and periodic boundary conditions (PBC). The voxel-based discretization of the representative volume element is conducted with digital image processing on the existing micrographs of DP600-grade steel. We show that unlike the considered isotropic mixture rules, which use only the phase volume fraction as the statistical microstructural descriptor, finite element method-based first-order asymptotic homogenization allows prediction of both phase content and directional dependence in the magnetic permeability by permitting an accurate consideration of the underlying phase geometry.

REACHING THE HIGH LEVEL OF MECHANICAL PROPERTIES IN THIN-WALLED TUBULAR PRODUCTS AND SHAPES OF HIGH STRENGTH STEELS

To produce thin-walled tubular products and profiles with high level of mechanical properties, it is advisable to use two-phase (DP) steel, which has a ferritic-martensitic microstructure. The main technological element in the production of such products, which provides a combination of high strength and ductility is a special heat treatment in the temperature range from A1 to A3. This heat treatment provides a microstructure consisting of a soft ferrite matrix containing martensite inclusions located at the grain boundaries. Tubular products and profiles made of high-strength steels are obtained in continuous units, in which the areas of heating, deformation and cooling are separated. In this case a water-air sprayer must be integrated into the mill line for controlled cooling of the outgoing product. In the case where the deformation process takes place at temperatures below A1, it is rational to carry out the heat treatment directly in the line with heating by means of a through-inductor followed by cooling.

Thermodynamic-Based Model Coupled with Phase Transformation Simulation to Predict the Ms Temperature in the Case of Two-Phase Steel

Thermodynamic-Based Model Coupled with Phase Transformation Simulation to Predict the Ms Temperature in the Case of Two-Phase Steel

Ductile Fracture Behavior for Two-phase Steel under Tensile Deformation with Strain Path Change

Ductile Fracture Behavior for Two-phase Steel under Tensile Deformation with Strain Path Change

Energy power parameter effect of hot rolling on the formation of the structure and properties of low-alloy steels

The temperature and degree of hot deformation for steel 10HFTBch have been determined. This made it possible to ensure an increase in the mechanical properties of this steel, namely, the ultimate strength up to 540–560 MPa, as well as the relative elongation up to 25–29 %. As a result, it became possible to increase the service life of wheels with increased carrying capacity. This, in turn, will make it possible to increase the load of the transported cargo by motor vehicles several times. The mechanism of the influence of the energy-power parameters of rolling on the formation of the macro- and microstructure of a two-phase steel in the process of hot deformation is disclosed. The applied scheme provided an increase in the homogeneity of the structure of the developed steel, which saved the central part of the rolled section from overheating. It has been established that a decrease in the temperature of the end of deformation leads to a decrease in the size of the recrystallized austenite grain, and, consequently, to a refinement of the ferrite grain. Also an important factor in preventing the growth of ferrite grains in the upper part of the ferritic region is the abolition of cooling of the steel in coils. The recommended mode for multicomponent alloy steel 10HFTBch is as follows: the temperature of the end of rolling is 850 °C, the beginning of accelerated cooling is 750 °C, and the temperature of strip coiling into a coil is 600 °C. The basis for ensuring the increased strength of two-phase steels is the ratio and distribution of structural fractions – ferrite (initial and precipitated from austenite), as well as martensite. When hardened by such traditional "martensite formations" as manganese, the ability to control properties is limited. This is reflected in a narrow range of variation in the strength and ductility of the developed steel. The optimal combination of strength characteristics of plastic properties reduces the metal consumption of the product by 15–25 %.

СУЧАСНІ ТЕНДЕНЦІЇ ВИРОБНИЦТВА КОРОЗІЙНОСТІЙКОГО І ВОГНЕСТІЙКОГО НАПРУЖЕНОГО АРМАТУРНОГО ПРОКАТУ

The aim of the work is to study modern methods of production in the world of corrosion-resistant and fire-resistant high-strength reinforced rolled steel, designed for pre-stressed reinforced concrete structures. The specific cost of reinforcement is determined by the ratio of its value to the design resistance and decreases with increasing strength class. In Ukraine, economically alloyed steel grades are used for the production of prestressed high-strength reinforcing steel with a diameter of 6-40 mm of periodic profile according to DSTU 3760: 2019. It is also possible to use thermal strengthening of rolled products from rolling heating in the rolling mill stream, or from special (separate) heating. Hardening, tempering and also cold deformation of smooth profiles with the subsequent drawing of a periodic profile are also applied. According to the Interstate GOST 34028-2016 for the countries of the Customs Union, high-strength reinforcing steel of periodic profile of class A600p is made in bars and skeins with a diameter of 10-40 mm, and classes A800 and A1000 only in bars with a diameter of 10-40 mm from low-alloy steel grades. Depending on the diameter of the reinforcing steel, different production methods are used. GOST 34028-2016 contains clear requirements for corrosion resistance and methods of its testing. Many foreign requirements for the production of high-strength prestressed reinforcement, depending on the diameter of the profile (6-50 mm) and the method of production use carbon steels with different maximum carbon content from 0.37 to 0.8%, maximum silicon content from 0.55 up to 2.0% and a maximum manganese content of 1.8 to 2.0%. Thermomechanical reinforcement of reinforcing steel from rolling heating in the flow of rolling mills, hardening from separate (special) heating followed by tempering and strengthening by mechanical extraction followed by low-temperature tempering are used. Corrosion is the main cause of damage and destruction of reinforced concrete structures and buildings of prestressed reinforced steel from carbon steels. This problem in the world today is solved with the use of stainless steels, which have high corrosion resistance and fire resistance. Prestressed stainless steel reinforcement has higher strength and, especially, ductility than carbon steel. Stainless steel grades are used for the production of prestressed reinforcing steel with a diameter of 5 to 75 mm. In the production of periodic profiles of stainless steel reinforcement, there are two main technological routes: hot rolling and cold rolling. A promising way is the use of controlled hot rolling and thermomechanical treatment. As the rolling temperature decreases, the hardness of the austenite phase increases. For two-phase stainless steels, this allows to achieve high strength and ductility. Examples of the use of prestressed high-strength rebar in the world are: the construction of sealed shells that prevent the release of radioactive substances into the environment in severe accidents at nuclear power plants; construction of tanks for nuclear waste; construction of offshore platforms for oil production; construction of sea and river bridges, long-span ceilings, high-rise buildings, roads and other similar facilities.

Steels for Making Standard Parts Using Cold Die Forging

The two-phase steels manufactured by means of cold die forging under the conditions of JSC “BelZAN” have good strength and ductility. At the same time, the use of the cold deformation method makes it possible to obtain parts of complex shapes. In the process of their production, production costs were reduced, as well as the influence of side factors on which the quality of the final product depends.

Correction to: Weldablity of the lap joint between a 5182 aluminum alloy and a DP1180 two-phase steel sheet

N. C. Lu, G. D. Hao, and Y. T. Wang, “Weldablity of the lap joint between a 5182 aluminum alloy and a DP1180 two-phase steel sheet,” Strength Mater., 52, 573–586 (2020), https://doi.org/10.1007/s11223-020-00209-3

Study of the structure and mechanical properties of engineering products made of austenitic-martensitic steel, using the metal magnetic memory technique

Spontaneous phase transformation in local areas of the austenitic microstructure to martensite with the release of carbides may appear during the manufacturing or operation of engineering products made of two-phase austenitic-martensitic steel grades. When inspecting the quality of products made of these steels, the problem of detecting the local zones of the martensitic phase and carbide precipitation in the product metal arises. The article presents the results of an inspection by means of the metal magnetic memory (MMM) technique of centrifugal compressor impellers made of austenitic-martensitic steel 07Cr16Ni6. It was demonstrated that in the areas of stray field indications detected by means of the MMM technique, strength properties deteriorate, the metal structure degrades with abrupt changing of the metal phase composition and a carbide network formation, unacceptable δ-ferrite, was detected in the structure, and micro- and macro-cracks were found.

Weldablity of the Lap Joint between a 5182 Aluminum Alloy and a DP1180 Two-Phase Steel Sheet

The welding process of the lap joint between a 5182 aluminum alloy and a DP1180 two-phase steel sheet (1.2 mm thick) is deeply studied by friction stir welding, defects not revealed, and high-quality welded joints were obtained. The steel plate pressed to 0.2 mm is placed under the aluminum plate. With a large-size friction stir head, the rotational speed was 800 rpm and the welding speed was 50 mm/min, respectively. Many steel particles flaking in the aluminum matrix were distributed in the vicinity of the interface of the weld zone; they were surrounded by a thick layer of an intermetallic compound. This continuous and uniform layer composed of Al4Fe (EDS analysis) was formed at the interface.

The microstructure and mechanical properties features of laser welded joints of low-carbon tubular steel

ABSTRACT Technological modes of laser welding is perfected and structural and phase features of the fusion zones structure (ZC) and thermal influence (ZTI) on low carbon steel tube 10G2FBYu is studied. Martensitic structures, characterized by high gradients of microhardness distribution (up to 500–650 HV) are formed in the welding joint after laser welding. This welding joint structure does not exert influence on the specimens mechanical properties under tension (the level of strength properties is 93–97 % of the base material), however, it leads to unsatisfactory indicators of destruction impact strength (KCV) and cold resistance (KCV–40 °С = 50 J/cm2). After annealing at 600 °C, the martensitic structure in the ZC decomposes into less intense tempering martensite and tempering sorbitol at the ZTI. In such a case the microhardness for samples with a welding joints equalizes to 300 HV, the KCV level in the test interval from +20 °С to – 40 °C rises to 200 J/cm2, and Tхv shifts to temperatures below – 60°C. Such characteristics are higher than the requirements of the DNV-OS-F101 standard and speak about the efficiency of the laser welding process for two-phase low carbon steel 10G2FBYu.

The effect of fluid velocity and microstructure on erosion corrosion of two-phase CK45 steel

The essential factor to reduce the overall cost in many industries which facing erosion-corrosion phenomenon is the choice of correct design and material selection. The effect of fluid flow on corrosion and erosion–corrosion of materials is a well-recognized phenomenon in chemical and process industries and oil and gas production. The most effective parameter of flow is fluid velocity and best method of determination of the effect of fluid velocity as well as the magnitude of erosion-corrosion synergistic interaction is based on the weight loss measurements. In this study, the effect of fluid velocity on erosive corrosion of two-phase steel CK45 with different microstructures was investigated. These microstructures were formed by austenitizing the samples at 740C° for 2 ​min and then by air cooling and quenching in water or by austempering at 400C° for 2 ​h. Erosion corrosion test was carried out on the water dissolved in 3 ​wt% sodium chloride and 1 ​wt% alumina particles at velocities of 5, 9 and 16 ​m/s. According to the results, the kinetics of erosion-corrosion was linear. Increasing fluid velocity from 5 ​m/s to 16 ​m/s erosion-corrosion rate increased 4 to 6 times depending on the microstructure. SEM examination revealed presence of cavitation phenomenon on the surface of the samples. The results confirm that the bainitic ferrite microstructure exhibited the least damage in the Condition which contain sand particles or cavitation in a corrosive medium.

Selective modification of dual phase steel DP 1000 by laser action using diffractive optical element

Experimental studies of shaping a CO2 laser beam with a reflective diffractive optical element have been performed. To increase the aperture of the initial beam, we used a collimator containing a system of two plane-convex spherical ZnSe lenses. For the focal line formed with the diffractive optical element in combination with the collimator, in addition to a 1.3-fold increase in the length, a decrease in the maximum beam power density was found to occur in the laser spot. It was demonstrated that under the laser action it is possible to generate in a two-phase steel sample regions of full hardening, selective hardening, and annealing, alongside the initial structure. The formation of such structures is due to the distribution pattern of temperature fields and a difference in the cooling rate across the volume of the heat affected zone.

Comparing In Situ DIC Results from an Etched Surface with a Gold Speckled Surface

A ferrite-pearlite two-phase steel was investigated using in situ scanning electron microscope (SEM) tensile testing combined with digital image correlation (DIC). Two different speckled patterns were used and compared. The first pattern was achieved by etching a polished surface in order to reveal the microstructural features. Second, a gold speckled pattern was obtained. Here, a continuous layer of gold was applied to a polished surface. This continuous layer was remodeled into gold nanoparticles by keeping the specimen at 180 °C for 96 h with an Ar/Styrene mixture flowing across the specimen surface. The result is randomly distributed gold nanoparticles on the surface. These particles and the etched microstructure were then used by the DIC software to correlate an image series to obtain the local strain field of the material. The differences between the two techniques are numerous. Considering the etched surface, most microstructural features were grain boundaries and pearlite lamellas. As a consequence, large areas within grains did not provide sufficient contrast for DIC, thus restricting maximum resolution. However, the technique is fast and does not expose the material to any elevated temperatures. In contrast, the gold remodeling method provides a finely dispersed gold speckle pattern on the surface, giving excellent contrast across the recorded area. DIC with gold particles achieved a spatial resolution of 0.096 µm, compared to 2.24 µm in the DIC for the etched specimen. As a result, DIC with gold speckles can resolve slip lines. Conversely, DIC with etched microstructure resolves local strains on grain level. However, it is less cumbersome and faster to perform the test on the etched specimen.