Dual-phase Behavior Research Articles

Hot deformation behavior and dynamic recrystallization of dual-phase (CrCoNi)94Al3Ta3 medium entropy alloy

The microstructural evolution and dynamic recrystallization (DRX) behavior of a dual-phase (CrCoNi)94Al3Ta3 medium entropy alloy (MEA) was studied using thermal simulated test machine at temperature ranging from 1000 ℃ to 1150 ℃ under strain rate of 0.001–1 s−1. The initial dual-phase microstructures were equiaxed grains with face-centered cubic structure (γ) and L12 phase (γ') precipitated homogeneously in the grain, besides a certain amount pinned at boundary. The stress-strain curves exhibited a typical DRX softening behavior, in which the flow stress was sensitive to deformation temperature and strain rate. The deformation activation energy was calculated to be 612.04 kJ/mol (γ + γ' dual-phase region) and 391.02 kJ/mol (γ single-phase region) respectively. The appropriate hot deformation parameters of (CrCoNi)94Al3Ta3 MEA were 1100 ℃/0.001 s−1 and 1150 ℃/0.01 s−1 based on the hot processing map and deformation microstructure. The discontinuous DRX transformed to continuous DRX depended on deformation temperature, this was because that the interaction between precipitates and dislocation was weakened as the deformation temperature beyond the dissolution temperature of L12 phase.

Influence of uniaxial and biaxial pre-straining on the low cycle fatigue performance of DP590 steel

The present work aims to examine the low cycle fatigue (LCF) behavior of dual-phase (DP590) steel subjected to different pre-straining (uniaxial and equi-biaxial) paths. The LCF tests reveal all specimens showed continuous cyclic softening throughout the fatigue life. However, the rate of cyclic softening is higher for the equi-biaxial pre-strain specimen. The rotation of one maximum shear stress plane during fatigue cycling after equi-biaxial pre-straining introduces non-proportional loading condition, thereby significantly reducing the fatigue life. The larger lattice rotation and in-grain misorientation due to the non-proportional loading is notable for the equi-biaxial pre-strain specimen.

Behavior of Dual-Phase (MnO-SiO2-Al2O3) + (SiO2) Inclusions in Saw Wire Steels During Hot Rolling and Cold Drawing

The behavior of dual-phase (MnO-SiO2-Al2O3) + (SiO2) inclusions in saw wire steels during hot rolling and cold drawing was investigated in detail. It was found that the inclusion matrix (glassy MnO-SiO2-Al2O3 (silicate)) manifested rheological properties and the precipitated SiO2 experienced poor deformation in hot rolling. After multi-pass hot rolling, these two phases gradually became separated from each other. The former was elongated into a thin strip, whereas the shape of the latter was deformed from spherical to ellipsoid. Despite their distinctive deformability during hot rolling, MnO-SiO2-Al2O3 and SiO2 were both crushed into smaller pieces during cold drawing. With the proceeding of drawing, shattered pieces became tiny and their interspaces were enlarged, thus causing a reduction in filament breakage. Based on these findings, inclusions were categorized by their melting points and Young’s moduli. Hence, the effects of inclusions on saw wires fabricated by hot rolling and cold drawing were more quantitatively evaluated, and the obtained results were found to be in good agreement with industrial findings.

Relationship of Microstructure and Mechanical Properties of Dual Phase Steel after Various Annealing Conditions

The development of ultrafine ferrite grain size has become one of attractive way how to improve the behavior of dual phase (DP) steels. The other possible way how to enhance mechanical properties of DP steels is to modify the chemical composition. Therefore object of our investigation was the dual phase steel with modified alloying (three times higher Cr content with addition of phosphorus). The dual phase steel was annealed in laboratory conditions in accordance with three specified annealing cycles: into intercritical region (780°C), into austenite region (920°C) and into austenite region (920°C) by subsequently cooling into intercritical region (780°C) with the hold at the temperature of 495°C. The obtained microstructure after selected annealing regimes consists of three phases (ferritic matrix, martensite and martensite/bainite grains) with different size and distribution. For studied annealing regimes were clearly defined mechanical properties such as: YS, UTS, elongation, n-parameter and ratio YS/UTS. It was defined the scheme of microstructure evolution on base of austenite grain size during the continual cooling process with defined three phases: 1) the hard martensite formed on the grain boundary; 2) the soft interior bainite and 3) the hard isolated martensite.

Effect of Exposure Face Orientation and Tilt Angle on Immersion Corrosion Behavior of Dual-Phase and Mild Steels

The present study aims to investigate the effect of the exposure angle (0°, 30°, 45°, 60° and near 90°) and the number of exposed faces (skyward and downward surfaces) on the immersion corrosion behavior of a dual phase and a mild steel in freely aerated stagnant 3.5% NaCl solution for a period of 10 days. In one case, two surfaces are exposed simultaneously, whereas in other case, one of the surfaces is exposed, while other is lacquered. Analysis shows that the corrosion rate of the skyward surface is considerably high when both the surfaces are exposed. The corrosion rate of the downward surface is higher than that of the skyward sample, when one of the surfaces is exposed. Moreover, the corrosion rate gradually decreases from zero to near-90° orientation for all the cases. Though the effect of tilt angle and exposed face does not depend on steel varieties, the dual-phase steel has higher corrosion resistance than the mild steel. Relative oxygen content, microcell formation, gravity effect and reaction nature with depth are the plausible reasons for the observed variation of corrosion behavior.

Research on spring-back behavior of high strength steel sheets

To investigate the spring-back behavior of dual-phase (DP) steel,V-shape spring-back experiments with different bending angles,relative bending radii and blank holding forces were carried out in this paper. It is concluded that with the increase of V-shape angle or blank holding force,the spring-back of DP steel sheets de- creases;while raising fillet radius of punch,which has the most apparent effects on spring-back,advances spring-back angle. Among DP590,DP780 and DP980,higher strength yields more notable spring-back due to larger elastic deformation. The difference of spring-back among these materials is relevant with the microstruc- ture and mechanical properties. The total elastic deformation approximately equals the ratio of the strength corre- sponding to the applied load to the modulus of elasticity.

Crystallization Kinetics for the Split Dual Phase Model of the Amorphous State of Polymers

We analyze constant rate cooling and heating crystallization kinetics of PET samples by DSC. The samples have various degrees of disentanglement, obtained by Rheo-Fluidification. According to the interactive Split Dual Phase model, the amorphous state is made up of two coupled and interactive amorphous phases. These two phases have distinct viscoelastic and thermodynamic characteristics (Tg, free volume, G′ and G″, etc.), which are determined by the potential energy of the conformers and by the state of entanglement of the macromolecular coils. Semi-crystalline polymers, such as polyethylene terephthalate (PET), are amorphous in the molten state and should have Dual Phase behavior. The phase duality should manifest itself during crystallization from the melt during cooling, or during cold crystallization while heating quenched samples. The purpose of this communication is to quantitatively describe the kinetics of crystallization of PET samples with a dual phase kinetics formulation, and determine the respective influence of molecular weight and degree of entanglement on the kinetics parameters, rate of crystallization and percentage of crystallinity.