Dynamic Strain Aging Effect Research Articles

Microstructural evolution and magnetic properties in strip cast non-oriented silicon steel produced by warm rolling

In this study, a specific warm rolling was implemented to process Fe-2.8%Si steel by novel twin-roll strip casting. The impact of warm deformation on mechanical behavior, microstructural evolution and magnetic properties is presented. The study indicated that dynamic strain aging (DSA) occurred in the temperature range of 150–300 °C. The elevated rolling temperature strengthened DSA effect and promoted the formation of shear bands. The nucleation process of Cube ({100} 〈001〉) grains during annealing was weakened on introducing warm rolling, while that of Goss grains ({110} < 001>) was enhanced. Moreover, the recrystallization texture pattern of (Cube + Goss) gradually transformed into a pattern of only pronounced Goss texture. The corresponding values of magnetic induction B50 at rolling direction and transverse direction were obviously improved. This confirms the feasibility of processing ultra-high-permeability non-oriented silicon steel based on twin-roll strip casting combined with DSA-control rolling. However, the rolling process increased the nucleation site for recrystallization and decreased the size of precipitates in annealed sheet, leading to a reduction in grain size and an increase in core loss.

Microstructure characteristics and properties of yttrium-bearing 9Cr ferritic-martensitic steel cladding tubes

Thin wall cladding tubes of yttrium-bearing 9Cr ferritic-martensitic steel have been fabricated by cold-rolling process, with the final dimensions of 6 mm outer diameter, 0.5 mm thickness and 3 m length. The changes of microstructure of hot-rolled plate, forged rod and the final tubes were attributed to the cold-rolling process and the intermediate heat treatment. Mechanical properties were tested from room temperature to 600 °C. The final tubes showed the strength level between the traditional ferritic-martensitic steel and the metallurgy alloyed oxide dispersion strengthened steel. It was also found that the degradation of ductility at 400 °C was related to the dynamic strain ageing (DSA) effect. At last, ultra-sound test, flattening test and flaring test were carried out to evaluated the qualities of the final tubes.

Temperature-Dependent Plastic Deformation Behavior of Cu-Ni Alloys: Coupled Influence of Stacking Fault Energy and Short Range Clustering

The uniaxial tensile tests were conducted at different temperatures to explore the coupled influence of stacking fault energy (SFE) and short-range clustering (SRC) on the plastic deformation behavior of Cu-Ni alloys. The results demonstrate that the ultimate tensile strength and uniform elongation decrease with increasing temperature due to the competitive influence of SFE and SRC. Dynamic strain aging (DSA) effect is observed at 200 and 250°C, and such an effect becomes more notable with increasing Ni content. The occurrence of DSA effect is thought to be caused by pinning of moving dislocations by SRC and diffusing solute atoms. The plastic deformation mechanisms for Cu-Ni alloys is mainly governed by wavy slip of dislocations at different temperatures, since the SFE of Cu-Ni alloys are very high especially at high temperatures, and the effect of SRC can be nearly ignored.

Mechanical behavior and deformation mechanism of 7075 aluminum alloy under solution induced dynamic strain aging

In this study the mechanical behavior and deformation mechanism of 7075 aluminum alloy sheets under dynamic strain aging induced by solution treatment were investigated. The uniaxial tensile tests were carried out at various strain rates (8.33 × 10−5 s−1, 1.67 × 10−3 s−1, 3.33 × 10−2 s−1 and 1.33 × 10−1 s−1) for samples treated by different solution processes (solution for 30 min at temperatures of 573 K, 623 K, 673 K and 748 K, and then quenching). The Portevin-Le Chatelier (PLC) effect (i.e., serration types of stress-strain curves, strain rate sensitivity (SRS) and critical strain) were analyzed, causing changes in tensile strength, work hardening rate and elongation. The morphology, sizes and quantities of precipitates under different solution-quenching conditions were observed by scanning electron microscope (SEM) and transmission electron microscope (TEM). The results show that the dissolution of secondary phase occurs during heat treatment, accompanied by coarsening behavior at lower temperatures, which leads to the transition characteristics of mechanical properties of the aluminum alloy in solid solution state. There exists a critical point of solution temperature (623K), namely, when the solution temperature is lower than this critical point, the microstructure after quenching is mainly composed of the matrix and secondary phase; otherwise it is mainly composed of solid solution. Therefore, the samples heated at different solution temperatures have different types of PLC effects. It is worth noting that the strong effect of dynamic strain aging induced at high solution temperature and low strain rate could simultaneously enhance the strength and toughness.

Effect of Intercritical Annealing Time at Pearlite Dissolution Finish Temperature (Ac1f) on Mechanical Properties of Low-Carbon Dual-Phase Steel

The effect of intercritical annealing at Ac1, Ac1f, and Ac3 temperatures followed by water quenching was studied on the microstructure and mechanical properties of a 0.035C-0.27Mn low-carbon steel. During short-term holding at Ac1 and Ac1f, some pearlite remained after quenching and the yield-point phenomenon was still detectable, which was related to the formation of small amount of martensite inside pearlite colonies and on ferrite grain boundaries with marginal effect on the surrounding ferrite phase. By increasing holding time at Ac1f, pearlite disappeared and DP microstructures were achieved with the disappearance of the yield-point phenomenon and the enhancement of the work-hardening capacity. At long holding times, however, the mechanical properties deteriorated mainly due to the coarsening of martensitic islands and disappearance of dynamic strain aging (Portevin–Le Chatelier) effect at room temperature.

Влияние особенностей формирования градиентной структуры при интенсивной пластической деформации сплавов с различными типами кристаллической решётки

Problem Statement (Relevance): The paper describes some features and prospective benefits of deformation by methods of drawing with shear (SD) and high pressure torsion (HPT) in a temperature range of dynamic strain aging (DSA) effect, which allow receiving a high complex of physical and mechanical properties. Objectives: The study aims to investigate and analyze features of the structure formation with the combined application of severe plastic deformation (SPD) and the DSA effect during deformation by drawing with shear and high pressure torsion, to establish patterns of the gradient structure formation. Methods Applied: 1. Computer simulation in Deform 3D software to investigate the stress-strain state on materials with various types of a crystalline lattice: copper grade M1 (FCC), Steel 10 (BCC) and titanium VT1-0 (HCP) and a further comparison with experimental results. 2. Microhardness measurement 3. Scanning and transmission electron microscopy. Originality: This research resulted in investigation of the combined effect of the DSA effect and SPD on the gradient structure formation and mechanical properties of metals with various crystalline lattices. Findings: the paper presents the results of the study of the structure formation during non-monotonous plastic deformation of the alloys (steel 10, copper and titanium) with various crystalline lattice types by SD, as well as ECAP and HPT of low-carbon steel in the temperature range of the DSA effect. Deformation mechanisms and features of the deformation behavior on a mesoscopic scale under various deformation treatment modes are analyzed. The temperature range of the DSA effect in steel 10 under ECAP and the fact of the gradient structure formation under HPT are established. Practical Relevance: The study helped to obtain data that can be used to choose the optimal deformation treatment mode with the DSA effect.

Strain Hardening, Damage and Fracture Behavior of Al-Added High Mn TWIP Steels

The strain hardening and damage behavior of Al-added twinning induced plasticity (TWIP) steels were investigated. The study was focused on comparing two different alloying concepts by varying C and Mn contents with stacking fault energy (SFE) values of 24 mJ/m 2 and 29 mJ/m 2 . The evolution of microstructure, deformation mechanisms and micro-cracks development with increasing deformation was analyzed. Al-addition has led to the decrease of C diffusivity and reduction in tendency for Mn-C short-range ordering resulting in the suppression of serrated flow caused due to dynamic strain aging (DSA) in an alloy with 0.3 wt.% C at room temperature and quasi-static testing, while DSA was delayed in an alloy with 0.6 wt.% C. However, an alloy with 0.6 wt.% C showing DSA effect exhibited enhanced strain hardening and ductility compared to an alloy with 0.3 wt.% C without DSA effect. Twinning was identified as the most predominant deformation mode in both the alloys, which occurred along with dislocation glide. Al-addition has increased SFE thereby delaying the nucleation of deformation twins and prolonged saturation of twinning, which resulted in micro-cracks initiation only just prior to necking or failure. The increased stress concentration caused by the interception of deformation twins or slip bands at grain boundaries (GB) has led to the development of micro-cracks mainly at GB and triple junctions. Deformation twins and slip bands played a vital role in assisting inter-granular crack initiation and propagation. Micro-cracks that developed at manganese sulfide and aluminum nitride inclusions showed no tendency for growth even after large deformation indicating the minimal detrimental effect on the tensile properties.

Effect of dynamic strain ageing on environmental degradation of fracture resistance of low-alloy RPV steels in high-temperature water environments

Elastic plastic fracture mechanics tests on different low-alloy reactor pressure vessel (RPV) steels in air and various simulated light water reactor environments revealed a clear, but moderate reduction of the fracture initiation resistance of RPV steels with high susceptibility to dynamic strain ageing (DSA) in high-temperature water (HTW). In HTW, the reduction of fracture initiation resistance increased with decreasing loading rate and was most pronounced in hydrogenated HTW. The stronger reduction of fracture resistance in hydrogenated HTW was mainly due to the localization of plastic deformation by interaction between DSA and hydrogen.

Mechanical Behavior of Inconel 625 at Elevated Temperatures

Inconel 625 is a nickel-based alloy that is mainly used in high-temperature applications. Inconel 625 exhibits an unstable plastic flow at elevated temperatures characterized by serrated yielding, well-known as the Portevin-Le Chatelier effect. The evaluation of the mechanical properties of Inconel 625 at high temperatures is the aim of this work. The tensile tests were executed in temperatures ranging from room temperature to 1000 °C with strain rates of 2 × 10−4 to 2 × 10−3 s−1. The creep tests were executed in the temperature range of 600–700 °C and in the stress range of 500–600 MPa in a constant load mode. The optical and scanning electron microscopes were used for surface fracture observation. In the curves obtained at 200–700 °C the serrated stress-strain behavior was observed, which was related to the dynamic strain aging effect. The yield strength and the elongation values show anomalous behavior as a function of the test temperature. An intergranular cracking was observed for a specimen tensile tested at 500 °C that can be attributed to the decohesion of the carbides along the grain boundaries. The fracture surface of the specimen tensile tested at 700 °C showed the predominance of transgranular cracking with tear dimples with a parabolic shape.

A Modified Johnson-Cook Model for Cp-Ti to Incorporate the Effects of Dynamic Strain Aging and Phase Transformation

A Modified Johnson-Cook Model for Cp-Ti to Incorporate the Effects of Dynamic Strain Aging and Phase Transformation

Dramatic Increase of Strength and Ductility in Fe–22Mn–1.0C Twinning‐Induced Plasticity Steel at Elevated Temperature

Tensile properties and microstructural evolutions of Fe–22Mn–1.0C (wt%) twinning‐induced plasticity steel are investigated in the temperature range from 293 to 443 K. An unexpected enhancement of strength and ductility is observed at the elevated temperature of 443 K (≈400 MPa ultimate tensile strength and ≈10% true strain improvements). The twinning capability is still kept stable with the increasing temperature, and the premature fracture is postponed by suppressing dynamic strain aging effect. As a result, the synchronous improvement of strength and plasticity is achieved at high deformation temperature.

Effect of Dynamic Strain Aging on Tensile Deformation of 20MnMoNi55 Alloy

Results obtained from the uniaxial tensile tests of 20MnMoNi55 low-alloy RPV steel at different temperatures (varying from 27 to 450 °C) and straining rates (varying from 10−5 to 10−1 s−1) reveal that the material response is sensitive to both temperature and strain rate. For the range of temperature varying from 200 to 400 °C, in combination with different strain rates, the material shows negative strain rate sensitivity along with different kinds of serrated flow (between 200 and 310 °C), commonly termed as Portevin–Le Chatelier effect (types A, B and C). The material behavior, in that temperature–strain rate window, is described by dynamic strain aging (DSA) effect, and the changes in the mechanical properties of the material are studied. The DSA attribute of 20MnMoNi55 steel is characterized by calculating the activation energy. The x-ray diffraction technique and atomic percentage analysis using energy-dispersive x-ray suggest that the manganese influences the interstitial (carbon and/or nitrogen) diffusion by forming Mn-C and/or Mn-N pair, which can be a plausible cause of DSA in the material.

High-Temperature Low-Cycle Fatigue Behavior of HS80H Ferritic–Martensitic Steel Under Dynamic Strain Aging

In this work, low-cycle fatigue tests were performed on HS80H ferritic–martensitic steel with the strain amplitudes ranging from 0.5 to 2.0% at room temperature and 350 °C. The cyclic stress response at 350 °C was found to be different from that at room temperature due to the effect of dynamic strain aging and showed a significant secondary hardening when the strain values were 0.5 and 0.7%. Furthermore, the dynamic strain aging effect also resulted in an abnormal increase in fatigue life when the strain was 0.7%, which was due to the change in elastic strain. Additionally, the elastic strain and fatigue life were bilinear relations in the double logarithmic coordinates. Finally, the transmission electron microscope observations showed that the dynamic strain aging led to the change in substructure, while the grain was refined.

Gradient structure formation in the process of severe plastic deformation of carbon steels under the conditions of the effect of dynamic strain aging

The formation of a gradient structure during the severe plastic deformation (SPD) by high-pressure torsion (HPT) of low- and medium-carbon steels under the influence of dynamic strain aging (DSA) is studied. Deformation mechanisms under various regimes of deformation processing are analyzed. The temperature ranges of the DSA effect during the ECAP processing of steel 10 and the fact of the formation of a gradient structure during the HPT processing under these conditions are established. It is shown that the deformation of carbon steels in the DSA temperature range enables controlling the structure of the deformed state.

Effect of copper and aluminum contents on wire drawing behavior in twinning-induced plasticity steels

Wire drawing behavior of the five TWIP steels having a stacking faulting energy (SFE) range of 17–41 mJ/m2 using different Cu and Al contents has been investigated to improve and predict the drawability in TWIP steels. Cu and Al played similar roles in TWIP steels during wire drawing: increase in drawability and yield strength but decrease in twin formation, strain hardening rate, and tensile strength. However, the effect of Al was higher than that of Cu and the 1.5% Cu addition in TWIP steel had the most excellent combination of strength, ductility, and drawability during wire drawing. The twin volume fraction of all the TWIP steels initially increased and then saturated with drawing strain. The 0CuAl steel had a higher twin volume fraction at all strain levels and saturated earlier than the other TWIP steels due to the low SFE and promoted dynamic strain aging effect, resulting in the earlier fracture of wire. The Al and Cu additions in TWIP steel can tailor the twinning rate with drawing strain and prevent the fast exhaustion of ductility or plastic deformation ability, finally increase the drawability. The reduction of area (RA) of hot rolled TWIP steels had a linear relationship with drawability; therefore, we can predict the drawability of TWIP steels by simply measuring the RA value of hot rolled TWIP steels.

Effect of dynamic strain aging and precipitation on the hot deformation behavior of 253MA heat-resistant alloy

In this research, we performed an experimental investigation into the influence of dynamic strain aging (DSA) and precipitation behavior on the plastic deformation and microstructure evolution in alloy 253MA considering its service temperature. The serrated flow behavior, stress anomaly behavior and negative strain rate sensitivity are considered as the manifestation of DSA within a certain temperature range (TDSA), which can be classified as low (550–700 °C), intermediate (600–750 °C) and high temperatures (700–790 °C) at 0.001 s−1, 0.01 s−1 and 0.1 s−1, respectively. The activation energy of DSA was determined to be 242 kJ/mol, indicating that the diffusion of substitutional solutes, such as Cr and Ni, is mainly responsible for the DSA phenomenon. The characteristic of dislocation substructures is prone to change from linear structure to cellularization structure with a rising deformation temperature in the DSA regime. The stress anomaly behavior can be attributed to the rapid dissolution of σ phase. The initiation of dynamic recrystallization should contribute to the disappearance of DSA by suppressing the dynamical solute atom–dislocation interaction.

Dynamic Strain Aging Behavior in Dual Phase and Multiphase High Strength Steels

Advanced high strength steels, especially dual and multiphase steels, exhibit interesting dynamic strain aging behavior when subjected to isothermal tests at varying strain rates. In this study, uniaxial tensile testing results are presented for two selected steels over a temperature range from 25 to 200 °C at strain rates from 5 × 10-4 to 5 × 10-1 s-1. At different temperature and strain rates, some specimens exhibit substantial dynamic strain aging (DSA) effects including negative rate sensitivity and formation of pronounced Portevin Le-Châtelier (PLC) bands resulting in inhomogeneous material deformation. Implications of DSA on performance consequences are addressed in the paper.

Cyclic hardening and dynamic strain aging during low-cycle fatigue of Cr-Mo tempered martensitic steel at elevated temperatures

Dynamic strain aging (DSA) has a noticeable impact on low cycle fatigue behavior of Cr-Mo tempered martensitic steel at elevated temperatures. At 350 °C, the stress response presented evidently secondary hardening phenomenon, and the fatigue life is significantly higher than room temperature which is contrary to the usual understanding. The analysis shows that the reason for the secondary hardening is mainly because of DSA which affects the evolution of dislocations. The influence process of the DSA effect on the dislocation evolution in low-cycle fatigue was first observed, which is from lath substructure to a smaller cell substructure at high temperature. Fracture observation indicates that the new dislocation structure promotes the crack propagation resistance of the material. The effect of DSA on the low cycle fatigue properties of high temperature provides a new idea for the study of fatigue resistance of materials.

Effect of strain rate and temperature on the serration behavior of SA508-III RPV steel in the dynamic strain aging process

Dynamic strain aging (DSA) effect on SA508-III reactor pressure vessel (RPV) steel was investigated. The SA508-III RPV steel was subjected to tension tests at different strain rates (1.1 × 10−5 s−1 and 6.6 × 10−5 s−1) and different temperatures (500 and 550 °C) to evaluate the influence of strain rate and temperature on the serrated flow behavior, which is the repetitive and discontinuous yielding phenomenon on the stress–strain curves. The higher temperature leads to the higher density of precipitates, M23C6 carbides and needle-like Mo2C carbides. It was found that the samples under tension test of 6.6 × 10−5 s−1 and 500 °C possess superior mechanical properties and mainly show A-type serrations on the tension test curves. Then, the local regress method was used to filter the DSA curves, thus to show the real trend of the curves. It has been found that the less time of interaction between dislocations and precipitates under higher strain rates leads to a higher strength of the sample. The more tiny-stress drops on the 550 °C serration curve can be attributed to the hardening phase, M23C6 carbides and needle-like Mo2C carbides. The higher percentage of the small stress drops on the serration curves represents the higher mechanical strength.

Hardness Evolution and High Temperature Mechanical Properties of Laser Welded DP980 Steel Joints

AbstractDP980 steels were joined using fiber laser welding. The welded joint was characterized in terms of hardness distribution and tensile behavior at room temperature, 150 ℃, and 300 ℃, respectively. The fine-grained martensite in supercritical heat affected zone (HAZ) resulted in the highest hardness (428 Hv), while the tempered martensite contributed to the hardness decreasing (‒31 Hv). Both the ultimate tensile strength and yield strength of the base metal and welded joint decreased at 150 ℃, and then increased at 300 ℃ due to dynamic strain aging (DSA). The welded joint exhibited slightly higher yield strength and lower elongation at all the test temperatures compared to base metal due to the hardened fusion zone. The energy absorption reduced slightly with increasing temperature both for base metal and welded joint, and the weld posed a minor effect on the energy absorption. Deformation was one of the requirements for DSA effect. DSA enhanced the hardness of base metal (+78 Hv) and softened zone (+53 Hv). HAZ was not softened enough to become the weakest position during tensile test.