Crussard-Jaoul Analysis Research Articles

Stress-induced martensite transformation and mechanical properties of fine-grained Ti-10V-2Fe-3Al alloy fabricated by friction stir processing

Ti-10 V-2Fe-3Al, as the metastable β-type titanium alloy, has several applications in the aerospace industry due to its good mechanical properties. However, the study of stress-induced martensitic transformation behavior and corresponding mechanical properties in its small-sized grains (<20 μm) needs to be further clarified. This study investigates the relationship between grain size, stress-induced martensitic transformation, and mechanical properties of Ti-10 V-2Fe-3Al after friction stir processing. When the spindle speed increased from 200 rpm-100 mm/min to 350 rpm-100 mm/min, the grain size grew from 7.53 μm to 13.06 μm, and the martensite triggering stress decreased from 287 MPa to 111 MPa. The phase boundaries formed by α" and β, as well as the grain boundaries formed by α" and α", enhanced the plasticity of Ti-10 V-2Fe-3Al. The Crussard-Jaoul analysis method was used to investigate the effect of stress-induced martensitic transformation on Ti-10 V-2Fe-3Al, it was found that the martensitic transformation leads to dynamic softening. The formation of α" martensite results in an increased work hardening rate.

Study on Strain Hardening and Cryogenic Toughness of Marine 10Ni5CrMoV Steel during Tempering

The tempering process is applied in marine 10Ni5CrMoV steel to study microstructure, and mechanical properties by multi‐scale characterizations, strain hardening behavior, and cryogenic toughening mechanism are further investigated. As the tempering temperature increases from 590 to 630 °C, the dislocation density decreases by up to 25% and the austenite volume fraction decreases by up to 35%. Additionally, the morphology of austenite changes from strip to bulk, which weakened the pinning effect on the laths, leading to a coarsened martensite and an increase in the equivalent grain size. Based on the modified Crussard–Jaoul analysis, the specimens at different tempering temperatures exhibit a single‐stage strain hardening behavior during plastic deformation. The increase in strength is attributed to the continuous transformation‐induced plasticity effect and the increasing dislocation density. Furthermore, high austenite volume fraction and the proportion of grain boundary misorientation above 45° promote the release of stress concentration and hinder the propagation of cracks. This results in an increase in the ductile–brittle transition temperature (DBTT) of the specimens from −105 to −135 °C. At a tempering temperature of 610 °C, the specimen demonstrates an outstanding balance between yield strength (868 MPa) and cryogenic toughness (DBTT of −135 °C).

Local electropulse-induced gradient and hierarchical architecture of soft-hard phase in 35CrMo steel

To improve the comprehensive mechanical properties while avoiding the overall heat treatment, this study provided a method to prepare structural steel with soft-hard phases arranged in complex gradient, hierarchical structures via processing a homogenous material using local electropulsing treatment (LEPT). The results show that ultimate tensile strength, elongation-to-failure, and curves area of the structural steel plate are about 1400 MPa, 15.93%, and 19,100 MPa·%, respectively, which are 16.5%, 34.7%, and 47.5% higher than the conventional quenched and tempered steel. The excellent mechanical properties of LEPTed specimens are mainly due to the local strengthening caused by the effects of pulse current, and the synergistic effect of hard and soft phases. The designed hardened units produced by LEPT exhibit hierarchical structure and gradient variations in texture and grain size. There also exists gradient hardness distribution in hardened units. These structures are produced due to the multi-scale effects of current and the gradient current density distribution. Moreover, due to the introduction of hardened units at another scale, there were four stages in the strain-hardening behavior of LEPT based on differential Crussard-Jaoul (DC-J) analysis, which deviates from the three stages of two-phase or multi-phase steels.

Low-Temperature Deformation Mechanism and Strain-Hardening Behaviour of Laser Welded Dual-Phase Steels

This paper analysed the change in microstructure after laser welding DP800 and DP1000, the effect of the laser welds on low temperatures deformation, and strain hardening behaviour when loaded at temperatures between −40 °C and 20 °C using quasi-static strain rates (1.7 × 10−2 s−1). The results showed that the fusion zone (FZ) was fully martensitic due to the rapid cooling during welding. Owing to the severity of the heat-affected zone, the joint efficiencies of DP800-DP800 and DP1000-DP1000 welds were 99.0% and 88.7%, respectively. The UTS, YS, and work hardening exponents of the welded joints increased slightly, while the strain hardening capacity of the base metals was much higher than those of the welded joints with decreasing temperatures. The evaluated work hardening exponents of the welded joints were determined using the Hollomon equation, Afrin equation, and Crussard-Jaoul analysis are in the range of 0.2–0.47, 0.24–0.59, and 0.45–0.71, respectively. The welded joints and the base metals demonstrated only stage III strain hardening, with DP800 joints exhibited excellent uniform and total elongation ranging between 8.0–8.7% and 10.4–14.2%, respectively. Fractures were located in the base metal of welded DP800 and SCHAZ of DP1000 welds, respectfully. The fracture surfaces demonstrated characteristic dimple fractures. The uniqueness of this study is found in its design, as there is currently no known literature on the low-temperature deformation mechanism and strain-hardening behaviour of similar DP800 and DP1000 welds.

Enhancing Strain Capacity by the Introduction of Pearlite in Bainite and Polygonal Ferrite Dual-Phase Pipeline Steel.

In this study the strain capacity and work-hardening behavior of bainite (B), bainite + polygonal ferrite (B + PF), and bainite + polygonal ferrite + pearlite (B + PF + P) microstructures are compared. The work hardening exponent (n), instantaneous work hardening value (ni), and differential Crussard-Jaoul (DC-J) analysis were used to analyze the deformation behavior. The best comprehensive mechanical properties were obtained by the introduction of the pearlite phase in B + PF dualphase with the tensile strength of 586 MPa and total elongation of 31.0%. The additional pearlite phase adjusted the strain distribution, which increased the initial work hardening exponent and then maintained the entire plastic deformation at a high level, thus delayed necking. The introduction of pearlite reduced the risk of micro-void initiation combined with the high frequency of high angle grain boundaries (HAGBs) in triple-phase steel, which led to a low crack propagation rate.

Effect of Bainite to Ferrite Yield Strength Ratio on the Deformability of Mesostructures for Ferrite/Bainite Dual-Phase Steels.

The strength and plasticity balance of F/B dual-phase X80 pipeline steels strongly depends on deformation compatibility between the soft phase of ferrite and the hard phase of bainite; thus, the tensile strength of ferrite and bainite, as non-negligible factors affecting the deformation compatibility, should be considered first. In this purely theoretical paper, an abstract representative volume elements (RVE) model was developed, based on the mesostructure of an F/B dual-phase X80 pipeline steel. The effect of the yield strength difference between bainite and ferrite on tensile properties and the strain hardening behaviors of the mesostructure was studied. The results show that deformation first occurs in ferrite, and strain and stress localize in ferrite prior to bainite. In the modified Crussard-Jaoul (C-J) analysis, as the yield strength ratio of bainite to ferrite () increases, the transition strain associated with the deformation transformation from ferrite soft phase deformation to uniform deformation of ferrite and bainite increases. Meanwhile, as the uncoordinated deformation of ferrite and bainite is enhanced, the strain localization factor (SLF) increases, especially the local strain concentration. Consequently, the yield, tensile strength, and yield ratio (yield strength/tensile strength) increase with the increase in . Inversely, the strain hardening exponent and uniform elongation decrease.

The significance of phase reversion-induced nanograined/ultrafine-grained (NG/UFG) structure on the strain hardening behavior and deformation mechanism in copper-bearing antimicrobial austenitic stainless steel

The unique concept of phase reversion involving severe deformation of parent austenite into martensite, followed by annealing for a short duration, whereby the strain-induced martensite reverts to austenite, was adopted to obtain nano-grained/ultrafine-grained (NG/UFG) structure in a Cu-bearing biomedical austenitic stainless steel resulting in high strength-high ductility combination. Work hardening and accompanying deformation mechanism are two important aspects that govern the mechanical behavior of biomedical devices. Thus, post-mortem electron microscopy of the strained region was carried out to explore the differences in the deformation mechanisms induced by grain refinement, while the strain hardening behavior was analyzed by Crussard-Jaoul (C-J) analysis of the tensile stress-strain data. The strain hardening behavior consisted of four stages and was strongly affected by grain structure. Twinning-induced plasticity (TWIP) was the governing deformation mechanism in the NG/UFG structure and contributed to good ductility. In striking contrast, transformation-induced plasticity (TRIP) contributed to high ductility in the coarse-grained (CG) counterpart and was the governing strain hardening mechanism. When the grain size is less than ~1 μm, the increase in the strain energy and the austenite stability significantly reduce the possibility of strain-induced martensite transformation such that there is a distinct transition in deformation mechanism from nanoscale twinning in the NG/UFG structure to strain-induced martensite in CG structure. The differences in the deformation mechanisms are explained in terms of austenite stability – strain energy relationship.

Microstructure, crystallographic texture and strain hardening behavior in hot tensile tests of UNS S32304 Lean Duplex stainless steel

Duplex stainless steels can be used for applications in the nuclear industry endorsing its choice as an external shield for Type B packages. The microstructure, crystallographic texture, and the strain hardening behavior of UNS S32304 duplex stainless steel was investigated in hot tensile tests by Electron Backscattering Diffraction technique. Interrupted hot tensile tests with strain rates ε˙ = 10−2 s−1 and ε˙ = 10−1 s−1 were carried out at 700 °C using a Thermomechanical Physical simulator. The α parameter of gamma distribution was associated for the first time with strain in ferrite and austenite phases through the Grain Orientation Spread parameter (GOS). The ferrite phase did not show the dynamic equilibrium between the stored energy and recovery rates. The average GOS in the ferrite phase was larger for ε˙ = 10−1 s−1 due to a smaller time available for dislocation annihilation and rearrangement in dynamic recovery. The grain rotation sequence <100> → <100> - <101> → <101> was found in ferrite phase. In the austenite phase, the dynamic recrystallization was not observed and the <111> and <100> fiber textures parallel to the tensile direction were strengthened. The austenite → ferrite phase transformation occurred during the hot tensile tests and showed the Kurdjumov-Sachs orientation relationship. The modified Crussard-Jaoul analysis showed six-strain hardening stages which were associated with the average GOS and austenite → ferrite phase transformation.

Microstructural evolution and strain hardening behavior of heat-treated 17-4 PH stainless steel

The present study focuses on the experimental investigation of the precipitation and dislocation induced strain hardening behavior and related microstructural evolution of the heat-treated 17-4 PH stainless steel. Tensile and compression tests were carried out at an ambient temperature, using a nominal strain rate of 1×10-3s-1 to evaluate the precipitation induced flow stress characteristics of the stainless steel grade in correlation with its microstructural attributes. Differential Crussard-Jaoul (C-J) analysis was performed to quantify the role of precipitate in governing the strain hardening rate. It has illustrated the multiple stages of strain hardening depicting the impact of microstructural constituents on the strain hardening behavior. Peak strength and hardening of the H900 condition, caused mainly due to the coherency of precipitates within the lath matrix, can be deduced from the increase in the precipitation-sensitive microstrain and dislocation density.

Effects of Dynamic Strain Aging on Strain Hardening Behavior, Dislocation Substructure, and Fracture Morphology in a Ferritic Stainless Steel

Dynamic strain aging at different temperatures and its effects on the strain hardening behavior, dislocation substructure and fracture morphology in a stainless steel grade 430 was investigated. Sheet type specimens were subjected to tensile tests performed at a temperature range of 298 K to 873 K. Subsequently, the strain hardening behavior of the material was depicted via modified Crussard–Jaoul analysis, strain hardening rate, and instantaneous strain hardening exponent curves. Changes in the dislocation substructure during the tests were characterized by means of X-ray diffraction and transmission electron microscopy. Scanning electron microscopy was used to investigate the fracture morphology of the specimens. The results indicated the occurrence of dynamic strain aging from 523 K to 773 K by the presence of the Portevin–Le Chatelier effect. These results were reinforced by the strain hardening analysis that revealed a three staged behavior at most of the studied temperatures, except during the dynamic strain aging regime, which presented an extra stage. Different substructures were observed as a function of the test temperatures: cellular dislocation substructure in the samples deformed at 298 K and 673 K, an array of straight and parallel dislocations in conjunction with a cellular substructure at 673 K, and finally a subgrained substructure with fine precipitates was formed at 873 K. A ductile surface fracture presenting a network of dimples and voids was present at all investigated temperatures, with a dimple size refinement being observed during the dynamic strain aging regime.

Correlation of ferrite and martensite micromechanical behavior with mechanical properties of ultrafine grained dual phase steels

Thermomechanical treatment was employed to produce ultrafine grained dual-phase (UFG DP) steels consisting of different volume fractions of martensite and different ferrite grain sizes. The effects of intercritical annealing temperature on the microstructure and deformation behavior of DP steels were investigated. The modified Crussard-Jaoul analysis illustrated four-stage deformation of the investigated DP steels. The ferrite nanoindentation response in the microstructures showed that increasing the intercritical annealing temperature from 780 to 820 °C, resulted in an increase in the ferrite nanohardness by about 46% due to a decrease in the average ferrite grain size by about 34%. The average martensite nanohardness decreased by about 18% with decreasing its carbon content by about 18%. The mechanical properties of UFG DP steels, such as strength, elongation, energy absorption, and strain hardening characteristics were well correlated with the ferrite and martensite micromechanical behavior.

Microstructure and Work Hardening Behavior of Micro-plasma Arc Welded AISI 316L Sheet Joint

The aim of this research is to investigate the microstructural changes and work hardening behavior of AISI 316L 0.5-mm-thick sheet due to micro-plasma arc welding. AISI 316L similar sheets were welded in single-pass square butt joint configuration. The microstructure in the fusion zone typically contains a variety of complex δ-ferrite-austenitic structure, which significantly increased hardness value compared to the base material because of rapid solidification of the weld pool. Systematic tensile test was performed to investigate strain rate sensitivity of the welded joint under quasi-static loading conditions. The multistage work hardening behavior was determined by Kocks–Mecking (K–M) model and differential Crussard–Jaoul analysis. In both the cases, stage III work hardening behavior and stage IV work hardening behavior were observed. The stress–strain curves of welded specimen at different strain rates were analyzed in terms of Hollomon, Ludwik and Swift equations to determine work hardening exponent values. The welded joints were ruptured in the transition zone of heat affected and fusion zones. The fractographic observation exhibited variation in dimple and void density over strain rate from 0.0001 to 0.0015 s−1.

Work hardening behaviour and damage mechanisms in carbide-free bainitic steel during uni-axial tensile deformation

The study has examined the work hardening characteristics and damage mechanisms of a newly developed carbide-free bainitic steel. These are correlated with the microstructural constituents using the established empirical equations and the experimental findings. Carbide-free bainitic steel has shown primarily three stages of deformation in modified Crussard-Jaoul analysis, which best describes the work hardening behaviour. Plastic deformation of retained austenite precedes the deformation of bainitic ferrite. The blocks of retained austenite transform to strain induced martensite at lower strain levels than the films of retained austenite. With increasing strain, cross slip assisted dynamic recovery, and sub-grain formation become predominant in bainitic ferrite. Although early void initiation occurs at the non-metallic inclusions, these do not play a significant role in the final fracture. Void initiation and splitting of phase boundaries due to strain incompatibility, decohesion of prior austenite grain boundaries and cracking of martensitic-austenitic constituents are the main damaging mechanisms.

Effects of martensite particle size and spatial distribution on work hardening behaviour of fine-grained dual-phase steel

ABSTRACTModel dual-phase steel microstructural variants having fine ferrite grain size and a range of martensite particle sizes and spatial distributions were produced by varying the starting microstructure prior to the intercritical annealing treatment. Superior tensile properties were obtained for the microstructural variant having the smallest (∼1 µm) uniform ferrite grain structure and a corresponding uniform distribution of small (∼0.5 µm) martensite particles. This microstructural variant also exhibited superior work hardening properties, as determined from a Crussard–Jaoul analysis and plots of instantaneous work hardening exponent vs. strain. The true work hardening rate had a positive dependence on at low strain ( < 2%) for all three microstructural variants, consistent with the geometrically necessary dislocation mechanism. At higher strains, Stage III work hardening is operative and the dislocation annihilation factor exhibited a positive dependence on .

Change in Tensile Properties of Dual-Phase Steels by Cu Addition

The effect of Cu addition on the tensile properties of dual-phase steels with various volume fractions of martensite was investigated. An increase in the intercritical-annealing temperature resulted in an increase in the volume fraction of martensite and in the hardness of steel. The Cu addition increased the hardness of steel for all volume fractions of martensite. The tensile properties strongly depended on the Cu addition and on the volume fraction of martensite. The Cu addition significantly increased the ultimate tensile stress and elongation, but it showed a negligible influence on the 0.2% proof stress. The Cu addition improved strength–ductility stability, which referred to the multiplication of ultimate tensile stress and uniform elongation, for all volume fractions of martensite. Modified Crussard–Jaoul analysis on the true stress–true strain curve indicated that the work-hardening behavior of steel was improved by adding Cu. In pre-strained steels, the dislocation density was increased by adding Cu for all volume fractions of martensite. The improvement in work-hardening behavior was explained by the increase in dislocation density attributed to the addition of Cu. Therefore, it could be concluded that the Cu addition could increase dislocation density and work hardening, thereby increasing the ultimate tensile stress and improving the strength–ductility stability of steel.

Influence of Temperature on Mechanical Properties, Fracture Morphology and Strain Hardening Behavior of a 304 Stainless Steel

The strain hardening behavior of an AISI 304 stainless steel at different temperatures was investigated in this work. Specimens were tensile tested up to rupture at temperatures of 25, 50, 75, 100, 125 and 150 oC by using a universal testing machine with an attached environmental test chamber. The induction of martensite by strain was assessed by X-ray diffraction and Rietveld refinement. The resultant fracture morphologies were analyzed by scanning electron microscopy. The changes in the mechanical properties as a function of temperature were evaluated through the variations in the stress-strain curve and the strain hardening behavior was described in terms of strain hardening rate, instantaneous strain hardening exponent and Crussard-Jaoul analysis. Six strain hardening stages were detected at lower temperatures, transitioning into three strain hardening stages at higher temperatures. Fracture surface was ductile at all studied temperatures, although differences in terms of dimple and void morphology were observed.

Microstructural and mechanical study in the plastic zone of ARMCO iron processed by ECAP

Plastic deformation of ARMCO iron processed by ECAP up to a maximum equivalent strain of sixteen (i.e., 1, 4, 8, and 16 ECAP passes) following route Bc was investigated by analyzing its microstructure and the stress-strain curves obtained after tensile tests at different levels of deformation. Three values of deformation (two in the plastic region taking into account the modified Crussard-Jaoul analysis and one after failure) were considered. Fractions of LAGB and HAGB, grain size and grain aspect ratio were calculated and compared for the different ECAP passes and tensile deformation levels. The dislocation density evolution calculated by the Bergström model for both the tensile curves and the ECAP curve showed a higher increase in the amount of dislocations during the initial stages of deformation than at higher values of deformation due to higher probabilities of dislocations annihilation. The strain hardening exponents calculated via the Bergström model for each ECAP pass shows that there is a continuous decrease in the strain hardening capacity until the eighth pass where a small increase with a subsequent stabilization was found. The dislocation densities calculated by the Estrin model presented a good correlation with values reported in bibliography for iron especially with those calculated by X-ray diffraction. This latter model predicted well the strain hardening evolution for stages III, IV and V for ARMCO iron processed by ECAP, where the main increments in hardening for stages IV and V were coming from the cell interiors.

Microstructure-property relationship in a high strength-high toughness combination ultra-heavy gauge offshore plate steel: The significance of multiphase microstructure

We elucidate here the microstructure-property relationship in high strength and high toughness 60mm thick ultra-heavy gauge plate steels characterized by ferrite-bainite multi-phase microstructure and compare with the conventional bainitic microstructure. Pilot-scale results indicated that high yield strength of ~486–508MPa with high ductility of ~10% in uniform elongation, low yield to tensile (Y/T) ratio of ~0.74–0.77, excellent low temperature toughness of ~186–228J at −60°C and good weldability are obtained in a multi-phase steel through combination of controlled rolling and accelerated cooling. The multi-phase microstructure steel consisted of quasi-polygonal ferrite and lath bainite with the corresponding phase proportion of 3:2 and 2:3 at 1/4 thickness (1/4t) and 1/2 thickness (1/2t) locations, respectively. The positive impact of multi-phase microstructure on ductility, Y/T ratio, toughness and weldability were attributed to the following aspects: (a) results from Crussard-Jaoul (C-J) analysis indicated that the soft ferrite phase in the multi-phase microstructure favorably modifies the work hardening behavior and results in high ductility and low Y/T ratio; (b) multi-phase microstructure is beneficial in enhancing toughness by enhancing initiation energy for nucleation of crack; (c) multi-phase microstructure improves the toughness of heat affected zone by altering the size and distribution of martensite/austenite (M/A) constituent.

Microstructure and Mechanical Properties of V-Nb Microalloyed Ultrafine-Grained Dual-Phase Steels Processed Through Severe Cold Rolling and Intercritical Annealing

Ultrafine-grained (UFG) dual-phase (DP) steel was produced by severe cold rolling (true strain of 2.4) and intercritical annealing of a low carbon V-Nb microalloyed steel in a temperature range of 1003 K to 1033 K (730 °C to 760 °C) for 2 minutes, and water quenching. The microstructure of UFG DP steels consisted of polygonal ferrite matrix with homogeneously distributed martensite islands (both of size <1 µm) and a small fraction of the inter lath films of retained austenite. The UFG DP steel produced through intercritical annealing at 1013 K (740 °C) has good combination of strength (1295 MPa) and ductility (uniform elongation, 13 pct). The nanoscale V- and Nb-based carbides/carbonitrides and spheroidized cementite particles have played a crucial role in achieving UFG DP microstructure and in improving the strength and work hardening. Analysis of work hardening behavior of the UFG DP steels through modified Crussard–Jaoul analysis showed a continuously varying work hardening rate response which could be approximated by 2 or 3 linear regimes. The transmission electron microscopy analysis on post tensile-tested samples indicated that these regimes are possibly related to the work hardening of ferrite, lath, and twin martensite, respectively.

Strain hardening behavior of ARMCO iron processed by ECAP

The strain hardening behavior of an ARMCO iron processed by ECAP at room temperature up to sixteen passes following route Bc was investigated through Hollomon and differential Crussard-Jaoul models. Results indicate that the Hollomon analysis shows some deviations from the experimentally determined true stress – true strain curves while the differential Crussard-Jaoul analysis based on the Ludwik equation and the modified Crussard- Jaoul analysis based on the Swift equation fit better when two work hardening exponents are considered. As expected, the strength of the material increased with the number of ECAP passes. Indeed the ultimate tensile stress reached a maximum of ~900MPa after 16 passes, which is more than three times higher than the UTS of the annealed material. Nevertheless, the strain hardening capacity of the material was reduced in comparison with the material without severe plastic deformation. For that reason the tensile ductility was also reduced at increasing ECAP passes. The increase in strength was attributed to the reduction of the grain size through refined sub-grains with high density of dislocations. After sixteenth passes the original grain size (namely 70 mm) was reduced down to 300 to 400 nm observing a good correspondence with the Hall-Petch relationship. The microstructural analysis, carried out by EBSD, showed an increasing amount in the fraction of high Angle Grain Boundaries (HAGB) after 1 pass due to the regeneration of the microstructure with a smaller grain size.