Cold-worked Samples Research Articles

Effect of martensitic reversal and grain size on the corrosion and wear behaviour of Cr-Mn steel

In this study, the effect of corrosion and wear behaviour of Cr-Mn steel on fine grains were investigated. The sample were solution annealed (SA) for 1 h at 1050 °C and then cold rolled (CW) to 30%. Further the cold rolled sample were thermally aged (CW + TA) 900 °C for four hours. The findings showed that under the 10 N applied load, wear resistance increased with an increase in hardness and martensite fraction of the cold worked (CW) samples. However, the Cr-Mn steel had the superior wear resistance after thermal ageing (TA). In microstructural examination deformation bands can also be visible in cold work samples. The analysis implies that the γ-phase is apparent across all peaks within the spectra of SA samples. In instances involving 30% cold work, prominent α′ martensite peaks were observed, accompanied by minimal ε-martensite peaks. Electrochemical impedance spectroscopy (EIS) analysis discloses a reduction in impedance and a concurrent increase in the defect density of the passive film. The CW+TA structure with good inclusive performances created an early constant hardened layer, which didn’t delaminate and peel off prematurely, thereby effectively increasing the wear resistance, according to analysis of the wear mechanism. The results also concluded that the corrosion resistance of CW sample decreases due to SIM formation, however CW+TA sample provide better corrosion resistance due to smaller and refined grain size.

Conventional Light Microscopy Reveals Beauty of Single Phase Cartridge Brass

Abstract This article describes sample preparation to create a visually impressive micrograph image of single-phase cartridge brass, C26000, an alloy composition of 70% copper and 30% zinc. C26000 was chosen due to the striking twins and large grain size that are easily generated by annealing a cold-worked sample, the large range of contrast and colors that can be created by etching, and the wide availability of the material. This entry won the Jacquet-Lucas Award for Best in Show at the 2021 International Metallographic Contest.

Enhanced pseudoelasticity of an Fe–Mn–Si-based shape memory alloy by applying microstructural engineering through recrystallization and precipitation

The aim of this work is to provide a novel understanding of pseudoelasticity mechanisms in an FeMnSi-based shape memory alloy and to utilize the identified parameters to control and enhance the mechanical behavior of the alloy. The alloy was processed by employing caliber rolling to an equivalent strain of 0.25 at room temperature. Various heat treatments from 530 to 1000 °C were applied to study the microstructural evolution and pseudoelasticity behavior during short-term post-deformation annealing (PDA) and aging. A minimum residual strain of 2.85% was achieved after 4% loading in tension by annealing the cold-worked sample at 925 °C for 50 min followed by aging at 750 °C for 6 h; this is the lowest ever reported residual strain for this alloy. Moreover, the absorbed energy increased from 17 to 22 J/cm3, indicating a 30% enhancement compared with the as-received aged sample. These improvements in pseudoelasticity and absorbed energy make this alloy more suitable for seismic damping application by providing more recentering after energy dissipation. The improvements are mainly attributed to grain refinement, which stimulates a uniform distribution of precipitates inside the austenite grains after PDA and aging. Additionally, grain refinement modifies the morphology and size of precipitates, resulting in an increased number of stacking faults and a high volume fraction of ε-martensite, and diminishes the probability of the intersection of ε-martensite laths with each other and subsequent α′-martensite formation.

Magnetic properties of equiatomic CrMnFeCoNi

Magnetic, specific heat, and structural properties of the equiatomic Cantor alloy system are reported for temperatures between 5 kelvin and 300 kelvin, and up to fields of 70 kilo-oersted. Magnetization measurements performed on as-cast, annealed, and cold-worked samples reveal a strong processing history dependence and that high-temperature annealing after cold-working does not restore the alloy to a pristine state. Measurements on known precipitates show that the two transitions, detected at 43 kelvin and 85 kelvin, are intrinsic to the Cantor alloy and not the result of an impurity phase. Experimental and ab initio density functional theory (DFT) computational results suggest that these transitions are a weak ferrimagnetic transition and a spin-glass-like transition, respectively, and magnetic and specific heat measurements provide evidence of significant Stoner enhancement and electron-electron interactions within the material.

Characterization of Dislocations in hcp ^4hbox {He} by Torsional Oscillator and Thermal Conductivity Measurements

We apply two complementary techniques for the characterization of mobile dislocations in samples of hcp ^4hbox {He} with the concentration of ^3hbox {He} sim 3times 10^{-7}, grown by the blocked capillary method at molar volume 19.5 hbox {cm}^3,hbox {mol}^{-1}, before and after annealing at temperatures 1.8–2.0 K, and also after work hardening by high-amplitude twisting at 0.03 K and successive recovery at 0.5–1.0 K. The first technique relies on the elastic response of solid helium to oscillatory twisting at frequencies 161 Hz and 931 Hz at temperatures below 1 K, where this response is affected by the presence of mobile dislocations with variable amounts of trapped ^3hbox {He} impurities. Monitoring the non-equilibrium amplitude dependence after moderate forcing allows to compute the length distribution n(L) of mobile dislocations (Iwasa in J Low Temp Phys 171:30, 2013; Fefferman et al. in Phys Rev B 89:014105, 2014). We also test methods of determining n(L) from the equilibrium temperature dependence of either real or imaginary part of the shear modulus at small strain amplitudes, based on the values of the damping force measured by Fefferman et al. [2]. The second technique utilizes measurements of thermal conductivity at temperatures below 0.4 K, i.e., of the dislocation-limited mean free path of thermal transverse phonons (Greenberg and Armstrong in Phys Rev B 20:1049, 1979; Armstrong et al. in Phys Rev B 20:1061, 1979). During a prolonged AC-twisting at a high amplitude of strain exceeding the yield stress, long dislocations disappear being replaced by many short ones which remain mobile. However, upon stopping this twisting, the majority of dislocations become immobilized until the sample is warmed up above 0.5 K to speed-up the recovery of dislocations to their mobile state (Day et al. in Phys Rev B 79:214524, 2009; Beamish and Franck in Phys Rev B 26:6104, 1982). This is different from the immobilization of dislocations by trapped ^3hbox {He} impurities, routinely observed at smaller strain amplitudes, which is characterized by much shorter relaxation times to effectively un-trap ^3hbox {He} atoms and make dislocations mobile again. We investigated the dynamics of the recovery of cold-worked samples, during which short segments quickly disappear, while the longest one appear after longer annealing times; the activation energy was estimated to be 22 K—pointing at the thermal vacancy-assisted process. A complementary characterization by the scattering rate of thermal transverse phonons off crystalline defects rules out non-interacting mobile dislocations as the dominant scatterer. The main conclusion is that while many properties of the sample are consistent with the theory of Granato and Lücke of isolated gliding dislocations (Granato and Lücke in J Appl Phys 27:583, 1956), several observations at low temperatures (^3hbox {He}-independent immobilization of dislocations after stopping high-amplitude twisting, sporadic avalanche-like relaxation of strain, flat temperature dependence of the phonon scattering rate) point at the presence of interacting dislocations, probably arranged into dislocation walls.

Influence of workpiece texture and strain hardening on chip formation during machining of Ti–6Al–4V alloy

The results of the investigation on the influence of texture on chip formation during machining of Ti–6Al–4V alloy are reported in this work. Different textures are produced in this alloy by cold-rolling as-received and annealed material to 30–47% reductions. As-received and annealed samples exhibited basal and transverse textures while in cold-worked material, the basal texture disappeared and, a texture component with (0001) pole inclined at 70° from the Z direction was observed. Machining was done in these thermo-mechanically processed plates at a low cutting speed of 0.8 m/min to avoid temperature rise and the consequent microstructural modification. As-received and annealed material exhibited saw-tooth morphology of chips, while samples deformed to cold-work of 40% and above produced continuous chips with fine serrations at the free surface. Machined chips have retained the transverse texture in annealed material with reduced intensity, while the basal texture has disappeared in deformed material. The possible slip systems responsible for the development of these textures were identified using Schmid factors. The difference in morphology of chips between annealed and cold-worked samples is explained based on texture developed during machining, which has a bearing on the strain necessary for fracture initiation in the primary shear zone, thus affecting the spatial frequency of segmentation.

Effect of recrystallization on degree of sensitization in nickel free austenitic stainless steel

PurposeEffect of grain size on degree of sensitization (DOS) was been evaluated in Nickel free steel. Manganese and nitrogen contained alloy is a Ni-free austenitic stainless steels (ASS) having type 202 grade. The main purpose of this investigation is to find the effect of recrystallization on the DOS of stainless steel after the thermo-mechanical processing (cold work and thermal aging).Design/methodology/approachIn the present investigation, the deformation of 202 grade analyzed using X-ray diffraction (XRD) and microstructural testing. Optical microstructure of Ni-free ASS has been done for cold worked samples with thermally aged at 900°C_6 h. Double loop electrochemical potentiodynamic reactivation test used for findings of degree of sensitization.FindingsNi-free ASS appears to be deformed more rapidly due to its higher stacking fault energy which gave results in rapid transformation from strain induced martensite to austenite in form of recrystallized grains, i.e. it concluded that as cold work percentage increases more rapidly recrystallization occurs. XRD results also indicate that more fraction of martensite formed as percentage of CW increases but as thermal aging reverted those all martensite to austenite. So investigation gives the conclusion which suggests that with high deformation at higher temperature and duration gives very less DOS.Originality/valueVarious literatures available for 300 series steel related to the effect of cold work on mechanical properties and sensitization mechanism. However, no one has investigated the effect of recrystallization through thermomechanical processing on the sensitization of nickel-free steel.

The Effect of Reversion of Strain-Induced Martensite (SIM) and Grain Refinement on the Intergranular Corrosion of High Mn Steel

The surface phase constituent of high-manganese austenitic stainless steel after cold work (15%, 30%, and 50%) and thermal aging at 900°C for 30 min and 6 h, was characterized using x-ray diffraction. The microstructural analysis was conducted using an optical microscope, a scanning electron microscope, and the electron backscatter diffraction technique. The double-loop electrochemical potentiokinetic reactivation test was used to measure the intergranular corrosion resistance (degrees of sensitization). The results showed that fine-recovered grains of austenite and strain-induced martensite together formed the surface of high-manganese steel after cold work. Because of the formation of strain-induced martensite in the cold-worked samples, their intergranular corrosion was much higher than that of the as-received sample. Also, the degree of sensitization of 15% cold work was higher (i.e., more intergranular corrosion) compared to the degrees of sensitization of 30% and 50% cold work. On the contrary, the intergranular corrosion of high-manganese austenitic stainless steel sample subjected to cold work was eliminated during thermal aging at 900°C for 6 h because of the reversion of strain-induced martensite and fine-reverted austenite grains. Owing to this grain refinement of austenite, faster diffusion rate of Cr at higher temperature and cold work helped healing of Cr-depletion zone in a shorter time. In other words, because the results showed that on 50% cold work and thermal aging at 900°C for 6 h, the high-manganese austenitic stainless steel does not become susceptible to intergranular corrosion. Hence, it could be beneficial to investigate the intergranular corrosion of high-manganese austenitic stainless steel.

Effect of grain refinement on sensitization of high manganese austenitic stainless steel

Effect of grain size on degree of sensitization (DOS) was been evaluated in Nickel free steel. Manganese and nitrogen contained alloy is a Ni free austenitic stainless steel (ASS) having type 202 grade. In the present investigation, the deformation of 202 grade analyzed using XRD and microstructural testing. Optical Microstructure of Ni free austenitic stainless steel (ASS) has been done for cold worked samples with thermally aged at 900 °C_6 Hrs. Ni free austenitic stainless steel (ASS) appears to be deformed more rapidly due to its higher stacking fault energy which gave results in rapid transformation from strain induced martensite to austenite in form of recrystallized grains, i.e., it concluded that as cold work percentage increases more rapidly recrystallization occurs. XRD results also indicate that more fraction of martensite formed as percentage of CW increases but as thermal ageing reverted those all martensite to austenite. Double Loop Electro-potentio Reactivation Method (DLEPR) test used for findings of degree of sensitization. So investigation gives the conclusion which suggest that with high deformation at higher temperature and duration gives very less degree of sensitization (DOS).

Precipitation processes and structural evolutions of various GPB zones and two types of S phases in a cold-rolled Al-Mg-Cu alloy

The Guinier–Preston–Bagaryatsky (GPB) zone and the S phase are the key strengthening precipitates in Al-Cu-Mg alloys. However, how their respective structures evolve during aging has not been fully understood. In this work, the age-hardening behavior and the precipitates in an Al–3Mg–1Cu (wt.%) alloy were investigated by means of Vickers hardness measurements, differential scanning calorimetry, transmission electron microscopy, and density functional theory calculations. A series of common GPB zones and a novel type of GPB zone named “GPBX” were observed in the cold-worked samples aged at 443 K for 20 min. In the subsequent aging, two types of S phases were found to coexist, labeled S-I and S-II phases. Density functional theory calculation results indicate that GPBX zone is stable and the S-I and S-II phases have almost the same formation enthalpy. Common GPB zones transform to S-I phases, while S-II phases are formed from GPBX zones preferentially along dislocation lines. The misorientation angles and morphologies of the S phases are also discussed. GPB zones were confirmed to be structurally linked to β” and U2 precipitates reported in 6xxx (Al-Mg-Si) series Al alloys. The revealed precipitate structures and their interrelationships may provide insights into future alloy design.

Effects of thermomechanical treatment on the microstructure, precipitation strengthening, internal friction, and thermal stability of Al–Er-Yb-Sc alloys with good electrical conductivity

Rare-earth elements improve the mechanical properties of aluminum owing to the formation of the L12-structured nanoprecipitates providing the precipitation strengthening effect. The precipitates type, size, and number density depend on the alloy chemical composition and a thermomechanical treatment regime. It is essential to develop the alloys and treatments, providing a combination of the enhanced mechanical strength and a high level of electrical conductivity. This study investigates the influence of thermomechanical treatments on the microstructure, precipitation strengthening, mechanical properties, and electrical conductivity of Al–Er-Yb-Sc alloys with differing Sc content. An as-cast structure of the alloys studied consists of a supersaturated aluminum solid solution and Al3(Er,Yb) phase particles of eutectic origin with the particle thickness of 50–200 nm. A significant strengthening during post-deformation annealing is achieved by precipitation of L12-Al3(Sc,Er,Yb) phase dispersoids of 4–8 nm in size. The mechanical spectroscopy method is successfully used to understand the precipitation kinetics of the studied alloys in comparison with analogous Al-Yb-Y-Sc alloys. This method is highly sensitive to lattice defects parameters, i.e., recrystallization and precipitation kinetics. High-scandium alloys demonstrate an increase of the hardness and tensile strength and insignificant changes in the internal friction background level during post-deformation annealing of cold-worked samples at 300 °C. The yield strength of the Al–Er-Yb-Sc alloys after post-deformation annealing is 142–231 MPa, elongation-to-failure is 3.6–13.5%, and electrical conductivity is 54.8–60.9% IACS, dependent on scandium content and annealing parameters. The studied alloys exhibit high thermal stability of the tensile properties, which remains unchanged during annealing at 300 °C for 100 h.

Uniaxial and biaxial ratcheting behavior of pressurized AISI 316L pipe under cyclic loading: Experiment and simulation

Ratcheting defined as the progressive accumulation of plastic strain occurring during cyclic loading in the presence of the mean stress is one of the most prevalent failure modes in engineering structures. Experimental studies were conducted to characterize the uniaxial and biaxial ratcheting responses of an AISI 316L pipe. Experimental results show that an obvious cyclic hardening occurs in the AISI 316L pipe under uniaxial strain loading. Uniaxial ratcheting rate obtained from the axial cyclic experiment reaches a quasi-steady rate after a certain number of loading cycles. Moreover, using a designed four-point bending experimental setup, different axial stress amplitudes in the presence of the constant hoop stress were considered to characterize the biaxial ratcheting response of the material. The ratcheting strain and ratcheting strain rate in the hoop direction increase with increasing axial stress amplitudes under the constant hoop stress. To simulate the uniaxial and biaxial ratcheting behavior of the AISI 316L pipe, the Chaboche nonlinear kinematic hardening model was used. Using the Particle Swarm Optimization (PSO) technique, parameters of the Chaboche model were identified efficiently from the monotonic response of a cold-worked sample. The elastic limit of the material was measured using a very careful quasi-static cyclic compression experiment. The procedure to calibrate the material parameters for the Chaboche model and finite element simulation results were validated well with experimental data for the AISI 316L pipe. It is shown that the Chaboche model with the suitably-calibrated parameters from the experimental study can be applied to rigorously predict the ratcheting behavior of the AISI 316L pipe under cyclic uniaxial and biaxial loading conditions.

Influence of Strain Rate and Percentage of Cold Work on Room-Temperature Deformation Behaviour of AISI 1015 Carbon Steel: Detailed Microstructures and Cold Workability Map Investigations

AISI 1015 low-carbon steel is being frequently applied in various steel industries, especially in the processing of parts by cold-forged, cold-headed and/or cold-formed machine tool parts. In this paper, the uniaxial compression test was conducted on AISI 1015 steel by varying the amount of percentage of cold work (PCW) and the strain rates (SRs). The PCW was varied from 15 to 65%, whereas the SR was increased from 1 × 10−4 to 1 × 10−1 s−1 with a step of 1000 times. The microstructural analyses of as-received and cold-deformed samples were carried out using various electron microscopes. The as-received microstructure revealed the presence of coarse α-ferrite and fine pearlite grains. Based on the process parameters, a cold workability map was developed and investigated by which the safe cold work parameters could be selected. The cold-deformed results through electron backscattered diffraction were explained. More elongated deformed grains (a fibre texture) were observed at low SR. A highly stressed equiaxed grain (spread texture) was obtained at a very high SR due to strain incompatibility. Finally, the work hardening behaviour was investigated as a function of SR for 65% cold-worked samples.

Fracture-mechanics-based evaluation of failure limit on pre-cracked and hydrided Zircaloy-4 cladding tube under biaxial stress states

ABSTRACTTo better understand the failure limit of fuel cladding during the pellet-cladding mechanical interaction (PCMI) phase of a reactivity-initiated accident (RIA), pre-cracked and hydrided cladding samples with base metal final heat-treatment status of cold worked (CW) and recrystallized (RX) were tested under biaxial stress conditions (strain ratios (εz/εθ) of 0 and 0.5). Displacement-controlled biaxial-expansion-due-to-compression (biaxial-EDC) tests were performed to obtain the hoop strain at failure (failure strain) of the samples. The conversion of the failure strains to J-integrals at failure (JIC) by finite-element analysis involving data of stress-relieved (SR) cladding specimens from our previous study revealed that the failure limit in the dimension of JIC unifies the effects of pre-crack depth. About 30–50% reduction in the JIC value was observed as the strain ratio increased from 0 to 0.5 irrespective of the annealing type, pre-crack depth, and hydrogen content. The rate of fractional decreases of JIC with increase of hydrogen content is in the order of CW>SR>RX, which are essentially independent of strain ratio for the CW and SR samples. The results were incorporated into the failure prediction model of the JAEA’s fuel performance code in the form of a correction factor that considers the biaxial loading effect.

On the Influence of Cold Working and Electrochemical Nitridation on the Corrosion Behaviour of 316L Austenitic Stainless Steel in Acidic Environment

The present paper investigates the effect of cold working and electrochemical nitridation on corrosion resistance of 316L austenitic stainless steel (ASS). The X-ray diffraction results showed that the strain-induced martensite is formed on cold work. Also, the volumetric fraction of strain induced martensite and dislocation density increased with increase in degree of cold work. The cold working process adversely affects the corrosion resistance of 316L ASS due to the formation of the strain-induced martensite and increased dislocation density. On electrochemical nitridation, the electrochemical results show the formation of stable passive film, thus improving the corrosion resistance of 316L ASS attributed to the formation of nitrides on the surface. Moreover, the beneficial effect of electrochemical nitridation is more pronounced in cold worked samples, thus the adverse effects of cold working can be overcome by electrochemical nitridation.

Effect of thermal aging on IGC of cold worked Cr-Mn austenitic stainless steel

PurposeThe purpose of this study is to investigate the effect of prior cold work after annealing and thermal ageing on intergranular corrosion or sensitization of Cr-Mn austenitic stainless steel (ASS) is necessary. Such a study is particularly important because ASS are mostly used and welded in mill-annealed condition, which is equivalent to fully annealed material with some cold worked (CW).Design/methodology/approachThe effect of 15% CW of 202 ASS were investigated using microstructural (optical microscope), mechanical (grain size and hardness) and electrochemical methods (double loop electrochemical reactivation [DLEPR]) followed by thermal ageing (800°C, 900°C and 1000°C).FindingsX-ray diffraction analysis shows the presence of martensite in CW samples. The increase in martensite formation (800°C and 900°C) can be observed with the variation of thermal ageing (TA) duration (1, 2 and 3 h). However, there was decreased in the formation of martensite at the temperature of 1000°C because of martensitic reversal. The DLEPR test result shows higher degree of sensitization (DOS) for 800°C and 900°C but for 1000°C, there was re-homogenization of samples which leads to lower DOS (thermal ageing for 1, 2 and 3 h).Originality/valueFor 300 series steel, there are various literature available for the effect of cold work on mechanical properties and DOS. However, no one has investigated the effect of cold work and thermal ageing on the sensitization of 202 Cr-Mn ASS.

Study on the Influence of Prior Cold Work on Precipitation Behavior of 304HCu Stainless Steel During Isothermal Aging

The precipitation strengthening behavior of 304HCu austenitic stainless steel during isothermal aging at 650 °C is studied under 10 and 20 pct prior cold-worked conditions. The age hardening behavior under these cold-working conditions have been studied using hardness and electrical conductivity measurements. The analysis of electrical conductivity and hardness variation, during isothermal aging at 650 °C using the Johnson–Mehl–Avrami equation, indicates an increase in precipitation kinetics in the matrix, influenced by the dislocations formed during cold working. Further, XRD profiles of different cold-worked samples obtained from the INDUS-2 synchrotron are able to indicate the formation of very fine precipitates during thermal aging and these findings are corroborated with conductivity and hardness changes. The observed change in precipitation kinetics due to deformation is analyzed to evaluate an equivalent change in activation energy which is attributed to an equivalent of increase in aging temperature.

Comparison of the transformation behavior of cold rolling with aging and hot extrusion with aging processed Ni50.3Ti29.7Hf20 high temperature shape memory alloy

Among NiTiHf high temperature shape memory alloys, nickel rich ternary Ni50.3Ti29.7Hf20 (at%) alloy has been studied extensively and found to be promising for high temperature applications especially in aerospace industry. NiTiHf alloys have very high strength and transformation temperatures (TTs) proportional to their hafnium percentage. Therefore, these alloys are accepted as a hard to deform material. Hot extrusion at 900 °C and solutionizing at 1050 °C-1100°C treatments have been generally used in literature for the homogenization of the cast microstructure and chemistry and thus, the strength of the material eventually increases. In this study, one set of the as cast Ni50.3Ti29.7Hf20 alloy was hot extruded at 900 °C and then aged at 550 °C for 3 h and the other set was solutionized at 1050 °C for 2 h, cold rolled for 10% at room temperature and then aged at 550 °C for 3 h. The TTs of the hot extruded, hot extruded and aged, solutionized, solutionized-cold rolled and aged samples were measured using DSC and heating-cooling experiments under increasing stress magnitudes starting from 100 MPa and increasing up to 600 MPa were conducted on all thermal and thermo-mechanically treated samples in order to compare the shape memory characteristics such as actuation strain, irrecoverable strain and TTs. The samples which were hot extruded and aged and solutionized-cold rolled and aged showed very high dimensional stability with no irrecoverable strain values up to 500 MPa. However, the actuation strain magnitudes of the cold rolled with aging processed sample were half of the actuation strain values of the sample which was hot extruded and aging treated. Additionally, higher undercooling and overheating were necessary to achieve full transformation in the cold worked samples. These results might be due to the very high dislocation density and texture formation which was induced during cold rolling process.

Effect of cold work and slow strain rate on 321SS stress corrosion cracking in abnormal conditions of simulated PWR primary environment

Abstract In this paper, stress corrosion cracking (SCC) behavior of 0%, 5%, 10% cold-worked (CW) 321 stainless steel (321 SS) in abnormal conditions of simulated pressurized water reactor (PWR) primary water was studied at two different slow strain rates of 4.2 × 10−6, 4.2 × 10−7. The experimental results show that with the increase of the degree of cold work, the internal grain of the sample is refined. The slip zone and deformation twins occur inside some grains. The SCC sensitivity of the strain rate of 4.2 × 10−7 S−1 is higher than the strain rate of 4.2 × 10−6 S−1. And the higher the degree of cold work, the higher the SCC sensitivity of the sample. Dynamic strain aging (DSA) occurs at 321 SS with different cold work degrees with a slow strain rate of 4.2 × 10−7 S−1. DSA makes the tensile zone near the fracture of 5% CW and 10% CW samples have higher vacancy defect density, which promotes the initiation and expansion of SCC crack.

Creep studies of Cold Worked Austenitic Stainless Steel

Ti modified 14Cr-15Ni austenitic stainless steel (SS) has been developed for nuclear fuel cladding and wrapper material for its superior creep strength and better void swelling resistance during service. Cold working induces high dislocation density network in the material. These dislocations interact with point defects, which are generated by neutron irradiation during service and facilitate recombination to make the material more void swelling resistant. In present investigation, creep behavior of various cold worked (up to 40%) samples in comparison with mill annealed samples was studied. Initially, the steel was solution treated at 1333 K for 30 minutes followed by cold rolling at room temperature. Uniaxial creep test was performed at 973 K for 200 MPa stress level. The effects of cold work as well as stress on creep behavior have been studied in this investigation. Cold worked samples exhibited better creep strength as compared to mill annealed samples. During creep exposure at 973 K, material showed phenomena of recovery as well as recrystallization due to initial cold working. This partial recovery and recrystallization in material also depend upon the applied stress and led to variation in creep strength of the material. Precipitation of carbides particles was seen to be accelerated at the grain boundaries and this phenomenon was more prominently observed in cold worked samples.