Total Elongation Values Research Articles

The effect of rolling direction and strain rates on the tensile properties of AA2024-T3 aluminum alloy

The AA2024-T3 alloy is a lightweight and durable material commonly used in the aerospace industry. This study investigates the impact of the rolling direction (RD) and strain rates on the alloy’s tensile properties. Tensile tests have been performed on samples oriented parallel and transverse to the rolling direction at varying strain rates (5, 25, and 125 mm/min). Samples parallel to the rolling direction have exhibited higher strength compared to those in the transverse direction (TD). At a strain rate of 5 mm/min, the maximum tensile strength in RD samples has been 530.72 MPa, while in TD samples, it has been 505.76 MPa. At 25 mm/min, the tensile strength has been 498.31 MPa in RD and 482.91 MPa in TD. At 125 mm/min, the tensile strength has been 508.52 MPa in RD and 480.36 MPa in TD. The increase in strain rate has had a complex effect on the mechanical properties. The total elongation values have also varied with strain rate, with the highest total elongation observed at 5 mm/min (0.168) in both RD and TD directions. These findings have highlighted the significant impact of the rolling direction and strain rate on the mechanical properties of the AA2024-T3 alloy, which should be considered in design and manufacturing processes.

Dual heterogeneous structure enabled ultrahigh strength and ductility across a broad temperature range in CrCoNi-based medium-entropy alloy

Developing alloys with exceptional strength-ductility combinations across a broad temperature range is crucial for advanced structural applications. The emerging face-centered cubic medium-entropy alloys (MEAs) demonstrate outstanding mechanical properties at both ambient and cryogenic temperatures. They are anticipated to extend their applicability to elevated temperatures, owing to their inherent advantages in leveraging multiple strengthening and deformation mechanisms. Here, a dual heterostructure, comprising of heterogeneous grain structure with heterogeneous distribution of the micro-scale Nb-rich Laves phases, is introduced in a CrCoNi-based MEA through thermo-mechanical processing. Additionally, a high-density nano-coherent γ' phase is introduced within the grains through isothermal aging treatments. The superior thermal stability of the heterogeneously distributed precipitates enables the dual heterostructure to persist at temperatures up to 1073 K, allowing the MEA to maintain excellent mechanical properties across a wide temperature range. The yield strength of the dual-heterogeneous-structured MEA reaches up to 1.2 GPa, 1.1 GPa, 0.8 GPa, and 0.6 GPa, coupled with total elongation values of 28.6 %, 28.4 %, 12.6 %, and 6.1 % at 93 K, 298 K, 873 K, and 1073 K, respectively. The high yield strength primarily stems from precipitation strengthening and hetero-deformation-induced strengthening. The high flow stress and low stacking fault energy of the dual-heterogeneous-structured MEA promote the formation of high-density stacking faults and nanotwins during deformation from 93 K to 1073 K, and their density increase with decreasing deformation temperature. This greatly contributes to the enhanced strain-hardening capability and ductility across a wide temperature range. This study offers a practical solution for designing dual-heterogeneous-structured MEAs with both high yield strength and large ductility across a wide temperature range.

Optimizing austenite and carbide content in medium carbon silicon-rich steel: A stepped partitioning strategy and analysis of strengthening and ductility enhancement mechanisms

To achieve the objective of enhancing the yield strength (YS) of quenching and partitioning (Q&P) steel without compromising tensile strength and ductility, a stepped partitioning (SP) strategy was proposed for Q&P treatment on medium carbon silicon-rich steel. The optimized partitioning strategy involves a two-stage partitioning, the first stage is conducted at temperatures above the martensite start (Ms) temperature, followed by the second stage carried out at a lower temperature for an extended period, involving isothermal partitioning. Experimental results demonstrate that the SP strategy yields a significant quantity of small carbides, with an average size of 59.02 nm, along with 15.71 vol% of retained austenite (RA) and a carbon concentration of 1.01 wt% in RA. Furthermore, the SP-treated specimen exhibits a remarkable balance of strength and ductility, showcasing YS, ultimate tensile strength (UTS), and total elongation (TE) values reaching 1732 MPa, 2263 MPa, and 14.9%, respectively. The microstructure evolution during tensile deformation demonstrates that RA in short-duration conventional partitioning specimens underwent premature martensitic transformation during tensile deformation due to early deformation, whereas RA in long time conventional partitioning specimens was overstabilized due to highest C concentration, which resulted in poor enhancement of strengthening and ductility by TRIP effect. In contrast, the SP strategy achieved a reasonable stability of RA, resulting in a simultaneous increase of tensile strength and ductility. Simultaneously, an analysis of precipitation strengthening indicates that the abundance of fine carbides in martensite contributes to an increase in YS due to precipitation strengthening.

Cold Formability of Twin-Roll Cast, Rolled and Annealed Mg Strips

This study investigates the cold formability of twin-roll cast and rolled magnesium strips, specifically focusing on AZ31 and ZAX210 alloys. The aim is to assess the suitability of these alloys for various forming processes. The mechanical properties and formability characteristics of the strips were thoroughly examined to provide insights into their potential applications in transportation industries such as automotive and aerospace. The AZ31 and ZAX210 alloys were subjected to twin-roll casting and rolling processes to produce thin strips. The resulting strips were then evaluated for their cold formability. The results indicate that both alloys exhibit favourable cold formability. The ZAX210 alloy, in particular, demonstrates medium strengths with an average tensile strength of approximately 240 MPa at room temperature. The 0.2% proof stress values range between 136 MPa and 159 MPa, depending on the sampling direction. The total elongation values vary from 28% in the transverse direction to 32% at a 45° angle, indicating excellent ductility. Comparing the two alloys, the AZ31 alloy shows higher strengths due to its higher aluminium content. However, it also exhibits a more pronounced directional dependence of mechanical properties due to the formation of a strong basal texture during hot rolling. The transverse direction experiences reduced total elongation compared to the rolling direction, achieving only about 50% of the total elongation. The average Erichsen Index recorded for AZ31 and ZAX210 strips were 4.9 mm and 7.1 mm, respectively. The ZAX210 strip displays superior formability, which can be attributed to the fine-grained microstructure and the texture softening resulting from the weakening of the basal texture intensity and the splitting of the basal pole towards the rolling direction. In conclusion, the investigated twin-roll cast, rolled and annealed AZ31 and ZAX210 magnesium strips exhibit promising cold formability characteristics. The findings of this study contribute to the understanding of their mechanical behaviour and can guide the selection and optimisation of these alloys for various forming applications.

The Effect of Deformation Temperature on the Deformation Mechanism of a Medium-Mn Advanced High-Strength Steel (AHSS)

The deformation mechanism of a medium-Mn advanced high strength steel (AHSS) over a temperature range from 25 °C to 400 °C has been studied. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the microstructures of specimens after the tensile test at different temperatures. Four deformation mechanisms were found, namely deformation-induced martensitic (DIM) transformation, deformation-induced bainitic (DIB) transformation, deformation twinning and dislocation glide. Among these deformation mechanisms, DIM and DIB were very effective mechanisms to contribute work hardening. The product of ultimate tensile strength (UTS) and total elongation (TEL) of the AHSS reached a value higher than 65 GPa%, when these two mechanisms occurred. The highest UTS × TEL value of 84 GPa% was obtained at 150 °C. From the results of the present research, it is suggested that warm working is a good processing route for obtaining a combination of high strength and high ductility in medium-Mn AHSS.

Observations of radiation-enhanced ductility in irradiated Inconel 718: Tensile properties, deformation behavior, and microstructure

An increase in ductility with radiation dose was observed and investigated during postirradiation evaluation of tensile properties, microstructure, deformation behavior, and fracture behavior of specimens from a solution-annealed Inconel 718 proton beam window operated at the Spallation Neutron Source. While in service, the window was irradiated with 940 MeV protons to a maximum dose of approximately 9.7 displacements per atom (dpa) at a calculated irradiation temperature of approximately 110 °C. The double-walled window was sampled after removal from service, and specimens from the samples were characterized using transmission electron microscopy and tensile testing accompanied by digital image correlation. The results showed that the window material had very high tensile strength and retained an appreciable amount of ductility after irradiation. Specimens irradiated to approximately 9 dpa had yield strengths of around 1 GPa while concurrently straining to approximately 19% total elongation before fracture. A steady increase in ductility was observed with increasing dose for the material tested; both uniform and total elongation values increased as the radiation dose increased from 2.5 to 9.7 dpa. High-resolution scanning transmission electron microscopy and electron energy-loss spectroscopy, performed at atomic resolution, showed the existence of nanometer scale stacking faults and nanometer size vacancy clusters associated with H and possibly He. These radiation-induced defect structures may have increased the ability of the material to strain-harden during deformation and increased the ductility with increasing dose. The results were encouraging and suggest that the mechanical performance of Inconel 718 after irradiation to 9.7 dpa is favorable and provided support to increase the proton beam window service lifetime to higher displacement dose levels.

A novel process combining thermal deformation and intercritical annealing to enhance mechanical properties and avoid Lüders strain of Fe-0.2C–7Mn TRIP steel

This paper proposed a novel process combining thermal deformation and intercritical annealing (IA) to enhance mechanical properties and avoid Lüders strain of Fe-0.2C–7Mn steel. The experiment results show that the prior microstructure, including prior austenite grain (PAG) size, dislocation density, carbides precipitation and stored deformation energy before IA have great impacts on the nucleation and growth of austenite during IA, and ultimately influence the morphology, grain size, volume fraction and stability of retained austenite (RA) after IA. The low temperature and relatively high strain rate deformation condition sample (referred as 1-LT/RHS) with film-like and block-like mixture morphology structure after IA exhibits the largest product of ultimate tensile strength and total elongation (UTS × TE) value (53 GPa∙%), due to the double-stage discontinuous transformation-induced plasticity (TRIP) effects. Block-like austenite dominates the 1st-stage plastic deformation, while film-like austenite dominates the 2nd-stage. Because the film-like austenite is more stable than the block-like, which is confirmed by the interrupted tensile tests and nanoindentation investigation. Besides, compared to the cold-rolled sample (referred as 3-CR) with single block-like structure after IA, the film-like ferrite in sample 1-LT/RHS initiate dislocation plasticity earlier than the block-like ferrite, resulting in the disappearance of Lüders strain. This is because the different formation mechanisms, leading to the initial dislocation density before deformation in film-like grains much higher than in block-like grains. Moreover, the procedure of this novel process is simple with low industrial cost, which can provide a new guidance for development of lower cost fabricating technology of medium Mn TRIP steel.

Damage Analysis of Third-Generation Advanced High-Strength Steel Based on the Gurson–Tvergaard–Needleman (GTN) Model

The third generation of advanced high-strength steels (AHSS) brought attention to the steel and automotive industries due to its good compromise between formability and production costs. This work evaluated a third-generation AHSS (USS CR980XG3TM) through microstructural and X-ray diffraction (XRD) analyses, uniaxial tensile and plane-strain tension testing, and numerical simulations. The damage behavior of this steel is described with the Gurson–Tvergaard–Needleman (GTN) model using an identification procedure based on the uniaxial tensile and initial microvoids data. The microstructure of the CR980XG3TM steel is composed of ferrite, martensite–austenite islands, and retained austenite with a volume fraction of 12.2%. The global formability of the CR980XG3TM steel, namely the product of the uniaxial tensile strength and total elongation values, is 24.3 GPa%. The Lankford coefficient shows a weak initial plastic anisotropy of the CR980XG3TM steel with the in-plane anisotropy close to zero (−0.079) and the normal anisotropy close to unity (0.917). The identified GTN parameters for the CR980XG3TM steel provided a good forecast for the limit strains defined according to ISO 12004-2 standard from the uniaxial tensile and plane-strain tension data.

Investigation of austenitising behaviour of medium-Mn steel in the hot-stamping heating process

In this study, the austenite transformation behaviour in a medium-Mn (MMn) steel is investigated during heat treatments that replicate those occurring in low-temperature hot stamping (LTHS), with the aim of better understanding this behaviour to optimise heat-treatment design. The austenitisation behaviour and critical phase transformation temperatures during the LTHS heating process and their dependence on heating conditions are investigated using dilatometry with a Gleeble 3800 thermal-mechanical simulator, covering heating rates of 1–25 °C s−1 and soaking temperatures of 630–900 °C. Both a higher heating rate and higher soaking temperature are found to be beneficial to shorten the time required for obtaining a given austenite fraction. The martensite start temperature (Ms) shows a rapid increase with increasing soaking temperatures when austenitisation is partial, and a slower increase after full austenitisation. Excellent ultimate tensile strength values of around 1750 MPa and total elongation values of around 9.3 % are obtained for the material after the LTHS heating process. A physically based model describing the austenitic transformation under these conditions has been adopted and calibrated. The model shows good agreement with austenitic transformation diagrams constructed from experimental data, and thus can function as a guide for selecting optimum heat-treatment parameters for LTHS.

Mechanical Performance of Artificial Hip Stems Manufactured by Hot Forging and Selective Laser Melting Using Biocompatible Ti-15Zr-4Nb Alloy.

We investigated the microstructures, tensile properties, fatigue strengths, and durability limits of hot-forged Ti-15Zr-4Nb (Ti-15-4) alloy artificial hip stems. These properties were compared with those of Ti-15Zr-4Nb-4Ta (Ti-15-4-4) and Ti-6Al-4V (Ti-6-4) alloy stems annealed after selective laser melting. The tensile and fatigue properties of test specimens cut from Ti-15-4 stems annealed after hot forging were excellent compared with those of the Alloclassic Zweymüller Stepless (SL) stem, which is used globally. The 0.2% proof stress (σ0.2%PS), ultimate tensile strength (σUTS), total elongation (TE) at breaking, and fatigue strength (σFS) after 107 cycles were 919 ± 10, 983 ± 9 MPa, 21 ± 1%, and 855 ± 14 MPa, respectively. The durability limit (PD) after 5 × 106 cycles of Ti-15-4 stems was excellent compared with that of the SL stem. The σUTS values of 90°- and 0°-direction-built Ti-15-4-4 rods were 1032 ± 1 and 1022 ± 2 MPa, and their TE values were 14 ± 1% and 16 ± 1%, respectively. The σFS values of annealed 90°-direction-built Ti-15-4-4 and Ti-6-4 rods were 640 ± 11 and 680 ± 37 MPa, respectively, which were close to that of the wrought Ti-15-4 rod (785 ± 17 MPa). These findings indicate that the hot forging and selective laser melting (SLM) techniques can also be applied to the manufacture of artificial hip prostheses. In particular, it was clarified that selective laser melting using Ti-15-4-4 and Ti-6-4 powders is useful for the low-cost manufacturing of custom-made artificial joint prostheses and other prosthetic implants.

The formation of the cross shear bands and its influence on dynamic recrystallization and mechanical properties under Turned-Reverse Rolling

Two rolling routes, traditional forward rolling (FR) and turned-reverse rolling (TRR, with tilting angle of 180° along transverse direction (TD)) were performed on AZ31B magnesium (Mg) alloy sheets. Different morphologies of shear bands and its influence on the dynamic recrystallization (DRX) and mechanical properties were investigated. The shear bands (SBs) in the FR and TRR samples show variant morphologies due to the different shear patterns. Especially, the cross shear stress results in a higher number fraction of discontinuous DRXed (DDRXed) grains with random orientation in the TRR sample, contributing to the weakening of {0001} basal texture, while continuous DRX (CDRX) dominates in the FR route, where most of DRXed grains inherit the parent orientation. Furthermore, the TRR sample shows a larger total elongation value (>35 %) than that of the FR sample without sacrificing the strength (∼275 MPa), which can be attributed to not only a more homogeneous strain in the cross SBs (CSRs) but also the activation of non-base slip in the DDRXed grains.

Влияние длительного отжига, моделирующего параметры сухого хранения ТВЭЛов ВВЭР-1000, на механические свойства оболочек из сплава Э110 в продольном направлении

Presented are the results of mechanical tensile tests of longitudinal (segmental) samples cut from the midsection of claddings spent as VVER-1000 FA during one- and six-year campaigns and subject to thermal tests in helium at 480 °С during 468 full days. An average burnup of these fuel rods achieved ~ 20 and ~ 70 (MW·day)/kg U, respectively. The tests followed the examinations for cladding mechanical properties performed using the tests results for ring samples cut from the specified fuel rods. These fuel rods were tested in the experiments to determine impact of long-term thermal tests that model dry storage conditions on mechanical properties of Zr E110 claddings. Based on mechanical tests results at room temperature and at 380 °С there was determined as follows: ultimate strength sв, yield strength s0,2 and total relative elongation d0 of claddings length-wise on the fuel rod segments at the fuel column midsection. The obtained characteristics were compared to corresponding values for initial (unirradiated) cladding tubes and mechanical test results of the ring samples in the transverse direction. Long-term thermal tests have led to partial return to initial (before operation) values sв, s0,2 and d0 of radiation-hardened claddings; this return was more prominent in the longitudinal direction than in the transverse one. A radiation hardening decrease was accompanied with an increase in total relative elongation values in both cladding directions. Anisotropy of yield strength has changed as well. These changes can be explained by partial annealing of radiation defects, which are obstacles to dislocation movements during cladding strain. The morphology of above radiation defects is different in various sliding planes in texturized grains of cladding material.

Investigation of the Dendritic Structure Influence on the Electrical and Mechanical Properties Diversification of the Continuously Casted Copper Strand.

The properties of copper in its solid state are strongly affected by the crystallization conditions of the liquid material. ETP grade copper (Electrolytic Tough Pitch Copper) contains oxygen, which causes Cu2O oxide to crystallize in the interdendritic spaces during solidification process which due to the shape of continuous casting mould and the feed of liquid copper during the crystallization process in strand casting might cause a high risk of macrosegregation of oxygen in the copper structure. In the current paper the implied interactions of the dendritic structure of the copper strand in terms of homogeneity at the cross-section of its electrical, mechanical and plastic properties determined based on the samples taken parallelly and perpendicularly to the surface of the dendritic boundaries were analysed. The obtained results were confronted with scanning electron microscopy (SEM) images of the fractures formed during uniaxial tensile test. It has been observed that when the crystallites were arranged perpendicularly to the tensile direction the yield strength (YS) was lower and the fractures were brittle. On the other hand, when the crystallites were arranged parallelly to the tensile direction the fractures were plastic and elongated necking was observed along with the higher YS and total elongation values. The differences in values vary in terms of the applied direction of the tensile force. A characteristic positioning of the Cu2O oxide particles inside the fracture depending on the crystallite alignment and the direction of the applied tensile force has been observed.

Wire arc additive manufacturing of high-strength low alloy steels: study of process parameters and their influence on the bead geometry and mechanical characteristics

Additive manufacturing (AM) is becoming increasingly popular since it offers flexibility to produce complex designs with less tooling and minimum material at shorter lead times. Wire arc additive manufacturing (WAAM) is a variant of additive manufacturing which allows economical production of large-scale and high-density parts. The WAAM process has been studied extensively on different steels; however, the influence of process parameters, specifically wire feed speed (WFS), travel speed (TS), and their ratio on bead geometry, microstructure, and mechanical properties, are yet to be studied. The present work aims at closing this gap by using the WAAM process with robotic cold metal transfer (CMT) technology to manufacture high-strength structural steel parts. For that purpose, single-bead welds were produced from HSLA steel by varying WFS between 5 and 10 m/min and the WFS to TS ratio between 10 and 20. Those variations produce heat inputs in the range of 266–619 J/mm. The results have shown that the wire feed speed to travel speed ratio is the major parameter to control the heat input. Increasing heat input increases characteristic bead dimension, whereas it reduces the hardness. In the second part of experiments, two single-bead walls were deposited via the parallel deposition strategy and one multiple-bead wall was produced using the oscillation strategy. The tensile properties were tested along two directions: parallel and perpendicular to deposition directions. For the yield strength and tensile strength, the difference between horizontally and vertically tested specimens was smaller than the standard deviations. On the other hand, the total and uniform elongation values exhibit up to 10% difference in the test direction, indicating anisotropy in ductility. Those tensile properties were attributed to repeated thermal cycles during the WAMM process, which can cause heat transfer in multiple directions. The yield strength of the multiple-bead wall produced via oscillation was lower, whereas its ductility was higher. The tensile properties and hardness differences were found to correlate well with the microstructure.

Significance of Martensite Reversion and Austenite Stability to the Mechanical Properties and Transformation-Induced Plasticity Effect of Austenitic Stainless Steels

The phenomena occurring during continuous heating of cold-rolled AISI 304L and AISI 316L stainless steels from room temperature up to 1150 °C were studied. X-ray diffraction (XRD), scanning electron microscopy (SEM), hardness measurement, and tensile testing were used for characterization. The XRD analysis revealed that the AISI 304L stainless steel was more susceptible to the strain-induced martensitic transformation during cold rolling, and the martensite reversion kinetics during annealing was faster in this stainless steel. The latter was related to the effect of molybdenum in AISI 316L stainless steel, and it was rationalized based on the concept of continuous heating reversion temperature. Due to the presence of the retained austenite in AISI 316L stainless steel, the strength fell more slowly during continuous heating and the equiaxed microstructure was obtained at higher temperatures after recrystallization of the retained austenite. The latter resulted in the micron-size grain sizes in the AISI 316L stainless steel while ultrafine-grained (UFG) microstructure was obtained for the AISI 304L stainless steel as revealed by SEM images. In general, higher ultimate tensile strength (UTS) and total elongation values were observed for the AISI 304L stainless steel. These were related to factors other than the grain size strengthening (as presented by the Hall–Petch law), where the transformation-induced plasticity (TRIP) effect was found to be a major parameter affecting the tensile strength and ductility of AISI 304L stainless steel and this effect became more pronounced at coarser grain sizes. However, the TRIP effect was marginal in the case of AISI 316L stainless steel. This revealed the importance of the stability of the austenite phase in determining the mechanical properties of austenitic stainless steels.

Experimental validation of tensile properties measured with thick samples taken from MEGAPIE target

A post-irradiation examination (PIE) was performed on samples from the MEGAPIE (MEGAwatt Pilot Experiment) project allotted to the Japan Atomic Energy Agency. The specimens for the tensile tests were prepared from components of the MEGAPIE target, such as the beam window and the flow guide tube, which were irradiated in flowing lead–bismuth eutectic (LBE). The specimens contained curvatures and their thicknesses were over two times larger than that of the standard specimen. The PIE revealed that there was no LBE effect on the tensile properties of the 316-stainless-steel (SS316L) and T91 samples within the dose range from 0.16 dpa to 1.74 dpa at room temperature, 250 °C, and 300 °C. However, the T91 specimens showed a 1.5–2.0 times larger total elongation (TE) compared to the literature values for a specimen with standard t/w (ratio of thickness to width). It could be suggested that the t/w and TE were strongly correlated. Then, we tried to investigate the effects of the curvature and the t/w on the TE by comparing unirradiated specimens. We found that there was no curvature effect on the tensile properties and no t/w dependence on the strength and uniform elongation. On the other hand, the TE increases with increasing t/w. Based on the experimental data, we correlated the TE with various specimens t/w to estimate appropriate TE values, including that for the standard specimen.

Effect of Aging on Structure and Properties of a Transformation-Induced Plasticity-Aided High-Manganese Steel

This paper reports the results of investigation on 0.1C-17Mn-5.5Ni-1.8Al-2.7W-4.6Mo-2.3Cu-0.002B steel designed to assume excellent combination of strength and toughness. The air induction melted steel was subjected to hot forging at 1200 °C followed by hot rolling in six passes from 1100 °C. The rolled samples were reheat-quenched from 1050 °C in iced water. The quenched samples were isochronally aged at temperatures within 500-650 °C at interval of 50 °C. The mechanical properties were determined by hardness measurement and tensile testing. Structural characterization was accomplished by x-ray diffraction, optical and electron microscopy. Differential scanning calorimetric study was conducted to understand the precipitation kinetics. A typical age-hardening behavior was noted in the aged samples due to the precipitation of M2C and Ni3Al. Strain hardening of martensite, precipitation hardening due to the presence of nanosized precipitates and Orowan hardening were found to be instrumental in attaining a maximum hardness of 723 HV. The microstructure of aged samples consists of retained austenite, e-martensite, α′-martensite and uniformly distributed nanosized precipitates of Ni3Al and M2C, lying broadly within two different size regimes. The sample peak aged at 550 °C attained a strength of 1.4 GPa at a total elongation value of 25%. The combination of high strength and high ductility has resulted from precipitation strengthening, TRIP phenomenon and high degree of structural fineness.

Precipitation behavior and austenite stability of Nb or Nb–Mo micro-alloyed warm-rolled medium-Mn steels

Precipitation behavior and austenite stability of the warm-rolled medium-Mn steels with different Nb/Mo additions annealed at different temperatures were investigated. The Nb or Nb–Mo additions decrease the volume fraction of retained austenite, but increase its mechanical stability. The Mo addition to the Nb-bearing steels can lead to a higher density and smaller mean size of the precipitates because of the decreased interfacial energy and enhanced precipitation kinetics. The optimal precipitation temperature of the designed steels is about 600 °C. The Nb–Mo bearing steels exhibit a mixture of equiaxed and lamellar grain morphologies, and exceptional mechanical properties, i.e. the average products of ultimate tensile strength and total elongation (PSE) values of approx. 62 GPa %. An increase in yield strength of 300 MPa can result from grain refinement and precipitation hardening by Nb–Mo addition.

Investigation of the Aging Behavior of a Cu–Ni–Si Rolled Alloy

The effect of the aging heat treatment on the mechanical properties and the microstructure of a medium strength high electrical conductivity Cu–Ni–Si alloy was investigated within the frame of this work. Tensile, bend and hardness testing, in addition to optical, scanning electron microscopy and electron backscatter diffraction, were employed as the main analytical techniques, in the context of the present investigation. Results showed that the average grain size did not exhibit major differences for different aging conditions, while the formation of a more oriented texture with the progression of the aging treatment was observed. Superior mechanical properties were identified in the peak-aged condition for the specimens aged at the lowest temperature. Post-necking and total elongation values increased substantially after extreme overaging. The bending surfaces exhibited a degradation up to the point of peak aging from where on an improvement of the bending folds’ quality was observed.

The influence of the applied type of cooling after eight-stage hot compression test on the structure and mechanical properties of TRIPLEX type steels

The aim of the work was to analyse the impact of an eight-stage hot compression process carried out on the Gleeble3800 simulator, with three cooling variants after thermo-mechanical treatment of Fe-Mn-Al-C steels for their structure and mechanical properties. Performed research allowed to evaluate the impact on the structure and properties of simulation conditions for multi-stage rolling of difficult-to-treat thermomechanical steels for which this treatment is the final process of obtaining ready-to-use high-strength construction steels. Applied thermo-mechanical treatment causes that the main process of removing the effects of strain hardening is dynamic recovery, and static and metadynamic recrystallisation taking place after the last deformation but also between successive deformations, which was also confirmed on the basis of structural analysis of the tested steel after different cooling variants. As a result of the eight-stage hot compression test, the ferrite changed its distribution from fine grains occurring at the boundaries of austenite grains after forging, to elongated grains in a perpendicular direction to the compression direction. Isothermal heating at 850°C for 30s resulted in obtaining a fine-grained structure, statically or metadynamically recrystallised. The maximum tensile strength of the tested steels is about 1250 MPa, and the total elongation value is about 27%.