Search

There has been a growing surge of interest in examining the shock response of titanium alloys, owing to their considerable potential for military applications. The present study aims to reveal the influence of phase stability on the shock-induced mechanical response and substructure evolution of a metastable β titanium alloy, namely, Ti-17. This investigation included extensive work, such as plate impact tests, quasi-static reloading compression tests, and electron microscope analyses. The microstructural evaluations following the shock-wave loading unveil planar slip as the prevailing deformation mechanism in Ti-17 with a bimodal microstructure with stable α and β phases. However, when the shock stress exceeds 10 GPa, the activation of { 10 1 ¯ 1 } α nano-sized twins was observed, leading to improved reloading ductility. This implies a novel strategy to achieve excellent strength-plasticity compatibility in titanium alloys through appropriate shock-wave loading. Conversely, in Ti-17 with an equiaxed β microstructure, the metastability of the β phase leads to the activation of shock-induced α″ martensite, shock-induced ω, and planar slip. Two distinct forms of interaction involving the α″ laths, i.e., shear and truncation, were also observed. Phase stability greatly influences substructure evolution, which ultimately controls the reloading mechanical properties of the postshock Ti-17 alloy. [ABSTRACT FROM AUTHOR]

This study investigates the effect of laser treatment parameters on the tensile behavior of H13 tool steel in both quenched and tempered conditions. The effects of varying laser parameters on ultimate tensile strength and elongation at fracture which is the aim of this research were explored by employing a bionic unit to apply laser treatment with two parallel lines on the steel surface. These parameters are crucial for understanding material performance under tensile stress. Statistical analysis, including an analysis of variance (ANOVA), and fractographic analysis using SEM were conducted to analyze the results. The findings reveal a significant enhancement in the ultimate tensile strength of the laser-treated samples, with values ranging between 1342.27 and 1497.25 MPa, surpassing the non-treated substrate's strength of 1247.23 MPa. However, a decrease in elongation at fracture was observed, indicating increased brittleness post-laser treatment, with elongation values notably lower than the non-treated sample's 14.71%. The hardness values within the laser-treated zone exhibited a high variance, with the highest values found in the hardened zone ranging from 65.7 to 61.4 HRC, suggesting the formation of fine carbides and lath martensite due to rapid cooling and martensitic transformation. Furthermore, the depth of the laser-transformed zone, significantly influenced by laser power, varied between 1.30 and 1.9 mm, highlighting the critical role of laser parameters in affecting material properties. The study highlights a critical balance between ductility and strength in laser-treated H13 tool steel, which is essential for optimizing the material's performance for industrial applications. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) is increasingly viable for the high-volume production of complex parts due to material and time savings, weight reduction, design optimization, and the development of new materials. Laser metal deposition (LMD), a specific AM process, offers high build rates and larger deposition volumes, making it cost-effective for industries such as aerospace and defense, which benefit from increased productivity and the ability to repair large components. Martensitic stainless steels are valued for their mechanical properties in these sectors, despite the challenges of maintaining these properties during LMD deposition. The purpose of this study was to evaluate the deposition parameters for laser cladding using LMD with AISI 431 martensitic stainless steel powder and to analyze the morphological aspects. Microstructural evolution was assessed using optical and electron microscopy, with samples produced by varying laser power (800, 1000, 1400, 1600 W) and scanning speed (9, 14, 16 mm/s). The results showed dilution values between 10 and 27% for power values of 1400 and 1600 W for all laser beam velocities tested. Microstructural characterization revealed martensite and ferrite phases in the deposits. Increasing the scanning speed resulted in higher dilution and wettability and decreased the height/width ratio of the deposits. The laser deposition parameters also affected the solidification parameters (G/R) and the cooling rate (G × R), which are critical for understanding the resulting microstructure and hardness of the deposits. This study highlights the importance of considering geometric and microstructural aspects in LMD for AISI 431 steel to ensure high productivity and optimal performance and demonstrates the potential of the LMD process for the deposition of martensitic stainless steel. [ABSTRACT FROM AUTHOR]

Given the critical role that metastable retained austenite (RA) plays in advanced high-strength steel (AHSS), there is significant interest in obtaining a comprehensive understanding of its stability, to achieve excellent mechanical properties. Despite considerable attention and numerous studies, the significance of individual contributions of various microstructural factors (size, crystallographic orientation, surrounding phases, etc.) on the stability of RA remain unclear, partly due to the difficulty of isolating the direct effects of these factors. In this study, we examined the influence of microstructural factors while minimizing the effect of chemical composition on the mechanical stability of RA. We accomplished this by comparing the austenite (γ) stability in two distinct microstructures: a two-phase RA/martensite microstructure and a one-phase γ microstructure, both with nearly identical γ compositions. We employed in situ high-energy X-ray diffraction during uniaxial tensile testing conducted at both room temperature and 100 °C, facilitating the continuous monitoring of microstructural changes during the deformation process. By establishing a direct correlation between the macroscopic tensile load, phase load partitioning, and the γ/RA transformation, we aimed to understand the significance of the microstructural factors on the mechanical stability of the RA. The results indicate that very fine RA size and the surrounding hard martensitic matrix (aside from contributing to load partitioning) contribute less significantly to RA stability during deformation than expected. The findings of this study emphasize the critical and distinct influence of microstructure on γ/RA stability. [ABSTRACT FROM AUTHOR]

The influence of simulated reheated coarse-grained heat-affected zones (CGHAZ) on the microstructural evolution and hydrogen embrittlement in high-strength naval steel was investigated by scanning electron microscopy, microhardness testing, electron backscatter diffraction, slow strain rate tensile test and fracture morphology analysis. Twinned martensites were observed in both the intercritical and super-critically reheated CGHAZ, with a widely spaced region in the former. Intercritical reheated coarse-grained HAZ (ICCGHAZ) was the weakest zone of reheated CGHAZ when the peak temperature was 660 °C, exhibiting the intergranular cracking feature. Twinned martensite and coarsening grain size were therefore concluded to be the main reasons for high hydrogen embrittlement susceptibility in the reheated CGHAZ. • The microstructural evolution in different regions of reheated HAZ was investigated. • Twinned martensite was the susceptible microstructure to hydrogen embrittlement. • Second peak temperature affected the formation of twins. • Inter-critical reheated CGHAZ was the weakest zone of reheated HAZ. [ABSTRACT FROM AUTHOR]

Ferroic materials enable a multitude of emerging applications, and optimum functional properties are achieved when ferromagnetic and ferroelectric properties are coupled to a first‐order ferroelastic transition. In bulk materials, this first‐order transition involves an invariant habit plane, connecting coexisting phases: austenite and martensite. Theory predicts that this plane should converge to a line in thin films, but experimental evidence is missing. Here, the martensitic and magnetic microstructure of a freestanding epitaxial magnetic shape memory film is analyzed. It is shown that the martensite microstructure is determined by an invariant line constraint using lattice parameters of both phases as the only input. This line constraint explains most of the observable features, which differ fundamentally from bulk and constrained films. Furthermore, this finite‐size effect creates a remarkable checkerboard magnetic domain pattern through multiferroic coupling. The findings highlight the decisive role of finite‐size effects in multiferroics. [ABSTRACT FROM AUTHOR]

In this work, Ti‐6Al‐4V alloy was joined by tungsten inert gas (TIG) welding and the plates were undergone through optical microscopy test, elemental study, tensile test, hardness test, and fractographic observation. Plate‐A, with low value of current input, possesses α + β bimodal structure at BM, acicular martensite at HAZ, and Widmanstätten structure with a low amount of martensite at the WZ. Plate‐B, with comparatively higher value of current during welding, possesses similar structure at the BM. The HAZ area was comparatively lesser with significant martensite formation, and the WZ contains considerable formation of Widmanstätten structure. The elemental composition of BM and WZ was established by EDS. The stress‐strain curves for both plates show that plate‐B has almost 3%, 8%, and 7% greater UTS, YS, and elongation, respectively, than plate‐A. The significant formation of Widmanstätten structure has made the WZ of plate‐B more ductile and tough, although the fractography analysis of both the plates has shown macrodimples and flowing sign of metal as indicators of good ductility. [ABSTRACT FROM AUTHOR]

The grain size of austenitic‐stainless‐cast steels is usually coarse and may be several hundred microns to millimeters, depending on solidification conditions and ingot geometry. During solidification, dendritic crystals grow into the supercooled melt and stop growing when they touch each other, which is accompanied by the formation of high‐angle grain boundaries. Further cooling of metastable austenitic steels with a martensite start temperature above room temperature can partially transform them into martensite. During subsequent heating above the austenite start temperature, also known as austenite reversion treatment (ART), the martensite transforms back into austenite. The resulting austenitic microstructure is thus significantly refined, leading to an even finer martensitic microstructure during subsequent cooling. To reduce the martensite formation capability, partitioning is carried out to enrich the austenite with C and N and thus improve the formability. In the present work, the temperature‐dependent phase transformation behavior of the martensitic–austenitic stainless X16CrNiMnN15‐3‐1 transformation‐induced‐plasticity‐cast steel is determined by means of dilatometry. The influence of a single or multiple ART on the resulting austenite grain size, the microstructure and the tensile properties are described. It is demonstrated that ultrahigh‐strength steels with good ductility can be achieved by using partitioning after ART. [ABSTRACT FROM AUTHOR]

The objective of this study was to examine the influence of martensite particle size on the formation of stress and strain in microstructures of dual-phase steels. In order to achieve this objective, the 3D representative volume element (RVE) method was utilized. Particle size distributions were obtained from the microstructures of DP600 and DP1000 dual-phase steels as they actually exist. Virtual dual-phase steel microstructures were generated according to the above distribution and subsequent validation analyses were performed. In the subsequent phase, microstructures of varying martensite particle sizes (1 µm, 1.98 µm, 3 µm for DP600 and 1.15 µm, 2 µm, 3 µm for DP1000) were formed, and the effects of particle size on deformation behavior under tensile loads were determined. The findings indicated that an increase in martensite particle size resulted in a reduction in tensile strength, accompanied by an increase in deformation amount. [ABSTRACT FROM AUTHOR]

A Cu–Ni‐alloyed medium‐Mn duplex low‐density steel with a composition of Fe–9Mn–5.5Al–0.3C–3Ni–1.5Cu (wt%) is prepared by near‐rapid solidification. The microstructure features of the alloy under as‐cast, cold‐rolling, and heat treatments are studied. The effect of Cu‐ and Ni‐alloying elements on the microstructure and precipitates is discussed. In the results, it is shown that martensite and nanoscale precipitates are found in the microstructure of near‐rapid solidification. The enrichment of Cu is found at the phase boundaries of austenite and ferrite. A large number of annealing twins are present in the microstructure of cold‐rolled and annealed alloy. In the first principles and thermodynamic calculations, it is shown that Ni element is capable to shorten the nucleation incubation time of Cu precipitates. In addition, the interface segregation of Ni and Al elements reduces the adhesion work of Cu particles with the matrix. Both Cu and Ni elements increase the stacking fault energy of the alloy, which is increased from 37.3 to 44.2 mJ m−2. The contributions of precipitation strengthening and twinning strengthening to the strength of the alloy are 72 and 86 MPa, respectively, while the dominant contribution of dislocation hardening to the strength is 326 MPa. [ABSTRACT FROM AUTHOR]

The present study utilizes selective laser melting (SLM) technology to fabricate NiTi alloy and investigates the deposition quality, microstructure, mechanical performances, and functional properties of the as‐deposited parts. The NiTi component is fabricated by SLM at a suitable energy density (60.61 J cm−3), resulting in favorable surface forming quality and only micron‐sized porosity defects present in the interior. Dense and fine B19' martensite is distributed within the epitaxial B2 austenite matrix that grows in the height direction through the melt pool boundary, along with the nanoscale Ti2Ni precipitates dispersedly distribute at B19' grain interiors and grain boundaries. Both tensile and compressive results indicate that the as‐deposited NiTi components acquire slightly inferior ductility but superior strength than that of traditionally manufactured NiTi alloys. The shape‐memory effect of NiTi components is significantly influenced by holding temperature, exhibiting good and stable shape‐memory effect above a holding temperature of 75 °C. Simultaneously, the compressive superelastic behavior of the NiTi component exhibits favorable stability, with a recoverable strain of ≈5.5%. Overall, the NiTi component fabricated in the present study exhibits favorable mechanical properties and functional performance attributed to its excellent deposition quality and dense microstructure. [ABSTRACT FROM AUTHOR]

Herein, electroshock treatment (EST) is used to tailor the microstructure and mechanical properties of (TiB + TiC)/Ti–6Al–4V titanium matrix composite (TMC). Microstructural characterization results indicate that short‐time EST can promote β phase transition, thereby refining the α phase in the matrix. EST with 0.06 s leads to significant change in morphology of TMC; the matrix is transformed to basketweave structure and the acicular secondary α and martensite phase are precipitated. The yield strength and hardness of TMC are improved by fine grain strengthening. Under EST, the distribution of texture becomes uniform and the texture intensity of α phase is reduced. The microstructural changes are mainly attributed to the thermal and athermal effects of EST, which facilitates phase transformation and grain refinement. This work indicates that EST is an efficient way to manipulate the microstructure and mechanical properties for strengthening TMCs. [ABSTRACT FROM AUTHOR]

Martensitic phase transformation of zirconia (ZrO2), when realized from the superelastic effect, has immense potential in energy applications, such as micro‐actuation and high‐energy dissipation/damping. In this study, martensitic transformation in ZrO2 is studied using a newly developed microscale phase field model, which is scale‐independent and contains an averaged gradient term. The model is implemented using the FEniCS package in Python. With a thorough explanation of the model construction, the mechanics of phase transformation are detailed, and the material behaviors under different stress conditions are discussed. Mesh sensitivity, multivariant evolution, and the effect of particle size are analyzed to understand the martensite evolution in superelastic ZrO2. This work provides new insight into the martensitic phase transformation behaviors of micron‐sized spherical ZrO2 particles. [ABSTRACT FROM AUTHOR]

The susceptibility of subzones of the coarse-grained heat-affected zone (CGHAZ) in X65 pipeline steel to hydrogen embrittlement was studied through an in situ crack-tip opening displacement test in an H 2 S-containing environment. The intercritically reheated CGHAZ (IC-CGHAZ) exhibited the highest embrittlement factor of 89.4%, compared to 64.0% for the sub-critically reheated CGHAZ (SC-CGHAZ). Hydrogen transportation by dislocations to massive-slender martensite/austenite (M/A) constituents initiated cracks in IC-CGHAZ. Deterioration of lath bainite (LB) boundaries, with separation of M/A-ferrite interface, accelerated crack propagation across prior austenite grains and promoted hydrogen-assisted degradation of fracture toughness. Reheated CGHAZ at a peak temperature of 620 °C led to an increased intensity of the {110} LB boundary texture by up to 52% in SC-CGHAZ. This enhanced texture facilitated dislocation slipping along {110} LB boundary planes, thereby promoting deformation compatibility and preventing the deterioration of LB boundaries in the presence of hydrogen. • SC-CGHAZ exhibits the lowest embrittlement factor of 64.0% in H 2 S. • Reheated CGHAZ at 620 °C leads to increased {110} LB boundary texture by up to 52%. • {110} LB boundary significantly influences cracking associated with hydrogen. [ABSTRACT FROM AUTHOR]

The present study explores the application of single‐step quenching and partitioning (QP) treatments to low‐silicon commercial AISI 4140 steel. Fractions between 4.6% and 7.8% of retained austenite (RA) are stabilized at room temperature. Specimens quenched at 240 °C and partitioned for 10 min exhibit the highest tensile strength, surpassing 2000 MPa, with an elongation at break of up to 10%. This condition marks the effectiveness of austenite in improving tensile properties. Partitioning times exceeding 5 min lead to a second deformation stage, linked to an intense strain‐induced transformation of austenite into martensite. Comparative quenching and tempering (QT) treatments are conducted to highlight the role of RA in enhancing ductility. The QP samples show improved ductility and strain hardening. Furthermore, an energetic approach is employed to highlight the stability of RA by analyzing the difference in the tensile curves observed between QP and QT conditions. A critical value for stability is reached between 5 and 10 min of partitioning. The work proves the viability of successfully applying QP on AISI 4140 achieving high mechanical properties and improved ductility. [ABSTRACT FROM AUTHOR]

To clarify the strengthening mechanisms of medium‐chromium stainless steels (SSs) with carbides, ferrite, and martensite, 17%Cr SSs with varying martensite contents have been prepared, and the influence of martensite on microstructure, mechanical properties, and fracture has been investigated. According to THERMOCALC calculations, 17%Cr SS undergo a reversible phase transition between austenite and ferrite + M23C6 through the diffusion of carbon in austenite and M23C6 in the temperature range of 850–1220 °C. As the martensite content increases, M23C6 decreases, the martensite grain size increases, and the ferrite grain size initially increases and then decreases. Meanwhile, the yield strength and ultimate tensile strength increase, while both the uniform and post‐uniform elongation decrease. It is also found a decrease in work‐hardening index and an increase in work‐hardening rate with increasing martensite content. Under tensile loading, three types of voids are present in 17%Cr SS: type A only in the grain boundary (GB) area with M23C6 in martensite‐free material and type B and C in ferrite grains close to martensite grains and at ferrite/martensite GBs, respectively. An increase in martensite content leads to more voids, indicating a reduction in material plasticity caused by martensite. [ABSTRACT FROM AUTHOR]

The prediction of the martensite start temperature (Ms) for steels based on their chemical compositions is a complex problem. Previous work has developed empirical, thermodynamic, and machine learning models to estimate Ms. However, the empirical models are limited to specific steel grades, the thermodynamic models rely on different model assumptions, and the machine learning models are based on a small number of data, are limited to specific steel grades, as well or are not available for easy use to the public. Herein, a new machine learning model for the prediction of Ms is developed on the basis of two publicly available datasets consisting of 1800 steels from different steel grades. Extensive hyperparameter tuning is performed to find the best artificial neural network for the dataset. The best model improves prediction accuracy compared to previous state of the art. Despite a very good prediction accuracy of the model, unexpected behavior is observed in specific unseen data. This opens up the discussion for the requirements of new metrics. The dataset and the model are freely available at https://github.com/EAH‐Materials. An easy‐to‐use web tool to estimate Ms without the need of programming based on the chemical composition can be found at https://eah‐jena‐ms‐predictor.streamlit.app/. [ABSTRACT FROM AUTHOR]

The ductility of a retained austenite (RA)‐bearing steel is conventionally correlated with the gradual transformation of RA into martensite during straining, i.e., transformation‐induced plasticity (TRIP) mechanism. Nevertheless, current experiments and mathematical calculations illustrate that most of the RA transformed into martensite at quite an early stage of tensile straining. The result shows that only 4% of leftover RA exists after the initial tensile loading. It looks like enough RA is not available to operate TRIP to obtain successive ductility in the steel. Inexplicably, current work exhibits the maximum uniform tensile elongation after the major martensite transformation, which contradicts the conventional TRIP‐driven ductility theory. Thus, only 4% RA could be one of the prime factors that operate unfailingly to impart ductility in the steel. This work has created an understanding of the possible factors responsible for the observed ductility in the current steel while TRIP is not operating. [ABSTRACT FROM AUTHOR]

The evolution of ductile iron with martensitic matrix during annealing at 700 °C was studied in the present study. The results showed that the ultrafine graphite nodules with a count of 8500 nod/mm2 and an average diameter of about 1 µm were obtained in ductile iron through annealing treatment. The martensite in ductile iron was first decomposed into granular cementite, and then, the granular cementite aggregated and gradually transformed into ultrafine graphite nodules. With the annealing time extended to 90 min, the martensite was completely transformed into ferrite and ultrafine graphite nodules. These results implied that martensite in ductile iron was a good starting microstructure for forming the high graphite nodules in ductile iron by solid phase transition. The precipitation of ultrafine graphite nodules improved strength and plasticity of ductile iron, which was mainly because ultrafine graphite nodules refined ferrite grains, weakened stress concentration, and hindered crack propagation during deformation. The present study provided a new method to increase graphite nodule count in ductile iron. [ABSTRACT FROM AUTHOR]

Copyright of Metal Working (1674-165X) is the property of Metal Working Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Light Industry Machinery is the property of Light Industry Machinery Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The formation of ε-martensite is generally considered as detrimental to cracking resistance. The essential work of fracture (EWF) of high-Mn steels with ε-martensite has been determined in the near plane-stress regime. The analysis of the thickness dependence of EWF shows that an alloy with more ε-martensite involves a higher work of material separation and a lower contribution from crack-tip necking. Therefore, the presence of ε-martensite leads to a lower cracking resistance at large thickness, but to an enhanced fracture toughness at small thickness. The beneficial effect of ε-martensite to the work of fracture is explained by an increased strength without any reduction of void spacing, and related to the ε-martensite/austenite plastic co-deformation and to microcrack blunting and crack branching. The key finding of the study is thus that the best compromise depends on the structural application which imposes the strength and stiffness requirements, hence the thickness. [ABSTRACT FROM AUTHOR]

40Cr10Si2Mo steel is widely utilized because of its excellent mechanical properties, with grain size being a critical factor determining subsequent phase transformation processes and material microstructure performance. This paper reports the use of high-temperature laser scanning confocal microscopy (HT-LSCM) for in situ observation experiments to systematically investigate the growth of austenite grains and the martensitic phase transformation mechanism in 40Cr10Si2Mo steel during an 1800-second isothermal hold at temperatures ranging from 900 °C to 1250 °C. A dynamic model of austenite grain growth is established to optimize the parameters of the austenitic process. The results indicate that the austenite grain size increases continuously with increasing temperature and prolonged time. The Dong model predicts grain sizes that align well with experimental values. Austenite grains grow through grain boundary migration and grain annexation, whereas the precipitation and dissolution of M(Cr, Mo)23C6 affect grain growth. With prolonged time, some grain boundaries extend into new boundaries through subgrain rotation. The fine grains at lower temperatures reduce the initial temperature of the martensite transition (Ms), and the primary martensite nucleates along the grain boundaries of the prior austenite. The secondary martensite is attached to the primary martensite nucleus at a certain angle and grows in parallel while inhibiting the phase transition of the surrounding untransformed austenite. [ABSTRACT FROM AUTHOR]

In this study, the microstructural evolution of the microstructure and phase transformation of the biomedical Ti-6Al-4V alloys fabricated by Selective Laser Melting (SLM) at various solution treatment temperatures was investigated in order to achieve the formation and stabilization of (α + β) lamella structure for the final products. Solution heat treatments were conducted at 850°C for 2.5 hours; at 950°C or 1020°C for 1 h and followed by cooling naturally in the oven. The α' martensite in the SLMed samples was transformed from the β phase after heat treatment and finally achieved the uniform (α + β) lamella structure in heat treated samples of Ti-6Al-4V alloys. The dependence of the transformation behavior of the β phase during the solution treatment was determined by the partitioning of α and β stabilizing elements. [ABSTRACT FROM AUTHOR]

The recycling of scrap could cause continuous enrichment of Sn in steels. To reveal the influences of Sn on the mechanical properties and microstructure evolution of high-strength low-alloy (HSLA) steels, HSLA steels with varying Sn contents were designed and a series of continuous cooling tests were conducted. The results show that the effect of Sn on microhardness is mainly affected by the cooling rate. Under cooling rates lower than 10 °C/s, the addition of Sn increases the microhardness due to the solid solution strengthening effect of Sn. The ferrite grain size decreases with the increase of Sn content at a cooling rate of 0.1 °C/s because of the possible solute drag effect of Sn, while no refining effect was found for cooling rates between 0.5 °C/s and 10 °C/s. Under cooling rates higher than 10 °C/s, Sn reduces the ferrite and bainite transformation start temperatures and increases the bainite and martensite phase fractions. The higher hard phase fraction with increasing Sn content results in a significant increase in microhardness, and the contribution of solid solution strengthening plays a supplementary role under this condition. As one of the major residual elements in scrap, the strengthening and hardenability increasing effects of Sn should not be overlooked and may even be properly utilized in alloy design. [ABSTRACT FROM AUTHOR]

The high temperature β/B2 phase field of Ti3Al-Nb based alloys was rarely studied due to limitation in experimental technique, but different states of this phase field lead to difference in subsequent phase transformation path and resulting microstructure. By controlling the heating temperature and dwell time of α2′ → β/B2 transformation and subsequent cooling rate, we achieved a new microstructure consisting of domains of the B2 phase with α2′ martensite occupying the disordered BCC domain walls, effectively forming a pseudo sub-grain microstructure. It is shown that the domain walls evolved from the disordered β phase in the β/B2 phase field. Such pseudo sub-grain boundaries refine the prior β grains by subdividing them into smaller α2 colonies that form during subsequent heat treatment in the α2′ + β/B2 phase field upon reheating, and improve the mechanical properties of the alloy. [ABSTRACT FROM AUTHOR]

The microstructure–texture–tensile property relationships in a Ni‐containing medium‐Mn steel (Ni‐MMS), subjected to limited thermomechanical processing steps (i.e., hot forging and hot rolling), have been established in this study. The microstructure of the specimens hot rolled (HR) at 1173 (HR‐1173K) and 1373 K (HR‐1373K) exhibits ferrite and austenite phases. The austenite phase fraction in the HR‐1173K specimen is found to be higher than the HR‐1373K condition. The volume fraction of austenite to martensite transformation during tensile testing is also observed to be higher in the HR‐1173K specimen (≈13%) than the HR‐1373K condition (≈2%). This suggests the occurrence of more efficient transformation‐induced plasticity effect in the HR‐1173K specimen in comparison to the HR‐1373K condition, resulting in improved strength–ductility synergy in the former specimen. The smaller grain size of both the phases and higher fraction of twin boundaries as well the evolution of higher intensity γ‐fiber <111>//ND in the HR‐1173K specimen leads to better tensile properties. In addition, the overall activation of the primary slip systems (combination of face‐centered cubic and body‐centered cubic phases slip system), estimated through visco‐plastic self‐consistent simulation, is higher in HR‐1173K specimens, resulting in improved strain hardening response as compared to HR‐1373K one. [ABSTRACT FROM AUTHOR]

The microstructure and hydrogen embrittlement sensitivity of two X65 pipeline steels at different t 8/5 (the time required to cool from 800 °C to 500 °C) were investigated employing thermal simulation. With the increase of t 8/5 for both steels, the martensite transferred to acicular ferrite (AF) and bainite, and further converts to bainite and martensite/austenite (M/A) constituents. Elongated polygonal Mn–Nb–S inclusions appear in steel A, which are easy to fall off and the hydrogen embrittlement sensitivity is thus increased. However, spherical Al–Ca–Nb–N–O–S inclusions appear in steel B, which can promote nucleation of AF, thus obtaining lower hydrogen embrittlement sensitivity under lower t 8/5. • The HE sensitivity of two X65 pipeline steels at different t 8/5 were investigated. • The elimination of M and the nucleation of AF can reduce HE sensitivity. • Elongated polygonal Mn–Nb–S inclusions easily shed and increase HE sensitivity. • Spherical Al–Ca–Nb–O–S inclusions promote AF nucleation and reduce HE sensitivity. [ABSTRACT FROM AUTHOR]

Lamellar heterostructure design is widely recognized as a potential method to improve strength and ductility simultaneously of high‐performance steel. However, the high mechanical contrast among soft/hard phase and inharmonic plastic deformation lead to complex fracture mechanisms and limit the improvement of plasticity. Herein, the plasticity and tensile fracture mechanisms of two types of δ‐ferrite and lath martensite heterolamellar steels with and without α‐ferrite are investigated. The sample without α‐ferrite shows a combination of cleavage in δ‐ferrite and dimple zones in the martensite. The microcracks initiate in the martensite early and the then the cleavage fracture occurs in the δ‐ferrite due to the stress concentration. In contrast, the sample with α‐ferrite has lower plasticity. Failure of the samples with α‐ferrite is govern by the microcracks initiating in the interface of martensite/α‐ferrite. Eliminating the impact of the effect of α‐ferrite, the total elongation increases from 8.9% to 11.6%, and the ultimate tensile strength (UTS) increases from 1567 to 1652 MPa. This study investigates the critical factor in plasticity control of dual‐phase heterostructure and promotes the development and application of lamellar structure. [ABSTRACT FROM AUTHOR]

This paper explores the potential to hot stamp third-generation steels, in this case, a 980 MPa grade, while retaining or improving on the as-received microstructure, in particular the retained austenite (RA) fraction, and corresponding strength and ductility. Three classes of thermomechanical processes were investigated using a thermo-mechanical simulator system (Gleeble 3500). The first two processing routes considered a quenching and partitioning process starting from either a fully austenitic condition prior to quenching, designated the "Q&P" process, or an inter-critical partial austenitic condition, designated the "IC Q&P" process. In the two simulated Q&P processes, the samples were quenched to a predetermined temperature and then immediately transferred to a partitioning furnace. In the third processing route, designated the "Q&T" process, the samples were partially austenitized and then quenched to room temperature, followed by a tempering process to restore ductility. The conventional Q&P process resulted in excessive martensite formation, with high hardness and low ductility. The Q&T process produced a tempered martensite microstructure with hardness equivalent to the as-received sheet but with lower elongation and bendability. The IC Q&P heat treatment process increased the amount of retained austenite compared to the as-received sheet which translated into a higher yield strength, total elongation, and v-bend fracture angle. The IC Q&P ultimate tensile strength was approximately 8% lower than that of the as-received material. A sensitivity study was conducted to evaluate the influence of variations (± 25 °C) in the intercritical austenitization temperature, quench temperature, and partitioning temperature on the resulting microstructure and microhardness. The final mechanical properties were observed to be relatively independent of these process variations, indicating that the IC Q&P hot stamping process appears to be robust. [ABSTRACT FROM AUTHOR]

SA516 Gr.70 steels were welded by friction stir welding (FSW) under various media of air, water, and water + CO2 cooling, and the effect of the cooling media on the microstructure and mechanical properties of joints was systematically analyzed. The nugget zone (NZ) under the air-cooling condition contained coarse bainite + martensite. Martensite was obtained by decreasing the cooling media temperature. Furthermore, tensile fracturing of the joints occurred in the basal metal (BM), and the ultimate tensile strength of the joints under various cooling media was similar to that of the BM. However, with decreasing cooling media temperature, the total elongation of the joints noticeably increased. Good strength (545 MPa) and elongation (16.8%) were obtained in the joints under the water + CO2 cooling condition since the fine martensite microstructure enhanced the plastic deformation capacity of the joints. In addition, in the NZ under water + CO2 cooling condition, good toughness of 110 J/cm2 was obtained due to a high fraction of high-angle boundaries and fine martensite. [ABSTRACT FROM AUTHOR]

This study employs the finite element method to investigate the microstructural evolution and deformation behavior of a 40Cr steel automobile front axle during the quenching process. By establishing a multi-physics field coupling model, the study elucidates the variation patterns of the microstructure field in the quenching process of the front axle under different immersion orientations. It is found that along the length direction, the bainite and martensite structures decrease from the center to the edge region, while the ferrite structure shows an increasing trend. Additionally, the influence of immersion orientation on the hardness of the front axle's microstructure and deformation behavior is thoroughly discussed. The results indicate that, firstly, when quenched horizontally, the hardness difference among different regions of the front axle is approximately 8.2 HRC, whereas it reaches 10.3 HRC when quenched vertically. Considering the uniformity of the microstructure, the horizontal immersion method is preferable. Secondly, due to the different immersion sequences in different regions of the front axle leading to varying heat transfer rates, as well as the different amounts of martensite structures obtained in different regions, the deformation decreases along the length direction from the center to the edge region. Horizontal immersion quenching, compared to vertical immersion, results in a reduction of approximately 56.2% and 48.9% in deformation on the representative central cross-section (A-A) and the total length of the front axle, respectively. Therefore, considering aspects such as microstructure uniformity and deformation, the horizontal immersion quenching orientation is more favorable. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental study designed to evaluate the effect of repeated stretching cycles on the electrical resistance change in a NiTi alloy wire. In particular, tests were carried out to determine the effect of the type of loading on resistance change in the investigated wires. Wires with a diameter of 100 μm were used in the research. The experiment was carried out on a dedicated test stand designed for this purpose. During the test, the samples were subjected to 40 identical tensile cycles. The electrical resistance, sample elongation, and tensile force during successive stretching cycles were measured. The conducted research demonstrated the impact of elongation and reorientation of the structure on the resistance change in NiTi alloy thin wires. The research included a comparison of the effect of two different types of loading on the electrical resistance change in the sample. During cyclic stretching of a NiTi alloy sample with constant displacement, a decrease in electrical resistance was observed after each successive stretching cycle. Alternatively, when stretching with a constant force, the value of electrical resistance increased. In both types of loads, the greatest change in resistance value was observed at the initial cycles. [ABSTRACT FROM AUTHOR]

We present an efficient approach to evaluate the size dependency of elastic and plastic properties of metallic polycrystalline materials. Specifically, we consider different volume fractions of ferrite and martensite phases for the construction of three macroscopic domains. Statistical Volume Elements (SVEs) of different sizes are extracted from these domains using the moving window method. Linear and Crystal Plasticity (CP) simulations provide elastic and plastic properties of the SVEs such as the bulk and shear moduli, yield strength, and hardening modulus. We use a variation-based criterion to determine the Representative Volume Element (RVE) size of these properties. This RVE size corresponds to a size beyond which the given property can be idealized as homogeneous. We also use anisotropy indices and an additional RVE size criterion to determine the size limits beyond which these properties can be idealized as isotropic. Numerical results show that the plastic properties often reach their homogeneity and isotropy limits at larger sizes compared to elastic properties. This effect is more pronounced for the hardening modulus compared to the yield strength. [ABSTRACT FROM AUTHOR]

By means of microstructure observation, phase analysis, and mechanical‐property tests, the effect of martensite–bainite (M–B) duplex microstructure on carbide precipitation and mechanical properties of M50 steel is studied. In that results, it is shown that the distribution of secondary carbides in specimens with M–B duplex microstructure is more uniform and finer, and the stability of retained austenite (RA) in the steel is also improved, so that the content of RA in specimens with M–B duplex microstructure is 2.34%, which is higher than the 0.94% of the specimens with full martensite microstructure. The M–B duplex microstructure leads to the reduction of tempering hardness of M50 steel to 60.9 unit of Rockwell hardness (HRC), compared to the 61.6 HRC of the specimens with full martensite microstructure, but the wear resistance is slightly enhanced. Moreover, the M–B duplex microstructure effectively improves the impact toughness and fatigue properties by refining the microstructure and carbides in the steel, and the increase amplitude is 47.4% and 41.0%, respectively. [ABSTRACT FROM AUTHOR]

By means of salt‐bath austempering treatment, microstructure observation, X‐Ray diffraction analysis, microhardness measurement, and friction and wear performance tests for 8Cr4Mo4V steels with standard composition and with trace addition of 0.005% boron, the effect of boron on the phase composition and mechanical properties of the steel is studied. The results show that trace element boron greatly increases the content of needle‐like lower bainite in the quenched microstructure, promotes the dissolution of undissolved carbides, reduces the content of M/A island, but coarsens grains. After tempering, trace element B increases the amount of bainite generation, refines the lath martensite, and significantly promotes the precipitation of carbides, whose size is finer, and the distribution is more dispersed. In terms of mechanical properties, trace element B improves the hardness by promoting the precipitation of the second phase and refining the lath martensite, and the increase in the bainite content changes the wear mechanism and enhances the wear resistance. [ABSTRACT FROM AUTHOR]

We study the structure and mechanical properties of 38G2F structural steel after quenching and high-temperature isothermal tempering of different durations. By analyzing the stress-strain diagrams in conventional and true coordinates, we reveal specific features of the deformation behavior of samples on the yield plateau and in the uniform stage of deformation. We also analyze the influence of the distribution of strain component εyy along the working part of the sample on the variations of strength and plastic characteristics of steel in different stages/periods of tension. [ABSTRACT FROM AUTHOR]

Changes in the structure, phase composition, chemical composition, Vickers microhardness, and contact modulus of elasticity of a high-strength titanium α + β-alloy of the VST2 martensitic class during quenching after heating in the 700 – 1000°Ñ range were studied using the methods of optical microscopy, XRD phase analysis, microindentation, and thermodynamic calculations in ThermoCalc. The experimental data were in good agreement with the results of thermodynamic calculations. Arelationship between changes in the microhardness and contact modulus of elasticity of VST2 alloy, quenched from 700 – 1000°C, and the structure and phase composition of the alloy during quenching was established. [ABSTRACT FROM AUTHOR]

Structure and mechanical properties for experimental heat-resistant steels with 12% Cr with a ferritic or ferritic- martensitic structure, as well as austenitic steel 08Kh18N10T after quenching from different temperatures (950 – 1250°C), are studied. The behavior of steels of different groups, classified according to structural features (grain size and phase content), under these conditions is analyzed. The effect of heating temperature for hardening on yield strength of steels at 20 and 720°C during static compression tests is demonstrated. [ABSTRACT FROM AUTHOR]

Pipe steel 06Mn2MoNb is studied after hot rolling and subsequent heat treatment, i.e., austenitizing at 980°C, 30 min and cooling at different rates. By means of orientation microscopy and crystallographic analysis using various orientation relationships the possibility is demonstrated of creating structural and textural characteristics based upon transformation products (martensite, bainite) of deformed austenite within the steel. It is shown that the crystallographic texture resulting from a multivariant γ → α-transformation may be explained by α-phase generation at crystallographically ordered boundaries between deformed γ-phase grains. [ABSTRACT FROM AUTHOR]

This article presents the results of research on a new combined process involving multi-cycle wire-drawing and subsequent cryogenic cooling after each deformation stage. For theoretical research, modeling in the Deform software was performed. The analysis of temperature fields and the martensitic component in all models showed that for both considered thicknesses, the most effective option is a low deformation velocity and the conduct of a process without heating. The least effective option is to use an increased thickness of the workpiece at an increased deformation velocity and the conduct of a process without of heating to ambient temperature, which acts as a local cooling of the axial zone of the workpiece with an increase in the workpiece thickness. An analysis of laboratory studies on this combined process revealed that in the absence of intermediate heating of a wire between deformation cycles, 100% martensite is formed in the structure. However, if intermediate heating to 20 °C between deformation cycles is carried out, a gradient distribution of martensite can be obtained. And, since the wire has a circular cross-section, in all cases, martensite is distributed symmetrically about the center of the workpiece. [ABSTRACT FROM AUTHOR]

The corrosion behavior of two different Cu–Al–Mn–Ni alloys, pseudoelastic and pseudoplastic, was studied in a 0.6 M sodium chloride aqueous solution by monitoring the open circuit potential for 100 h and characterizing the resulting corrosion products. Electrochemical impedance spectroscopy analysis detected three processes related to the electrochemical double layer, a passive film and a diffusive contribution associated with the dissolution/precipitation of corrosion products. Potentiodynamic scans revealed a cathodically controlled corrosion mechanism and the presence of active–passive behavior at anodic potentials for both alloys studied. Polarization of the samples at selected potentials in the anodic branch allowed the investigation of the reactions involved, highlighting an improved corrosion resistance of the pseudoelastic alloy. The corrosion rates of the pseudoelastic and pseudoplastic alloys, after 100 h of immersion, were determined to be 0.007 and 0.011 mmpy, respectively. The post‐experiment characterization was carried out by means of scanning electron microscopy, micro‐Raman spectroscopy and X‐ray diffraction, supporting the electrochemical results. [ABSTRACT FROM AUTHOR]

By analyzing element segregation and dendritic growth kinetics in combination with microstructure observation and thermodynamic calculation, the influence mechanism of vanadium addition on the dendritic structure and precipitated phase in 30Cr15Mo1N ingots was elucidated. With vanadium addition, the carbonitride types in 30Cr15Mo1N ingots include lamellar M23(C,N)6, globular M2(C,N), and blocky M(C,N). The as-cast structure of the 30Cr15Mo1N ingot is divided into two parts: the dendritic structure, which is mainly composed of martensite and residual austenite, and the interdendritic region, which is primarily composed of precipitated phases like proeutectoid ferrite and carbonitrides. On the one hand, increasing the vanadium content can reduce the amount of martensite and residual austenite in the ingot by suppressing the growth of dendrites and reducing the size of dendrites. On the other hand, the amount of proeutectoid ferrite in the 30Cr15Mo1N ingots increased with an increase in vanadium content and distance from the center due to element segregation in the residual molten steel of the interdendritic region. Under the combined effect of element segregation in the interdendritic region and restricted dendritic growth, the size of carbonitrides showed an increasing trend with increasing the vanadium content. [ABSTRACT FROM AUTHOR]

SA516 Gr.70 steel exhibits an excellent combination of toughness and plasticity, which is widely used in the cryogenic field. However, the presence of coarse grain in fusion-welded joints degrades the toughness and ductility of the joint. In this work, SA516 Gr.70 steel was welded using friction stir welding at rotation rates of 400–800 rpm, and the microstructural evolution and mechanical properties of joints were investigated. At 800 rpm, coarse martensite was found in the nugget zone (NZ), and with the decrease of rotation rate, some bainite was also observed besides martensite. The yield strength of joints at different rotation rates was significantly higher than that of base metal (BM). With decreasing rotation rate, the elongation of the joint increases significantly, and the highest elongation of 13.6% is obtained at 400 rpm since the joint with low hardness difference has more areas participating in coordinated deformation, alleviating the concentration of strain at BM. In addition, with the decrease of rotation rate, the toughness of NZ is improved. Finally, the maximum impact energy of 109 J/cm2 was obtained in the NZ at 400 rpm, depending on the finer grains and the presence of bainite. [ABSTRACT FROM AUTHOR]

This work is a study aimed at optimizing the process of superarc metallization, with a focus on the effect of voltage on the properties of the spraying coatings. In this work, 30HGSA grade steel wire was used for the coating of 45 steel, widely used in mechanical engineering. The use of supersonic arc metallizer SX-600 allowed to obtain coatings at different voltages (32 V, 38 V and 44 V) and the same current strength. Various metallization process parameters such as material feed rate, voltage, current, distance and nozzle geometry are discussed in this paper. Using various analytical techniques including X-ray diffraction analysis, microscopy, microhardness and corrosion resistance tests, the qualities of the coatings were evaluated. Particular attention was paid to analyzing the phase composition of the coatings, porosity, substrate bond strength and tribological characteristics. It was found that the voltage during the supersonic arc metallization process has a significant effect on these characteristics. The selected optimum voltage allows to obtain dense and homogeneous coatings with improved performance properties. The results of the study revealed that the best physical and mechanical properties were exhibited by the sample processed at 38 V, which showed lower porosity and improved strength characteristics compared to the other samples. These findings can be used to improve manufacturing processes in industries such as automotive and mechanical engineering, where restoration and improved performance of worn parts is required. [ABSTRACT FROM AUTHOR]

This paper introduces an innovative approach that enables the automated and precise prediction of steel's chemical composition based on the desired Jominy curve. The microstructure, and in fact the presence of martensite, is decisive for the hardness of the steel, so the study considered the occurrence of this phase at particular distances from the quenched end of the Jominy sample. Steels for quenching and tempering and case hardening were investigated. With the representative collected dataset of hardness values from the quenched end of the Jominy specimen, microstructure and chemical composition of steels, the complex regression model was made using supervised artificial neural networks. The balance between cost and required hardenability can be achieved through optimizing the chemical composition of steel. This model of designing steel with required hardenability can be of great benefit in the mechanical engineering and manufacturing industry. The model is verified experimentally. [ABSTRACT FROM AUTHOR]

The damage to the shear-punched surface layers such as strain-hardening, strain-induced martensite transformation, and micro-void initiation behaviors was evaluated in the third-generation low-carbon advanced ultrahigh-strength TRIP-aided bainitic ferrite (TBF), bainitic ferrite–martensite (TBM), and martensite (TM) steels. In addition, the surface layer damage was related to (1) the mean normal stress generated during shear-punching and (2) microstructural properties such as the matrix structure, retained austenite characteristics, and second-phase properties. The shear-punched surface layer damage was produced under the mean normal stress between zero and negative in all the steels. The TBM and TM steels achieved relatively small surface layer damage. The small surface layer damage resulted in excellent cold stretch-flangeability, with a high crack-propagation/void-connection resistance on hole expansion. [ABSTRACT FROM AUTHOR]

The aim of the present work is to evaluate the effect of ultrafast heating on the microstructure and mechanical properties of hot forming steel. The initial microstructure utilized in this study was a cold-rolled microstructure, and the test steel was heated to full austenitization at a rate of 200 °C/s, followed by water quenching. It was observed that the ultrafast heating process significantly refines both the prior austenite grains and martensite laths while inheriting high-density dislocations from the initial cold-rolled microstructure. Consequently, the coupling mechanism between dislocation strengthening and grain refinement strengthening remarkably enhanced both the yield strength and ultimate tensile strength of the test steel. Eventually, the yield strength of the hot forming steel reached 1524 MPa, along with an ultimate tensile strength of 2221 MPa and uniform elongation of 5.2%. [ABSTRACT FROM AUTHOR]

In this paper, the nucleation and growth of austenite are controlled through a two-step annealing process to achieve multi-scale distribution and content increase of retained austenite in low manganese series medium-Mn steel. Combining SEM, EBSD, AES, and other experimental equipment, the evolution rules of the microstructure, properties, and element distribution behavior of the test steel during the annealing process are studied. Compared with one-step annealing, the two-step annealing significantly broadens the size distribution range of retained austenite. In the first step, after annealing at a higher intercritical temperature (760 °C), the ferrite and the M/A island are obtained, completing the initial partition of Mn and the refinement of microstructures. During the second step of annealing (720 °C), the primary Mn-rich martensite region provides higher nucleation driving force and finer dispersed nucleation sites, promoting the nucleation and growth of reverse transformation austenite. At the same time, the metastable-retained austenite formed after the first step of annealing continues to grow through interface movement. Furthermore, a high proportion (23.4%) of retained austenite with multi-scale distribution is formed in the final microstructure, and the product of strength and elongation increased from 21.8 GPa·% by the one-step annealing process to 30.1 GPa·%. [ABSTRACT FROM AUTHOR]

This study examines the microstructure, mechanical properties, and precipitation behavior of 1000 MPa grade GEN3 steel when subjected to various quenching processes, with a focus on the quench and partition (Q&P) technique. The Q&P-treated samples achieved 1300 MPa tensile strength and demonstrated superior yield strength, attributed to their refined substructure and their large amounts of precipitates. The quenched samples exhibited the thinnest martensite laths due to the highest martensite volume. Despite the as-annealed samples having the smallest grain size, the Q&P treatment resulted in optimal microstructural refinement results and a high dislocation density, reaching 1.15 × 1015 m−2. Analysis of the precipitates revealed the presence of V8C7, M7C3, M2C, and Ti(C, N) across various heat treatments. The application of the McCall–Boyd method and the Ashby–Orowan correction model indicated that quench and tempered (Q&T) samples contained the largest volume of fine precipitates, contributing to their high yield strengths. These findings offer valuable insights for optimizing heat treatment processes to develop advanced high-strength steels for industrial applications. [ABSTRACT FROM AUTHOR]