Fine Martensite Research Articles

Scan Strategy Effect on the Mechanical Properties and Microstructure of Directed Energy Deposited 18Ni300 Maraging Steel

Although the laser scan strategy does not affect the energy density of laser-based additive manufacturing, changes in laser scan direction critically influence the residual stress and microstructure of metallic components. However, only a limited number of studies have investigated the role of laser scan strategy on the microstructure and mechanical properties of additively manufactured maraging steels. Therefore, this study examines the effect of laser scan strategy on the mechanical properties of 18Ni300 maraging steel. Different laser scan strategies influence the morphologies of the molten pool, where retained austenite is concentrated in 18Ni300 maraging steel. The 45o sample exhibits a denser molten pool distribution compared to the other samples due to reduced layer overlapping. Because of the plastic strain incompatibility between martensite and austenite at the molten pool boundary, this dense molten pool distribution in the 45o sample resulted in the highest back-stress hardening. Additionally, the minimal layer overlapping in the 45o sample reduces heat exposure during laser-based additive manufacturing, leading to a finer martensite block and lath size. By combining high back-stress hardening with a fine martensite block and lath size, the 45o sample achieved the highest tensile property compared to the other samples. These results indicate that the selection of laser scan strategy is crucial for designing a heterogeneous microstructure in additively manufactured parts, which can enhance mechanical properties, even with the same energy density.

Effect of martensite morphologies on corrosion in sea water of X52 dual phase steel

This study investigates the effect of martensite morphologies on the corrosion behavior of X52 dual-phase steel when exposed to seawater. The steel underwent three different heat treatments: direct quenching (DQ), step quenching (SQ), and intermediate quenching (IQ) at 760°C and 800°C, in order to achieve varying martensite structures. The direct quenching (DQ) treatment resulted in the formation of fine martensite, evenly distributed throughout the ferrite matrix. The intermediate quenching (IQ) treatment led to the formation of martensite along the ferrite/ferrite grain boundaries. In contrast, the step quenching (SQ) treatment produced a banded morphology of martensite and ferrite. We studied the corrosion behavior using Tafel polarization techniques in a saltwater solution. We observed that the morphology and quantity of martensite influence the corrosion behavior. The corrosion rate of the direct quenching (DQ) treatment was lower compared to that of the step quenching (SQ), intermediate quenching (IQ), and the initial untreated state.

Evolution of Microstructure and Hardness during Carburization Heat Treatment of Heavy-duty Gear Steels: Numerical Prediction and Experimental Study

Abstract In order to solve the problems of long process cycle, low efficiency and high cost in the carburization heat treatment process of 18Cr2Ni4WA heavy-duty gear steel. The carbon concentration distribution of 18Cr2Ni4WA steel under conventional carburizing process at 930℃ was studied by combining numerical simulation with experimental research. The results show that the carbon concentration distribution predicted by the simulation is in good agreement with the experimental results. The microstructure of the surface layer after low-temperature tempering consists mainly of fine acicular tempered martensite, while the core consists mainly of lath tempered martensite and bainite. The increase in hardness after carburization is mainly attributed to the solid solution strengthening of the carbon atoms. The increase in hardness after cryogenic treatment is mainly attributed to the precipitation strengthening of the carbides. In addition, compared to the conventional carburization at 930°C, the high temperature carburizations at 950°C and 970°C reduced the carburization time by 37.2% and 53.5%, respectively.

Microstructure and mechanical properties of thin-walled TA1 titanium pipes fabricated by high-frequency induction welding

High frequency induction welding (HFIW) was effectively employed for the high-speed fabrication of thin-walled TA1 titanium pipes (TWTPs) with a nominal wall thickness of ∼0.6 mm. The microstructure and mechanical properties of TWTPs manufactured under varying welding parameters were investigated. The weld zone (WZ) exhibits a waist shape measuring ∼622 μm in width, and the width of the heat-affected zone (HAZ) spans between 763 and 864 μm. Both the WZ and HAZ are composed of a mixture of coarse serrated α grains with fine acicular and twins, while the BM retains equiaxed grains. This unique microstructure was resulted from the thermal cycling during HFIW, contributing to a notable increase in microhardness within the WZ compared to both the HAZ and the BM. Optimal manufacturing conditions were identified at a welding power of 14.4 kW, a welding speed of 60 m/min, an opening angle of 6°, and a squeeze displacement of 0.2 mm, yielding the TWIP with a tensile strength of ∼307 MPa and tensile elongation of ∼27%. Tensile fracture analysis revealed that failure predominantly occurred within the BM, underlining a ductile fracture mode characterized by pronounced dimple formations. The enhanced mechanical performance of the weld joints can be attributed to the heterogenous microstructure in the WZ, where the presence of large serrated α-grains enhances ductility, and the fine martensite and twins contribute to the high strength.

Role of prior austenite grain boundary and retained austenite in strain localization of medium-carbon high-strength steels

Exploring the micromechanical behavior of lath-martensitic quenching and tempering (Q&T), as well as quenching and partitioning (Q&P) steels presents a significant challenge due to their complex multi-phase constituents and hierarchical structures. This study conducts a comprehensive comparative analysis using medium-carbon Q&T and Q&P steels with identical chemical compositions. Atom probe tomography (APT) was used to investigate the distribution of chemical elements, while high-resolution digital image correlation (HR-DIC) provided insights into nanoscopic strain localization and partitioning. Both Q&T and Q&P steels exhibit significant strain localization at prior austenite grain boundaries (PAGBs) due to substantial carbon segregation. Strain localization in Q&T steel at PAGBs and packet boundaries strongly depends on preferred geometric orientations, with boundaries inclined 45° to the loading direction experiencing severe deformation. Conversely, in Q&P steel, PAGBs adjacent to large clusters of fine lath martensite, lacking a packet with a longitudinal direction parallel to boundaries and a feasible in-lath slip system, primarily undergo deformation. Carbon partitioning from martensite to retained austenite (RA), along with coexisting carbon and manganese segregation at phase interfaces, stabilizes the RA, resulting in a neighborhood-dependent deformation behavior of RA. The existence of RA not only absorbs carbon, maintaining low strength and high deformability, but also uniformly distributes and induces stable interfaces to hinder the formation of large packets with easily activated in-lath slip transmission.

Effects of Cooling Media on Microstructure and Mechanical Properties in Friction Stir Welded SA516 Gr.70 Cryogenic Steel Joints.

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.

Achieving 1.7 GPa Considerable Ductility High-Strength Low-Alloy Steel Using Hot-Rolling and Tempering Processes.

To achieve a balanced combination of high strength and high plasticity in high-strength low-alloy (HSLA) steel through a hot-rolling process, post-heat treatment is essential. The effects of post-roll air cooling and oil quenching and subsequent tempering treatment on the microstructure and mechanical properties of HSLA steels were investigated, and the relevant strengthening and toughening mechanisms were analyzed. The microstructure after hot rolling consists of fine martensite and/or bainite with a high density of internal dislocations and lattice defects. Grain boundary strengthening and dislocation strengthening are the main strengthening mechanisms. After tempering, the specimens' microstructures are dominated by tempered martensite, with fine carbides precipitated inside. The oil-quenched and tempered specimens exhibit tempering performance, with a yield strength (YS) of 1410.5 MPa, an ultimate tensile strength (UTS) of 1758.6 MPa, and an elongation of 15.02%, which realizes the optimization of the comprehensive performance of HSLA steel.

Dislocation accumulation-induced strength-ductility synergy in TRIP-aided duplex stainless steel

In this study, we investigate the intrinsic mechanism of intensive and progressive transformation-induced plasticity (TRIP) effects and their different strength-ductility synergies using a resource-efficient 15Cr-2Ni duplex stainless steel. The progressive TRIP material exhibits a ductility that is more than twice that of the intensive TRIP material, as well as, a larger product of the ultimate tensile strength and ductility. This is attributed to the dislocation accumulation caused by different grain sizes of strain-induced martensite depending on the stability of the γ phase, which determines the strength and work hardening of steel. When the stability is low, the γ phase is sensitive to loaded stress and transformed into dispersed fine martensite immediately after yielding at a high rate. It induces a sigmoid-shaped dislocation accumulation to an approximately 10-fold increase in the dislocation density at a limited strain, resulting in intensive work hardening and a large ultimate tensile strength. As the stability is adequate, the γ phase is transformed into coarse martensite laths with a high critical load stress, which is initiated from a delayed strain at an extremely low rate and steadily accelerated as the strain increases. This process induces a gradually increased dislocation accumulation to a 2–3-fold increase in the dislocation density at large strains, resulting in progressive work hardening and an excellent ductility.

Effect of multi-element synergistic addition on the microstructure evolution and performance enhancement of laser hot-wire cladded Fe-based alloy

To satisfy the requirements of hardness and corrosion resistance for laser additive manufacturing of hydraulic supports, this study applied the synergistic addition of C, B, Cr, Ni, Nb and Mo elements in Fe-based alloys. The multi-phases, martensite + austenite + ferrite were designed. The microstructure, hardness and corrosion resistance of the coatings were analyzed. Increasing the C and B contents could significantly increase the hardness of the coatings, while the corrosion resistance was decreased. The corrosion resistance of the coatings was determined by the Cr contents. However, increasing the Cr contents to 20.0 wt % resulted in the ferrite structure with lower hardness (21 HRC). The coatings with 0.25 wt % C, 1.2 wt % B and 19.0 wt % Cr showed the optimal matching of hardness (56 HRC) and corrosion resistance (survived in neutral salt spray test≥300h). The resulted coatings were mainly consisted of dendritic structure. Fine lath martensite phase was dominant in the dendrite regions. The interdendritic regions were consisted of nano-sized intermetallics with a mixture of σ+Nb + FeNb + Cr2Nb+(Fe,Cr)2B + NbC compounds. These interdendritic regions (14.2 GPa) showed higher hardness than that of the dendritic regions (7.1 GPa). The high Cr contents with finer dendritic structures were the major mechanisms for the excellent combination of hardness and corrosion resistance. The precipitation and growth mechanisms of the interdendritic phases were elaborated. This work provides a valuable reference for laser hot-wire cladding to prepare Fe-based alloys with high hardness and excellent corrosion resistance.

A comprehensive study on the microstructure evolution and mechanical property characterization of selective laser melted 18Ni300 stainless steel during heat treatment processes

The influence of different heat treatment processes on the microstructure and mechanical properties of 18Ni300 stainless steel manufactured by selective laser melting has been investigated in the present study. The microstructures, nanoprecipitates, and mechanical properties of the differently heat-treated samples were analyzed using various precision instruments. Compared with a non-treated 18Ni300 stainless steel sample, the results showed that the microstructure was mainly composed of fine lath-like martensite, with a large number of nano-precipitates dispersed both within the martensite and in the boundaries. In addition, there was a preserved amount of austenite between the lath-like martensite and the spherical nanoprecipitate in the SAT sample. The interactions between the martensite matrix and the nanoprecipitates and dislocations were assumed to be the main reason for the high strength of 18Ni300 stainless steel. These precipitates included rod-shaped or needle-shaped, Ni3Ti, Ni3Mo, and Ni3(Ti, Mo) nano-precipitates, as well as spherical Ti–Al nano-oxidized precipitates and massive Ni-rich precipitates. The shear and by-pass mechanisms between the strengthened nano-precipitate and the dislocations were found to depend on the size of the nanoprecipitate. The influence of the nanoprecipitation on the indentation hardness became more evident after heat treatment, but the effect on the indentation modulus was not that obvious. The AT- and SAT-treatments significantly improve the strength, hardness, and modulus of samples but were found to reduce the toughness and plasticity. After the AT- and SAT-treatments, the protrusions became smaller, and the small isometric protrusion of a shear lip became significantly smaller than for the as-built material.

Effect of microstructural features on the fatigue behavior of ultra-high strength press hardened steels

Nowadays, high-strength press-hardened steels (PHS) have gained wide applications in automotive body-in-white owing to excellent mechanical properties. Nevertheless, the fatigue properties of high-strength PHS and associated failure mechanisms have not been clearly revealed, which restricts their potential applications in other parts of automobiles involving fluctuating and repetitive stresses, such as wheels or beams. In this work, the fatigue behavior of 1900 and 2000 MPa grade PHS is systematically studied, with the main focus on the associated deformation and fatigue cracking mechanisms. The fatigue behavior of these two steels is similar, and the ratio of fatigue strength to tensile strength is around 0.5. The fatigue damage mechanism of high-strength PHS is dominated by surface cracking, as the fine martensite structures reduce the stress concentration and cracking at small-sized inclusions. This work can provide guidance for the application of high-strength PHS in alternating loads scenarios.

Dynamic Response of Ti-6Al-2Zr-1Mo-1V Alloy Manufactured by Laser Powder-Bed Fusion.

Titanium parts fabricated by additive manufacturing, i.e., laser or electron beam-powder bed fusion (L- or EB-PBF), usually exhibit columnar grain structures along the build direction, resulting in both microstructural and mechanical anisotropy. Post-heat treatments are usually used to reduce or eliminate such anisotropy. In this work, Ti-6Al-2Zr-1Mo-1V (TA15) alloy samples were fabricated by L-PBF to investigate the effect of post-heat treatment and load direction on the dynamic response of the samples. Post-heat treatments included single-step annealing at 800 °C (HT) and a hot isotropic press (HIP). The as-built and heat-treated samples were dynamically compressed using a split Hopkinson pressure bar at a strain rate of 3000 s-1 along the horizontal and vertical directions paralleled to the load direction. The microstructural observation revealed that the as-built TA15 sample exhibited columnar grains with fine martensite inside. The HT sample exhibited a fine lamellar structure, whereas the HIP sample exhibited a coarse lamellar structure. The dynamic compression results showed that post-heat treatment at 800 °C led to reduced flow stress but enhanced uniform plastic strain and damage absorption work. However, the HIP samples exhibited both higher stress, uniform plastic strain, and damage absorption work owing to the microstructure coarsening. Additionally, the load direction had a subtle influence on the flow stress, indicating the negligible anisotropy of flow stress in the samples. However, there was more significant anisotropy of the uniform plastic strain and damage absorption. The samples had a higher load-bearing capacity when dynamically compressed perpendicular to the build direction.

Microstructure and Mechanical Properties of Laser Direct Energy Deposited Martensitic Stainless Steel 410.

The aim of this work is to study the phase transformations, microstructures, and mechanical properties of martensitic stainless steel (MSS) 410 deposits produced by laser powder-directed energy deposition (LP-DED) additive manufacturing. The LP-DED MSS 410 deposits underwent post-heat treatment, which included austenitizing at 980 °C for 3 h, followed by different tempering treatments at the temperatures of 250, 600, and 750 °C for 5 h, respectively. The analyses of phase transformations and microstructural evolutions of LP-DED MSS 410 were carried out using X-ray diffraction, SEM-EDS, and EBSD. Vickers hardness and tensile strength properties were also measured to analyze the effects of the different tempering heat treatments. It revealed that the as-built MSS 410 has very fine lath martensite, high hardness of about 480 HV1.0, and tensile strength of about 1280 MPa, but elongation was much lower than the post-heat-treated ones. Precipitations of chromium carbide (Cr23C6) were most commonly observed at the grain boundaries and the entire matrix at the tempering temperatures of 600 °C and 750 °C. In general, the tensile strength decreased from 1381 MPa to 688 MPa as tempering temperatures increased to 750 °C from 250 °C. Additionally, as the tempering temperature increased, the chromium carbide and tempered martensite structures became coarser.

Microstructural evolution and carbides precipitation behavior and their effects on mechanical property of Nb–Ti microalloyed FB590 steel

Ferrite-bainite dual phase steels have been widely used in automobile manufacturing industry due to their high strength and excellent hole expansion performance. In this study, the effects of coiling temperature on mechanical properties and hole expansion performance of low carbon Nb–Ti micro-alloyed FB590 ferrite-bainite steel have been studied. Additionally, the microstructure evolution and carbide precipitation behavior during hot rolling and coiling processes have been investigated. The influence mechanism of microstructures and carbides on both mechanical properties and hole expansion performance has also been discussed. The results suggest that the fraction of the retained austenite and the martensite decreases gradually with increasing coiling temperatures from 450 °C to 500 °C. The main reason for the formation of martensite and retained austenite in steel CT450 coiled at 450 °C is that the coiling temperature is near the martensitic transformation temperature Ms. Increasing the coiling temperature to 500 °C which is above the Ms leads to ferritic and bainitic structure. The carbides precipitation behavior has been studied by TEM, thermodynamic and kinetics calculation. The results show that the size of the carbides increases with increasing coiling temperatures from 450 °C to 500 °C. Most of the large size carbides above 100 nm with high percent of Ti are the undissolved particles in austenite during slab heating. The medium size particles between 50 nm and 100 nm and enriched in Ti precipitate during rough rolling at higher temperature, while the particles smaller than 50 nm enriched in Nb precipitate during finish rolling and coiling processes. The strength of the steel is effectively increased by the fine carbides and martensite formed at low coiling temperature of 450 °C. With increasing coiling temperature from 450 °C to 500 °C, the steel's strength decreases from 630 MPa to 591 MPa, while the HER are improved from 76.8 % to 119.9 % due to the reduction of martensite and retained austenite. Although the strength is a little reduced due to the coarsening of carbides and reducing of the martensite, the plasticity and hole expansion performance is improved significantly with the coiling temperature of 500 °C.

Effect of quenching and tempering on microstructure and corrosion resistance of aerospace-bearing steel

CSS-42L steel is not only highly competitive for aerospace bearing applications but also for core components such as gears and shafts used in high-temperature or corrosive environments. This puts higher requirements on its microstructure, mechanical properties, and corrosion resistance. In this paper, CSS-42L steel was subjected to quenching, cryogenic and tempering treatments to study the effects of different heat treatments on the microstructure, hardness, and corrosion resistance of CSS-42L steel. It was found that the microstructure of the specimen after quenching contained martensite, a large amount of residual austenite, and trace amounts of fine carbides, and its hardness and corrosion resistance were improved. The residual austenite in the tempered sample underwent almost complete decomposition and transformed into fine martensite, and numerous finely dispersed and uniformly distributed carbides were precipitated, its hardness was further increased to 578.6 Hv concerning the quenched specimen, but concurrently exhibited a decrease in corrosion resistance. CSS-42L steel can be hardened by quenching, cryogenic and tempering to obtain martensite, but fine martensite reduces corrosion resistance. Since the amount of martensite or residual austenite affects the mechanical properties and corrosion resistance of CSS-42L bearing steel, the ratio of martensite and residual austenite needs to be adjusted to obtain optimum mechanical properties and corrosion resistance.

Investigation on the formation mechanism of collapse defects, microstructural evolution and mechanical properties in full penetration laser welding of thick-section steel

In this paper, we described full penetration laser welding (FPLW), a process capable of achieving single-pass welding of thick-section steel. This work summarized a welding process window encompassing various typical formations, including those well-formed and collapse defects. Furthermore, collapse defects were categorized as “collapse formation with backside humping” and “collapse formation with underfill”. High-speed camera (HSC) images reveal that the formation mechanisms of these two defects are attributed to the accumulation of liquid metal at the rear edge of the bottom molten pool and the ejection of a large amount of liquid metal from the weld in a spatter form, respectively. A computational fluid dynamics (CFD) numerical simulation model well-aligned with the experimental results has been established. The analysis of the molten pool flow behavior and keyhole evolution revealed that during well-formed welding, the keyhole status in the welding process exhibits a periodic closure-collapse mode. This periodic mode can instantaneously release the pressure at the bottom of the keyhole, inhibiting the excessive accumulation of liquid metal at the bottom of the weld and thus inhibiting the formation of collapse defects. The cooling rate in the upper part of the weld exceeds that in the middle and lower parts, primarily resulting in the formation of fine acicular ferrite and martensite. The increased tensile strength exhibited by the welded joint relative to the base material predominantly emanates from the mechanisms of grain boundary reinforcement and dislocation strengthening, precisely caused by the refined microstructure.

Effect of laser hardening and post hardening shot peening on residual stress evolution in X5CrNiCuNb16-4 steel for steam turbine blade applications

Laser-hardening process produces higher surface hardness and provides deeper hardness profile into the material. This increment in hardness reduces water-droplet erosion on steam turbine blades. In the present study, a steam turbine blade profile was subjected to laser-hardening process primarily on the suction side of the profile. This hardening process transformed tempered martensite structure of the unaffected material to a fine martensite structure at the processed zone with an intermediate transition zone being present in between them. The fine martensite was responsible for spike in hardness profile at the surface. When the laser-hardened blade was subjected to operational stresses, a number of parallel cracks formed on the blade profile in the direction perpendicular to the blade axis. Detailed investigations in the form of residual stress mapping revealed that a narrow interfacial region beside laser-hardened zone over the profile of the processed blade material, indicated presence of tensile residual stresses. This region was responsible for the formation of parallel cracks over the blade profile. A shot peening process was introduced post laser-hardening which resulted in the elimination of the tensile residual stress, thus, mitigating crack formation over the blade profiles upon application of operational stresses.

Fine martensite and beta-grain variational effects on mechanical properties of Ti–6Al–4V while laser parameters change in laser powder bed fusion

In this study, several variations of Ti–6Al–4V β-grains and α′-martensites were observed while changing the combinations of laser parameters and keeping the energy density (ED) constant in the laser powder bed fusion (LPBF) process. Several combinations of laser power, scanning speed, and hatch spacing were considered, resulting in high product density between 99.3% and 100.0%. Accordingly, tensile specimens were fabricated to observe the above strategic fabrication and microstructural effects on tensile properties. At the same time, microhardness was also measured to observe the similarities. However, the size and shape of the β-grains differed significantly, while the scanning speed gradually decreased along with the laser power, with the shape changing from irregular to classically hexagonal and the size increasing sharply. Using the results of differential thermal analysis (DTA), it can be said that most of the tertiary and quaternary α′-martensites formed after the following few thermal cycles below 370 °C. Similarly, the α′-particles decomposed and formed β-particles due to thermal treatment at 370 °C. Therefore, a denser and higher number of tertiary and quaternary α′-martensites and a lower number of primary and secondary α′-martensites occurred, while the cooling rate decreased and the number of thermal cycles increased due to a lower scanning speed. These phenomena increased the hardness 370–395 HV and deteriorated the yield strength 1250-840 MPa. Changes in track overlap (hatch spacing) of 30–50% affect mechanical and microstructural characteristics more than track overlap of 10–25%. The columnar β-grains became longer and wider as the lane overlap increased from 30 to 50%. At the same time, some β-grains also changed to contain finer and fewer α′-martensites. These factors reduced both hardness and tensile properties.

Microstructure and mechanical properties of laser welded Ti-6Al-4V (TC4) titanium alloy joints

Laser beam welding (LBW) was applied to join 3 mm thick TC4 titanium alloy plates in this study. Three-factor and three-level orthogonal experiments were designed to choose the best welding parameters through the analysis of range and variance. The microstructures of the welded joints were analyzed by optical microscopy (OM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The mechanical properties of the welded joints were analyzed by tensile tests. The experimental results indicated that the defocused position had the largest effect, followed by the laser power and welding speed. The optimal welding parameters were laser power 2.3 kW, welding speed 0.04 m/s and defocused position 0 mm. The heat-affected zone (HAZ) consisted of α′ martensite, primary α phase (αp) and primary β phase (βp). In the fusion zone (FZ), the acicular α′ martensite was distributed in the β columnar grains. The tensile strength of the laser welded joint under the optimal welding parameters was 985 MPa, which is less than that of the base metal (BM). The peak value of the grain misorientation angle in the HAZ was related to the amount of martensite. The laser welded joints with finer martensite and equiaxed α + β would have better mechanical properties. The grains in the HAZ had a preferred orientation in the {001} direction.

Effect of cyclic heat treatment on microstructure and tensile property of a laser powder-bed fusion-manufactured Ti–6Al–2Zr–1Mo–1V alloy

Laser powder-bed fusion (L-PBF) is increasingly being employed to fabricate titanium components for aerospace applications. However, L-PBF fabricated titanium alloy parts typically exhibit high strength but low ductility because of fine α′ martensite. Post-heat treatment is essential to compose α′ into stable α, thereby achieving improved ductility. In this study, we put forward a novel post-heat treatment, i.e., a cyclic treatment that included multiple cycles of low-to-high and high-to-low temperature annealing, to improve the ductility of an L-PBF fabricated Ti–6Al–2Zr–1Mo–1V (TA15) alloy. Its effect on the microstructures and tensile properties was investigated. The results showed that the as-fabricated TA15 alloy exhibited fine martensite, leading to high strength (i.e., an ultimate tensile strength of 1168 MPa) and low ductility (i.e., an elongation of 7.1 %). Conventional post-heat treatments introduced lamellar α+β structures and resulted in improved ductility of 9–13.9 % and reduced strength of 896–1070 MPa. The cyclic multistep treatment created trimodal structures of α-laths, equiaxed α, and thin film β. Especially, it contributed to the formation of up to 57 % equiaxed α grains compared to less than 5 % in the conventional treatments, leading to the enhanced ductility. This specific structure displayed superior properties, an ultimate tensile strength of ∼900 MPa, and elongation of ∼16 %, which are comparable to the TA15 alloy wrought counterparts. The optimized strength and ductility also demonstrated the potential of cyclic multistep treatment to enhance the performance of other additive manufactured titanium alloys.