Wire+arc additive manufacture is developed for producing large-scale metallic components. In this paper, maraging steel parts were produced, and the microstructure and mechanical properties were ...investigated. The microhardness and tensile strength of the as deposited alloy reduced from the bottom to the top due to the transient thermal cycling, which resulted in partial aging and non-uniform formation of intermetallic compounds along the building direction. Solutionizing, followed by 3h aging, significantly reduced the microstructural heterogeneity and increased the mechanical properties by 24.7% through the formation of large amounts of finely distributed precipitates. The as deposited alloy possessed superior strength to the wrought alloy in solutionized condition but inferior to the later in aged condition, which was attributed to the less pronounced aging response of the low-angle columnar grains characterized microstructure and the presence of retained and reverted austenite.
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•Wire+arc additive manufacture (WAAM) was applied to produce maraging steel structures.•Microstructure evolution of WAAM alloy was characterized and correlated with the layer-by-layer building manner.•Mechanical properties of WAAM alloy were tested and correlated with the aging response of WAAM microstructure.•Retained austenite content was measured and correlated with the tensile strength loss.
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IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UM, UPCLJ, UPUK, ZRSKP
The present research investigates the high-temperature behavior of laser powder bed fused (LPBF) Fe–Cr–Ni–Al maraging stainless steel (equivalent to PH13–8Mo). Fully dense PH13–8Mo samples are ...printed using an EOS M290 printer, and the effect of different heat treatments on high-temperature behavior and microstructure development is investigated. The material is studied under as-printed (AP), austenitized aged (AA, austenitized at 900 °C for 1 h followed by aging at 530 °C for 3 h), and direct-aged (DA, aged at 530 °C for 3 h) conditions. Uniaxial compression tests are conducted using a Gleeble® 3500 thermal-mechanical simulator at 400 °C and 500 °C at a quasi-static strain rate of 0.0001 s−1 to a final true strain of 0.2, while the microstructure characterization is performed using Electron Backscatter Diffraction and Transmission Electron Microscopy. At room temperature, the AA sample shows the highest hardness (strength), but at temperatures of 400 °C and 500 °C, the DA sample possesses the highest strength. Interestingly, the AP sample exhibits comparable strength to the DA sample at 500 °C, which could indicate for applications at these high temperatures, LPBF-PH13-8 Mo does not require any heat treatment.
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IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Maraging steels such as 18Ni-300 (1.2709) are characterized by high yield and tensile strength together with good toughness making them interesting materials for aerospace, automotive and tooling ...sectors as well as for bearing gears parts. The low carbon martensite matrix combined with the nanosized intermetallic precipitates are responsible for the peculiar mechanical properties. Thanks to the very low carbon content, these steels are easily weldable and therefore suitable for additive manufacturing (AM) techniques, such as laser-based powder bed fusion (LPBF). Indeed, this technique was recently adopted in tooling and molding industry to produce inserts with conformal cooling channels capable to improve inserts and cores lifetime enhancing productivity. These types of components usually undergo severe stress conditions, wear phenomena and even aggressive environments.
This work aims at comparing the tribological and corrosion behaviour of 1.2709 maraging steel samples produced by both forging and LPBF technique. Conventional samples were investigated after solution annealing and aging treatment while AM samples were directly aged. Aging parameters were chosen to achieve the same hardness values for both the production conditions. Samples sliding wear behaviour was investigated through pin-on-disc tests using 100Cr6 steel ball as counterpart (ASTM G99) at three different sliding velocities, while potentiodynamic polarization measurements (ASTM G3) were conducted in 3.5 wt % NaCl solution.
Microstructural analyses and hardness measurements were carried out on as-aged samples. The corrosion damage and the wear mechanism were investigated by means of scanning electron microscope (SEM). For the considered heat treatment, results show only small differences on the wear and corrosion behaviors between forged and AM samples, despite differences in the microstructural morphology, demonstrating the reliability of AM components.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
High-performance grade 300 maraging steels were fabricated by selective laser melting (SLM) and different heat treatments were applied for improving their mechanical properties. The microstructural ...evolutions, nanoprecipitation behaviors and mechanical properties of the as-fabricated and heat-treated SLM parts were carefully characterized and analysed. The evolutions of the massive submicron sized cellular and elongated acicular microstructures are illustrated and theoretically explained. Nanoprecipitates triggered by intrinsic heat treatment and amorphous phases in as-fabricated specimens are observed by TEM. High-resolution TEM (HRTEM) images of the age hardened specimens clearly exhibit massive nanosized needle-shaped nanoprecipitates Ni3X (X=Ti, Al, Mo) and 50–60nm sized spherical core-shell structural nanoparticles embedded in amorphous matrix. XRD analyses reveal austenite reversion and probable phase transformations during heat treatments. The hardness and tensile strength of the as-fabricated and age-treated SLM specimens absolutely meet the standard wrought requirements. Furthermore, the lost ductility after aging can be compensated by preposed solution treatments. Relationships between massive nanoprecipitates and dramatically improved mechanical performances of age hardened specimens are elaborately analysed and perfectly explained by Orowan mechanism. This study demonstrates that high-performance grade 300 maraging steels, which is comparable to the standard wrought levels, can be produced by SLM additive manufacturing.
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•Evolutions of the typical SLMed microstructures are illustrated and theoretically explained.•Precipitation behavior and phase transformation of SLMed maraging steel are characterized by TEM and XRD.•Significant improvement of strength after solution and aging treatment was evaluated and explained.•Relationships between massive nanoprecipitates and improved mechanical performances are elucidated.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
This work analyzed the role of unique cell structures in hydrogen embrittlement of additively manufactured maraging steel. For comparison, some as built samples were solution treated to eliminate ...cell structures, producing the typical martensite where dislocations randomly distributed. By contrast, the cell structures constituted by dislocation tangles in as built samples introduced more hydrogen traps and delayed hydrogen diffusion, but caused much higher HE susceptibility, because the hydrogen accumulation around cell walls created locally hydrogen-enriched environment for the grain boundaries closely adjacent to cell walls, increasing the risk of intergranular cracking. Hydrogen susceptibility was markedly reduced after eliminating cell structures.
•Cell walls deteriorated the hydrogen environment of grain boundaries closely nearby.•Eliminating cell walls by solution treatment markedly improved hydrogen resistance.•Cell structures improved strength and uniform deformation ability in as built state.•Hydrogen diffusion processes were numerically simulated for deep cognizance.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
To elucidate the relationship between microstructural characteristics and mechanical properties in additively manufactured (AM) maraging steel, this study introduces a computational approach that ...addresses two fundamental challenges. Firstly, it addresses the creation of representative volume elements (RVEs) that mimic the observed microstructural complexities, such as meltpool boundaries, prior austenite grains, packets and blocks of lath martensite. This is accomplished through the application of Potts Monte-Carlo methods and grain segmentation techniques in accordance with the Kurdjumov–Sachs orientation relationship. Secondly, this study develops a comprehensive crystal plasticity (CP) model encompassing both bcc and fcc plasticity. Inspired by atomistic and discrete dislocation dynamics studies, the proposed CP model incorporates characteristics intrinsic to bcc plasticity, including non-Schmid effects, dislocation and precipitate strengthening, and Hall–Petch type strengthening of elongated martensitic blocks. Utilizing the created RVEs and the proposed CP framework, finite element simulations are conducted based on an update-Lagrangian formulation. The purpose of this study is to investigate the deformation behavior, texture evolution, tension–compression asymmetry, and evolution in dislocation density in RVEs representative of as-built and heat-treated samples of maraging steel. This computational approach and its findings deepen our understanding of the intricate interplay between microstructural characteristics and mechanical properties in maraging steel and also provide valuable guidelines for refining its additive manufacturing and heat treatment processes.
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•Dual-phase crystal plasticity model (fcc & bcc) successfully describes maraging steel.•High resolution FEM simulations elucidate deformation behavior of lath martensite.•The importance of meltpool boundaries emerges notably for high fraction of austenite.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Development of precipitation strengthening steels with ultrahigh strength and high ductility requires thorough understanding of nanoscale precipitation mechanisms. In this study, atom probe ...tomography (APT), HRTEM and first-principles calculations were used to reveal an interesting co-precipitation mechanism of Ni3Ti and Mo-rich nanoparticles in a 2.5 GPa grade maraging steel. The Ni–Ti rich clusters preferentially nucleate from the supersaturated solid solution and grow into Ni3Ti with extension of aging time, meanwhile the rejection of Mo atoms leads to heterogeneous precipitation of Mo-rich nanoparticles adjacent to the Ni3Ti particles and finally forms a core-shell structure along with Ni3Ti phase. Calculations of interaction energy between alloying elements in different aging process exhibit that the preferential formation of Ni–Ti rich cluster is due to the low interaction energy between Ni and Ti atoms, however, the Ni–Ti cluster is only a transitional phase, and when stable Ni3Ti is formed, Mo atoms are rejected from Ni3Ti to form a core-shell structure along with Ni3Ti precipitates. Finally, four modified theoretical prediction models are introduced to describe the yield strength as a function of microstructure and precipitates characteristics of the experimental steel.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This contribution investigates the effects of process parameter changes on residual stresses in printed maraging steel X3NiCoMoTi18-9-5. A series of samples was produced using direct metal laser ...sintering (DMLS) on an EOS M290 machine. Printed components typically exhibit undesirable tensile residual stresses (RS), which can lead to deformations and cracks. To reduce RS, different parameter sets were tested. The following parameters were tested: change of the build strategy from stripes to chessboard, time homogenization, change of the complex VED parameter, thermal treatment modification, and building platform preheating change. Residual stress evaluation was performed using the drilling method in subsurface area and X-ray diffraction in the surface area.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The influences of various process parameters on densification behavior, surface morphology, microstructure, and mechanical properties of selective laser melted (SLMed) maraging steel have been ...investigated. A process map for the SLM of maraging steel has been constructed. There exists a relatively large processing window, where sound products with relatively high relative density and good surface quality can be obtained. As-built specimens contained martensite matrix with trace amount of austenite phase. The quantity of austenite phase increased during aging treatment due to reversion of martensite to austenite. Solution treatment/aging resulted in elimination of the austenite phase and formation of intermetallic precipitates in the martensite matrix. The as-built and aged specimens exhibited almost the same average grain size, while solution treatment/aging resulted in grain growth of the martensite matrix and a significant change in grain orientation. The results indicated that the SLMed specimens with the building direction parallel to the loading direction had much lower elongation than those with the building direction perpendicular to the loading direction. The maximum tensile strength and hardness obtained were 2033MPa and 618HV respectively, after solution treatment at 820°C for 1h and aging at 460°C for 5h.
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•A process map for selective laser melting (SLM) of maraging steel has been constructed.•Relations among process parameters, microstructure, and mechanical properties of SLMed maraging steel have been clarified.•Aging promoted reversion of martensite to austenite, but solution treatment and aging led to elimination of austenite.•Specimens built parallel to loading direction had lower elongation than those built perpendicular to loading direction.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The synergistic effects of Mo, Ti, and Cr on nanoscale precipitation and mechanical properties of maraging stainless steels were systematically studied using high-resolution scanning transmission ...electron microscopy, atom probe tomography (APT), thermodynamic and first-principles calculations, and mechanical tests. Our results reveal a notable precipitation pathway involving the co-precipitation of Ni3Ti, Mo-enriched, and Cr-rich precipitates; their formations are not separated, but rather highly interacted. The APT results indicate that Mo partitions to the Ni3Ti precipitate core in the early stage of precipitation, which doubles the number density of Ni3Ti precipitates. Our calculations indicate that the Mo partitioning not only increases the chemical driving force, but also reduces the strain energy for nucleation, thereby accelerating Ni3Ti precipitation. As the precipitation proceeds, Mo atoms are rejected from the Ni3Ti precipitate core to the interface between the Ni3Ti precipitates and matrix, which leads to the heterogeneous nucleation of Mo-enriched precipitates on the outer surface of the Ni3Ti precipitates. This results in a substantial size refinement of Mo-enriched precipitates. In addition, the formation of Ni3Ti precipitates consumes Ni from the matrix, which substantially inhibits the spinodal decomposition and refines the size of Cr-rich precipitates. The cooperative strengthening of Ni3Ti, Mo-enriched, and Cr-rich co-precipitates leads to the development of new steels with a strength of 1.8 GPa; the contributions of these precipitates to the strengthening were quantitatively evaluated in terms of precipitate shearing and Orowan dislocation looping mechanisms.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
