Grade Maraging Steel Research Articles

Hot deformation behavior of laser powder bed fusion newly developed MS400 grade maraging steel

AbstractIn this work, the hot deformation mechanism of as-printed laser powder bed fusion process (LPBF) newly developed MS400 grade maraging steel was investigated. The optimization processes allowed for obtaining samples with an average density of 8.200 ± 0.002 g cm−3 and hardness of 417 ± 5 HV. The hot compression procedure of maraging steel was carried out with the DIL 805 A/D dilatometer at different temperatures in the range of 1050 °C-1200 °C and strain rates of 0.01 s−1–1 s−1 in an inert gas atmosphere. The measured melt flow stress data were used to develop a constitutive model to determine the behavior of the alloy during hot deformation. The proposed equation can be used as an input to the finite element analysis to obtain the flow stress at a given strain, strain rate and temperature, useful for predicting flow localization or fracture during thermomechanical simulation. The activation energy for hot deformation was calculated to be 388.174 kJ mol−1, which corresponds to that of M350 grade. The proposed equation can be used during finite element analysis to calculate the flow stress at any strain, strain rate and temperature to determine the location of a flow or crack during a thermomechanical simulation.

Embrittlement Fracture Behavior and Mechanical Properties in Heat-Affected Zone of Welded Maraging Steel.

In welded maraging steels, mechanical properties, particularly ductility and toughness, are often compromised in the heat-affected zone (HAZ). This study focuses on 300-grade maraging steel bars, solution annealed at 1123 K for 1.5 h (5.4 ks) and welded using gas tungsten arc welding, followed by a post-weld heat treatment at 753 K for 13.33 h (48 ks). In situ observations during three-point bending tests on HAZ samples featuring coarsened prior austenite grain sizes were conducted to examine damage behavior and the crack path near the crack tip. The main crack initiated at the peak applied load during the bending test and, upon further loading, exhibited significant deflection and extension accompanied by numerous microcracks and localized crack branching. Distinctive damage features, such as transgranular cracking across block regions, intense intergranular cracking along packet boundaries with a pronounced shear component, and crowding of microcracks ahead of the crack tip, were observed in the HAZ sample during the in situ test. The interaction between the main crack tip and microcracks and its influence on the local crack propagation driving force was discussed using fracture mechanics. Experimental results, including tensile fracture surface observations and in situ images, along with analysis of the stress anti-shielding effect by microcracks, suggest that the HAZ sample exhibits embrittlement fracture behavior with lower ductility and toughness compared to the base metal sample.

A novel approach to suppression of reverted austenite in aerospace grade thick maraging steel weldments using the turbo-TIG welding process

This research examines aerospace grade-maraging steel weldments produced by the novel Turbo-TIG welding technique. The vital challenge in welding maraging steel is the development of reverted austenite in the weld region and HAZ. This reverted austenite degrades the mechanical characteristics of weldments. MDN 250 maraging steel with a 12 mm thick plate was welded at a high speed of 300 mm/min with consistent quality using the Turbo-TIG welding technique. The objective of the present work is to suppress the reverted austenite in the 12 mm thick plate of MDN 250 using the Turbo-TIG welding technique. Three different postweld heat treatments were applied, namely, (i) aging heat treatment (AT), (ii) solutionizing + aging (ST), and (iii) homogenization + solutionizing + aging (HT). The microstructure and X-ray diffraction analysis of the weld zone under AT and ST conditions demonstrate the existence of reverted austenite in the grain boundary regions. The SEM/EDS analysis of the weld zone of welded, AT, and ST conditions indicated Ni, Mo, and Ti microsegregation from the center matrix to the grain boundary regions. In contrast, neither microsegregation nor austenite reversion occurred in the HT condition. The tensile test demonstrates a maximum strength of 1797 MPa (UTS) under HT conditions. Likewise, the microhardness of the HT conditions exhibits a higher hardness of 552 HV in the fusion zone. In light of the metallurgical and mechanical characteristics of the weld, the HT heat treatments provide better weld performance in the case of Turbo-TIG welding of maraging steel grade MDN 250.

Wire-arc directed energy deposition of monolithic and bimetallic structures of maraging 250 steel

ABSTRACT Metal additive manufacturing is rapidly growing as a new paradigm in on-demand customised production, where high-performance bimetallic structures demand increasingly high-performance materials such as maraging steel grade 250 (M250). The behaviour of advanced materials in additively manufactured systems requires comprehensive understanding before it is possible to move beyond their use in simplistic monolithic designs. This study demonstrates the use of M250 in radial bimetallic near-net representative structures based on a comprehensive study of M250 in wire-arc additive depositions. Monolithic structures are first produced with minimal defects, confirmed by X-ray imaging. Phase, microstructure, and tensile properties are compared for heat-treated specimens and as-processed counterparts. EBSD and Charpy impact testing is performed, fracture morphology is compared, and microhardness is determined. Representative radial bimetallic structures are produced and similarly investigated, revealing anticipated microstructure. Our results demonstrate that a comprehensive understanding of advanced additive materials allows complete design flexibility.

Comparison of corrosion behaviour on 18% Ni 250 grade maraging steel under weld aged condition in NaCl and H<SUB align="right">2SO<SUB align="right">4

Comparison of corrosion behaviour on 18% Ni 250 grade maraging steel under weld aged condition in NaCl and H<SUB align="right">2SO<SUB align="right">4

Achieving good ductility in 2.1 GPa grade maraging steel

Maraging steels with ultrahigh strength are important for structural applications, but their low ductility severely limits engineering applications. Here we demonstrate improved ductility can be achieved in 0.18C10Ni8Co3Cr1.6Al1Mo1W maraging steel. This steel exhibits a high yield strength of 1.75 GPa, an ultrahigh tensile strength of 2.09 GPa and a uniform elongation of 5 %. Such good strength-ductility synergy arises from a unique microstructure: a refined hierarchical martensite matrix with dense coherent B2-nanoprecipitates. Strengthening models indicate that the ultrahigh strength can be attributed to block boundary strengthening, dislocation strengthening and precipitation strengthening. Utilizing transmission electron microscope coupled with geometric phase analysis at interrupted deformation stages, we reveal dynamic dislocation-nanoprecipitate and dislocation-dislocation interactions. Notably, mobile dislocations not only cut through nanoprecipitates but also penetrate pre-existing dislocation substructures and lath boundaries. Such deformation behaviors promote dislocation multiplication and accumulation, thereby conferring good strain hardening and ductility.

Experimental optimization on mechanical properties of 18Ni-300 maraging steel produced by direct metal laser sintering

Maraging steel material characteristics are greatly affected by build orientation and scanning strategies during manufacturing. This research aims to examine the effect of various build orientations and scan strategies on the ultimate strength and microhardness of 18 Ni-300 grade maraging steel. The maraging steel is made using a technology called direct metal laser sintering. Using the Analysis of Variance approach, the effects of processing factors like build orientation, scan techniques, and type of process on ultimate strength, microhardness, and roughness are optimized. The properties tend to be greater in the horizontal orientation when using the XY scan strategy as a result of thermal history variations,. The mechanical performances of maraging steel components in terms of strength values observed were lower in the vertical position compared to all other orientations. The tests are carried out using an L27 orthogonal array and a Taguchi design of experiment. Build orientation XZ, scan method XY, and Solution-aging-aging(SAAT) has the most significant influence on the final ultimate strength, microhardness, and roughness of all the input factors. A2B2C3 is the optimal combination level of control factors. Additionally, a percentage inaccuracy was identified after conducting confirmation tests on the most prominent experimental data.

Effect of strain rate on the compressive strength and texture of maraging steel grade 250

The present study demonstrates the effect of strain rates (in terms of cross head velocities of 0.1, 0.5 and 1 mm/min) during uniaxial compression test of cold rolled and annealed maraging steel (grade 250) on microstructure, texture and mechanical properties. The texture developed at lowest (0.1 mm/min) and highest (1 mm/min) strain rate facilitates the grains of the microstructure to take the equiaxed shape and bring some degree of uniformity as compared to the grains of starting (cold rolled and annealed) material. At intermediate (0.5 mm/min) strain rate the grains reorient towards the starting texture which provides a similarity in the microstructure of this and starting materials. The hardness and compressive strength at 15% total true strain of the alloy increases with increase in strain rates during the compression test. The role of texture in strengthening of compressed samples deformed with different strain rates as compared to the starting sample has been explained by the near Goss recrystallization component ((111) [1-1 0 ]) which is present in the starting material and remains absent in all the compressed samples. The (111)-fibre formation is observed to be an important phenomenon in this alloy. The (111)-fibre is strengthened in the starting material and the material compressed with 0.5 mm/min. The intensity of (111)-fibre becomes weaker for the samples compressed with lowest (0.1 mm/min) and highest (1 mm/min) strain rates and results in improved microstructure of the alloy.

Comparison of Corrosion Behaviour on 18% Ni 250 Grade Maraging Steel Under weld aged condition in NaCl and H2SO4

Comparison of Corrosion Behaviour on 18% Ni 250 Grade Maraging Steel Under weld aged condition in NaCl and H2SO4

Development of a low heat-input welding technique for joining thick plates of 250 grade maraging steel to fabricate rocket motor casings

• A low heat-input welding technique for the fabrication of rocket motor casing was devised and implemented. • The novel DP-GMAW reduced heat-input by 67% and RA by 49% compared to conventional GMAW. • DP-GMAW improved weld properties compared to GMAW. Maraging steels are ultra-high strength steels, which are most widely used in different strategic sectors. These steels are well-suited for the fabrication of rocket motor casings, which involves welding as one of the critical manufacturing processes. The major concern regarding welding of maraging steel is the formation of reverted austenite (RA) phase, which deteriorates the mechanical performance of the joints. The conventional arc welding processes involve higher heat-input during welding; the available literature indicates that segregation of alloying elements and the resultant formation of RA are promoted by high heat-input. The present study adopted a novel dual-pulse gas metal arc welding (DP-GMAW) technique, which reduces the heat-input during welding by current pulsing approach. The Dual pulsing approach was capable of 67% reduction of heat-input and 49% reduction of RA when compared to conventional gas metal arc welding (GMAW).

Effect of heat treatment on the microstructure and mechanical properties of 2.4 GPa grade maraging steel fabricated by laser powder bed fusion

The effects of three different heat treatments (direct aging, austenitizing–aging, and solutionizing–austenitizing–aging) on the meso-/micro-structures and the mechanical properties of the 18 wt% Ni-350 maraging steel (M350), specifically designed for ultra-high strength, additively manufactured using the laser powder bed fusion (LPBF) are studied. In both the as printed and directly aged conditions, the dendritic growth induced cellular structures constitute the unit microstructural features of the martensite; the martensitic transformation in these conditions occurs within the cell matrix and the cell boundaries act as the preferred sites for the austenite retention/reversion. The cell structures partially dissolve upon the austenitizing–aging heat treatment, while solutionizing fully erases them; both these heat treatments can facilitate the formation of the conventional packet–block–lath hierarchy, which is absent in the as printed and directed aged samples. Uniaxial tensile and mode I fracture toughness measurements reveal that the presence of the austenite in the directly aged M350 maraging steel lowers its strength but increases the fracture toughness. The absence of austenite in the other two heat treatment conditions results in high strength, but lower toughness. These findings shed light on understanding fundamental relationship between the unique features of the LPBF process and the martensitic transformation in maraging steels.

Development of Multipass Gas Tungsten Arc Welding Technique for Aerospace Grade 18% Ni-Co-Mo Based Maraging Steel to Improve the Metallurgical and Mechanical Properties by Reducing Austenite Pools

Abstract The maraging steel is an impeccable choice for aerospace applications due to its high strength and excellent toughness. Welding is importantly involved in fabricating various structures out of maraging steel. Gas tungsten arc welding (GTAW) is the most commonly adopted technique for joining maraging steel. However, the major concern regarding the welding of maraging steel is the formation of the reverted austenite phase in the fusion zone and the heat affected zone. This reverted austenite deteriorates the mechanical property performance of welded joints. The present study focuses on GTAW of 12 mm thick MDN 250 maraging steel. An attempt was made to suppress the reverted austenite by employing suitable post-weld heat treatments. Three different types of post-weld heat treatments were adopted, i.e, (i) direct aging (W-DA), (ii) solutionizing + aging (W-SA), and (iii) homogenizing + solutionizing + aging (W-HSA). The micrograph and XRD analysis of the fusion zone with W-DA and W-SA conditions reveal the presence of reverted austenite. The SEM/EDAX examination of the fusion zone of as-welded, W-DA, and W-SA conditions revealed micro-segregation of Ni, Mo, and Ti elements from the matrix to the grain boundaries. On the other hand, the W-HSA condition was free from micro-segregation and austenite reversion. Electron backscatter diffraction (EBSD) analysis was used to estimate the percentage of reverted austenite in the fusion zone. The tensile test shows the highest strength of 1721 MPa (UTS) in W-HSA conditions. Similarly, the microhardness of the W-HSA conditions depicts a higher hardness with an even distribution in the microhardness values across the weldment. Hence, considering both metallurgical and mechanical examination of the weldment, the W-HSA heat treatments give superior properties in the case of GTA welded MDN 250 grade maraging steel.

Numerical investigation into laser-based powder bed fusion of cantilevers produced in 300-grade maraging steel

Laser-based powder bed fusion of 300-grade maraging steel allows the production of parts with a high hardness, which improves the service life and wear resistance of tooling or mould insert produced from this material. The material typically consists of a martensitic matrix material, with retained austenite and nano-precipitation. The transformation from austenite to martensite has been linked to compressive stresses at the surface of parts produced in 300-grade maraging steel. In a cantilever beam-type part, this means that after cutting from the base-plate, the part will bend downwards, which is the opposite direction from the deformation found in most other materials after additive manufacturing. One way to gain insight into processing 300-grade maraging steel, while limiting the number of test samples that need to be printed, is by means of a numerical model. Using previously established models, additive manufacturing of a cantilever part in 300-grade maraging steel is simulated. Inclusion of the transformation from austenite to martensite into a numerical simulation of the laser-based powder bed fusion revealed the origin of the compressive stress at the surface of a simple cantilever beam-type sample. Additionally, changing the effective laser power through the laser absorptivity shows that the behaviour of the post-cutting deformation flips as compared to more conventional materials. Information about the laser absorption coefficient is rare, while it can greatly affect the results of a simulation. It is included in the presented result through the effective laser power, which is the product of the input laser power and laser absorption coefficient. When the effective laser power is changed from 95 W to 47.5 W, the cantilever bends upwards rather than downwards after release from the base plate. The results demonstrate the major influence played by the laser absorption coefficient on the simulation, an aspect to which little attention is paid in literature, but is proven to be one of the main factors to determine the component distortions after the laser-based powder bed fusion process.

Technology development for in-situ measurement of residual stress in arc welded joints of MDN 250 by portable Cosα X-ray diffraction method

Residual stresses are inherent stresses that exist in engineering components even though no external load is applied. They are caused by the non-uniform volumetric shift of the metallic component during manufacturing processes. Welding is a key manufacturing technique that has a substantial impact on the economy since it is required for the production of a diverse variety of products used in the engineering sector. The residual stress primarily affects the stability, durability and performance of the welded joints. Hence its determination is of utmost importance. X-ray diffraction (XRD) is the most commonly used method for residual stress analysis. There are mainly two approaches for measuring residual stress using XRD; one is the sin2ψ method and the other is the cosα method. The residual stress measurements using the cosα method are handy, quick and convenient compared to the sin2ψ method. This method is well suited for welded joints, as it provides flexibility for testing immediately after the welding operation. Apart from residual stress measurements, the cosα method also gives valuable insights in the form of Debye-Scherrer (DS) rings and full width at half maximum. The present study focuses on the development of a novel technique that not only enables residual stress measurement but also provides a quantitative estimation of hardness and qualitative estimation of grain size without performing metallurgical or mechanical characterization. The material used for the present study is an arc-welded joint of MDN 250 grade maraging steel. The residual stress results show a compressive profile throughout the weldment, with a maximum value of compressive residual stress of 428 MPa at the fusion zone.

HEAT TREATMENT EFFECT ON MARAGING STEEL MANUFACTURED BY LASER POWDER BED FUSION TECHNOLOGY: MICROSTRUCTURE AND MECHANICAL PROPERTIES

Laser Powder Bed Fusion (L-PBF) is a widespread additive manufacturing technology in industrial applications, for metal components manufacturing. Maraging steel is a special class of Fe-Ni alloys, typically used in the aerospace and tooling sectors due to their good combination of mechanical strength and toughness. This work analyses the heat treatment effect on the microstructure and hardness value of 300-grade maraging steel manufactured by the L-PBF process. The considered heat treatment consists of a solution annealing treatment followed by quenching and ageing hardening treatment. The effect of ageing temperature is reported, in a wide temperature range. Results show that solution annealing treatment fully dissolves the solidification structure caused by the L-PBF process. Moreover, the ageing hardening treatment has a significant impact on the hardness, hence on strength, of L-PBF maraging steel. The optimal ageing conditions for the L-PBF maraging steel are identified and reported: in particular, results show that the hardness of 583 HV is achieved following ageing treatment at 490 °C for 6 hours. A higher treatment temperature leads to over-ageing resulting in a decrease of hardness. Conversely, an excessive ageing time does not seem to affect the hardness value, for the ageing temperature of 490 °C.

Influence of Austenitization Parameters on the Precipitation Sequence and the Chemical Homogenization of Austenite in a High-Performance Fe–Ni–Cr–Al–Ti–Mo Stainless Maraging Steel

MLX19 stainless maraging steel grade exhibits a mechanical strength/fracture toughness balance within the required range for landing gear applications. However, the microstructure after the heat treatment still needs to be precisely controlled to obtain a better repeatability of the mechanical properties. This work shows that austenitizing is a critical stage. The influence of austenitization treatment parameters on the microstructure obtained after quenching was thus precisely quantified. It was first revealed that, after a standard austenitization at 850 °C and for specific heating rates and holding times, undissolved β-NiAl precipitates, reaching sizes up to 500 nm, still remain in the as-quenched state, in addition to a high retained austenite fraction. It was also found that large amounts of retained austenite are the result of local heterogeneities in the chemical composition of the austenitic phase prior to quenching, while the undissolved precipitates change the overall chemical composition of the austenitic matrix. New austenitization conditions were thus proposed, leading to a better homogeneity of the chemical composition of the martensitic matrix after quenching.

Oxide layer characterization by XRD and Rietveld refinements in maraging steel 300 aged in steam atmosphere

Maraging steels are martensitic steels hardened by precipitation of intermetallic compounds in thermal aging, with good machining properties and high strength, fracture toughness and corrosion resistance, being used in aircraft parts and rocket motor-case, tooling applications and nuclear plants. During thermal aging in steam atmosphere a protective and corrosion resistant oxide layer is formed over the bulk. In this work, conventional Bragg-Brentano geometry was used to identify the phases formed in four specimens of maraging steel grade 300 with different surface finishes that were previously solution annealed twice at (950 ± 5) °C for 1 h, air-cooled, and submitted to oxidation process under positive pressure about 1.5 kPa of steam at (480 ± 5) °C for 6 h, followed by forced air-cooling. Diffraction patterns were measured employing CuKα radiation, ranging 20º < 2θ < 85º and the Rietveld method was used to better characterize the structures identified. Through Rietveld refinements it was possible to conclude that the layer formed during heat treatment process is constituted by a transition metallic phase with a quasi-cubic face centered unit cell, and an oxide layer that includes hematite, magnetite and a spinel structure type MFe2O4, where M could be an alloying element, for all analyzed samples.

Characterization of bi-layers formed over maraging steel 300 during aging process with steam atmosphere by GIXRD and SEM

Maraging steels are martensitic steels hardened by precipitation during thermal aging, with good machining properties and high strength and corrosion resistance. It is well suited for applications which require high strength-to-weight material, being used in aerospace, aeronautics and nuclear industries. A protective and corrosion resistant oxide layer can be formed during age hardening if treated in steam atmosphere. This work aims to use grazing incidence X-ray diffraction (GIXRD) to evaluate qualitatively the thickness of the layers formed during this process. GIXRD and scanning electron microscopy (SEM) were employed to identify and order the layered structure formed on four specimens of maraging steel grade 300 with different surface finishes that were previously solution annealed twice at (950 ± 5) °C for 1 h, air-cooled, and submitted to oxidation process under positive pressure around 1.5 kPa of steam at (480 ± 5) °C for 6 h followed by forced air cooling. The diffraction patterns were measured employing CuKα radiation and parallel beam, in step scan mode, using incident angles varying from 0.2º to 4.0º and 20º < 2θ < 85º. The results revealed the formation of two layers, the innermost was formed by γ-iron (austenite – fcc) phase followed by a mixture of oxides (hematite and magnetite) on the top, regardless of surface finish, which was confirmed by the SEM analysis that also allowed the measurement of the average layer’s thickness of oxides (1.130 ± 0.094) µm and austenite (0.507 ± 0.090) µm phases, and corroborated the qualitative thicknesses analysis made from GIXRD results.

Analysis of Stress-Strain Curves to Predict Dynamic Recrystallization During Hot Deformation of M300 Grade Maraging Steel

18Ni-2000 MPa maraging steel (M300 grade) is extensively used for performance critical aerospace applications where strength-toughness balance is the basis for material selection. The key to achieve the desired mechanical properties in the final product is to process the material under conditions that will impart an equiaxed, fine grained microstructure. This in turn is controlled by the selected deformation processing conditions such as strain, strain rate and temperature. Therefore, hot deformation behavior of the material is usually studied under wide temperature, and strain rate ranges to map the microstructural evolution with specimens deformed to a given strain. However, the effect of strain on the microstructural evolution, its effect on the initiation and termination of dynamic recrystallization are essential to obtain balanced mechanical properties. In this study, analysis of stress-strain curves was conducted with an intention to obtain fine prior austenite grain (PAG) size through dynamic recrystallization (DRX), and the same was verified experimentally from the microstructures evolved through hot isothermal compression tests on cylindrical specimens subjected to different strains. A single peak type DRX curve was identified for analysis from the high temperature stress-strain curves. The theoretically determined critical strain was used to experimentally verify the initiation of DRX (DRXI) and transition from DRX dominant region to grain growth dominant region (DRXT). Hot isothermal compression tests have been conducted at T=1100°C and e = 0.1s−1 and obtained PAG size of 7.68 µm in the specimen deformed to theoretically determined optimum strain of 0.6, thereby validating the used models.

An investigation of the anisotropic properties of heat-treated maraging steel grade 300 processed by laser powder bed fusion

In order to explore the possibilities enabled by laser beam powder bed fusion of metals (PBF-LB/M), reliable material models are necessary to optimize designs with respect to weight and stiffness. Due to the unique processing conditions in PBF-LB/M, materials often develop a dominating microstructure that leads to anisotropic mechanical properties, and thus isotropic material models fail to account for the orientation-dependent mechanical properties. To investigate the anisotropy of 18Ni300 maraging steel, tensile specimens were built in seven different orientations. The specimens were heat treated at two different conditions and tested for their tensile properties using digital image correlation (DIC) technique. The microstructure and fracture surfaces are investigated with scanning electron microscope and electron backscatter diffraction. The tensile properties are typical for the material, with a yield strength in the range of 1850 MPa to 1950 MPa, and ultimate tensile strength in the range of 1900 MPa to 2000 MPa. The elastic modulus is 180 GPa, and the elongation at fracture is in the range of 2–6% for all specimens. The strain fields analysed with DIC reveals anisotropic straining in both the elastic and plastic parts of the flow curve for both direct ageing and solution treatment plus ageing specimens. In the former condition, the elastic anisotropy is dictated by the fraction of melt pool boundaries on the transverse surfaces of the specimens. When the material is solution treated prior to ageing, the melt pool boundary effect was supressed.