Showing papers on "Maraging steel published in 2018"

The influence of aging temperature and aging time on the mechanical and tribological properties of selective laser melted maraging 18Ni-300 steel

Abstract: Selective laser melting (SLM) is an additive manufacturing and 3D printing technology which offers flexibility in geometric design and rapid production of complex structures. Maraging steels have high strength and good ductility, and therefore have been widely used in aerospace and tooling sectors for many years. This work aims to study the influence of aging temperature and aging time on the microstructure, mechanical property (hardness, strength and ductility) and tribological property of SLM maraging 18Ni-300 steel. The results reveal that the aging conditions had a significant impact on the strength and wear-resistance of the SLM maraging steel. The optimal aging conditions for the SLM maraging steel produced in this work were 490 °C for 3 h under which strength and wear-resistance were maximised. Lower or higher aging temperature led to under-aging or over-aging phenomena, reducing the strength and wear-resistance performance. Shorter or longer aging time also resulted in the decrease of strength and wear-resistance performance of the SLM maraging steel as compared with the optimal conditions. The variation of the mechanical and tribological properties is primarily due to changes in phase compositions and microstructures of the SLM maraging steels.

Fatigue Response of As-Built DMLS Maraging Steel and Effects of Aging, Machining, and Peening Treatments

Abstract: The main motivations for this study arise from the need for an assessment of the fatigue performance of DMLS-produced Maraging Steel MS1, when it is used in the “as fabricated” state. The literature indicates a lack of knowledge from this point of view; moreover, the great potentials of the additive process may be more and more incremented, if an easier and cheaper procedure could be used after the building stage. The topic has been tackled experimentally, investigating the impact of heat treatment, machining, and micro-shot-peening on the fatigue strength with respect to the “as built state”. The results indicate that heat treatment may improve the fatigue response, as an effect of the relaxation of the process-induced tensile residual stresses. Machining can also be effective, but it must be followed (not preceded) by shot-peening, to benefit from the compressive residual stress state generated by the latter. Moreover, heat treatment and machining are related by a strong positive interaction, meaning their effects are synergistically magnified when they are applied together. The experimental study has been completed by fractographic as well as micrographic analyses, investigating the impact of the heat treatment on the actual microstructure induced by the stacking process.

Effect of laser scanning strategies on texture, physical and mechanical properties of laser sintered maraging steel

Abstract: Direct Metal Laser Sintering (DMLS) is one of the most emerging metal Additive Manufacturing (AM) process due to its ability to quickly form complex designs with maximal surface finish. In this research, DMLS is used to additively manufacture 18% Ni maraging steel 300 samples by adopting a bidirectional and a cross-directional laser scanning strategy. The density, surface finish, texture, residual stress and mechanical properties of the DMLSed samples are investigated. Higher densification and surface finish are obtained using the cross-directional scan strategy. The formation of γ-austenite in the bi-directional scanning strategy is found to be nearly 60% in comparison to the cross-directional scan strategy. A preferential growth of columnar cells followed by epitaxial formation was found in both the directions for cross-directional scan strategy due to the rotation of heat flux and transformation of strong crystallographic texture into weaker ones. This resulted in a reduction of anisotropy and higher compressive residual stresses and mechanical properties. The outcomes of this research are likely to help in a better understanding of the DMLS AM process for fabrication of high surface finish, density and mechanical properties maraging steel parts by controlling their crystallographic texture.

Crystallographic Features of Microstructure in Maraging Steel Fabricated by Selective Laser Melting

Abstract: This study characterizes the microstructure and its associated crystallographic features of bulk maraging steels fabricated by selective laser melting (SLM) combined with a powder bed technique. The fabricated sample exhibited characteristic melt pools in which the regions had locally melted and rapidly solidified. A major part of these melt pools corresponded with the ferrite (α) matrix, which exhibited a lath martensite structure with a high density of dislocations. A number of fine retained austenite (γ) with a orientation along the build direction was often localized around the melt pool boundaries. The orientation relationship of these fine γ grains with respect to the adjacent α grains in the martensite structure was (111)γ//(011)α and [-101]γ//[-1-11]α (Kurdjumov–Sachs orientation relationship). Using the obtained results, we inferred the microstructure development of maraging steels during the SLM process. The results depict that new and diverse high-strength materials can be used to develop industrial molds and dies.

Milling of maraging steel components produced by selective laser melting

Abstract: This paper presents an experimental study of milling operations performed on 18Ni(300) maraging steel components produced by selective laser melting (SLM). The aim was to identify the manufacturing process chain to obtain the best properties of finished 18Ni(300) molds produced by a combination of additive and subtractive manufacturing methods. The SLM process variables taken into consideration were the build direction and post-build heat treatment, while cutting speed was considered as the only process variable for the milling phase. Surface roughness and hardness, cutting forces and tool wear were considered for the evaluation of the optimal manufacturing process parameters.

Low-Cycle Fatigue Behaviour of AISI 18Ni300 Maraging Steel Produced by Selective Laser Melting

Abstract: Selective laser melting has received a great deal of attention in recent years. Nevertheless, research has been mainly focused on the technical issues and their relationship with the final microstructure and monotonic properties. Fatigue behaviour has rarely been addressed, and the emphasis has been placed on high-cycle regimes. The aim of this paper is, therefore, to study, in a systematic manner, the cyclic plastic behaviour of AISI 18Ni300 maraging steel manufactured by selective laser melting. For this purpose, low-cycle fatigue tests, under fully-reversed strain-controlled conditions, with strain amplitudes ranging from 0.3% to 1.0%, were performed. After testing, fracture surfaces were examined by scanning electron microscopy to identify the main fatigue damage mechanisms. The analysis of results showed a non-Masing material, with a slight strain-softening behaviour, and non-linear response in both the elastic and plastic regimes. In addition, this steel exhibited a very low transition life of about 35 reversals, far below the values of conventional materials with equivalent monotonic mechanical properties, which can be attributed to the combination of high strength and low ductility. The total strain energy density, irrespective of strain amplitude, revealed itself to be a quite stable parameter throughout the lifetime. Finally, the SEM analysis showed for almost all the tested samples cracks initiated from the surface and inner defects which propagated through the rest of the cross section. A ductile/brittle fracture, with a predominance of brittle fracture, was observed in the samples, owing to the presence of defects which make it easier to spread the microcracks.

Selective laser melting of tungsten carbide reinforced maraging steel composite

Abstract: In this work, tungsten carbide (WC) reinforced maraging steel matrix composites were in-situ manufactured by selective laser melting (SLM) from powder mixture. The SLM processed samples presented high relative density (over 99%) with a homogenous distribution of WC. The as-fabricated surface quality of SLM processed samples was improved significantly by the addition of WC. Focused ion beam and transmission electron microscopy were employed to characterize the interfacial properties between tungsten carbide and steel matrix. The elemental analysis indicates that metallurgical bonding appears at interfacial region due to the diffusion. Tensile behavior of SLM processed maraging steel was different from their composite with several WC contents.

Selective laser melting of maraging steel: mechanical properties development and its application in mold

Abstract: Purpose This paper aims to verify whether selective laser melting (SLM) could be used for manufacturing mold with conformal cooling channels and determine whether the mechanical properties development of SLM manufacturing maraging steel mold would be beneficial to improve the quality of mold. Design/methodology/approach A series of block specimens and cylindrical tensile specimens are manufactured by SLM, and then are heat treated by solution treatment (ST) and solution treatment + aging treatment (ST + AT), respectively. The development of microstructure, microhardness and tensile strength of specimens is investigated. Then, a mold with conformal cooling channels is designed and manufactured by SLM and machined after ST with microhardness decreasing. Findings The morphology of microstructure varies widely under different heat treatment. The microhardness and tensile strength decrease after ST with cellular structure broken, which is conducive to mechanical finishing for mold to improve surface accuracy. After that, the hardness and strength of the mold increase significantly by AT with the precipitation of Ni3Mo, Fe2Mo and Ni3Ti particles. The maraging steel mold with conformal cooling channels can be manufactured by SLM successfully. And the surface accuracy of mold could be improved easily by machining. Originality/value Compared with the traditional mold with simple cooling channels, the mold with conformal cooling channels can be manufactured by SLM directly. The hardness of maraging steel mold manufactured by SLM can be reduced through ST, which is conducive to mechanical finishing for overcoming the defect of low precision of SLM directly manufacturing mold. This provides a new way for manufacturing mold of high quality.

Strengthening of cobalt-free 19Ni3Mo1.5Ti maraging steel through high-density and low lattice misfit nanoscale precipitates

Abstract: The concept of low lattice misfit and high-density of nanoscale precipitates obtained through solution treatment was adopted to obtain ultrahigh strength maraging steel without compromising elongation. An “ultrahigh strength-high toughness” combination was successfully obtained in 19Ni3Mo1.5Ti maraging steel with ultimate strength of ~1858 MPa and static toughness of ~110 MJ m−3. Maraging steel had extremely high density (2.3 × 1024 m−3) of nanoscale precipitates with minimum lattice misfit of less than 1% at the solutionization temperature of 820 °C. Two kinds of nanoscale precipitates, namely, η-Ni3(Ti,Mo) and B2-Ni(Mo,Fe) contributed to ultrahigh strength. The size of nanoscale precipitates governed the movement of dislocations, cutting versus by-passing. Theoretical estimate of ordering and modulus contribution to strengthening suggested that ordering had a dominant influence on strength. The toughness was closely related to the characteristic evolution of nanoscale precipitates such that the high density of nanoscale precipitates contributed to increase of elastic deformation and low lattice misfit contributed to increase of uniform deformation. The nanoscale size and low lattice misfit of precipitates were the underlying reasons for the high-performance of maraging steel. Moreover, the combination of high-density of nanoscale precipitates and low lattice misfit is envisaged to facilitate the futuristic design and development of next generation of structural alloys.

Design and Implementation of a Multisensor Coaxial Monitoring System With Correction Strategies for Selective Laser Melting of a Maraging Steel

Abstract: Development of monitoring devices becomes crucially important in selective laser melting due to the high process complexity and the high value of the products obtained. This work discusses the design of a coaxial monitoring system for SLM using multiple sensors. In particular, an optical model is developed for the propagation of the process emission from the workpiece to the monitoring module. The model is used to determine the field of view around the monitored zone. The lens arrangements and the optical filters are chosen according to the model results. They were implemented to construct a monitoring module consisting of two CCD cameras viewing visible and near-infrared wavelength bands, as well as a photodiode viewing the back-reflected laser emission, all integrated in a coaxial configuration. The system 1 Corresponding author information can be added as a footnote. 2 functionality is tested with a prototype SLM machine during the processing of 18Ni300 maraging steel, a material known to be prone to porosity. In particular, different remelting strategies were employed as possible correction strategies to reduce porosity. The signals were interpreted as being indicators of the change in absorptivity of the laser light by the powder bed, of the plasma and molten pool, as well as of the evolution of the temperature field.

Numerical tools to investigate mechanical and fatigue properties of additively manufactured MS1-H13 hybrid steels

Abstract: Additive manufacturing (AM) has been recently used to deposit metal powder on top of conventional metals. Of particular interest is hybrid additively manufactured steels which were found to be a suitable solution to benefit from features of each metal at different spots of a mechanical component. Due to its superior mechanical characteristics, maraging steel (MS1) has recently attracted tremendous attention for additive manufacturing applications mainly in aerospace, tool and die, and marine industries or to be 3D printed on top of other metals as a hybrid product using different techniques such as Direct Metal Laser Sintering (DMLS). In this paper a predictive finite element (FE) model and a combined analytical-numerical framework were developed to evaluate the mechanical performance of hybrid additively manufactured components and facilitate the prediction of hardness and fatigue life of these parts. The proposed tools were employed in two scopes: First to simulate the indentation hardness test of hybrid DMLS-MS1-H13 steels; and second to calculate fatigue crack nucleation life of maraging steel including defects (i.e. welding residual stresses). Parameters such as local and global displacements, changes in Young’s modulus, and hardness, high cycle fatigue life, welding temperature distribution, and residual stress were investigated. The hardness experiments were carried out to improve the reported data found in similar studies, which were used as the main resource to validate the proposed numerical framework. The capabilities of the presented frameworks enable this work to target existing ambiguities in additively manufactured mechanical components.

Austenite reversion in 18% Ni maraging steel and its weldments

Abstract: In the heat-treated condition, 18% Ni maraging steels have a microstructure of aged martensite and essentially no austenite. However, austenite can form if the material is overaged. This has been termed as austenite reversion, a subject which has received much attention, because it importantly influences properties and performance of the steel. Reversion of austenite in fusion zones of weld joints in these steels has also been widely studied. Because of microsegregation, austenite reversion in the fusion zone is accelerated. Reverted austenite in the fusion zone strongly influences the performance of the weld joints. The present review critically analyses the published work on austenite reversion and its effects on properties and performance, covering both base metal and weld joints.

Effects of cold rolling on the microstructure and properties of Fe-Cr-Ni-Mo-Ti maraging steel

Abstract: The effects of cold deformation on the evolution of the microstructure and mechanical properties of Fe-Cr-Ni-Mo-Ti maraging steel were investigated. The microstructural changes during cold rolling were observed using optical microscopy (OM), electron back-scattered diffraction (EBSD), transmission electron microscopy (TEM) and X-ray diffraction (XRD), which were related to the mechanical properties as measured by micro-hardness and tensile testing. The remaining austenite in the as-quenched specimens was found to transform into martensite during cold deformation. High-density dislocations were produced in the martensite matrix by plastic deformation, which accelerate the aging response by promoting the formation of η-Ni3Ti precipitates. The strain hardening was partially conserved due to static recovery during the aging process. The cold rolled steel showed a very high hardening response, resulting in an increase in yield strength during the subsequently aging treatment at 510 °C, with a detectable loss in ductility.

Influence of defects on axial fatigue strength of maraging steel specimens produced by additive manufacturing

Abstract: Nowadays many materials such as steels, aluminium and titanium alloys can be realised by powder bed solutions melting subsequently powder layers by means of a laser or electron beam (Laser Beam Melting – LBM and Electron Beam Melting – EBM). The microstructure realised by layer-by-layer solidification having high cooling rate cannot be considered isotropic. Therefore, the mechanical properties could be influenced by the building direction. Regarding maraging steel, the study of the influence of the building direction and the heat treatment on the static and axial fatigue strength has been investigated in a previous contribution. A large scatter of the fatigue test results was found because of the presence of detrimental surface and subsurface defects. The aim of this contribution is to present additional axial fatigue test results of maraging steel characterized by different build orientation and providing an analysis of the defects observed at the crack initiation area of the fracture surface.

On the origin and contribution of extended kinks and jogs and stacking fault ribbons to deformation behavior in an ultrahigh strength cobalt-free maraging steel with high density of low lattice misfit precipitates

Abstract: We elucidate here the deformation mechanisms and underlying reasons that contributed to high ductility (10.2%) and high static toughness (112.5 MJ m−3) in an ultrahigh strength (1860 MPa) cobalt-free 19Ni3Mo1.5Ti maraging steel characterized by high density (2.3 × 1024 m−3) of η-Ni3(Ti,Mo) and B2-Ni(Mo,Fe) nanoscale precipitates with low lattice misfit of ＜1% with the martensite matrix. Multiple deformation processes occurred during plastic deformation. Lath-morphology of martensite was dramatically segmented with angles of 30°, 60° or 120° with large pile-up of dislocations at the segmented boundaries. This occurred because of the interactive ability of edge and screw dislocations along the martensite habit planes, which led to kinks and jogs. The low lattice misfit (0.6% ~ 0.9%) precipitates interacted with dislocations leaving stacking fault ribbons within precipitates that build a large long range of back stress producing a high strain-hardening response. Additionally, nanoscale twinning occurred. The above contributions to ductility are envisaged to be in addition to the significantly reduced elastic interaction between the low lattice misfit nanoscale precipitates and dislocations that reduces the ability for crack initiation at the particle-matrix interface.

Investigation on the process and microstructure evolution during direct laser metal deposition of 18Ni300

Abstract: Purpose Additive manufacturing is a fabrication technology with flexibility and economy. 18Ni300 is one of maraging steels with ultra-high strength, superior toughness, so it is an excellent candidate of structural material. This paper aims to explore the feasibility of using direct laser metal deposition method to fabricate18Ni300, and the evolution of its microstructure and defects is studied. Design/methodology/approach The experiments were conceived from single-trace-single-layer (STSL) test to multi-trace-multi-layers (MTML) test via single-trace-multi-layers (STML) test. The microstructure, defects and mechanical properties were analyzed. Findings The STML results showed that the columnar/equiaxed transformation occurred at the top part and the grain size increased with the layer number increasing, and it was explained by an innovative attempt combining columnar/equiaxed transformation model and the change of grain size. The MTML test with the interlayer orthogonal parallel reciprocating scanning pattern resulted in the grain growing along orthogonal directions; with the increase of overlap rate, the length and the area of the columnar grain decreased. What is more, the later deposition layer had lower micro-hardness value because of heat history. Originality/value Direct laser metal deposition method was a novel additive manufacturing method to manufacture 18Ni300 components, as 18Ni300 maraging steel was mainly manufactured by selective laser melting (SLM) method nowadays. It was useful to manufacture maraging steel parts using direct laser deposition method because it could manufacture larger parts than SLM method. Influence of processing parameters on forming quality and microstructure evolution was studied. The findings will be helpful to understand the forming mechanism of laser additive manufacturing of 18Ni300 components.