Papers by Keyword: Maraging Steel

Abstract: Additive Manufacturing enables the production of intricate geometries and products with improved strength-to-weight ratios, driving its applications in defence, aerospace, and automobile sectors. Maraging steel and Superalloy Inconel 625 are renowned for their excellent mechanical properties and are candidate materials for high performance applications. It is essential to study the fatigue behaviour of additively manufactured samples prior to their deployment in real working environments, as their mechanical properties and fatigue behaviour differ from those of conventionally manufactured materials. In the present study, low cycle fatigue (LCF) behaviour of Maraging steel (M300) and Inconel 625, at different strain amplitudes and heat treatment conditions were evaluated. Fractographic characterization was conducted using scanning electron microscopy (SEM). To understand the effect of build orientation on LCF behaviour, the maraging steel samples were also tested in different build orientations (0^o and 90^o). It was found that build orientation significantly affected the fatigue life of additive manufactured maraging steel samples. The LCF study was also done at different strain amplitudes for Inconel 625 and results indicated that there was drastic decrease in fatigue life at higher strain amplitudes. It was observed that defects introduced due to layer wise processing of additive samples have adverse effect on fatigue life. Ultrasonic shot peening was also applied to the additively manufactured fatigue samples to examine its impact on fatigue life.

Abstract: Magnetron sputtering was utilised to deposit submicron-sized speckle patterns for microscale digital image correlation (DIC) of 18Ni-300 maraging steel. A Taguchi orthogonal array consisting of four configurations was used to investigate the influence of magnetron sputtering parameters (i.e. sputter current, sputter duration, and chamber pressure during sputtering) on the resultant speckle characteristics. Increasing the sputter current resulted in larger-sized speckles, while increasing the sputter duration resulted in larger-sized speckles at expenses size uniformity of speckles. A higher chamber pressure retards the transport of speckles resulting either in low deposition rate or much less uniform sizes of speckles. Among the configurations studied, configuration I (75 mA, 240 s, 3 Pa) produced speckle patterns that were most suitable for microscale DIC as its speckles were adequately smaller and more uniform in size. In-situ tensile test with DIC strain distribution mapping on sample deposited with speckle pattern configuration I shows a strain resolution of about 71 nm, and slip bands with widths measured between 240 to 400 nm, indicating the speckle pattern was suitable, enabling further study on deformation mechanism.

Abstract: The fatigue strength of maraging steel, which is an ultra-high-strength steel, is relatively low, compared to that of conventional high-strength steel. The fatigue life of a structure is highly dependent on the surface conditions, because fatigue cracks generally start at the surface of the material. In particular, surface cracks considerably degrade the fatigue limit. To expand the application range of maraging steel, it is necessary to improve the fatigue limit, and render the surface cracks harmless. This study aims to investigate the effect of shot peening (SP) on the fatigue strength of maraging steel with surface cracks. The SP application introduced a compressive residual stress from the specimen surface to a depth of 170 μm, and increased the fatigue limit by 77 %. The estimated crack size that can be rendered harmless, based on fracture mechanics, is (0.170 − 0.202) μm in the range As = (1.0 − 0.1). The intersections of the harmless crack sizes were determined at depth. A semicircular surface crack below this value is harmless in terms of fatigue limit. The usefulness of non-destructive inspection (NDI) and non-damaging technology was evaluated in relation to a_hml, a_NDI, a_25,50, and As. Thus, the SP process can improve the reliability of the maraging steel. Compressive residual stress is the dominant factor to improve fatigue strength and render the surface crack harmless.

Abstract: Anisotropy in tensile behaviour, plastic flow behaviour, and low cycle fatigue (LCF) behaviour of additively manufactured (AM) maraging steel in different build orientations are presented and compared with conventionally manufactured maraging steel. Also, the effect of heat treatment (namely, solution treatment and ageing) on tensile behaviour and low-cycle fatigue behaviour were studied. The AM maraging steel showed more anisotropy in as-built (AB) condition and moderate anisotropy in heat-treated (HT) condition. Experimental engineering stress-engineering strain and true stress-true strain data of AB AM maraging steel and HT conditions have been analysed using Hollomon, Ludwik, Swift, Ludwigson, and Voce plastic flow relationships. It is also observed that the 0° oriented specimen exhibits better tensile and LCF behaviour as compared to the 90° oriented specimen in AB and HT conditions.

Abstract: The present work was aimed at increasing the fatigue life of laser powder bed fusion manufactured maraging steel (MS) using surface modification. Samples were manufactured to investigatethe mechanical properties of the material with two types of heat treatment routes that were both subjected to severe shot peening (SSP). In addition, bending fatigue testing was utilized to reveal theeffect of shot peening (SP) and SSP on fatigue resistance of the MS. Microhardness profiles weremeasured near the surface and electron backscatter diffraction analysis was used for microstructuralanalysis. A thin layer of austenite was noted on the surface making it a softer section, which SP orSSP was able to transform. The fatigue life of the MS was notably icreased by the SP processing andeven greater improvement was achieved with the SSP, which raised the fatigue limit of the materialfrom 200 MPa to nearly 500 MPa.

Abstract: An additively manufactured M789 steel was deposited on wrought precipitation-hardening N709 steel to form a hybrid alloy using the laser powder bed fusion (LPBF) process. After tensile testing, failure in the as-printed (AP) state was detected in the M789 section with a peak strength of 1019 MPa, consistent with the nanoindentation measurement across the M789-N709 interface. The application of heat treatment of the hybrid alloy shifted the failure zone to the N709 alloy with a peak strength of 1600 MPa. The high strength of M789 after heat treatment was due to the formation of the η-phase during aging. A robust metallurgical bond was successfully formed between the two alloys since the fracture did not occur in the interface for both the AP and heat treated (HT) states during tensile testing.

Abstract: The prospect of converting an entire assembly of parts with challenging geometry to a single part with sectional variation of properties has stimulated a growing interest in multi-material Additive Manufacturing (AM). Accordingly, the present work utilized a dual-metal Laser Powder Bed Fusion (LPBF) technique to manufacture a multi-material component, consisting of Co-Cr-Mo alloy (MP1) and maraging steel (MS1) in a single manufacturing process. The research also attempted to establish a heat treatment strategy compatible with these alloys. The resulting heat treatment effects on the microstructure, texture, and microhardness were investigated. Diffusion calculation results suggested an overall diffusion depth of 120 μm in the interface after heat treatment, which can increase the resulting joint strength if intermetallic precipitation is avoided. Electron Backscatter Diffraction (EBSD) analysis of the heat-treated samples showed that both the base metal regions retained the dominant fiber textures after printing, which is the <110> || building direction (BD) fiber texture for the MP1 region and the <111> || BD and <100> || BD fiber textures for the MS1 region. Nanoindentation tests also revealed a considerably higher hardness in the MS1 region and a slight reduction of hardness in the MP1 region after heat treatment, which can be early evidence of the successful application of the heat treatment strategy to both base metals. Future work will investigate the mechanical properties of the as-printed and heat-treated samples and verify if any precipitates formed in the MS1-MP1 interface.

Abstract: The quality of metallic additive manufacturing outputs is heavily dependent on the employed processing parameters. Hence, the assessment and definition of the input variables appropriate to the material in question is of vital importance, in order to optimise the attainable properties and minimise wasted feed stock in failed trials. In this work, optimal parameters for 18Ni300 Maraging steel are found for deposition in an H13 substrate. Additinally, the influence of pre-heating in depositions on a DIN CK45 steel are analysed by optical microscopy (OM) and microhardness measurements along the interface, and mechanical characterisation of DED-produced 18Ni300 is performed, as well as a bi-metallic alloy comprised of 18Ni300 and CK45, through the production and testing of tensile specimens.

Abstract: The influence of SLM process parameters (i.e. laser power, scanning speed, and hatch spacing) on the microstructure and mechanical properties of 3D printed 18Ni-300 maraging steel was investigated. In experiments on 3D printed scan tracks, better fusion of powder material was achieved in parameter configurations with higher linear energy density (i.e. LED ≥ 375.00 J m^-1). A higher LED indicates that more laser energy is transferred to the powder material, resulting in complete melting of the powder and the creation of a microstructure with less defects. In experiments on fully built samples, higher relative density was achieved when the hatch spacing was increased or the scanning speed was decreased. Fully built samples produced using parameter configuration B-2 (300 W, 700 mm s^-1, 0.10 mm) have higher relative density and ultimate tensile strength as compared to the other parameter configurations.

Abstract: The diagrams of isothermal transformation based on kinetic curves R = (τ) for retained austenite in high-strength alloy low-carbon at overcooling have been built. It is shown that the temperature of quenching influences the stability at overcooling and resistance to isothermal transformation of austenite at sub-zero temperatures.