Papers by Keyword: 17-4 PH Stainless Steel

Abstract: This study explores the impact of heat treatment parameters on the hardness and microstructure of 17-4PH stainless steel samples fabricated by additive manufacturing, with a focus on dimensional changes throughout the process. The additive manufacturing method used was Bound Metal Deposition (BMD), which includes digital scanning, 3D metal printing, sintering, and post-processing. It was observed that the printed parts undergo a substantial size increase 16.96% (height) and 18.14% (diameter) to compensate for material loss during the binder removal stage in sintering. Although the sintered parts shrink relative to the printed samples, they remain 3.25% taller and 6.05% wider than the original CAD dimensions. Following sintering, the samples underwent solution treatment and aging at various temperatures and times. Microstructural analysis post-solution treatment revealed a martensitic structure as the predominant phase. Aging caused the formation of strengthening precipitates, leading to peak hardness values of 422.0 and 303.0 HV0.5 at aging temperatures of 480 °C and 620 °C for 1 hour, respectively. Dimensional changes during the precipitation hardening stage were minimal and considered negligible.

Abstract: 17-4 Precipitation hardenable (PH) stainless steel (SS) is useful for applications that require a combination of high strength and corrosion resistance. However, when produced through selective laser melting (SLM), it has a distinct microstructure with significant composition and phase variations based on the process parameters and post processing heat treatment conditions. Therefore, the present study examines how process parameters, such as scanning speed and hatch distance, affect the microstructural, and corrosion characteristics of additively manufactured (AM) 17-4 PH stainless steel samples. Post-processing heat treatment resulted in a uniform and reproducible microstructure in SLM samples. Heat-treated AM samples were assessed in a 3.5 wt. % NaCl solution using electrochemical impedance spectroscopy (EIS). The specimen with an energy density of 39.06 J/mm³ exhibited the lowest open circuit potential value, indicating a favorable tendency to form a passive film. The sample with 66.96 J/mm³ exhibits enhanced corrosion resistance attributed to robust protective performance facilitated by a dense network of precipitates and finer grain size. This heightened resistance is further supported by the sample's highest corrosion layer resistance and charge transfer resistance.

Abstract: This paper investigates the machinability of Selective Laser Melted 17-4 Precipitation Hardening Stainless Steel (17-4 PH SS). For this purpose, turning tests were carried out on wrought and SLM specimens and the results were compared. Wear tool, surface roughness, surface integrity and chip morphology were analyzed for both materials. For the tested cutting conditions, the machinability of the SLM material was inferior to that of the commercial material. Dissimilarities in machinability between both materials are a consequence of variations in their microstructures resulting from the manufacturing process.

Abstract: Metal injection molding (MIM) is a near net shape manufacturing technique for producing small, complex, precision parts in mass production. MIM process is manufacturing method that combines traditional shape-making capability of plastic injection molding and the materials flexibility of powder metallurgy. The process consists of the following four steps: mixing of metal powder and binder, injection molding to shape the component, debinding to remove the binder in the component, sintering to consolidate the debound parts. In this research, the physical and mechanical properties of metal injection molded 17-4 PH stainless steel were investigated with the variation of sintering temperatures (1300 °C - 1360 °C) and atmosphere conditions (argon and vacuum conditions). The relative density, microstructure, distortion, and hardness are measured and analyzed in this study. The results show that highest relative density of 87%, relative homogeneous shrinkage and high hardness are achieved by sintering at 1360 °C for 1.5 hours and argon atmosphere. At the same sintering temperature and time, sintering in vacuum shows lower relative density (81%) than that in argon condition due to pores growth. The pore growths were not observed in the argon atmosphere. It can be concluded that sintering stages more rapidly under vacuum condition. The hardness measurements result also showed that high hardness is obtained by high density parts. The optimum average hardness obtained in this study is 239 HV. However, the hardness properties results are still lower than 280 HV according to MPIF Standard 35 for MIM parts.

Abstract: Water atomized and gas atomized 17-4 PH stainless steel powder were used as feedstock in selective laser melting process. Gas atomized powder revealed single martensitic phase after printing and heat treatment. As-printed water atomized powder contained dual martensitic and austenitic phase. The H900 heat treatment cycle was not effective in enhancing mechanical properties of the water atomized powder after laser melting. However, after solutionizing at 1315 oC and aging at 482oC fully martensitic structure was observed with yield strength of 1000 MPa and ultimate tensile strength of 1261 MPa which are comparable to those of gas atomized, 1254 MPa and 1300 MPa, respectively. Improved mechanical properties in water atomized powder was found to be related to presence of finer martensite. Our results imply that water atomized powder is a promising cheaper feedstock alternative to gas atomized powder.

Abstract: Malocclusion is one of the common problems encountered in the teeth and mouth of Indonesian people. This country is also confronted with problems that the bracket have to been imported from abroad. The purpose of this study is to produce national orthodontic bracket by metal injection molding (MIM) process in Indonesia, particularly by using vacuum sintering for 17-4 PH stainless steel because it is a material commonly used for orthodontic bracket. Sintering conducted at four different temperatures, at 1320 °C, 1340 °C, 1360 °C, and 1380 °C. The results showed that there are inclusions in sintering products. The relative density increases with increasing temperature sintering because the area of porosity are reduced. In addition, the results of sintering at 1360 °C has optimal hardness, which is amounted to 395 HV and higher than commercial bracket.

Abstract: Greatbatch Medical, specializing in orthopedic implants and instruments, is currently utilizing direct metal laser sintering (DMLS) technology to develop concept prototypes. Greatbatch uses EOS GP1 Stainless Steel which adheres to the American standard for 17-4 Precipitation Hardened SS. Following DMLS, Greatbatch heat treats its parts to obtain desirable mechanical properties. In this study, three different heat treatment methods were examined: heat treatment and stress relief (HT+SR), stress relief (SR), and solution aging and annealing (SAA). The Vickers Hardness Test and the Tensile Strength Test were used to assess the mechanical properties of each sample. The research also included grain structure analysis using a Scanning Electron Microscope and surface roughness studies via profilometer measurements. For example, the HT+SR sample yielded 456 HV (hardness), an ultimate tensile strength of 1319 MPa, an yield strength of 1120 MPa, and 6.36% elongation. It was found that compared to the untreated sample, HT+SR decreased the total elongation by 73% and SAA decreased total elongation by 17% and additionally decreased hardness by 17%. It was learnt that stress relieving the part after DMLS was the superior method of choice based on its resulting mechanical properties. It was found that the grain structure of the non-treated sample resembled a solution treated sample and the stress-relieved sample actually matched an age-hardened sample. The sample that was precipitation hardened was actually over-aged. Thus it was found that the DMLS process seemed to be acting as an aging process while simultaneously building the part. Further studies in examining specific effects of DMLS and how it impacts what order heat treatments should follow would be appropriate.

Abstract: The combustor chamber, diffuser and nozzle are the main components of the ramjet engine. In this study, the thermal strength of the combustion chamber of the ramjet engine was evaluated. The combustion chamber consists of an Inconel alloy 718 liner and a 17-4Ph stainless steel housing. The liner is rapidly heated to a high temperature. The heated liner is cooled with a film cooling method that forms a cold boundary layer to separate the hot gas from the surface of the liner. The thermo-structural analysis is evaluated the thermal strength of super alloy structure with various thermal insulation performances by finite element method with code MSC/Nastran. The result of the analysis is compared with accelerated stress rupture test. The experiment is performed to get safety design and estimate actually life-time for combustor chamber under high temperature. In general, the work in this paper is helpful to further improve the understanding and evaluation of thermal strength of the super alloy structure with various thermal insulation performances.

Abstract: The microstructures and mechanical properties of 17-4 PH stainless steel at each steps of heat treatment, such as homogenizing, solid solution treatment followed by aging treatment, longterm aging at 400 °C, and recovery treatment, in order to obtain a better understanding of the embrittlement phenomena on aging, was investigated. As the homogenizing treatment time increased, the length of δ-ferrite decreased and elongated shape of δ-ferrite turned to sphere shape with the decrease of volume fraction. The solution treated specimen mainly consists of lath martensite with a small fraction of elongated δ-ferrite. The spherical particles existed a little in the martensite matrix, while no precipitates were found in the δ-ferrite at the solution treated specimen. As the aging treatment temperature increased, the strength decreased while the toughness increased. The fcc Cu-rich particles precipitated in the δ-ferrite during the long-term aging at 400 °C after the solution heat treatment. This precipitation causes the aged hardening after long-term aging accompanied by decreases in elongation and charpy V-notch energy absorption. The strength and elongation was restored after recovery treatment and the fcc-Cu precipitated were almost dissolved into the δ-ferrite matrix.

Abstract: The embrittlement fracture mechanism caused by microstructural evolution of 17-4 PH stainless steel at long term aging was studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The solution treated specimen consists largely of lath martensite with a small fraction of elongated δ-ferrite. The spherical particles existed a little in the martensite matrix, while no precipitates were present in the δ-ferrite at the solution treated specimen as non-aging. The precipitation of Fe-Cu in the δ-ferrite causes the aged hardening after long term aging accormpanied by decreases in elongation and charpy V-notch energy absorption. The increased fraction of brittle fracture on the fractured surface by impact and tensile test reveals that the embrittlement of the 17-4 PH alloys during long term aging is mainly caused by the precipitation hardening in the δ-ferrite matrix.