Papers by Keyword: 304 Stainless Steel

Abstract: Bipolar plate is the key component of proton exchange membrane fuel cells. Due to the factors of rapid and mass production, the stamping process is selected to manufacture the bipolar metal plates. First, the stress-strain curve is performed by universal material testing machine.The stress-strain curve is necessary for bipolar plate stamping simultion. The maximum forging load and effective stress distribution of bipolar plate stamping are determined by finite element analysis. Finally, the effect of the traditional crank stamping on the flatness and section thickness of stainless steel bipolar plate are observed by experiments.

Abstract: Stainless steel will become one of the main substrate materials for flexible large-scale displays. As the substrate of the flexible displays, the biggest problem of stainless steel is that the surface roughness is too large. It is necessary to polish the surface of stainless steel with ultra-precision. Chemical mechanical polishing (CMP) technology will be one of the most practical processing technologies to make the surface of stainless steel ultra-smooth and damage-free. In this paper, the material removal rate (MRR) and surface roughness were studied based on the hydrogen peroxide oxidant and ferric chloride oxidant with different surfactants in chemical mechanical polishing (CMP) slurry by experiments. The results show that it can obtain the maximum of the MRR and the optimal surface quality when using 0.04 wt% sodium hexadecyl sulfate as the surfactant of the hydrogen peroxide-oxalic acid based polishing slurry and when using 0.2 wt% nonylphenol ethoxylate or 0.8 wt% OP-10 emulsifier as the surfactant of the of ferric chloride-oxalic acid based polishing slurry. The results of this study can provide a reference for further research on the chemical mechanical polishing of stainless steel.

Abstract: Peritectic transformation contraction of ferrite to austenite plays an important role in the formation of cracks for steels. In order to evaluate the peritectic transformation contraction of steels at the initial solidification, the solidification of 304 stainless steel under different cooling rates were carried out by using high temperature laser confocal microscopy, and then the surface roughness and peritectic transformation contraction were analysed in combination with the microstructure of solidified steel. The result shows that the solidification model of 304 stainless steel was ferrite-austenite model in the experiments, and peritectic transformation occurred during solidification. The residual ferrite in the as-cast structure were vermicular, skeletal and reticular in turn with the increase of cooling rate. The volume contraction caused by peritectic transformation resulted in wrinkles (surface roughness) appearing on the grain surface. The peritectic transformation contraction that was affected by surface roughness increased first and then decreased with cooling rate increasing, indicating the peritectic transformation contraction can be evaluated by the surface roughness.

Abstract: Herein, solid-state diffusion-coupled joints (DCJs) were prepared in vacuum between stainless steel (SS) and Ti6Al4V by means of a pure niobium (Nb) interlayer (~200-μm thickness) using uni-axial compressive pressure of 4 MPa at 875 °C for 15 to 120 min. Interfacial characterization revealed the existence of successive layer wise Fe–Nb-based intermetallics like FeNb+(Nb) and Fe₂Nb at Nb|SS interfaces of DCJs processed from 60 to 120 min, but the DCJs processed for shorter duration (from 15 to 30 min) do not reveal any intermetallics; however, the DCJs processed for 45 min revealed a single reaction layer of FeNb whereas that of Ti6Al4V|Nb interfaces revealed solid solution behaviour for all bonding time intervals. Required chemical analysis (in at. pct) of the reaction products was found out using spectroscope and X-ray diffractometer. Mechanical characterization (at 32 °C) of the DCJs was carried out with a microhardness tester and tensile testing facility. Ti6Al4V|Nb interface experienced a hardness of ~298 HV (for all bonding time), whereas Nb|SS interface experienced ~200 HV for 15 and 30 min and ~650 HV for 45 min and longer. DCJs treated for 60 min have better strength properties. Manifestation of reaction layers: FeNb, FeNb+(Nb), and Fe₂Nb have significant effect on the strength. From the interfacial microhardness, path and surface of fracture surfaces characterizations, it was revealed that failure of the DCJs was transmitted seemingly along Nb|SS interfaces. The analytical finding of intrinsic diffusivity of Ti atoms in Nb along Ti6Al4V|Nb interface is higher by one order of magnitude than the diffusivity results of Fe atoms in Nb along the Nb|SS interface. Experimental evidences show that the growth of the reaction products along Ti6Al4V|Nb interface (adj. R-Square=0.982) and Nb|SS interface (adj. R-Square=0.999) follows a parabolic law. Recently, researchers considered diffusion coupling as the key technology to fabricate Ti|Al|Al-C_f biomimetic structure, graphite|Nb|Cu for fusion reactor devices, Ni|Ni₃Al for MEMS applications, hybrid heat exchangers for nuclear applications, etc.

Abstract: During the last decades, biomaterials have been deeply studied to perform and improve coatings for biomedical devices. Metallic materials, especially in the orthopedic field, represent the most common material used for different type of devices thanks to their good mechanical properties. Nevertheless, low/medium resistance to corrosion and low osteointegration ability characterizes these materials. To overcome these problems, the use of biocoatings on metals substrate is largely diffused. In fact, biocoatings have a key role to confer biocompatibility properties, to inhibit corrosion and thus improve the lifetime of implanted devices. In this work, the attention was focused on Hydroxyapatite-Chitosan (HA/CS) and Hydroxyapatite-Polyvinylacetate (HA/PVAc) composites, that have been studied as biocoatings for 304 SS based devices. Hydroxyapatite was selected for its osteoconductivity thanks to its chemical structure similar to bones. Furthermore, Chitosan and Polyvinylacetate are largely used yet in medical field (e.g. antibacterial agent or drug deliver) and in this work were used to create a synergic interaction with hydroxyapatite to increase the strength and bioactivity of coating. Biocotings were obtained by galvanic deposition process that does not require an external power supply. It is a spontaneous electrochemical deposition in which materials with different standard electrochemical potential were short-circuited and immersed in an electrolytic solution. Electrons supply for the cathodic reaction in the noblest material comes from oxidation of the less noble material. SEM, EDS, XRD and RAMAN were performed for chemical-physics characterization of biocoatings. Polarization and impedance measurements have been carried out to evaluate corrosion behavior. Besides, in-vitro cytotoxicity assays have been done for the biological features.

Abstract: The corrosion characteristics of 316SS and 304SS in subcritical and supercritical aqueous systems including chloride of approximate 4600 mg/L at 25 MPa and 250 °C, 350 °C, 425 °C, and 520 °C are comparatively investigated. Some local corrosion areas occurred on the surfaces of SS316, not on that of 304SS, at 250 °C and 425 °C, while at 350 °C, all the sample surfaces were covered by large amounts of corrosion products and clay materials due to the predominant precipitation for the formation of the outer subscale. Whether in reducing subcritical and supercritical industrial sludge suspension or in oxidizing supercritical sludge system, 304SS owns better corrosion resistance than 316SS due to higher chromium concentration of former.

Abstract: With the ongoing development of product process, there is a growing demand on micro products. Though the macro-drawing process has been well-developed, the design concepts may not be directly applicable to the micro-drawing due to the size effect occurred in the micro-forming processes. In the present study, experiments were conducted first to establish the stress-strain curves, r-values and work hardening exponents of 304 stainless steel sheets with different grain sizes. The experiment results reveal that the stress-strain and r-value become smaller and the work hardening exponent increases for larger grain sizes. The difference between stress-strain curves in various directions of 0°, 45° and 90°, respectively, is significant when the grain size increases. The stamping of a vibration motor shell of cell phone, which bears a circular cylindrical shape, was also examined in the present study. The finite element simulations were performed to evaluate the formability of the multi-stage drawing process with initial die design. The forming characteristics were identified and an optimum die design was then developed with the use of the finite element analysis. The stamping process with multi-stage tooling design based on the finite element analysis was implemented and the actual stamping experiments were conducted to verify finite element analysis. The experimental results confirm the validity of the modified tooling design and the efficiency of the finite element analysis.

Abstract: In order to fabricate the micro cavity with complex structure on stainless steel, the technology of micro electrochemical machining based on surface modification by fiber laser is adopted. Heating scan on the surface of 304 stainless steel by using fiber laser can realize marking. In the process of laser heating and metal melting on the surface of 304 stainless steel, oxide layer can be formed and phase transformation can also occur, and the corrosion resistance layer with predefined pattern is formed. In the next process of micro electrochemical machining, the laser masking layer severs as the protective layer to realize micro machining of micro cavity. A newly developed device of electrochemical micro machining based on surface modification by fiber laser can meet the micro machining requirement. After laser masking processing through laser scanning on the surface of the 304 stainless steel, the passivation electrolyte and high-frequence-pulse electrochemical machining power supply were adopted, and the samples with typical structures by using electrochemical micromachining with fiber laser masking were fabricated.

Abstract: Welding dissimilar materials has been widely applied in industries. Some of them are considered this as a strategy to develop their future technology products. Aluminum alloy and stainless steel have differences in physical, thermal, mechanical and metallurgic properties. However, selecting a suitable welding process and welding rods can solve this problem. This research aimed to investigate the T-joint welding between A6061 aluminum alloy and SUS304 stainless steel using new welding rods, Aluma-Steel by the Tungsten Inert Gas (TIG) welding process. The mechanical properties, the characteristics of microstructure, and component analysis of the welds have been investigated by the mechanical testing, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). As a result, the fracture occurred at the adjacent area between welding seam and A6061 alloys plate. The thermal cracking appeared at central welding-seam along the base metals if high welding current. A large amount of copper elements found in the welds due to using the new welding rod, Aluma-Steel rod.

Abstract: The implementation of boronizing in low alloy steel had been implemented tremendously in past years as this method offers excellent surface protection that led to enhancement of hardness and wear of the material. In conjunction to that, few parameters had been recognized as the factor that promotes boron diffusion into the surface of the material which is the selection of boronizing temperature and time. This study concentrated on the effect of pack boronizing on the boride layer thickness of 304 stainless steel which contained high amount of alloying elements. The microstructural analysis and boron layer thickness was measured and observed using optical microscopy and SEM analyzer. The microhardness of the material was measured using Vickers microhardness tester. The results portrayed that boronizing successfully induced boronizing layer containing FeB and Fe₂B phases with thickness of 15μm. This resulted in major improvement of the microhardness values with improvement of 5 times compared to non-boronized samples.