Fatigue performance of low temperature nitrided AISI 321 grade austenitic stainless steel (original) (raw)
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Structural and wear and characteristic of low temperaturenitrided stainless steel
2006
An investigation to structural and wear behaviour of nitrided AISI 316 L stainless steel resulting from low temperature fluidized bed nitriding has been made in the present work. It was found that the wear resistance of nitrided specimens was related to the formation of a precipitation-free hardened layer on the austenitic surface. In the present laboratory experiments, the precipitation-free or S phase layer with a surface hardness of ~1350 HV0.5 was produced at a nitriding condition of 450 °C for 6h. The formation of this S phase layer significantly improved wear resistance of the stainless steel. Wear track observation by SEM revealed that the specimens without formation of S phase layer produced heavy scars due to tearing and local plastic deformation. The present work also suggests that fluidized bed heat treatment furnace can be utilised for nitriding the austenitic stainless steels at low temperatures below 500 °C to produce S phase nitrdid layer without losing the stainless ...
SN Applied Sciences
By comparing the behavior of 13%Cr-4Ni and 13%Cr-6Ni alloys, this paper investigated the effect of Ni and Mn enrichment on the amount, mechanical stability, and microstructure of reformed austenite. 4%Ni and 6%Ni-1.5%Mn weld multilayer deposits were made and heat treated to stabilize various amounts of austenite content at room temperature. The maximum austenite content has been obtained at the same temperature (630 °C for 1 h) for both alloys, but 3.6 times more austenite content was formed in the 6%Ni steel. For both alloys similar austenite contents were obtained by postweld heat treating at different temperatures and were compared experimentally. Results showed that with the addition of Ni and Mn, thinner and lower Ni content austenite was formed. Moreover, austenite generated at lower temperature was mechanically more stable under low cycle fatigue loading. Its rate of transformation has been reduced by a factor of 2.3, resulting in the stabilization of twice more austenite after 20 cycles at 2% strain considering the results of the present study, it is concluded that Ni and Mn contents do significantly affect the mechanical stability of reformed austenite; furthermore austenite lamellae morphology and thickness also seem to play a significant role in stabilizing this phase.
Surface and Coatings Technology, 2007
AISI 304 austenitic stainless steel samples were plasma nitrided at 420°C for 6 h in vacuum atmosphere by glow discharge technique, in the presence of nitrogen gas. Plain fatigue and fretting fatigue tests were carried out on unnitrided and plasma nitrided samples. Plasma nitrided samples exhibited higher surface hardness, compressive residual stresses at the surface and lower surface roughness compared with unnitrided samples. However, plasma nitrided samples exhibited inferior plain fatigue and fretting fatigue lives compared with unnitrided samples. This was attributed to segregation of chromium at the grain boundaries of plasma nitrided specimens which might have weakened the regions near grain boundaries resulting in early crack initiation and accelerated crack propagation.
Effect of Plasma Nitriding on Fatigue Behavior of 316L Stainless Steel
NEUMANN:STEELS O-BK, 2000
The Ti-6Al-4V alloy is widely used in the manufacture of components that must have low density and high corrosion resistance and fatigue strength. The fatigue strength can be improved by surface modification. The aim of this study was to determine the influence of plasma nitriding on the fatigue behavior of a Ti-6Al-4V alloy with a lamellar microstructure (Widmanstätten type). Nitriding was executed at 720 • C for 4 h in an atmosphere with N 2 , Ar, and H 2. Microstructure characterization of the samples was carried out by X-ray diffraction analysis, optical microscopy, and scanning electron microscopy. The average roughness of the specimens was determined, and fatigue tests were executed in a bending-rotating machine with reverse tension cycles (R = −1). X-ray diffraction analysis of the nitrided alloy revealed the following matrix phases: α, β, ε-Ti 2 N, and δ-TiN. A nitrogen diffusion layer was formed between the substrate and the titanium nitrides. Plasma nitriding resulted in an increase in low-cycle fatigue strength, whereas at high cycles of 200 MPa, both conditions exhibited similar behaviors. The fracture surface of the fatigue-tested specimens clearly revealed the lamellar microstructure. The fracture mechanism in the non-nitrided specimens appears to be due to cracking at the interface of the α and β phases of the lamellar microstructure.
Low temperature nitriding, nitrocarburising and carburising of AISI 316L austenitic stainless steel
International Heat Treatment and Surface Engineering, 2011
AISI 316L grade ASTM F138 austenitic stainless steel specimens were low temperature plasma nitrided (LTPN), nitrocarburised (LTPNC) and carburised (LTPC) using different gas mixtures. Different expanded austenite layers formed after each thermochemical treatment. LTPN and LTPCN led to formation of nitrogen supersaturated expanded austenite (c N). After LTPN, a second carbon expanded austenite (c C) layer was formed beneath the nitrogen expanded austenite layer (c N). LTPC led to formation of a carbon supersaturated expanded austenite (c C). Scanning electron microscopy, XRD and microhardness were used to characterise the expanded austenite layers formed on the surface of the specimens. Different mechanisms of formation and growth of the layers are pointed out. XRD results show that the lattice parameter of nitrogen expanded austenite (c N) is higher than that calculated for carbon expanded austenite c C. As a consequence, the lattice expansion Da/a for the nitrogen rich (c N) phase is higher than the one observed for the (c C) phase and the nitrogen rich expanded austenite layer displays higher hardness than the carbon rich expanded austenite layer. The LTPNC bilayer displays a less steep hardness gradient, indicating that the carbon rich expanded austenite layer can grant mechanical support to the harder nitrogen rich layer.
Challenges in Mechanics of Time Dependent Materials, Fracture, Fatigue, Failure and Damage Evolution, Volume 2”, proceedings of the 2019 Annual Conference on Experimental and Applied Mechanics, 2019
Preliminary investigation on mechanical properties of a Nb-strengthened and nitrogen-stabilized Fe-25wt.%Ni-20Cr (Alloy 709) advanced austenitic stainless steel suggests that it might be a potential candidate for Sodium-Cooled Fast Reactor (SFR), which has higher technology readiness level for deployment. However, the creep-fatigue deformation behaviour is unknown for this alloy. To understand high temperature creep-fatigue interaction of the Alloy 709, straincontrolled low-cycle fatigue (LCF) tests were performed at strain amplitudes ranging from 0.15% to 0.6% with fully reversible cycle of triangular waveform at 750 • C in air following ASTM standard E2714-13. In addition, different hold times of 1, 10, 30 and 60 min were introduced at the maximum tensile strain to investigate the effect of the creep damage on the fatigue-life at strain amplitude of 0.5% at 750 • C. During continuous cyclic loading, fatigue life is found to decrease with increase in strain amplitude. The creep-fatigue life and the number of cycles to crack initiation are found to decrease with increasing hold time indicating the rapid initiation and propagation of cracks. The fractographs of the samples deformed at 0.5% strain amplitude indicated that fatigue might have been the dominant mode of deformation whereas, for the sample deformed at the same strain amplitude with different hold times, both fatigue and creep have contributed to the overall deformation of the alloy. Further studies are underway to carry out creep-fatigue tests at different hold times, strain ranges, and temperatures as well as microstructural characterization of the samples following deformation.
CORROSION AND CORROSION FATIGUE BEHAVIOR OF LOW NICKEL HIGH NITROGEN AUSTENITIC STAINLESS STEEL
Austenitic stainless steels are widely used for variety of orthopaedic implantsbecause of their acceptable bio compatibility and low cost compared to other implant materials, however, high nickel content in these steels is known to aggravate existing dermatitis, cause sarcoma, allergy and likely have carcinogenic effect in human body. The present investigation compares corrosion and corrosion fatigue behavior of a relatively low nickel and highnitrogen stainless steel (216L) in simulated body fluid environment with that of the conventional 316L stainless steel used as bioimplant. Both, the potentiodynamic and EIS analysis showed higher resistance of the 216L against pitting corrosion than that of 316L. Corrosion fatigue life of the 216L in stress control mode was significantly higher than that of the 316L at ≤ ±450 MPa, however, there was opposite trend at high stress amplitudes. In strain control fatigue, life of the 216L was found to be longer than that of 316L both in air as well as insimulate body fluid(SBF). The improved corrosion resistance of the 216L steel is due to the oxide filmof higher breakdown potential and lower capacitance due to presence of nitrogen to cause significant increase in resistance against corrosion fatigue and increased stability of the austenite.
Materials Science and Technology, 2007
The present paper investigates completely reversed room temperature low cycle fatigue (LCF) behaviour of solution annealed austenitic stainless steel AISI 316L with two different grain sizes of 90 and 139 mm developed by solution annealing treatment at 1050 and 1150uC respectively and at six strain amplitudes ranging between ¡0?375 and ¡1?00%. Complete cyclic hardening has been observed for both the grain sizes. While fine grained steel shows an improvement in cyclic life compared with that of coarse grained steel for strain amplitudes ¡0?375 and ¡0?50%, and perfectly follows the Coffin-Manson (C-M) behaviour within the experimental domain, higher cyclic life with bilinear CM behaviour is observed in the case of coarse grained steel at ¡0?625% strain amplitude and above. Optical microscopy of fatigue fracture surfaces reveals the formation of martensite on cyclic straining predominantly at higher strain amplitudes.
Microstructure and Hardness of High Temperature Gas Nitrided AISI 420 Martensitic Stainless Steel
MATEC Web of Conferences, 2014
This study examined the microstructure and hardness of as-received and nitrided AISI 420 martensitic stainless steels. High temperature gas nitriding was employed to treat the steels at 1200 o C for one hour and four hours using nitrogen gas, followed by furnace cooled. Chromium nitride and iron nitride were formed and concentrated at the outmost surface area of the steels since this region contained the highest concentration of nitrogen. The grain size enlarged at the interior region of the nitrided steels due to nitriding at temperature above the recrystallization temperature of the steel and followed by slow cooling. The nitrided steels produced higher surface hardness compared to as-received steel due to the presence of nitrogen and the precipitation of nitrides. Harder steel was produced when nitriding at four hours compared to one hour since more nitrogen permeated into the steel. a Corresponding