Phase Transformations in Nitrided Iron Powders

Yurovskikh, А. S.; Kardonina, N. I.; Kolpakov, A. S.

doi:10.1007/s11041-015-9913-3

Cited by 6 publications

(7 citation statements)

References 21 publications

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“…as reported by Smirnov and Kuleshov [13]. In the nitriding temperature range of 480-580 • C, the free enthalpy of reaction (7) is positive (the system absorbs heat from the environment), so the reaction can occur only to the left, which makes γ'-Fe 4 N nitride the most thermally unstable phase in the Fe-N system [14]. Similarly, the reaction…”

Section: Fe-n 2 Equilibriumsupporting

confidence: 54%

“…However, there is no evidence that the iron nitride layer can be the source of nitrogen for the internal nitriding zone. Results of research carried out on pure iron tend to rule this out and suggest that the nitrogen flux from the decomposition of the iron nitride layer is directed outwards rather than inwards [14,16,27]. However, no reports either confirm or deny the described phenomena in the case the nitrided substrate contains alloying elements of nitrogen-forming properties.…”

Section: Stability Of Iron Nitridesmentioning

confidence: 95%

“…During annealing, it dissociates and forms nitrogen austenite and nitrogen gas. Various researchers indicated that during vacuum annealing of γ' nitride at temperatures above 650 • C, this phenomenon can occur intensively until the temperature reaches 850 • C, where the denitrification of the austenite lattice ends [14,16,25,26]. Based on studies of nitrided iron powder, Kardonina et al [16] showed that during annealing to 400 • C in a vacuum, the lattice parameters of all nitride phases increase due to thermal expansion.…”

Section: Stability Of Iron Nitridesmentioning

confidence: 99%

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The Stability of the Layer Nitrided in Low-Pressure Nitriding Process

2023

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The kinetics of the nitrided layer thickness growth and its structure depend on the nitrogen flux from the atmosphere to the nitrided surface. A nitrogen flux to the surface is more significant than a diffusion flux into the substrate, during forming surface iron nitrides and the internal nitriding zone. For pure iron, nitrided under low pressure, cutting off the nitriding atmosphere creates a flux from the subsurface layer of nitrides to the surface. The purpose of this paper is to determine the direction of the nitrogen flux in a similar situation for steels containing nitride-forming elements, thus answering the question of the stability of the layer nitrided under such conditions. The surface of X37CrMoV5-1 steel was nitrided under low pressure (of 24 hPa) and annealed in a vacuum or nitrogen. The microstructure, thickness of the nitride layers nitrided layers, the thickness of the internal nitriding zone, surface hardness and stresses were examined. The highest values of the nitrided layer properties were observed for the samples saturated only with nitrogen obtained from ammonia dissociation or additionally heated in nitrogen. It has been shown that using a pure vacuum during the annealing stage leads to unfavourable changes in the structure of the nitrided layer formed and, in particular, to the decomposition of the iron nitride layer formed at the saturation stage and occurrence of the tensile stresses—what excludes practical application of such layer. Ultimately, it has been shown that in the low-pressure nitriding process, the stability of the nitride layer of the nitrided surface strongly depends on the annealing atmosphere during the annealing stage, while the stability of the internal nitriding zone remains mainly at the same level.

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Section: Fe-n 2 Equilibriumsupporting

confidence: 54%

Section: Stability Of Iron Nitridesmentioning

confidence: 95%

Section: Stability Of Iron Nitridesmentioning

confidence: 99%

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The Stability of the Layer Nitrided in Low-Pressure Nitriding Process

2023

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“…Therefore, it is a very good material for high-density magnetic storage media [10]. However, the α"-Fe 16 N 2 nitride decomposes to α-Fe and γ -Fe 4 N at 200 • C and then completely converts Metals 2023, 13, 1060 2 of 12 to α-Fe at 300 • C [11,12]. Its low thermal resistance reduces its attractiveness.…”

Section: Introductionmentioning

confidence: 99%

Mechanical and Magnetic Investigations of Balls Made of AISI 1010 and AISI 1085 Steels after Nitriding and Annealing

Kaczmarek

Michalski

Frączek

et al. 2023

Metals

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This paper discusses the changes in the phase composition and magnetic properties of the AISI 1010 and AISI 1085 steels that were nitrided at 570 °C in an ammonia atmosphere for 5 h and that were then annealed at 520 °C in a N2/Ar atmosphere for 4 h. The test samples were made in the form of balls with diameters of less than 5 mm. The thickness of the obtained iron nitride layers was assessed through metallographic tests, while the phase composition was verified through X-ray tests. The magnetic properties were determined using ferromagnetic resonance (FMR) and superconducting quantum interference device (SQUID) techniques. Our research shows that, during the annealing of iron nitrides with a structure of ε + γ′, the ε phase decomposes first. As a result of this process, an increase in the content of the γ′ phase of the iron nitride is observed. When the ε phase is completely decomposed, the γ′ phase begins to decompose. The observed FMR signals did not come from isolated ions but from more magnetically complex systems, e.g., Fe–Fe pairs or iron clusters. Studies have shown that nitriding and annealing can be used to modify the magnetic properties of the tested steels.

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“…At the same time, a decrease in the intensity of reflections of the ε phase from 500 • C was observed, until their full disappearance at 560 • C and simultaneous growth in the intensity of the lines of γ'reflect absorption of the ε-nitride by the γ'-phase in the heating process. In [8], a thermogravimetric study was carried out under continuous heating at a rate of 30 K/min in an argon atmosphere at 20-1100 • C, with the results showing that the most thermally stable materials from the standpoint of preservation of nitrogen are powders with a developed ε phase surface layer. A very high temperature range for the start of denitrification (820-850 • C), at a mean rate of nitrogen emission equal to 0.8-0.9 wt.%/min, was detected for powders nitrided for 5 and 8 h, containing 37 and 18 wt.% ε-nitride in the surface layers, respectively.…”

Section: Introductionmentioning

confidence: 99%

Applying the FMR Technique to Analyzing the Influence of Nitriding on the Magnetic Properties of Steel

et al. 2022

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This paper presents the relationship between the chemical composition and size of steel balls, the parameters of the nitriding process, and their magnetic properties, defined in this study by ferromagnetic resonance (FMR) and SQUID. Balls made from AISI 1010 and AISI 52100 steels, with diameters of 2.5 and 3 mm, respectively, were investigated. On samples made of AISI 1010 and AISI 52100 steel, single-phase layers of iron nitrides γ’ with a thickness of gmp = 50 and 37 μm, respectively, were produced. Then, the samples were annealed at a temperature of 520 °C for 4 h in an inert atmosphere (N2/Ar) at a pressure of 200 Pa. After the nitriding processes, steel balls were subjected to standard physical metallurgy and X-ray examinations. During annealing of nitrided layers with a two-phase layer of iron nitrides, at first, the transformation of the ε phase into the γ’ phase with the release of nitrogen into the atmosphere takes place. The FMR signals did not originate from isolated ions, but from more magnetically complex systems, e.g., Fe–Fe pairs or iron clusters, while the observed FMR line position is normally even lower and occurs for a magnetic induction below 200 mT. The fact that the magnetic centers did not contain mainly isolated Fe ions, additionally confirmed the abnormal increase in resonance signal intensity as a function of temperature, which is a behavior inconsistent with the Curie–Weiss law. The results obtained from measurements by the SQUID method, recording variations in magnetization as a function of temperature, confirm the untypical reinforcement of the magnetic conditions of the samples with the increase in temperature. For the samples tested, the magnetization was relatively weaker when the tests were conducted in a stronger magnetic field.

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Phase Transformations in Nitrided Iron Powders

Cited by 6 publications

References 21 publications

The Stability of the Layer Nitrided in Low-Pressure Nitriding Process

The Stability of the Layer Nitrided in Low-Pressure Nitriding Process

Mechanical and Magnetic Investigations of Balls Made of AISI 1010 and AISI 1085 Steels after Nitriding and Annealing

Applying the FMR Technique to Analyzing the Influence of Nitriding on the Magnetic Properties of Steel

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