Simultaneous control of the nitrogen and carbon activities during nitrocarburising of iron

Leineweber, Andreas; Gressmann, T.; Mittemeijer, E. J.

doi:10.1016/j.surfcoat.2011.11.035

Cited by 31 publications

(19 citation statements)

References 25 publications

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“…[7,59,60] By applying a high flow rate (500 ml min À1 ), the composition of the gas atmosphere remains constant. In an ideal case, thus, a local equilibrium at the surface of the specimen is achieved.…”

Section: Methodsmentioning

confidence: 99%

“…The temperature was controlled within 1 K. Two different types of atmospheres were chosen, leading to distinctly different types of compound-layer microstructures. The values of the experimental parameters for all experiments, together with the resulting thermodynamic activities of N (reference state N 2 gas at 1Â10 5 Pa) and C (reference state graphite at 1Â10 5 Pa) [7,59] as calculated using the data for the Gibbs energies of the gaseous species given in Reference 62, are given in Table III. Except for a few cases, a treatment time of 4 hours was applied.…”

Section: Methodsmentioning

confidence: 99%

“…As discussed elsewhere, [7,12] whereas local solid-solid equilibria can occur at each depth, corresponding to the local gross (laterally averaged) composition, within the compound layer, this may not occur at the gas-solid interface, i.e., at the surface of the compound layer, where moreover at most a stationary state may be established. [10,61] Then, recognizing that in gaseous nitrocarburizing, as compared to gaseous nitriding, distinctly more reactions participate at the gas/solid interface, [59,60] it may be understood that the microstructures obtained upon nitriding are more uniform than those obtained upon nitrocarburizing (cf. Sections IV-A and IV-B).…”

Section: B Nitriding Of Fe-c Alloysmentioning

confidence: 99%

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The $$\upalpha +\upvarepsilon $$ Two-Phase Equilibrium in the Fe-N-C System: Experimental Investigations and Thermodynamic Calculations

Göhring

Leineweber

Mittemeijer

2016

Metall Mater Trans A

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The present work is dedicated to investigating the occurrence of the a þ e equilibrium at temperatures typically applied for nitrocarburizing treatments. To this end, pearlitic Fe-C specimens were treated between 823 K and 863 K (550°C and 590°C) in gaseous nitriding and gaseous nitrocarburizing atmospheres, allowing control of the chemical potentials of N and C. Subsequently, the resulting compound-layer microstructures were investigated using light microscopy and X-ray diffraction. Thermodynamic calculations, adopting several models for the Fe-N-C system from the literature, were performed, showing significantly different predictions for both the sequence of the invariant reactions and their temperatures. Comparison of the experimental data and the theoretical calculations led to the conclusion that none of the models from the literature is able to realistically describe the experimentally observed constitution in the Fe-N-C system in the considered temperature range. Values/value ranges for the temperatures of the invariant reactions were obtained.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: B Nitriding Of Fe-c Alloysmentioning

confidence: 99%

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The $$\upalpha +\upvarepsilon $$ Two-Phase Equilibrium in the Fe-N-C System: Experimental Investigations and Thermodynamic Calculations

Göhring

Leineweber

Mittemeijer

2016

Metall Mater Trans A

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“…The approach used involved adding ac ertain amount of CO gas to am ild nitriding(NH 3 /H 2 )atmosphere (see Table 2), resulting in no definable Ca ctivity, but aw ell-defined Na ctivity [1,30,31]. The Fe-C specimens weret reated witha tmospheres that control the most importantc arburising reactions, neglecting formation of CH 4 and other organicc ompounds.…”

Section: Nitrocarburising Treatmentmentioning

confidence: 99%

“…The Fe-C specimens weret reated witha tmospheres that control the most importantc arburising reactions, neglecting formation of CH 4 and other organicc ompounds. By setting the Cactivity pertaining to these governing reactions equal, au nique Ca ctivity can be assigned to the gas phase [1,30,31]. At 853 K, nitrocarburising of pearlitic specimensu singt he atmospheres listed in Table 2r esults in pure e layers [5].…”

Section: Nitrocarburising Treatmentmentioning

confidence: 99%

Microstructural development and crystallographic properties of decomposing Fe–N–C compound layers

Göhring

Kante

Leineweber

et al. 2016

International Journal of Materials Research

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The microstructural development of Fe–N–C compound layers resulting from nitrocarburising and heat treatments applied to Fe–N and Fe–C alloys was investigated. Slow cooling or secondary annealing, instead of quenching, after the end of the nitrocarburising treatment causes decomposition of γ-Fe[N,C] and ∊-Fe3(N,C)1+x in the compound layer. The resulting decomposition microstructures were analysed by, in particular, light microscopy and electron backscatter diffraction, and X-ray diffraction and electron probe micro-analysis, revealing their constitution and crystallographic properties. The results are discussed in comparison to data obtained from undecomposed, i. e. quenched, specimens and to data reported in the literature.

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Nitriding of White‐Solidified Fe–C–Si Alloys: Diffusion Path Concept Applied to Inhomogeneous Microstructures

2021

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Gray-solidified cast irons are frequently used to manufacture machine and engine parts due to their low cost, good compressive strength, and high damping capacity. [1,2] Their use is, however, often limited by poor surface hardness and corrosion resistance. Both can be notably improved by a duplex surface treatment developed in recent years. [3][4][5][6] First, the surface of the cast iron is remelted, e.g., by an electron beam or plasma arc. This produces a white-solidified, ledeburitic [7,8] surface layer, which is hard and abrasion-resistant. Afterward, the material is nitrided to enhance the corrosion resistance by the formation of a dense surface layer composed of the main Fe (carbo)nitrides, γ 0 -Fe 4 (N,C) and ε-Fe 3 (N,C) 1þx (Table 1), denoted compound layer. Note that nitriding without remelting leads to less favorable microstructures because coarse graphite particles contained in gray-solidified cast irons are detrimental to the compound layer formation. [3,4,[9][10][11] Although the general advantages of the previously described duplex treatment have been demonstrated, the nitriding behavior of the white-solidified surface layers turns out to be complex and incompletely understood. [12][13][14][15][16][17][18][19] The research of the current authors [12,18,19] aims at elucidating the complex nitriding behavior of the remelted surface layers by controlled gas nitriding of white-solidified Fe-3.5 wt% C-0/1.5/3 wt% Si alloys, serving as model alloys for commercially available ferritic cast iron grades subjected to remelting and nitriding. Note that, in contrast to ferritic cast irons, pearlitic cast irons often contain non-negligible additions of Mn and Cu, which may additionally affect the nitriding behavior. [17] The microstructure of white-solidified Fe-3.5 wt% C-1.5/3 wt% Si alloys, having C and Si contents typical of cast irons, is mainly composed of coarse eutectic cementite plates, θ-Fe 3 C 1Àz (Table 1), embedded in ferrite and pearlite. [20,21] The latter result from the decomposition of primary and eutectic γ-Fe during cooling after solidification. In addition, a minor volume fraction of Fe 23 Si 5 C 4 -type silicocarbide (Table 1) is contained in the alloys. [22][23][24] The distribution of Si in the white-solidified microstructure is very heterogeneous. The Si/Fe atomic ratio in the eutectic and pearlitic θ is u Si,θ < 3 Â 10 À4 and, here, considered negligible, say u Si,θ ! 0. [12] The Si/Fe atomic ratio in Fe 23 Si 5 C 4 is u Si,Fe 23 Si 5 C 4 % 0.22; however, it might take also values slightly different from 0.22 due to a possibly mixed Fe/Si site [23,24] and extended lattice defects affecting the composition. [22] The Si content in α-Fe relates to the Si content of γ-Fe, which is affected by Si segregation during solidification. The Si content in the center of γ-Fe dendrites is typically similar to the Si content of the alloy, while the outer rim of dendrites and last-to-freeze regions are enriched in Si. [25] The Si content in eutectic γ-Fe is higher

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Simultaneous control of the nitrogen and carbon activities during nitrocarburising of iron

Cited by 31 publications

References 25 publications

The $$\upalpha +\upvarepsilon $$ Two-Phase Equilibrium in the Fe-N-C System: Experimental Investigations and Thermodynamic Calculations

The $$\upalpha +\upvarepsilon $$ Two-Phase Equilibrium in the Fe-N-C System: Experimental Investigations and Thermodynamic Calculations

Microstructural development and crystallographic properties of decomposing Fe–N–C compound layers

Nitriding of White‐Solidified Fe–C–Si Alloys: Diffusion Path Concept Applied to Inhomogeneous Microstructures

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