The Experts below are selected from a list of 303 Experts worldwide ranked by ideXlab platform

Arthur H Heuer - One of the best experts on this subject based on the ideXlab platform.

  • colossal interstitial supersaturation in delta ferrite in stainless steels i low temperature Carburization
    Acta Materialia, 2015
    Co-Authors: Danqi Wang, Reza Sharghimoshtaghin, F Ernst, H Kahn, C W Chen, J C Dalton, Fan Yang, Richard E A Williams, David W Mccomb, Arthur H Heuer
    Abstract:

    Abstract Low-temperature Carburization has been successfully used to surface harden 17-7 precipitation-hardening (PH) and 2205 duplex stainless steels. After Carburization, the delta ferrite grains in both alloys near the free surface show a uniform weak contrast under conventional transmission electron microscopy (TEM). Spatially resolved compositional analysis shows that these delta ferrite grains possess enormous carbon contents (as high as 18 at.%) in solid solution, but structurally there is no detectable tetragonality (

  • low temperature Carburization of the ni base superalloy in718 improvements in surface hardness and crevice corrosion resistance
    Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2010
    Co-Authors: Reza Sharghimoshtaghin, Harold Kahn, Yindong Ge, Xiaoting Gu, Farrel J Martin, Paul M Natishan, Roy J Rayne, G M Michal, F Ernst, Arthur H Heuer
    Abstract:

    “Case-hardening” of the Ni-base superalloy IN718 has been achieved by low-temperature gas-phase Carburization. After Carburization under optimum conditions, the hardened surface layer (the “case”) has about twice the hardness of the core (HV of ≈800) and contains ≈12 at pct carbon in interstitial solid solution. This causes a lattice parameter expansion of ≈1 pct perpendicular to the surface and, because of the mechanical constraint provided by the noncarburized core below, develops a large biaxial surface compressive residual stress (≈1.9 GPa) parallel to the surface. Microstructural studies and X-ray diffractometry reveal no carbide precipitates in the case. In agreement with this observation, low-temperature Carburization does not compromise the ductility and actually improves the crevice corrosion resistance of the alloy.

  • carbon supersaturation due to paraequilibrium Carburization stainless steels with greatly improved mechanical properties
    Acta Materialia, 2006
    Co-Authors: G M Michal, F Ernst, H Kahn, Y Cao, Fumiyasu Oba, N Agarwal, Arthur H Heuer
    Abstract:

    Abstract Low-temperature gas-phase Carburization has been used to generate very high surface interstitial carbon contents, up to ∼12 at.%, in a 316L austenitic stainless steel. The high interstitial content leads to substantial surface hardening (Vickers hardness of ∼12 GPa, equivalent to Rockwell C of ∼71.5) with essentially no loss of ductility and with no carbide formation. Residual compressive stresses accompanying the low-temperature Carburization enhance the high-cycle fatigue resistance, while the hardening enhances the wear resistance. These remarkable improvements in mechanical properties arise because the Carburization is carried out at temperatures where “paraequilibrium”, rather than conventional thermodynamic equilibrium, determines the phase composition; paraequilibrium can be realized under conditions where substitutional solutes such as Cr and Ni are immobile whereas interstitial solutes such as carbon are not.

Yawei Peng - One of the best experts on this subject based on the ideXlab platform.

  • effect of low temperature surface Carburization on stress corrosion cracking of aisi 304 austenitic stainless steel
    Surface & Coatings Technology, 2017
    Co-Authors: Yawei Peng, Chaoming Chen, Jianming Gong, Yong Jiang, Zhe Liu
    Abstract:

    Abstract The effect of low-temperature surface Carburization on the stress corrosion cracking (SCC) behavior of AISI 304 austenitic stainless steel in boiling magnesium chloride (MgCl2) solution at 155 ± 1 °C was investigated. The SCC tests were carried out for untreated and carburized AISI 304 with varying four-point bend loading. In order to elucidate the influence of low-temperature surface Carburization on SCC resistance, optical microscope (OM), scanning electron microscope (SEM), X-ray diffractometry (XRD) and residual stress analyzer were used. The results show that the tensile stress on the surface of untreated four-point bend loaded AISI 304 and the occurrence of pits during SCC tests had bad influence on the SCC resistance. The surface of carburized four-point bend loaded AISI 304 was in a state of compressive stress over the whole loading range due to the presence of Carburization-induced huge compressive residual stress. The chloride-induced SCC resistance of AISI 304 can be obviously improved by low-temperature surface Carburization due the Carburization-induced compressive residual stress and the improved pitting corrosion resistance. The Carburization-induced compressive residual stress was the dominant reason for the improvement of SCC resistance. No relaxation happened in Carburization-induced compressive residual stress and the phase of the expanded austenite was stable during SCC tests.

  • the effect of plastic pre strain on low temperature surface Carburization of aisi 304 austenitic stainless steel
    Surface & Coatings Technology, 2016
    Co-Authors: Yawei Peng, Jianming Gong, Yong Jiang, Dongsong Rong
    Abstract:

    Abstract In this paper, the influence of plastic pre-strain on low-temperature surface Carburization of AISI 304 austenitic stainless steel was investigated. The materials were strained to different degrees of engineering strain including 5%, 10%, 15%, 20% and 25%. Low-temperature surface Carburization of the pre-strained specimens was performed at 470 °C for 30 h. In order to elucidate the effect of plastic pre-strain on low-temperature surface Carburization, optical microscopy (OM), X-ray diffractometer (XRD), scanning electron probe micro-analyzer (EPMA), microhardness tester and residual stress analyzer were used. Meanwhile, dislocation density and the martensite volume fraction of the pre-strained specimens were quantitatively measured by means of XRD analysis. Based on the experimental results, the role of dislocations and martensite on carbon diffusion and related phase transformation during low-temperature surface Carburization was discussed. The results show that the thicknesses of the carburized layers are independent of the pre-strain degree. Dislocations and strain-induced martensite almost have no effect on the growth of the carburized layers at the given carburizing temperature. Increasing dislocation density does not promote the development of carbides formation, while strain-induced martensite does. Due to the supersaturated carbon atoms introduced into the materials during Carburization, strain-induced martensite transforms into austenite. As a result of Carburization, an outstanding strengthening layer of the material develops, and plastic pre-strain has no effect on strengthening of Carburization.

  • Influence of Plastic Pre-Strain on Low-Temperature Gas Carburization of 316L Austenitic Stainless Steel
    Applied Mechanics and Materials, 2016
    Co-Authors: Yawei Peng, Jianming Gong, Yong Jiang, Dongsong Rong
    Abstract:

    In this paper, the influence of pre-strain on low-temperature gas Carburization of 316L austenitic stainless steel was investigated. A group of flat specimens were uniaxial tensile to several levels of pre-strain including 5%, 10%, 15%, 20% and 25% engineering strain. Then, the pre-strained specimens was treated by low-temperature gas Carburization at 470 °C for 30 h. In order to elucidate the effect of pre-strain on low-temperature gas Carburization, optical microscopy (OM), X-ray diffractometer (XRD), scanning electron probe micro-analyzer (EPMA), microhardness tester and residual stress analyzer were used. Meanwhile, dislocation density of the pre-strained specimens was semi-quantitatively measured by means of X-ray diffraction analysis and the role of dislocation density on carbon diffusion during low-temperature gas Carburization was discussed. The results show as follow: (1) the thicknesses of the carburized layers are independent of the pre-strain degree. (2) dislocation density increases with the increasing pre-strain, but almost has no effect on carbon diffusion at the given carburizing temperature. (3) an outstanding surface with hardness (≈ 1150 HV0.1) and compressive residual stress (≈1900 MPa) is introduced by low-temperature gas Carburization, and the strengthening results of Carburization are unaffected by pre-strain.

Thomas L Sheppard - One of the best experts on this subject based on the ideXlab platform.

  • reduction and Carburization of iron oxides for fischer tropsch synthesis
    Journal of Energy Chemistry, 2020
    Co-Authors: Monia Runge Nielsen, Xi Liu, Asger Barkholt Moss, Anton Simon Bjornlund, Axel Knopgericke, Alexander Yu Klyushin, Jandierk Grunwaldt, Thomas L Sheppard
    Abstract:

    Abstract The activation of iron oxide Fischer–Tropsch Synthesis (FTS) catalysts was investigated during pretreatment: reduction in hydrogen followed by Carburization in either CO or syngas mixture, or simultaneously reduction and Carburization in syngas. A combination of different complementary in situ techniques was used to gain insight into the behavior of Fe-based FTS catalysts during activation. In situ XRD was used to identify the crystalline structures present during both reduction in hydrogen and Carburization. An increase in reduction rate was established when increasing the temperature. A complete reduction was demonstrated in the ETEM and a grain size dependency was proven, i.e. bigger grains need higher temperature in order to reduce. XPS and XAS both indicate the formation of a small amount of carbonaceous species at the surface of the bulk metallic iron during Carburization.

Dongsong Rong - One of the best experts on this subject based on the ideXlab platform.

  • the effect of plastic pre strain on low temperature surface Carburization of aisi 304 austenitic stainless steel
    Surface & Coatings Technology, 2016
    Co-Authors: Yawei Peng, Jianming Gong, Yong Jiang, Dongsong Rong
    Abstract:

    Abstract In this paper, the influence of plastic pre-strain on low-temperature surface Carburization of AISI 304 austenitic stainless steel was investigated. The materials were strained to different degrees of engineering strain including 5%, 10%, 15%, 20% and 25%. Low-temperature surface Carburization of the pre-strained specimens was performed at 470 °C for 30 h. In order to elucidate the effect of plastic pre-strain on low-temperature surface Carburization, optical microscopy (OM), X-ray diffractometer (XRD), scanning electron probe micro-analyzer (EPMA), microhardness tester and residual stress analyzer were used. Meanwhile, dislocation density and the martensite volume fraction of the pre-strained specimens were quantitatively measured by means of XRD analysis. Based on the experimental results, the role of dislocations and martensite on carbon diffusion and related phase transformation during low-temperature surface Carburization was discussed. The results show that the thicknesses of the carburized layers are independent of the pre-strain degree. Dislocations and strain-induced martensite almost have no effect on the growth of the carburized layers at the given carburizing temperature. Increasing dislocation density does not promote the development of carbides formation, while strain-induced martensite does. Due to the supersaturated carbon atoms introduced into the materials during Carburization, strain-induced martensite transforms into austenite. As a result of Carburization, an outstanding strengthening layer of the material develops, and plastic pre-strain has no effect on strengthening of Carburization.

  • Influence of Plastic Pre-Strain on Low-Temperature Gas Carburization of 316L Austenitic Stainless Steel
    Applied Mechanics and Materials, 2016
    Co-Authors: Yawei Peng, Jianming Gong, Yong Jiang, Dongsong Rong
    Abstract:

    In this paper, the influence of pre-strain on low-temperature gas Carburization of 316L austenitic stainless steel was investigated. A group of flat specimens were uniaxial tensile to several levels of pre-strain including 5%, 10%, 15%, 20% and 25% engineering strain. Then, the pre-strained specimens was treated by low-temperature gas Carburization at 470 °C for 30 h. In order to elucidate the effect of pre-strain on low-temperature gas Carburization, optical microscopy (OM), X-ray diffractometer (XRD), scanning electron probe micro-analyzer (EPMA), microhardness tester and residual stress analyzer were used. Meanwhile, dislocation density of the pre-strained specimens was semi-quantitatively measured by means of X-ray diffraction analysis and the role of dislocation density on carbon diffusion during low-temperature gas Carburization was discussed. The results show as follow: (1) the thicknesses of the carburized layers are independent of the pre-strain degree. (2) dislocation density increases with the increasing pre-strain, but almost has no effect on carbon diffusion at the given carburizing temperature. (3) an outstanding surface with hardness (≈ 1150 HV0.1) and compressive residual stress (≈1900 MPa) is introduced by low-temperature gas Carburization, and the strengthening results of Carburization are unaffected by pre-strain.

Yong Yang - One of the best experts on this subject based on the ideXlab platform.

  • tuning Carburization behaviors of metallic iron catalysts with potassium promoter and co syngas c2h4 c2h2 gases
    Journal of Catalysis, 2019
    Co-Authors: Liwei Niu, Xingwu Liu, Jinjia Liu, Xi Liu, Xiaodong Wen, Yong Yang
    Abstract:

    Abstract Iron carbide phase formation during Carburization of α-Fe catalysts were studied using in situ XRD, where the effect of varying carbon chemical potentials of CO/syngas/C 2 H 4 /C 2 H 2 gases and potassium promoter on the Carburization behaviors was studied. The actual Carburization capability of these gases follows an order of 2% CO/He  2 H 4 /He  2 /He  2 H 2 /He, which does not correlate well with the theoretical carbon chemical potential. In addition, the Carburization rate and the formation of carbon-rich iron carbides are favored by potassium under CO or syngas, while inhibited by potassium under C 2 H 4 or C 2 H 2 . Temperature programmed Carburization together with pulse experiments and DFT calculations indicate that the potassium promoter could weaken the adsorption ability of the C 2 H 4 and C 2 H 2 and thus reduce their Carburization capabilities.

  • effect of Carburization protocols on molybdenum carbide synthesis and study on its performance in co hydrogenation
    Catalysis Today, 2016
    Co-Authors: Yong Yang
    Abstract:

    Abstract Molybdenum carbides were prepared under different Carburization conditions. The role of Carburization protocol was studied while their CO hydrogenating performances were evaluated in a fixed-bed reactor at 280 °C, 3.1 MPa, and H2/CO = 2.0. The structure of the carbides mainly depended on the type and concentration of carbon source while the crystallite size depended on carbon source and temperature. The surface area, morphology and surface carbon deposition phenomenon of the carbides were sensitive to heating rate and holding time other than the above factors. Though the bulk structure was the same at a Carburization temperature range from 630 to 760 °C, the Carburization degree of the carbides was changing continuously. This diversity led the bond strength of molecular adsorbed CO weaken at a higher Carburization temperature while the adsorptive strength of H2 was hardly changed. Both the adsorptive quantities of CO and H2 followed the same trend, with the highest amount on the carbide prepared at 630 °C. The activities of the catalysts correlated well with their adsorptive quantities of CO and H2, and the product selectivity was related to their hydrogenation capacity.