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1.
Reinhard Schneider Eckhard Pippel Jrg Woltersdorf Silke Strauß Hans Jürgen Grabke 《国际钢铁研究》1997,68(7):326-332
Microstructural and microchemical investigations were carried out on nickel and Inconel 600 after exposure to strongly carburizing atmospheres at temperatures of about 600 to 650°C to study their metal dusting behaviour. Contrary to iron and low-alloy steels, where metal dusting proceeds via the formation and disintegration of a metastable carbide M3C, both nickel and Inconel 600 directly disintegrate. Inside the metal this disintegration proceeds by formation of thin graphite filaments of nearly 10 nm in diameter, the atomic basal planes of which are oriented perpendicular to the surface thus effecting a high reactivity at the growth front. Subsequently, fine particles or larger parts of the metal surface layer are released, which are buried in the deposited graphite layer on the surface. In case of Inconel 600, containing Cr with mass contents of about 15%, the disintegration can be delayed by the formation of a chromium oxide layer, but no safe protection against metal dusting is obtained. 相似文献
2.
It is considered that the use of prereduced ferrous materials and sources of metallic iron such as direct reduced iron (DRI)
or hot briquetted iron (HBI) improves the productivity of the blast furnace (BF). However, oxidation of DRI/HBI can occur
in the upper zone of the BF, which may increase the content of the reducing gases but may not decrease the coke rate substantially.
The behavior of DRI and HBI was investigated by measuring the rate of oxidation of the materials in CO2 gas in a temperature range of 400 °C to 900 °C. In addition, the microstructure of “as-received” and oxidized materials was
examined. The iron oxide phases formed due to oxidation were determined using X-ray diffraction (XRD) and a vibrating sample
magnetometer. The results of isothermal experiments indicated that the kinetics of oxidation of metallic iron is slow at 400
°C. In DRI samples, the initial rate is controlled by the limited mixed control of chemical kinetics at the iron/iron oxide
interface and pore mass transfer, whereas gas diffusion in pores is the rate governing step during the final stages of oxidation.
The oxidation of wustite from iron is found to be faster than the oxidation of the former to magnetite. The structure of DRI
after oxidation resembled a “reverse topochemical-oxide on the surface metal in the center” structure at 600 °C to 700 °C.
The final iron oxide phase formed in DRI after oxidation was magnetite and not hematite. The oxidation of HBI was limited
to the surface of the samples at lower temperatures; at 900 °C, moderate oxidation was observed and a topochemical iron oxide
layer was formed. 相似文献
3.
Andr Schneider Gerhard Inden Hans Jürgen Grabke Qing Wei Eckhard Pippel Jrg Woltersdorf 《国际钢铁研究》2000,71(5):179-184
The high temperature corrosion process metal dusting leads to the formation and decomposition of metastable iron carbides at the surface of iron samples. A small amount of H2S in the carburising atmosphere causes the adsorption of sulphur onto the sample surface, which decreases the carbon transfer rate and retards or suppresses the start of metal dusting. The extent of retardation of metal dusting depends on temperature, carbon activity and H2S content. The higher the carbon activity the higher the H2S content required for suppression of metal dusting. At very high carbon activities a second iron carbide, Fe5C2 (Hägg carbide), forms on the cementite surface. The carburisation experiments were conducted at 500°C using CO‐H2‐H2O‐H2S gas mixtures. The microstructural investigations show that both metastable carbides decompose during metal dusting. 相似文献
4.
The objective of this study is to determine whether the oxidation of Alloys 600 and 690 in supercritical water occurs by the same mechanism in subcritical water. Coupons of Alloys 690 and 600 were exposed to hydrogenated subcritical and supercritical water from 633 K to 673 K (360 °C to 400 °C) and the oxidation behavior was observed. By all measures of oxide character and behavior, the oxidation process is the same above and below the supercritical line. Similar oxide morphologies, structures, and chemistries were observed for each alloy across the critical point, indicating that the oxidation mechanism is the same in both subcritical and supercritical water. Oxidation results in a multi-layer oxide structure composed of particles of NiO and NiFe2O4 formed by precipitation on the outer surface and a chromium-rich inner oxide layer formed by diffusion of oxygen to the metal-oxide interface. The inner oxide on Alloy 600 is less chromium rich than that observed on Alloy 690 and is accompanied by preferential oxidation of grain boundaries. The inner oxide on Alloy 690 initially forms by internal oxidation before a protective layer of chromium-rich MO is formed with Cr2O3 at the metal-oxide interface. Grain boundaries in Alloy 690 act as fast diffusion paths for chromium that forms a protective Cr2O3 layer at the surface, preventing grain boundary oxidation from occurring. 相似文献
5.
E. Mohammadi Zahrani A. M. Alfantazi 《Metallurgical and Materials Transactions A》2012,43(8):2857-2868
Corrosion behavior and degradation mechanisms of alloy 625 under a 47.288 PbSO4-12.776 Pb3O4-6.844PbCl2-23.108ZnO-10CdO (wt pct) molten salt mixture under air atmosphere were studied at 873?K, 973?K, and 1073?K (600?°C, 700?°C, and 800?°C). Electrochemical impedance spectroscopy (EIS), open circuit potential (OCP) measurements, and potentiodynamic polarization techniques were used to evaluate the degradation mechanisms and characterize the corrosion behavior of the alloy. Morphology, chemical composition, and phase structure of the corrosion products and surface layers of the corroded specimens were studied by scanning electron microscopy/energy-dispersive X-ray (SEM/EDX) and X-ray map analyses. Results confirmed that during the exposure of alloy 625 to the molten salt, chromium was mainly dissolved through an active oxidation process as CrO3, Cr2O3, and CrNbO4, while nickel dissolved only as NiO in the system. Formation of a porous and nonprotective oxide layer with low resistance is responsible for the weak protective properties of the barrier layer at high temperatures of 973?K and 1073?K (700?°C and 800?°C). There were two kinds of attack for INCONEL 625, including general surface corrosion and pitting. Pitting corrosion occurred due to the breakdown of the initial oxide layer by molten salt dissolution of the oxide or oxide cracking. 相似文献
6.
《Acta Metallurgica Materialia》1995,43(2):769-779
The microstructure and chemistry of interfaces between sputter-deposited Nb coatings and (0001) sapphire surfaces, with and without interlayers of Cr and Sb, have been determined by using high resolution transmission electron microscopy (HRTEM). The changes in the microstructure and chemistry in the interfacial region resulting from annealing the samples are determined. All samples were annealed at 600°C for 24 h and 1200°C for 10 min, except the Nb/Sb sapphire samples which were heat-treated at 400 and 600°C with a 24 h hold time. All interface systems in the as-deposited state feature a 2.5 nm thick uniform Al2O3 layer, caused by sputter-cleaning of the sapphire surface prior to any interlayer or coating deposition. After annealing at 1200°C for 10 min, the amorphous layer completely recrystallizes, and hemispherical voids, 10–20 nm diameter, are formed at the Nb/Al2O3 interface. In the Nb/Cr/Al2O3 system, in addition to voids and the recrystallization of the amorphous layer, the continuous Cr layer is reduced to a Cr2Nb intermetallic reaction compound. Finally, for the Nb/Sb/Al2O3 samples, annealing at 400°C for 24 h results in a hitherto unreported, Nb-Sb amorphization reaction. 相似文献
7.
A. M. Shabani T. Jalal A. Saatchi M. Monir Vaghefi 《Transactions of the Indian Institute of Metals》2017,70(6):1519-1525
The metal dusting behavior of Iron–Chromium–Nickel heat resistant HP–Nb steel specimen was investigated at the outer surfaces while the methane gas was passed inside the hole of the specimen. After an exposure of 130 h in a flowing methane (CH4) gas at 680 °C, different dispersed corrosion products were formed on the outer surface of the specimen near the hole. Conventional metallography and scanning electron microscopy were used to identify the microstructure of the reaction products. Energy dispersive X-ray spectroscopy was used for microchemical analysis. The phases produced on the surface were identified by X-ray diffraction. Some of reaction products found as surface deposits on the outer surfaces of specimen near the hole contained Fe and Cr carbides, Fe, Cr and Ni oxides, scale of Ni, Fe particles and free C. Results revealed that carbon nano-filaments materials could be formed during disintegration of heat resistant HP–Nb steel under metal dusting environment. 相似文献
8.
Steels containing 0.2 pet C and 0 to 12 pct Cr have been tempered for different times or recrystallized at 700°C and subsequently
tensile tested at 100°C temperature intervals in the range 0° to 700°C. At all temperatures, the strength of the as-tempered
steels depends primarily on the dislocation structure inherited from the martensite transformation and work softening observed
during deformation at 600° and 700° is attributable to recovery of this structure. Strain enhanced precipitation of M3C is observed after deformation at 200° to 600°C in all the steels, independent of the nature of the carbide present after
tempering. Serrated yielding occurs at temperatures increasing from 200° to 400°C with increasing chromium content and is
associated with an increase in strength and strain-hardening rate in all cases. It is concluded that dynamic strain-aging
results from dislocation locking by chromium-interstitial complexes in the alloy steels.
T. Mukherjee, formerly Research Student, Department of Metallurgy, University of Sheffield, Sheffield England.
This paper is based upon a thesis submitted by T. Mukherjee in partial fulfillment of the requirements of the degree of Doctor
of Philosophy at the University of Sheffield. 相似文献
9.
Influence of annealing treatment on the formation of nano/submicron grain size AISI 301 Austenitic stainless steels 总被引:1,自引:0,他引:1
D. L. Johannsen A. Kyrolainen P. J. Ferreira 《Metallurgical and Materials Transactions A》2006,37(8):2325-2338
Nano/submicron austenitic stainless steels have attracted increasing attention over the past few years due to fine structural
control for tailoring engineering properties. At the nano/submicron grain scales, grain boundary strengthening can be significant,
while ductility remains attractive. To achieve a nano/submicron grain size, metastable austenitic stainless steels are heavily
cold-worked, and annealed to convert the deformation-induced martensite formed during cold rolling into austenite. The amount
of reverted austenite is a function of annealing temperature. In this work, an AISI 301 metastable austenitic stainless steel
is 90 pct cold-rolled and subsequently annealed at temperatures varying from 600 °C to 900 °C for a dwelling time of 30 minutes.
The effects of annealing on the microstructure, average austenite grain size, martensite-to-austenite ratio, and carbide formation
are determined. Analysis of the as-cold-rolled microstructure reveals that a 90 pct cold reduction produces a combination
of lath type and dislocation cell-type martensitic structure. For the annealed samples, the average austenite grain size increases
from 0.28 μm at 600 °C to 5.85 μm at 900 °C. On the other hand, the amount of reverted austenite exhibits a maximum at 750
°C, where austenite grains with an average grain size of 1.7 μm compose approximately 95 pct of the microstructure. Annealing
temperatures above 750 °C show an increase in the amount of martensite. Upon annealing, (Fe, Cr, Mo)23C6 carbides form within the grains and at the grain boundaries. 相似文献
10.
11.
Creep Rupture Strength and Microstructure of Low C-10Cr-2Mo Heat-Resisting Steels with V and Nb 总被引:1,自引:0,他引:1
T. Fujita K. Asakura T. Sawada T. Takamatsu Y. Otoguro 《Metallurgical and Materials Transactions A》1981,12(6):1071-1079
The new ferritic heat-resisting steels of 0.05C-10Cr-2Mo-0.10V-0.05Nb (Cb) composition with high creep rupture strength and
good ductility have already been reported. The optimum amounts of V and Nb that can be added to the 0.05C-10Cr-2Mo steels
and their effects on the creep rupture strength and microstructure of the steels have been studied in this experiment. The
optimum amounts of V and Nb are about 0.10 pct V and 0.05 pct Nb at 600 °C for 10,000 h, but shift to 0.18 pct V and 0.05
pct Nb at 650 °C. Nb-bearing steels are preferred to other grades on the short-time side, because NbC precipitation during
initial tempering stages delays recovery of martensite. On the long-time side, however, V-bearing steels have higher creep
rupture strength. By adding V to the steels, electron microscopic examination reveals a stable microstructure, retardation
during creep of the softening of tempered martensite, fine and uniform distribution of precipitates, and promotion of the
precipitation of Fe2Mo. 相似文献
12.
Carbide precipitation and high-temperature strength of hot-rolled high-strength,low-alloy steels containing Nb and Mo 总被引:5,自引:0,他引:5
Won-Beom Lee Seung-Gab Hong Chan-Gyung Park Sung-Ho Park 《Metallurgical and Materials Transactions A》2002,33(6):1689-1698
The effects of a Mo addition on both the precipitation kinetics and high-temperature strength of a Nb carbide have been investigated
in the hot-rolled high-strength, low-alloy (HSLA) steels containing both Nb and Mo. These steels were fabricated by four-pass
hot rolling and coiling at 650°C, 600°C, and 550°C. Microstructural analysis of the carbides has been performed using field-emission
gun transmission electron microscopy (TEM) employing energy-dispersive X-ray spectroscopy (EDS). The steels containing both
Nb and Mo exhibited a higher strength at high temperatures (∼600 °C) in comparison to the steel containing only Nb. The addition
of Mo increased the hardenability and led to the refinement of the bainitic microstructure. The proportion of the bainitic
phase increased with the increase of Mo content. The TEM observations revealed that the steels containing both Nb and Mo exhibited
fine (<10 nm) and uniformly distributed metal carbide (MC)-type carbides, while the carbides were coarse and sparsely distributed
in the steels containing Nb only. The EDS analysis also indicated that the fine MC carbides contain both Nb and Mo, and the
ratio of Mo/Nb was higher in the finer carbides. In addition, electron diffraction analysis revealed that most of the MC carbides
had one variant of the B-N relationship ((100)MC//(100)ferrite, [011]MC//[010]ferrite) with the matrix, suggesting that they were formed in the ferrite region. That is, the addition of Mo increased the nucleation
sites of MC carbides in addition to the bainitic transformation, which resulted in finer and denser MC carbides. It is, thus,
believed that the enhanced high-temperature strength of the steels containing both Nb and Mo was attributed to both bainitic
transformation hardening and the precipitation hardening caused by uniform distribution of fine MC particles. 相似文献
13.
Kyoung Rae Jo Lawrence Cho Jong Han Oh Myoung Soo Kim Ki Cheol Kang Bruno C. De Cooman 《Metallurgical and Materials Transactions A》2017,48(8):3635-3641
Third generation advanced high-strength steels achieve an excellent strength–ductility balance using a cost-effective alloy composition. During the continuous annealing of medium Mn steel, the formation of an external selective oxide layer of MnO has a negative impact on the coating quality after galvanizing. A procedure to reduce the selective oxide was therefore developed. It involves annealing in the temperature range of 1073 K to 1323 K (800 °C to 1050 °C) in a HNx gas atmosphere. Annealing at higher temperatures and the use of larger H2 volume fractions are shown to make the gas atmosphere reducing with respect to MnO. The reduction of the surface MnO layer was observed by SEM, GDOES, and cross-sectional TEM analysis. 相似文献
14.
Jessica R. Chocha Pooja A. Chhelavda J. A. Bhalodia 《Transactions of the Indian Institute of Metals》2011,64(1-2):159-163
A new simple route was used to synthesize nanosized crystalline La0.67Ca0.33MnO3 perovskite type complex oxide by simple citrate pyrolysis process using a metal salts, La, Ca, Mn as starting materials. To obtain the LCMO nanoparticles the precursor was carried out at various calcination temperatures viz. 500° C, 600° C, 700° C, 800° C for very short time only ~ 60 minutes. The synthesized LCMO nanoparticles were characterized by powder XRD, FTIR, TGA/DTA, SEM. The precursor could be completely decomposed into complex oxide at temperature below 500° C according to the TGA/DTA results. XRD demonstrates that the decomposed species is composed of perovskite-type structure at calcination temperature of 600° C for 60 minutes. The crystalline size that depends on the calcination temperature of the precursor is in the range of 11–22 nm as determined by Scherrer Formula. All the prepared samples have high purity perovskite structure which is orthorhombic. The chemical bonds were identified by the measurements of Infrared IR transmission spectra carried out with powder samples in which KBr was used as a carrier. The IR spectra revealed that stretching and bending modes influenced by calcination temperature. Morphology and grain size were studied through scanning electron microscopy. 相似文献
15.
Because of the effect of silicon on the formation of oxide scale, red scale is the main surface defect of hot-rolled Fe-Si plate, making the scale difficult for descaling compared with carbon steel. Thermogravimetric analyzer (TGA) is used to simulate isothermal oxidation process of Fe-1.5Si alloy for 60 min under air condition, and the temperature range is from 700 to 1200 °C. Electron probe microanalysis (EPMA) is used to observe cross-sectional scale morphology and analyze elemental distribution of the scale. Relational graph of temperature, scale thickness and scale structure is obtained. It is found that scale structure (outer Fe oxide layer+inner FeO/Fe2SiO4 layer+internal Si oxide precipitates) is almost unchanged with temperature except at 1000 and 1200 °C. At 1000 °C internal Si oxide precipitates cannot be found at the subsurface of the alloy, and at 1200 °C FeO/Fe2 SiO4 not only forms a layer as usual but also penetrates into the outer Fe oxide layer deeply. 相似文献
16.
V. V. Berezovskaya M. V. Kostina E. V. Blinov I. O. Bannykh V. E. Bobrova V. P. Mel’nik 《Russian Metallurgy (Metally)》2008,(1):29-33
The structure and corrosion properties of two high-nitrogen 05Kh20AN8MF steels additionally alloyed with 9 and 17% Mn have been studied. Metallographic, X-ray diffraction, and fractographic studies show that both steels have an austenitic structure and high plasticity properties after quenching from 1100 and 1100°C and subsequent aging at 500°C for 2 h. The steel alloyed with 9% Mn and 0.58% V exhibit a higher strength. Both steels have a higher corrosion resistance in a 3.5% NaCl aqueous solution than 12Kh18N9T steel. After aging at 400–600°C, the corrosion rate and the sensitivity to stress corrosion cracking increase. 相似文献
17.
V. V. Moskvichev N. V. Sukhodoeva E. N. Fedorova A. S. Popov 《Russian Metallurgy (Metally)》2017,2017(10):884-889
The microstructure of the oxide layer is studied and the adhesion energy of the metal/oxide interface is determined after high-temperature isothermal oxidation (T = 1150°C) of a single-crystal commercial René N5 nickel alloy. Experiments upon heating and rapid cooling are performed to initiate failure of the oxide layer. The elastic energy of the metal/oxide interface is determined using the model of circular buckling followed by edge delamination. Calculations are conducted for a homogeneous alumina layer and with allowance for the multilayer structure that forms at the initial stages of alloy oxidation. The adhesion energy is 72 and 27 J/m2 for these cases, respectively. 相似文献
18.
Hyo Kyung Sung Sang Yong Shin Byoungchul Hwang Chang Gil Lee Nack J. Kim Sunghak Lee 《Metallurgical and Materials Transactions A》2011,42(7):1827-1835
Six ultra-low-carbon high-strength bainitic steel plates were fabricated by controlling rolling and cooling conditions, and
effects of bainitic microstructure on tensile and Charpy impact properties were investigated. The microstructural evolution
was more critically affected by start cooling temperature and cooling rate than by finish rolling temperature. Bainitic microstructures
such as granular bainites (GBs) and bainitic ferrites (BFs) were well developed as the start cooling temperature decreased
or the cooling rate increased. When the steels cooled from 973 K or 873 K (700 °C or 600 °C) were compared under the same
cooling rate of 10 K/s (10 °C/s), the steels cooled from 973 K (700 °C) consisted mainly of coarse GBs, while the steels cooled
from 873 K (600 °C) contained a considerable amount of BFs having high strength, thereby resulting in the higher strength
but the lower ductility and upper shelf energy (USE). When the steels cooled from 673 K (400 °C) at a cooling rate of 10 K/s
(10 °C/s) or 0.1 K/s (0.1 °C/s) were compared under the same start cooling temperature of 873 K (600 °C), the fast cooled
specimens were composed mainly of coarse GBs or BFs, while the slowly cooled specimens were composed mainly of acicular ferrites
(AFs). Since AFs had small effective grain size and contained secondary phases finely distributed at grain boundaries, the
slowly cooled specimens had a good combination of strength, ductility, and USE, together with very low energy transition temperature
(ETT). 相似文献
19.
Arvind Agarwal Lalitha R. Katipelli Narendra B. Dahotre 《Metallurgical and Materials Transactions A》2000,31(2):461-473
The effects of long duration exposure of laser surface engineered composite boride coating on plain carbon steel in air at
high temperatures were investigated in this study. Exposures at 600 °C, 800 °C, and 1000 °C for 10, 30, and 50 hours of composite-TiB2 coated samples were conducted to study oxide scale growth and morphology. Kinetics of oxidation of the coating during elevated
temperature exposures were separately studied using the thermogravimetric analysis (TGA) technique. The oxidation rate for
all samples was parabolic in nature and the oxidation kinetic rate constant, K, increased with increasing temperature of exposure. Activation energy, Q for composite TiB2 coating was found to be 205 kJ/mol. A thick (>35 μm) oxide layer formed for all duration of exposure at temperatures ≥800 °C. In case of 1000 °C exposure, a very thick (>150
μm) oxide layer was formed, which was separated from the substrate. X-ray diffractometry analysis revealed the complex nonstoichiometric
nature of the oxides of type Ti
a
O
b
, Fe
m
O
n
, and Fe
x
Ti
y
O
z
. Profilometric measurements indicated an increase in the surface roughness of the oxide layer with an increase in temperature
of exposure. These physical observations indicated that the nature and morphology of the oxides formed at various temperatures
and duration of exposure are complex. 相似文献
20.
The study and application of the materials that are stable in the temperature range up to 1000°C are necessary to repair forming dies operating in this range. Nickel-based alloys can be used for this purpose. The structural state of a nickel alloy layer deposited onto a KhV4F tool steel and then heat treated is investigated. KhV4F tool steel (RF GOST) samples are subjected to laser deposition using a pulsed Nd:YAG laser. A nickel-based material (0.02C–73.8Ni–2.5Nb–19.5Cr–1.9Fe–2.8Mn) is employed for laser deposition. After laser deposition, the samples are subjected to heat treatment at 400°C for 5 h, 600°C for 1 h, 800°C for 1 h, and 1000°C for 1 h. The microstructure, the phase composition, and the microhardness of the deposited layer are studied. The structure of the initial deposited layer has relatively large grains (20–40 μm in size). The morphology is characterized by a cellular–dendritic structure in the transition zone. The following two structural constituents with a characteristic dendritic structure are revealed: a supersaturated nickel-based γ solid solution and a chromium-based bcc α solid solution. In the initial state and after heat treatment, the hardness of the deposited material (210–240 HV0.1) is lower than the hardness of the base material (400–440 HV0.1). Only after heat treatment at 600°C for 1 h, the hardness increases to 240–250 HV0.1. Structure heredity in the form of a dendritic morphology is observed at temperatures of 400, 600, and 800°C. The following sharp change in the structural state is detected upon heat treatment at 1000°C for 1 h: the dendritic morphology changes into a typical α + γ crystalline structure. The hardness of the base material decreases significantly to 160–180 HV0.1. The low hardness of the deposited layer implies the use of the layer material in limited volume to repair the forming surfaces of dies and molds for die casting. However, the high ductility of the deposited layer of the nickel-based material is a prerequisite for a high stability under thermocycling loading conditions. 相似文献