Effect of Isothermal Temperature on Microstructure and Mechanical Properties of High Al–Low Si TRIP Steel

In this study, the effect of isothermal temperature on microstructure and mechanical properties of a high Al–low Si TRIP steel was investigated using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, electron back scattered diffraction, and tensile test. The results show that typical microstructure containing ferrite, bainite, and retained austenite can be obtained when two-stage heat treatment process was utilized. When annealing temperature is 840 °C and austempering temperature is 400 °C, the tensile strength is 542 MPa and the product of strength and elongation is 17,685 MPa%. The morphologies and stability of the retained austenite in low silicon/high aluminum TRIP steel were finally discussed.     

Simulation of κ-Carbide Precipitation Kinetics in Aged Low-Density Fe–Mn–Al–C Steels and Its Effects on Strengthening

Fe–Al–Mn–C alloy systems are low-density austenite-based steels that show excellent mechanical properties. After aging such steels at adequate temperatures for adequate time, nano-scale precipitates such as κ-carbide form, which have profound effects on the mechanical properties. Therefore, it is important to predict the amount and size of the generated κ-carbide precipitates in order to control the mechanical properties of low-density steels. In this study, the microstructure and mechanical properties of aged low-density austenitic steel were characterized. Thermo-kinetic simulations of the aging process were used to predict the size and phase fraction of κ-carbide after different aging periods, and these results were validated by comparison with experimental data derived from dark-field transmission electron microscopy images. Based on these results, models for precipitation strengthening based on different mechanisms were assessed. The measured increase in the strength of aged specimens was compared with that calculated from the models to determine the exact precipitation strengthening mechanism.     

Effect of Intergranular Precipitation on the Internal Oxidation Behavior of Cr–Mn–N Austenitic Stainless Steels

The effect of intergranular precipitation on the internal oxidation behavior of Cr–Mn–N austenitic steels at 1000 °C in dry air atmosphere was investigated using scanning electron microscope, transmission electron microscope, and X-ray diffraction analysis. The results show that intergranular M23C6 carbide morphologies play an important role on the internal oxidation behavior of Cr–Mn–N steels. During the period of the oxidation, both discontinuous chain-shaped and continuous film-shaped intergranular M23C6 carbides precipitated along the grain boundaries. Internal oxides of silica preferentially intruded into the matrix along grain boundaries with discontinuous M23C6 carbide particles, while silica was obviously restricted at the interfaces between the external scale and matrix on the occasion of continuous film-shaped M23C6 carbides. It is seemed that reasonable microstructure could improve the oxidation resistance of Cr–Mn–N steels.     

Wear Resistance of Austenitic Steel Fe–17Mn–6Si–0.3C with High Silicon and High Manganese

To solve the problem of poor wear resistance in conventional Hadfield steels under medium and low stress,a new kind of steel with high silicon and high manganese Fe–17Mn–6Si–0.3C was designed and its wear resistance was studied.The results showed that it exhibited better wear resistance than conventional Hadfield steel in both dry friction and abrasive friction.The better wear resistance of the new steel with high silicon and high manganese resulted from the stressinduced γ→ε martensitic transformation.     

Effect of Ultrasonic Impact on the Microstructure of Welded Joint of 2195 Al–Li Alloy

It is known that an ultrasonic impact during tungsten inert gas welding can refine the grains and improve the mechanical properties of the welded joints of aluminum alloys. However, the influence mechanism of the ultrasonic impact on the microstructures is still unclear. In this research, the effects of the mechanical and ultrasonic impact on the microstructures of the welded joint of 2195 Al–Li alloy are analyzed. It is found that the mechanical impact could not refine the grains, but the ultrasonic impact could refine the grains. The grains become smaller in the weld center with an increase in the ultrasonic amplitude. Possible mechanisms for the grain refinement are discussed. The results show that the small temperature gradient promotes formation of the equiaxed grain and the cavitation promotes heterogeneous nucleation.     

Investigation on the Effect of Sub-Zero Treatment on Micro-Hardness and Microstructure of GTAW Welded Al–Si–Mg–Mn Alloy

In this work, the effect of sub-zero treatment on the mechanical properties of an Al–Si–Mg–Mn alloy welded by GTAW (gas tungsten arc welding) leads to significant softening in the welded region. The latter is due to melting and resolidification in the welded region, which have resulted in decomposition of the strengthening precipitates. The experiments were performed on GTAW welded plates of 6 mm thickness by varying the heat inputs, namely, of 370, 317.1, 277.5, 246.4, and 222 J/mm, and sub-zero treatment time periods. The Sub-Zero treatment was performed at–45°C using dry ice; hardness and microstructure investigations were performed in the welded region of the Al?Si–Mg–Mn alloy that was studied in two different conditions, namely, as-welded and in that formed after post weld sub-zero treatment with artificial aging. It was found that the post weld Sub-Zero treatment followed by artificial aging had led to realization of significantly higher hardness values in the welded region due to the recurrence of the precipitation sequence.     

Hot Deformation and Dynamic Recrystallization Behavior of Austenite-Based Low-Density Fe–Mn–Al–C Steel

The hot deformation and dynamic recrystallization(DRX) behavior of austenite-based Fe–27Mn–11.5Al–0.95 C steel with a density of 6.55 g cm-3were investigated by compressive deformation at the temperature range of900–1150 °C and strain rate of 0.01–10 s-1. Typical DRX behavior was observed under chosen deformation conditions and yield-point-elongation-like effect caused by DRX of d-ferrite. The flow stress characteristics were determined by DRX of the d-ferrite at early stage and the austenite at later stage, respectively. On the basis of hyperbolic sine function and linear fitting, the calculated thermal activation energy for the experimental steel was 294.204 k J mol-1. The occurrence of DRX for both the austenite and the d-ferrite was estimated and plotted by related Zener–Hollomon equations. A DRX kinetic model of the steel was established by flow stress and peak strain without considering dynamic recovery and d-ferrite DRX. The effects of deformation temperature and strain rate on DRX volume fraction were discussed in detail. Increasing deformation temperature or strain rate contributes to DRX of both the austenite and the d-ferrite, whereas a lower strain rate leads to the austenite grains growth and the d-ferrite evolution, from banded to island-like structure.     

Effect of niobium and grain boundary density on the fire resistance of Fe–C–Mn steel

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The Effect of La on the Microstructure and Corrosion-resistance of Hot-dipped Aluminizing Steel

THE HOT-DIPPED ALUMINUM technology of metalsurface is a traditional technology of surfacedisposal[1|21adding some rare-earth during thehot-dipped aluminum process can effect the technologyof hot-dipped aluminum and the microstructure ofhot-dipped aluminizing layer'31,so the surfacecapability of metal is greatly increased,forming a newtechnology of hot-dipped aluminum.After hot-dippedaluminum steel,metal surface has excellent corrosionresistance,high temperature oxidation,especiallycorro…     

Effect of Ag on the Microstructure,Mechanical and Bio-corrosion Properties of Fe–30Mn Alloy

In the current work, biodegradable Fe–30 Mn– X Ag( X = 1, 2, 5, 10 wt%) alloys were prepared by the rapid solidifi cation with copper-mold-casting technology. Phase analysis demonstrates that Fe–30 Mn– X Ag alloys consist of austenite γ phase with a fcc structure and martensite ε phase with a hcp structure. The yield strength of the samples increases with increasing Ag contents. Compared with Fe–30 Mn alloy, the degradation rates of Fe–30 Mn– X Ag in Hank's solution are signifi cantly improved. Cytotoxicity evaluation reveals that the Fe–30 Mn–1 Ag and Fe–30 Mn–2 Ag alloys perform less toxicity on the Human Umbilical Vein Endothelial Cells(HUVEC), while Fe–30 Mn–5 Ag and Fe–30 Mn–10 Ag alloys perform no toxicity on it. The contact angles of deionized water on the Fe–30 Mn– X Ag alloy surface were ranged from 55° to 69°, which is benefi cial to the adhesion and growth of the cells. Besides, the addition of Ag leads to a much lower M/H slope, particularly for the Fe–30 Mn–5 Ag alloy exhibiting a non-magnetic property as SS316 L. Therefore, the present Fe–30 Mn– X Ag alloys would be potential candidates for degradable metals.     

Effect of Al content on oxidation behaviour of ternary Fe–Al–C alloys

Iron aluminides produced by the electroslag refining technique, having the compositions: (1) Fe–16Al–1C, (2) Fe–10Al–1C, and (3) Fe–8Al–1C were used to investigate the effect of Al on the oxidation behaviour of the Fe–1C–Al system at 700 to 1000 °C. Prior to oxidation studies, phase and microstructure of alloys were analysed. The carbide phase, Fe₃AlC_0.69, was found to be distributed in the Fe₃Al matrix in alloy 1 and α (Fe–Al) matrix in alloys 2 and 3. The low Al content alloys displayed inversion in the oxidation kinetics below 800 °C, while, high Al content alloy displayed inversion phenomena at 1000 °C. The mechanism involving inversion in oxidation kinetics was found to be different in the two cases. In the former, it was attributed to the preferential oxidation of Al, while in the latter, to the phase transformation within the Al₂O₃. Carbides in the alloy having low Al content showed instability during oxidation.     

Influence of Microstructural Evolution on the Hot Deformation Behavior of an Fe–Mn–Al Duplex Lightweight Steel

The hot deformation behavior of Fe–26 Mn–6.2 Al–0.05 C steel was studied by experimental hot compression tests in the temperature range of 800–1050 °C and strain rate range of 0.01–30 s21 on a Gleeble-3500 thermal simulation machine. The microstructural evolution during the corresponding thermal process was observed in situ by confocal laser scanning microscopy. Electron backscattered diffraction and transmission electron microscopy analyses were carried out to observe the microstructural morphology before and after the hot deformation. Furthermore, interrupted compression tests were conducted to correlate the microstructural characteristics and softening mechanisms at different deformation stages.The results showed that hot compression tests of this steel were all carried out on a duplex matrix composed of austenite and d-ferrite. As the deformation temperature increased from 800 to 1050 °C, the volume fraction of austenite decreased from 70.9% to 44.0%, while that of d-ferrite increased from 29.1% to 56.0%. Due to the different stress exponents(n) and apparent activation energies(Q), the generated strain was mostly accommodated by d-ferrite at the commencement of deformation, and then both dynamic recovery and dynamic recrystallization occurred earlier in d-ferrite than in austenite.This interaction of strain partitioning and unsynchronized softening behavior caused an abnormal hot deformation behavior profile in the Fe–Mn–Al duplex steel, such as yield-like behavior, peculiar work-hardening behavior, and dynamic softening behavior, which are influenced by not only temperature and strain rate but also by microstructural evolution.     

Effect of Microstructure on the Internal Oxidation of Two-Phase Fe–Y Alloys

This work demonstrated the role of microstructure on the internal oxidation rate of two-phase alloys. Fe–Y alloys with Y contents between 1.5 and 15 wt% were employed as a model system. Alloys were prepared by arc-melting and the starting structures were as-solidified mixtures of Fe + Fe₁₇Y₂ intermetallic. An alloy with 1.5 wt% Y was cold-rolled to alter the intermetallic morphology. Oxidation was conducted in an Fe–FeO Rhines pack at 600, 700, and 800 °C up to 72 h. Pre- and post-oxidation microstructures were characterized with electron microscopy. Consistent with other studies, only the Fe₁₇Y₂ phase oxidized. Transmission electron microscopy showed the Fe₁₇Y₂ transformed into nanometer-scale oxides. Oxidation rates were always greater than those predicted by Wagner theory. Parabolic kinetics were obeyed until approximately 10 h. During this time the parabolic rate constants decreased with wt% Y. The effect of alloy microstructure on oxidation kinetics was attributed to connectivity of the Fe₁₇Y₂ phase.     

High-temperature Oxidation Behavior of a High Manganese Austenitic Steel Fe–25Mn–3Cr–3Al–0.3C–0.01N

In this paper, a Fe–Mn–Al–C austenitic steel with certain addition of Cr and N alloy was used as experimental material. By using the SETSYS Evolution synchronous differential thermal analysis apparatus, the scanning electron microscope(SEM), the electron microprobe(EPMA) and the X-ray diffraction(XRD), the high-temperature oxidation behavior microstructure and the phase compositions of this steel in air at 600–1,000 °C for 8 h have been studied. The results show that in the whole oxidation temperature range, there are three distinct stages in the mass gain curves at temperature higher than 800 °C and the oxidation process can be divided into two stages at temperature lower than 800 °C.At the earlier stage the gain rate of the weight oxidized in temperature range of 850 °C to 1,000 °C are extremely lower.The oxidation products having different surface microstructures and phase compositions were produced in oxidation reaction at different temperatures. The phase compositions of oxide scale formed at 1,000 °C are composed of Fe and Mn oxide without Cr. However, protective film of Cr oxide with complicated structure can be formed when the oxidation temperature is lower than 800 °C.     

Effect of deformation and annealing on the formation and reversion of ε-martensite in an Fe–Mn–C alloy

Microstructure and texture evolution during cold rolling and subsequent annealing were studied in an Fe–22 wt.% Mn–0.376 wt.% C alloy. During rolling the deformation mechanisms were found to be dislocation slip, mechanical twinning, deformation-induced ε-martensite transformation and shear banding. At higher strains, the brass-type texture with a spread towards the Goss-type texture dominated. A decrease in the Cu- and S- components was attributed to the preferential transformation to ε-martensite in Cu- and S-oriented grains. The texture of ε-martensite was sharp and could be described as {1 1 2 9}〈3 3 6 2〉. The orientation relationship {1 1 1}^γ//{0 0 0 1}^ε and 〈110〉^γ//〈1 1 –2 0〉^ε between ε-martensite and austenite was observed but only certain variants were selected. On subsequent annealing, the ε-martensite transformed reversely to austenite by a diffusionless mechanism. Changes in length along rolling, normal and transverse directions on heating were anisotropic due to a combination of volume expansion and shape memory effects. The S-texture component increased significantly due to transformation from the ε-martensite.     

Influence of Chromium and Nickel Variation on the Microstructure,Carbide Morphology and Corrosion Behaviour in Fe–Mn–Cr–Cu based Austenitic White Irons

The aim of the work is to develop a low-cost cast iron having comparable corrosion resistance with that of Ni-Resist cast iron but free from graphitic corrosion. In experimental alloys, austenitic matrix was found in both as-cast and heat treated conditions. The volume fraction of austenite also increased with increase of heat treatment temperature and time at temperature. X-ray diffractometry, energy dispersive analysis and optical microscopy were employed to investigate the microstructural features. Hardness testing and corrosion study were carried out. The corrosion rates were in the proximity of those of Ni-Resist irons especially on heat treatment at higher temperatures.     

Effect of Addition of 4 % Al on the High Temperature Oxidation and Nitridation of a 20Cr–25Ni Austenitic Stainless Steel

In high temperature applications, the alumina forming austenites (AFA) have recently gained more focus. These utilise the advantageous effect of Al on oxidation resistance, and also have good mechanical properties. Two experimental alloys [20Cr–25Ni–1Mn–0.5Si–Fe (wt.%)] were prepared. To one of the alloys 3.77 wt.% Al was added. The alloys were studied in air and air/water at 700 °C and 1,000 °C, in a sulphidising/chlorinating environment at 700 °C and in a nitriding atmosphere at 1,000 °C. The time of exposure was 100 h, except for one 1,000 h exposure in air/water. At 700 °C in air and air/water, the AFA displayed lower mass gain than the reference material. After exposure in the sulphidising-chlorinating environment, the material displayed a surface alumina layer with some spallation. In air or air/water at 1,000 °C, internal aluminium nitride and alumina formation occurred, appreciably reducing the sound metal thickness. The nitridation was enhanced in the nitriding environment.     

Effects of Solution Treatment on the Microstructure,Tensile Properties,and Impact Toughness of an Al–5.0Mg–3.0Zn–1.0Cu Cast Alloy

This study investigates the eff ect of solution treatment(at 470 °C for 0–48 h) on the microstructural evolution,tensile properties,and impact properties of an Al–5.0Mg–3.0Zn–1.0Cu(wt%) alloy prepared by permanent gravity casting.The results show that the as-cast microstructure consists of α-Al dendrites and a network-like pattern of T-Mg_(32)(AlZnCu) 49 phases.Most of the T-phases were dissolved within 24 h at 470 ℃;and a further prolonging of solution time resulted in a rapid growth of α-Al grains.No transformation from the T-phase to the S-Al_2CuMg phase was discovered in this alloy.Both the tensile properties and impact toughness increased quickly,reached a maximum peak value,and decreased gradually as the solution treatment proceeded.The impact toughness is more closely related to the elongation,and the relationship between impact toughness and elongation appears to obey an equation:IT = 8.43 EL-3.46.After optimal solution treatment at 470 ℃ for 24 h,this alloy exhibits excellent mechanical properties with the ultimate tensile strength,yield strength,elongation and impact toughness being 431.6 MPa,270.1 MPa,19.4% and 154.7 kJ/m~2,which are comparable to that of a wrought Al–6.0 Mg–0.7 Mn alloy(5E06,a 5 xxx aluminum alloy).Due to its excellent comprehensive combination of mechanical properties,this cast alloy has high potential for use in components which require medium strength,high ductility and high toughness.