Microstructure evolution during tempering of martensitic Fe–C–Cr alloys at 700 °C

Hou, Ziyong; Babu, R. Prasath; Hedström, Peter; Odqvist, Joakim

doi:10.1007/s10853-018-2036-7

Cited by 17 publications

(11 citation statements)

References 36 publications

(78 reference statements)

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“…As the tempering temperature increased, the carbon content in RA first increased and then decreased (Figure 8b). Compared with the as-rolled rail, the carbon content of RA in the tempered rail was larger due to the diffusion of carbon from bainite and martensite into austenite [23,24]. This means that the RA became more stable after tempering because the stability of RA was largely influenced by its carbon content.…”

Section: Retained Austenitementioning

confidence: 99%

“…It is noted that the coefficients (0.000095 and 0.00056) before x Mn and x Al in Equation (1) are too small to obviously affect the calculation of carbon content in RA, so the effects of Mn and Al concentrations on the carbon content in RA could be ignored normally. According to the carbon content of RA and the contents of other alloy elements in as-rolled rail, the bainite transformation starting temperature (Bs), martensite transformation starting temperature (Ms) and time-temperature-transformation (TTT) curves of the RA for as-rolled rail were calculated using the JMatpro software [24] and the results are shown in Figure 9. The size of RA was very small and RA should contain many dislocations due to the displacive nature of bainite transformation.…”

Section: Retained Austenitementioning

confidence: 99%

See 1 more Smart Citation

Effects of Tempering on the Microstructure and Properties of a High-Strength Bainite Rail Steel with Good Toughness

Zhu

Zhou

et al. 2018

Metals

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An advanced bainite rail with high strength-toughness combination was produced in a steel mill and the effects of tempering on the microstructure and properties of the bainite rail steel were investigated by optical microscopy, transmission electron microscopy, electron back-scattering diffraction and X-ray diffraction. Results indicate that the tensile strength, elongation and impact toughness were about 1470 MPa, 14.5% and 83 J/cm 2 , respectively, after tempering at 400 • C for 200 min. Therefore, a high-strength bainite rail steel with good toughness was developed. In addition, the amount of retained austenite (RA) decreased due to bainite transformation after low-temperature tempering (300 • C) and RA almost disappeared after high-temperature tempering (500 • C). Moreover, as the tempering temperature increased, the tensile strength of the rail head first decreased due to the decreased dislocation density and carbon content in bainite ferrite and the coarseness of bainite ferrite, and then increased because of carbide precipitation at high-temperature tempering. Furthermore, RA played a significant role in the toughness of bainite rail. The elongation and toughness of the rail obviously decreased after tempering at 500 • C for 200 min because of the disappearance of RA and appearance of carbides.

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Section: Retained Austenitementioning

confidence: 99%

Section: Retained Austenitementioning

confidence: 99%

Effects of Tempering on the Microstructure and Properties of a High-Strength Bainite Rail Steel with Good Toughness

Zhu

Zhou

et al. 2018

Metals

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“…There is an advanced growth model implemented in TC-PRISMA, which accounts for the change in operating tie-line, but unfortunately simulations using this model were not possible. The nucleation sites were set as dislocations due to the martensitic microstructure of the as-quenched samples, and an initial value of 1.2 9 10 15 m -2 was used as taken from literature for similar microstructures [37,41]. The input parameters including nucleation site type, dislocation density, and interfacial energy were varied within reasonable ranges to study the influence on the simulation results.…”

Section: Kinetic Modelsmentioning

confidence: 99%

“…The input parameters including nucleation site type, dislocation density, and interfacial energy were varied within reasonable ranges to study the influence on the simulation results. The interfacial energy of M 3 C/BCC-a was varied from 0.1 to 1 J m -2 , and the dislocation density was varied from 10 14 to 10 16 m -2 [41].…”

Section: Kinetic Modelsmentioning

confidence: 99%

Early stages of cementite precipitation during tempering of 1C–1Cr martensitic steel

et al. 2019

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The precipitation of cementite (M 3 C) from as-quenched martensite during tempering at 500 and 700°C was investigated in a Fe-1C-1Cr (wt%) alloy. Tempering for a short duration at 700°C results in a Cr/Fe ratio in the core region of M 3 C precipitates which is equal to the bulk alloy composition, while a shell on the surface of the precipitates exhibits a higher Cr concentration. With a prolonged tempering up to 5 h, the shell concentration gradually increases toward the equilibrium value, but the core region has not yet reached the equilibrium value. After tempering for 5 s at 500°C, there is no Cr enrichment found at the M 3 C-matrix interface, while a transition to partitioning of Cr is found during the first 5 min of tempering at 500°C. These experimental results indicate that M 3 C grows without significant partitioning of substitutional elements at both temperatures initially, i.e., growth is carbon diffusion controlled. This stage is, however, very short, and soon after 5 s at 700°C and 5 min at 500°C, Cr diffusion becomes important. Calculations using the diffusion simulation software DICTRA and precipitation simulation software TC-PRISMA were performed. The diffusion simulations using the local equilibrium interface condition show excellent agreement with experiments concerning Cr enrichment of the particles, but the size evolution is overestimated. On the other hand, the precipitation simulations underestimate the size evolution. It is suggested that a major improvement in the precipitation model could be achieved by implementing a modified nucleation model that considers nucleation far from the equilibrium composition.

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“…The preparation of extraction replica is a traditional but important sample preparation methodology for the study of precipitates, nonmetallic inclusions and microstructures in different kinds of materials. [84][85][86][87][88][89][90][91][92][93][94] The extraction replica samples are usually prepared by first grinding, polishing and slightly etching the bulk sample, before a replica foil such as carbon of approximately 20 nm thickness is deposited on the etched surface using a coating instrument, e.g., Gatan 682 PECS TM (precision etching and coating system). [95] Thereafter, the coated film is cut into approximately 2 Â 2 mm 2 grids by a razor blade and then these smaller films are floated off in an etchant suitable for the studied material, utilizing either electro-etching or chemical etching.…”

Section: Chemical Extractionmentioning

confidence: 99%

On the role of transmission electron microscopy for precipitation analysis in metallic materials

Zhou

Babu

Hou

et al. 2021

Critical Reviews in Solid State and Materials Sciences

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Precipitation hardening is one of the most important strengthening mechanisms in metallic materials, and thus, controlling precipitation is often critical in optimizing mechanical performance. Also other performance requirements such as functional and degradation properties are critically depending on precipitation. Control of precipitation in metallic materials is, thus, vital, and the approach presently in the limelight for this purpose is an integrated approach of theory, computations and experimental characterization. An empirical understanding is essential to build physical models upon and, furthermore, quantitative experimental data is needed to build databases and to calibrate the models. The most versatile tool for precipitation characterization is the transmission electron microscope (TEM). The TEM has sufficient resolving power to image even the finest precipitates, and with TEMbased microanalysis, overall quantitative data such as particle size distribution, volume fraction and number density of particles can be gathered. Moreover, details of precipitate structure, morphology and chemistry, can be revealed. TEM-based postmortem and in situ analysis of precipitation has made significant progress over the last decade, largely stimulated by the widespread application of aberration corrected microscopes and accompanying novel analytics. The purpose of this report is to review these recent developments in precipitation analysis methodology, including sample preparation. Application examples are provided for precipitation analysis in metals, and future prospects are discussed.

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Microstructure evolution during tempering of martensitic Fe–C–Cr alloys at 700 °C

Cited by 17 publications

References 36 publications

Effects of Tempering on the Microstructure and Properties of a High-Strength Bainite Rail Steel with Good Toughness

Effects of Tempering on the Microstructure and Properties of a High-Strength Bainite Rail Steel with Good Toughness

Early stages of cementite precipitation during tempering of 1C–1Cr martensitic steel

On the role of transmission electron microscopy for precipitation analysis in metallic materials

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