The Role of Deformation in Coarsening of M23C6 Carbide Particles in 9% Cr Steel

Tkachev, E.; Belyakov, Andrey; Kaibyshev, Rustam

doi:10.1134/s0031918x20060162

Cited by 17 publications

(4 citation statements)

References 28 publications

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“…that atomic diffusion would be encouraged in the fine grain region during aging, resulting in the promotion of precipitate coarsening 41) . In addition, effects of the initial distribution of precipitates are considered 42) .…”

Section: Discussionmentioning

confidence: 99%

Microstructural Changes in 9Cr-1Mo-V-Nb Weld Metal after Aging at 1013 K

et al. 2024

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In order to understand microstructural changes in 9Cr-1Mo-V-Nb weld metal after long term use, microstructure and precipitates distribution before and after aging at 1013K were investigated. In the weld metal, regions with coarse or fine prior austenite grains were observed due to thermal cycle during welding. In the coarse grain region, precipitate particles inferred to M 23 C 6 were densely located on grain boundaries, however, in the fine grain regions, they were sparsely observed not only on grain boundaries but also inside grains. Post weld heat treatment (1013K/7.7h) followed by aging (1013K/100h) led to ferrite grains formation in the fine grain region. EBSD analysis implied that dislocation density in ferrite grains was low. After the aging, mean diameter of particles became coarser and interparticle spacing became sparser in the fine grain region than in the coarse grain region. On the other hand, dislocation density calculated by hardness in martensite structure was almost no deference between these regions before and after the aging. Therefore, it was suggested that ferrite grains were formed because pinning energy by precipitate particles locally reduced in the fine grain region.

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Section: Discussionmentioning

confidence: 99%

Microstructural Changes in 9Cr-1Mo-V-Nb Weld Metal after Aging at 1013 K

et al. 2024

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“…Tkachev etal. 62 reported that the coarsening of M 23 C 6 transpired due to their interaction with dislocations and the occurrence of grain boundary diffusion mechanism.…”

Section: Stir Zone Microstructuresmentioning

confidence: 99%

Unravelling the microstructure – indentation creep resistance relationships for friction stir welded modified 9Cr-1Mo steel and LN-type 316 stainless-steel dissimilar joints

krishna¹,

Lakshminarayanan²,

Vasantharaja

et al. 2023

Proceedings of the Institution of Mechanical Engineers, Part L:

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In this article, the indentation creep characteristics and the microstructures are assessed for the friction stir welded modified 9Cr-1Mo steel and LN-type 316 SS dissimilar joint. Microstructures are characterized for the post-weld heat treated and indentation crept samples at different conditions with optical microscopy, scanning electron microscope and energy dispersive X-ray spectroscopy. Distinct heat-affected zones were revealed with the refined and reformed martensite (α′) and austenite (γ) structures that formed in view of the distinct thermal conductivity property and the differences in lower critical(Ac1) and upper critical(Ac3) transformation temperatures. The size of prior austenite grain sizes was found to be varied significantly at the different regions. Indentation creep data were acquired in distinct weld zones at 873, 898 and 923 K. Zone-wise indentation depth, steady-state creep behaviour (SSCR) and activation energy ( Q) were evaluated and correlated with the microstructures. The formation of small prior austenitic grain (PAG) structures and the grain boundary vacancies has led to maximum creep deformation (86.83%) at the heat affected zone of the modified 9Cr-1Mo steel. Furthermore, the reduction in lath structures and the formation of tiny α′ with soft substructures have lowered the hardness values to around 210 ± 21 HV, which is 20 HV less than the post weld heat treated sample. In the stir zone, the presence of dynamically refined and rich γ along with fine α′ layers has improved the steady-state creep rate of 9.112 E-7, which is less than the modified 9Cr-1Mo steel and the heat affected zone at modified 9Cr-1Mo side. The coarse austenite structures that existed in the LN-type 316 base metal have resisted more creep damage and exhibited high activation energy (i.e. 490 kJ mol−1) than the stir zone and heat affected zone of the LN-type 316 SS.

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“…The work done by the external force on the deformation zone during high-temperature stretching caused the temperature of it to be higher than tensile temperature, which provided thermodynamic conditions for the redissolution of small carbides near the fracture zone and the grain growth of large carbides [25,26]. Due to the low thermal activation energies of M 7 C 3 and M 23 C 6 carbides [27], Cr-containing carbides grew significantly during high-temperature stretching.…”

Section: Precipitate Phase Analysismentioning

confidence: 99%

Microstructure Evolution and Fracture Mechanism of 55NiCrMoV7 Hot-Working Die Steel during High-Temperature Tensile

Yuan

Wang

Shi

et al. 2023

Metals

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In this paper, through high-temperature tensile tests of 55NiCrMoV7 steel, high-temperature fracture behavior, microstructure evolution, and carbide distribution characteristics of both the thermal–mechanical coupling zone (fracture zone) and thermal stress zone (clamping zone) at different temperatures were studied. Intrinsic relationships between high-temperature fractures and carbide types, distribution and size were revealed, and evolution mechanisms of microstructure near cracks in 55NiCrMoV7 hot-working die steel during high-temperature deformation was clarified. Samples were stretched at different temperatures from 25 °C to 700 °C, and microscopic examinations were carried out using SEM and TEM. The results showed the following. With the increase in temperature, tensile strength and yield strength decreased, elongation and reduction of area increased, and fracture mode changed from brittle fracture to ductile fracture by transition temperature at about 400 °C. During high-temperature deformation, the grain dislocation density decreased and the tempered martensite decomposed, recovered, recrystallized, and then grain grew. M7C3 and M23C6 carbides precipitated and grew along the grain boundary, and a small amount of fine granular MC carbides was dispersed in the grain. The work done by the external force on the deformation zone would cause the temperature of it to be higher than the tensile temperature, which provides thermodynamic conditions for the redissolution of small carbides near the fracture zone and the grain growth of large carbides, resulting in a decrease in small carbides and increase in large carbides in thermal–mechanical coupling zones.

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The Role of Deformation in Coarsening of M23C6 Carbide Particles in 9% Cr Steel

Cited by 17 publications

References 28 publications

Microstructural Changes in 9Cr-1Mo-V-Nb Weld Metal after Aging at 1013 K

Microstructural Changes in 9Cr-1Mo-V-Nb Weld Metal after Aging at 1013 K

Unravelling the microstructure – indentation creep resistance relationships for friction stir welded modified 9Cr-1Mo steel and LN-type 316 stainless-steel dissimilar joints

Microstructure Evolution and Fracture Mechanism of 55NiCrMoV7 Hot-Working Die Steel during High-Temperature Tensile

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