Effect of Niobium on the Ferrite Continuous-Cooling-Transformation (CCT) Curve of Ultrahigh-Thickness Cr-Mo Steel

Lee, Sanghoon; Na, Hye-Sung; Kim, Byung–Hoon; Kim, Dong-Jin; Kang, Chung Gil

doi:10.1007/s11661-013-1616-z

Cited by 8 publications

(3 citation statements)

References 20 publications

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“…Dislocations accumulated easily and the formation of the dislocation structure of slip bands with a high free energy was accelerated both within the matrix and at the grain boundaries, since undissolved NbC and Nb carbides formed by deformation acted as pinning points that prohibited the motion of dislocations. Furthermore, NbC acted as potential nucleation sites, accelerating the transformation from austenite to ferrite [34]. Accordingly, it is likely that nucleation actively occurred throughout the grains and at the grain boundaries of Nb steel, resulting in the formation of a uniform ultrafine structure in Nb steel, in contrast to 0.2% carbon steel with a bimodal structure, as schematically illustrated in Fig.…”

Section: Microstructural Evolution Of Low-carbon Steels With Differenmentioning

confidence: 99%

Effect of carbon content on formation of bimodal microstructure and mechanical properties of low-carbon steels subjected to heavy-reduction single-pass hot/warm deformation

Park

2014

Materials Science and Engineering: A

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A compression test simulating heavy-reduction single-pass rolling was conducted to investigate the microstructural evolution based on the formation of a bimodal structure and the mechanical properties of 0.01% and 0.1% carbon steels and niobium steel. When thermomechanical processing was conducted near and above the critical transformation temperature (A c3 ), microstructures of all steels were significantly refined and consisted of equiaxed grains without elongated grains. Nevertheless, these microstructures showed weak or no formation of the bimodal structure or coarse grains with decreasing carbon content, while they showed bimodal structure formation when 0.2% carbon steel was used in our previous © 2014. This manuscript version is made available under the Elsevier user license http://www.elsevier.com/open-access/userlicense/1.0/ research. The average grain size of Nb steel was about 2 m and its microstructure was uniformly refined. These may be attributed to a decrease in the number of nucleation sites with decreasing carbon content in low-carbon steels and the occurrence of nucleation at grain boundaries as well as in grain interiors in Nb steel during processing. Mechanical properties of all steels deformed above the critical transformation temperature exhibited high performance characteristics with superior strength and marked elongation. Their fractographs indicated ductile fracture, which was revealed by SEM observation after a tensile test.

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Section: Microstructural Evolution Of Low-carbon Steels With Differenmentioning

confidence: 99%

Effect of carbon content on formation of bimodal microstructure and mechanical properties of low-carbon steels subjected to heavy-reduction single-pass hot/warm deformation

Park

2014

Materials Science and Engineering: A

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“…The element addition range was selected within the range of chemical requirements of ASTM F11. In addition, Nb and Ti microalloyed steel were selected for the study on whether hardness and toughness were improved when the content of certain elements was added [21,22]. The basic alloys and element addition ranges are shown in Table 1.…”

Section: Methodsmentioning

confidence: 99%

Thermodynamic Alloy Design of High Strength and Toughness in 300 mm Thick Pressure Vessel Wall of 1.25Cr-0.5Mo Steel

Kim

Lee

et al. 2018

Metals

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Abstract:In the 21st century, there is an increasing need for high-capacity, high-efficiency, and environmentally friendly power generation systems. The environmentally friendly integrated gasification combined-cycle (IGCC) technology has received particular attention. IGCC pressure vessels require a high-temperature strength and creep strength exceeding those of existing pressure vessels because the operating temperature of the reactor is increased for improved capacity and efficiency. Therefore, high-pressure vessels with thicker walls than those in existing pressure vessels (≤200 mm) must be designed. The primary focus of this research is the development of an IGCC pressure vessel with a fully bainitic structure in the middle portion of the 300 mm thick Cr-Mo steel walls. For this purpose, the effects of the alloy content and cooling rates on the ferrite precipitation and phase transformation behaviors were investigated using JMatPro modeling and thermodynamic calculation; the results were then optimized. Candidate alloys from the simulated results were tested experimentally.

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“…The microstructure in edge of rod is sorbite. In central segregation area, the sorbite transformation is avoided, and microstructure at room temperature is martensite [20].…”

Section: Epma-wds Microanalysismentioning

confidence: 99%

Causes and Control Mechanism of Abnormal Structure in the Center of SWRH82B Wire-Rod-Steel

Liao¹,

Wei

Li³

et al. 2019

MSF

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The cause of drawing fracture of SWRH82B wire rods was analyzed by using optical microscopy, scanning electron microscope - energy dispersive spectrometer and electron probe micro-analyzer - wavelength dispersive spectrometer. A multivariate diffusion model was established in Thermo-Cale, and the effects of temperature and time on diffusion behavior of alloys were studied. Results show that cementite network and martensite in the center area of rod is main cause of tensile fracture. There is serious segregation of chromium and manganese in the central area. The CCT curve moves to right, and critical cooling rate of martensite decreases. With high cooling rate, time for eutectoid transition is insufficient, and martensite transformation occurs in segregation band. The segregation of phosphorus further worsen the brittleness of steel. With increase of heating temperature and duration of heating time, segregation in final product is reduced, and content of cementite network and martensite decreases. When the temperature is maintained at 1050 °C for 600 s, there is no segregation of phosphorus and carbon. The diffusion of chromium is even when temperature is maintained at 1150 °C for 5400 s, and an even diffusion of manganese is obtained when temperature is maintained at 1200 °C for 3000 s. In stelmor air cooling process, the key point is keeping cooling rate low to extend holding time, and to optimize microstructure and properties.

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Effect of Niobium on the Ferrite Continuous-Cooling-Transformation (CCT) Curve of Ultrahigh-Thickness Cr-Mo Steel

Cited by 8 publications

References 20 publications

Effect of carbon content on formation of bimodal microstructure and mechanical properties of low-carbon steels subjected to heavy-reduction single-pass hot/warm deformation

Effect of carbon content on formation of bimodal microstructure and mechanical properties of low-carbon steels subjected to heavy-reduction single-pass hot/warm deformation

Thermodynamic Alloy Design of High Strength and Toughness in 300 mm Thick Pressure Vessel Wall of 1.25Cr-0.5Mo Steel

Causes and Control Mechanism of Abnormal Structure in the Center of SWRH82B Wire-Rod-Steel

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