Improvement of creep strength by fine distribution of TiC in 9Cr ferritic heat resistant steel

Taneike, Masaki; Fujitsuna, Nobuyuki; Abe, Fujio

doi:10.1179/026708304225022322

Cited by 23 publications

(20 citation statements)

References 10 publications

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“…The dispersion of nanosize TiC carbides also results in a significant decrease in the minimum creep rate and a significant increase in the time to rupture of 9% Cr steel [45]. To utilize TiC in 9% Cr steel, however, it is crucial to reduce the nitrogen concentration to a very low level, so as to promote the formation of very fine and thermally stable TiC particles and also to eliminate TiN.…”

Section: Creep-strengthening Mechanismmentioning

confidence: 99%

Precipitate design for creep strengthening of 9% Cr tempered martensitic steel for ultra-supercritical power plants

Abe

2008

Science and Technology of Advanced Materials

458

163

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To cite this article: Fujio Abe (2008) Precipitate design for creep strengthening of 9% Cr tempered martensitic steel for ultra-supercritical power plants, Science Abstract It is crucial for the carbon concentration of 9% Cr steel to be reduced to a very low level, so as to promote the formation of MX nitrides rich in vanadium as very fine and thermally stable particles to enable prolonged periods of exposure at elevated temperatures and also to eliminate Cr-rich carbides M 23 C 6 . Sub-boundary hardening, which is inversely proportional to the width of laths and blocks, is shown to be the most important strengthening mechanism for creep and is enhanced by the fine dispersion of precipitates along boundaries. The suppression of particle coarsening during creep and the maintenance of a homogeneous distribution of M 23 C 6 carbides near prior austenite grain boundaries, which precipitate during tempering and are less fine, are effective for preventing the long-term degradation of creep strength and for improving long-term creep strength. This can be achieved by the addition of boron. The steels considered in this paper exhibit higher creep strength at 650• C than existing high-strength steels used for thick section boiler components.

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Section: Creep-strengthening Mechanismmentioning

confidence: 99%

Precipitate design for creep strengthening of 9% Cr tempered martensitic steel for ultra-supercritical power plants

Abe

2008

Science and Technology of Advanced Materials

458

163

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“….................. (8) where l is the length of the sides of the cubic nuclei, Δgv is the chemical free energy change due to the formation of the precipitate phase (also called the driving force for nucleation) which has a negative sign in case of an oversaturated matrix, Δgs is the misfit strain energy due to the formation of the precipitate in the host lattice and γeff is the effective interface energy of a precipitate which interacts with a nearby dislocation strain field. The effective surface energy is calculated according to: 29) ................... (9) where γ is the interface energy between TiC and ferrite (0.339 Jm -2 ), 30) G is the shear modulus of the matrix, b the Burgers vector of the dislocation, v the Poisson's ratio of the matrix (calculated to be 0.286 by same approach as for the value of G) 17) and e T is the relative lattice misfit (6% according to).…”

Section: Nucleation Of Ticmentioning

confidence: 99%

“…In addition to enhancing strength, thermally stable precipitates are also known to improve the temperature resistance of steels, by acting as pinning points for movement of dislocations. 7) The high thermal stability of TiC precipitates 8) therefore makes medium-carbon steel with a small addition of Ti an interesting candidate for high-strength engine fasteners intended for service temperatures which exceed the current limit of 300°C. The mechanical properties of such fasteners will be directly related to the martensite microstructure with precipitates.…”

Section: Introductionmentioning

confidence: 99%

Modelling the Evolution of Multiple Hardening Mechanisms during Tempering of Fe–C–Mn–Ti Martensite

et al. 2015

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We model the hardness evolution of martensite during tempering as a linear addition of multiple hardening mechanisms that is combined with a microstructural Kampmann-Wagner-Numerical (KWN) model to simulate the nucleation and growth of TiC-precipitates during tempering. The combined model is fitted to the measured hardness evolution during tempering at 300°C and 550°C of martensitic steels with and without the addition of titanium. The model predicts TiC-precipitate sizes in agreement with experimental observations and generates fitting parameters in good agreement with literature. The microstructural components that give the highest contribution to the overall hardness are Fe3C precipitates (88 HV) and dislocations (54 HV). Both Fe3C-and dislocation-strengthening decreases rapidly during the initial stage and stabilise after 10 minutes of tempering. The model shows that the decrease in dislocation density due to recovery is slowed down due to the presence of TiC-precipitates. Titanium atoms in solid solution give a stable hardness contribution (25 HV) throughout the tempering process. TiC-precipitate strengthening generates a minor contribution (3.5 HV). The model shows that less than 1% of the equilibrium volume fraction of TiC-precipitates forms during isothermal tempering at 550°C due to the large misfit strain (1.34 GJ/m 3 ) and a limited density of potential nucleation sites in the martensite. The model shows that the hardness of tempered martensitic steels could potentially be increased by increasing the TiC-precipitate density by reducing the misfit strain.

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“…However, literature shows that the creep properties of martensitic steel for applications in power plants are improved by the presence of alloy carbides. [12][13][14] Moreover, a report has demonstrated the combined improvement of the room temperature and high temperature tensile strengths of martensite due to a fine dispersion of alloy carbides. 15) Creep measurements are very time consuming.…”

Section: Introductionmentioning

confidence: 99%

A Comparison between Ultra-high-strength and Conventional High-strength Fastener Steels: Mechanical Properties at Elevated Temperature and Microstructural Mechanisms

et al. 2016

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A comparison is made between the mechanical properties of the ultra-high-strength steel KNDS4 of fastener grade 14.9 and of conventional, high-strength steels 34Cr4 of fastener grade 12.9 and 33B2 of grade 10.9. The results show that the ratio of the yield strength at elevated temperatures to the yield strength at room temperature is higher for the ultra-high-strength steel than for both conventional highstrength steels, especially at 500°C. Moreover, the results show a trend in which the nano-indentation creep rate is lower as the strength of the steels is higher. The improved mechanical properties of the KNDS4 steel compared to the conventional high-strength steels are related to the smaller size of the alloy carbides in the KNDS4 steel. Furthermore, the effect of an alternative (industrial) heat-treatment on the evolution of the microstructure and hardness of the KNDS4 steel was investigated. Changing the industrial heat treatment can increase the hardness of KNDS4 by about 8%, since more alloy carbides can nucleate and grow. However, the standard industrial heat treatment results in a refinement of the martensite microstructure (grain size), which might be more beneficial for the toughness of the steel. Independent of the heat treatment, the mechanical performance of KNDS4 fasteners at elevated temperature and the low nano-indentation creep rates are two strong indicators that fasteners made from KNDS4 steel might be used at higher service temperatures than traditional high strength fasteners.

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Improvement of creep strength by fine distribution of TiC in 9Cr ferritic heat resistant steel

Cited by 23 publications

References 10 publications

Precipitate design for creep strengthening of 9% Cr tempered martensitic steel for ultra-supercritical power plants

Precipitate design for creep strengthening of 9% Cr tempered martensitic steel for ultra-supercritical power plants

Modelling the Evolution of Multiple Hardening Mechanisms during Tempering of Fe–C–Mn–Ti Martensite

A Comparison between Ultra-high-strength and Conventional High-strength Fastener Steels: Mechanical Properties at Elevated Temperature and Microstructural Mechanisms

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