Effects of Chemical Compositions and Heat Treatments on Creep Rupture Strength of 12 wt%Cr Heat Resistant Steels for Boiler

Iseda, A.; Teranishi, Hiroshi; Masuyama, Fujimitsu

doi:10.2355/tetsutohagane1955.76.7_1076

Cited by 41 publications

(15 citation statements)

References 3 publications

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“…The above explanation on the high temperature tempering is supported by the literature: Iseta et al 23) reported that the rupture strength of 12Cr steel with small amount of Nb, V and N which tempered at 800°C is much higher than that tempered at 750°C when the rupture time is exceeding 5000 h. They explained the phenomenon as follows. In the case of tempering at 800°C, fine MX particles in lath structures were found even in the ruptured specimen which was tested at 650°C for about 6 000 h, but fine particles were not found in the specimen tempered at 750°C.…”

Section: Relation Between the Phenomenon And Creepsupporting

confidence: 73%

Precipitation Behavior of NbC in 9%Cr1%Mo0.2%VNb Steel.

et al. 2001

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Dissolved Nb in both austetinic and ferritic phases of 9%Cr1%Mo0.2%VNb steel was measured using an inductively coupled plasma atomic emission spectroscope (ICP), and the microstructure has been characterized using a field emission scanning electron microscope of a ultra high resolution type and an analytical electron microscope. The dissolved Nb in austenitic phase measured by ICP is in agreement with that predicted by a phase equilibrium calculation system. However, the measured values of dissolved Nb in the specimens which are heat-treated for 2 h just below A C1 are much higher than the calculated values. It is newly confirmed by both chemical and physical analyses that the fine NbC particles which are preformed at 950°C and stable at this temperature are on one occasion re-dissolved into the matrix by the subsequent heat treatment at 800°C for 2 h. This fact suggests that high temperature tempering is recommended in order to improve creep resistance of high Cr heat resisting steels which contain strong carbo-nitride formers.

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Section: Relation Between the Phenomenon And Creepsupporting

confidence: 73%

Precipitation Behavior of NbC in 9%Cr1%Mo0.2%VNb Steel.

et al. 2001

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“…The specimen tempered at the lower temperature (750°C) has higher dislocation density and longer rupture life at high stress. 42,43) Its superior creep rupture strength usually disappears at longer rupture life. 18,19,42) The low temperature tempering sometime gives shorter rupture life at low stress as seen in Fig.…”

Section: Dislocation Substructurementioning

confidence: 99%

“…10, since a high density of dislocations enhances quick recovery. 42,44) It should be noted that a material with a high density of dislocations is useless unless its premature recovery of dislocation substructure is prevented by some means.…”

Section: Dislocation Substructurementioning

confidence: 99%

Advances in Physical Metallurgy and Processing of Steels. Strengthening Mechanisms of Creep Resistant Tempered Martensitic Steel.

2001

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The creep deformation resistance and rupture life of high Cr ferritic steel with a tempered martensitic lath structure are critically reviewed on the basis of experimental data. Special attention is directed to the following three subjects: creep mechanism of the ferritic steel, its alloy design for further strengthening, and loss of its creep rupture strength after long-term use.The high Cr ferritic steel is characterized by its fine subgrain structure with a high density of free dislocations within the subgrains. The dislocation substructure is the most densely distributed obstacle to dislocation motion in the steel. Its recovery controls creep rate and rupture life at elevated temperatures. Improvement of creep strength of the steel requires a fine subgrain structure with a high density of free dislocations. A sufficient number of pinning particles (MX particles in subgrain interior and M 23 C 6 particles on sub-boundaries) are necessary to cancel a large driving force for recovery due to the high dislocation density. Coarsening and agglomeration of the pinning particles have to be delayed by an appropriate alloy design of the steel.Creep rupture strength of the high Cr ferritic steel decreases quickly after long-term use. A significant improvement of creep rupture strength can be achieved if we can prevent the loss of rupture strength. In the steel tempered at high temperature, enhanced recovery of the subgrain structure along grain boundaries is the cause of the premature failure and the consequent loss of rupture strength. However, the scenario is not always applicable. Further studies are needed to solve this important problem of high Cr ferritic steel. MX particles are necessary to retain a fine subgrain structure and to achieve the excellent creep strength of the high Cr ferritic steel. Strengthening mechanism of the MX particles is another important problem left unsolved.KEY WORDS: steel for elevated temperature service; creep; strengthening mechanism; alloy design; microstructure; microstructural degradation.

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“…The recovery of the martensitic microstructure accelerated by the coarsening of M 23 C 6 carbides near PAGBs [27] and the Fe 2 W Laves phase [6], the loss of creep ductility [7], the recovery of excess dislocations resulting from low-temperature tempering [28], and the inhomogeneous microstructure recovery due to the presence of δ-ferrite [29,30] have also been proposed as mechanisms of long-term creep strength loss in 9-12% Cr steels.…”

Section: Mechanisms Of Creep Strength Loss In 9-12% Cr Steelsmentioning

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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Effects of Chemical Compositions and Heat Treatments on Creep Rupture Strength of 12 wt%Cr Heat Resistant Steels for Boiler

Cited by 41 publications

References 3 publications

Precipitation Behavior of NbC in 9%Cr1%Mo0.2%VNb Steel.

Precipitation Behavior of NbC in 9%Cr1%Mo0.2%VNb Steel.

Advances in Physical Metallurgy and Processing of Steels. Strengthening Mechanisms of Creep Resistant Tempered Martensitic Steel.

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

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