Influence of W and Ta content on microstructural characteristics in heat treated 9Cr-reduced activation ferritic/martensitic steels

Ravikirana, .; Mythili, R.; Raju, S.; Saroja, S.; Jayakumar, T.; Rajendrakumar, E.

doi:10.1016/j.matchar.2013.08.003

Cited by 32 publications

(14 citation statements)

References 19 publications

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“…However, there is considerable scatter among the distribution of lath sizes, reflecting probably the inhomogeneous character of lath size distribution in the virgin martensite obtained upon normalizing treatment. In Figure b, the microstructure that develops upon tempering shows clearly the presence of carbides, mostly of cubic M 23 C 6 type, with M = Cr, W, and Fe and possibly some MX …”

Section: Resultsmentioning

confidence: 99%

High‐Temperature Phase Stability of 9Cr–W–Ta–V–C Based Reduced Activation Ferritic–Martensitic (RAFM) Steels: Effect of W and Ta Additions

Kirana

Raju

Mythili

et al. 2015

steel research int.

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The high‐temperature phase stability of reduced activation ferritic–martensitic steels having various W and Ta contents has been investigated using calorimetry, microscopy, and thermodynamic simulations. Calorimetric studies revealed the following transformation sequence as a function of increasing temperature upon slow heating at 1 K min−1: α‐ferrite (ferromagnetic) + M23C6 + MX → α‐ferrite (paramagnetic) + M23C6 + MX → γ‐austenite + M23C6 + MX → γ + MX → γ → δ+ γ → γ + δ + L → δ + L → liquid. This is fully supported by equilibrium thermodynamic simulations. It is found that the complete dissolution of M23C6 carbide required significant overheating above Ac3 that is, α + M23C6 + MX → γ + MX transformation finish temperature. The measured values of lattice parameter, Curie temperature, liquidus, solidus, and carbide dissolution temperatures, as well as melting enthalpy, did not reveal a drastic variation with W content, from 0 to 0.2 wt%. However, the measured dissolution temperature of MX phase exhibited a mild increase with Ta content, for up to about 0.2 wt%. The extent of dissolution of M23C6 especially around Ac3 temperature is found to depend on heating rate. Higher heating rates and higher W content yielded inhomogeneous austenite and this is found to have significant influence on subsequent γ‐austenite → α′‐martensite formation during cooling. The critical cooling rate for γ → α′‐martensite formation is found to be 6 K min−1, for all the RAFM steels. Electron microscopy and thermodynamic simulations support the possibility of simultaneous presence of two types of MX type carbonitrides at service conditions.

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Section: Resultsmentioning

confidence: 99%

High‐Temperature Phase Stability of 9Cr–W–Ta–V–C Based Reduced Activation Ferritic–Martensitic (RAFM) Steels: Effect of W and Ta Additions

Kirana

Raju

Mythili

et al. 2015

steel research int.

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“…Chemical composition of RAFM steels studied. (Ravikirana et al 2013). A predominantly lath martensite structure was observed from a typical transmssion electron micrograph of the 1⋅4W-0⋅06Ta steel shown in figure 1(b).…”

Section: Effect Of W and Ta On Microstructural Characteristicsmentioning

confidence: 91%

“…This suggests that the coarsening of M 23 C 6 is controlled by W addition. The increase in number density of fine precipitates in 1⋅4W-0⋅06Ta and 2W-0⋅06Ta steel with high W is due to M 23 C 6 , whereas in 1W-0⋅14Ta with high Ta, the chemistry of the Ta-rich MX is unaltered with the range of Ta content 83-100 wt%; the number density of MX carbides is expected to be high (Ravikirana et al 2013) due to the increased Ta content of the steel.…”

Section: Microstructure and Microchemistry During Initial Stages Of Tmentioning

confidence: 96%

“…However, within this range, a decrease in Fe concentration and increase in Cr and W concentrations, with tempering time is observed at all temperatures. With increase in the W content of steels, the W content of M 23 C 6 increased while that of Cr and Fe decreased at any temperature, which suggests the replacement of Fe by W in the M 23 C 6 lattice (Ravikirana et al 2013). Ta-rich MX carbides showed the variation of Ta content in the range 83-100 wt%, whereas the V-rich MX showed 62-76 wt% of V and 24-38 wt% Ta, which was found to be independent of the Ta content of the steel or the heat treatment given to the steel.…”

Section: Role Of W On Microchemistry Of M 23 Cmentioning

confidence: 98%

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Effect of alloy content on microstructure and microchemistry of phases during short term thermal exposure of 9Cr-W-Ta-0⋅1C reduced activation ferritic/martensitic (RAFM) steels

et al. 2014

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This paper presents the results of an experimental study on the microstructural evolution in 9Cr reduced activation ferritic/martensitic steels during short term thermal exposures. Since the microstructure is strongly influenced by the alloying additions, mainly W, Ta and C contents, the effect of varying W and Ta contents on the martensite structure that forms during normalizing treatment and the subsequent changes during tempering of the martensite in the temperature regime of 923-1033 K have been studied. Microstructural changes like subgrain formation and nature of precipitates have been evaluated and correlated to hardness variations. The systematic change in size distribution and microchemistry of M 23 C 6 carbide is studied with variation in W content at different temperatures.

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“…The precipitation of carbonitrides prior to M 23 C 6 during tempering leads to a consumption of carbon concentration in the carbon-supersaturated martensitic matrix and correspondingly decreases the volume fraction and mean size of M 23 C 6 [15]. On the other hand, the addition of tantalum would significantly increase the number of undissolved TaC during the austenitizing [20], which in turn leads to a decrease in carbon content in matrix and thus refine M 23 C 6 carbide. Figure 3 shows the tensile strength of the RAFM steels with the tantalum content at room and high temperatures.…”

Section: Microstructuresmentioning

confidence: 99%

Improvement of High-Temperature Mechanical Properties of Low-Carbon RAFM Steel by MX Precipitates

Chen

Liu

Xiao

et al. 2018

Acta Metall. Sin. (Engl. Lett.)

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To investigate the influence of tantalum content on high-temperature mechanical properties of low-carbon reduced activation ferritic/martensitic (RAFM) steels, RAFM steels containing different tantalum contents (0 and 0.073%) were fabricated, and the tensile tests at room temperature and high temperature were performed, as well as the creep tests were conducted at 550°C with the applied stress of 180 and 220 MPa. It was found that 0.073% tantalum addition results in the increase in amount of stable carbonitrides (MX), and the creep rupture time of the steel under 180 MPa is obviously increased. In addition, the increase in MX caused by tantalum addition also leads to the improvement of high-temperature tensile strength. The improvement of high-temperature mechanical properties of RAFM steels is primarily related to the evolution of precipitates.Acta Metallurgica Sinica (English Letters) (2018) 31:706-712 https://doi.org/10.1007/s40195-018-0703-y( 0123456789().,-volV) (0123456789().,-volV)

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Influence of W and Ta content on microstructural characteristics in heat treated 9Cr-reduced activation ferritic/martensitic steels

Cited by 32 publications

References 19 publications

High‐Temperature Phase Stability of 9Cr–W–Ta–V–C Based Reduced Activation Ferritic–Martensitic (RAFM) Steels: Effect of W and Ta Additions

High‐Temperature Phase Stability of 9Cr–W–Ta–V–C Based Reduced Activation Ferritic–Martensitic (RAFM) Steels: Effect of W and Ta Additions

Effect of alloy content on microstructure and microchemistry of phases during short term thermal exposure of 9Cr-W-Ta-0⋅1C reduced activation ferritic/martensitic (RAFM) steels

Improvement of High-Temperature Mechanical Properties of Low-Carbon RAFM Steel by MX Precipitates

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