Evolution of phases during tempering of P91 steel at 760℃ for varying tempering time and their effect on microstructure and mechanical properties
01 Dec 2017-Vol. 231, Iss: 6, pp 0954408916656678
TL;DR: In this paper, a systematic study has been undertaken with regard to the effects of tempering time on room temperature mechanical properties of P91 (X10CrMoVNNB9-1) steel.
Abstract: In the present investigation, a systematic study has been undertaken with regard to the effects of tempering time on room temperature mechanical properties of P91 (X10CrMoVNNB9-1) steel. Samples cut from P91 (X10CrMoVNNB9-1) industrial pipe were normalized at 1040 ℃ for 40 min and then tempered at 760 ℃ for different tempering times starting from 2 h to 8 h. Detailed analysis of microstructure, particle size, inter-particle spacing, and secondary phase carbide particles of the tempered samples was conducted by secondary electron microscopy technique. Optical microscopy was also utilized to characterize the tempered samples and for the measurement of grain size. In order to reveal the various phases formed during tempering of P91 (X10CrMoVNNB9-1) steel, X-ray diffraction was carried out. To study the fracture surface morphology of tensile tested and impact tested specimen field-emission scanning electron microscopy was carried out. The effect of tempering time on the microstructural parameters revealed an ...
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TL;DR: In this article, microstructure evolution in P91 steel and their weldments are reviewed in as-virgin and heat treatment and creep exposure condition, and the role of grain coarsening, Cr/Fe ratio, lath widening and dislocation density on creep rupture life of base metal and weldments is discussed.
155 citations
TL;DR: In this paper, the effect of heat treatment condition and diffusible hydrogen level on microstructure and mechanical properties of multi-pass shielded metal arc welded (SMAW) P91 steel butt joints of 18mm thickness has been studied.
81 citations
17 May 2017-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the effect of activating flux tungsten inert gas (A-TIG) welding on the microstructural, mechanical and corrosion behaviour of the 316L stainless steel (SS) and P91 steel weldment was enunciated.
Abstract: The current work enunciated the effect of activating flux tungsten inert gas (A-TIG) welding on the microstructural, mechanical and corrosion behaviour of the 316L stainless steel (SS) and P91 steel weldment. The current study also demonstrated the comprehensive structure–property relationships of dissimilar joint weldment using the collective techniques of optical macro and microscopy, electron microscopy, and Energy-dispersive X-ray spectroscopy (EDS) techniques. Microstructure study reveals the presence of delta ferrite, austenite and martensite in different zones of the weldment. The dissimilar steel weldment failed from the 316L side fusion boundary during the tensile testing. Maximum impact energy was absorbed by the 316L SS side heat affected zone (HAZ) while minimum by P91 steel side HAZ during the Charpy toughness test. The potentiodynamic test result suggested that the P91 side fusion boundary had minimum corrosion and pitting potential in all the weldment.
73 citations
05 Jan 2018-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the effect of varying heat treatment on tensile properties and hardness of P91 pipe weldments were studied for V-groove and narrowgroove weld designs.
Abstract: Creep strength enhanced ferritic/martensitic P91 steel is considered as a candidate material for the reactor pressure vessels and reactor internals of Very High Temperature Reactor (VHTR). Heterogeneous microstructure formation across the P91 weldments lead to premature Type IV cracking and makes the weldability of P91 steel a serious issue. The present research work describes the effect of normalizing and tempering (N&T) treatment on microstructure evolution in various zones of gas tungsten arc welded (GTAW) P91 pipe weldments. For N&T treatment, P91 pipe weldments were subjected to various normalizing (950–1150 °C) and tempering (730–800 °C) temperature. The effect of varying heat treatment on tensile properties and hardness of P91 pipe weldments were studied for V-groove and narrow-groove weld designs. The effect of increase in normalizing temperature (fixed tempering temperature) resulted in increase in strength and hardness, while increase in tempering temperature (fixed normalizing temperature) resulted in the decrease in strength and hardness of P91 steel weldments. The better combination of strength, ductility and microstructure were obtained for the maximum normalizing temperature of 1050 °C and tempering temperature of 760 °C.
67 citations
08 Feb 2017-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the effect of post weld heat treatment and normalized and tempered (N&T) heat treatment on tensile properties and hardness variation of P91 weldments was investigated.
Abstract: In Very High Temperature Reactor (VHTR), The Nb-V modified 9Cr-1Mo (P91) creep strength enhanced ferritic (CSEF) steel is currently considered as a candidate material for reactor internals and reactor pressure vessels (RPVs). After the welding of P91 steel, the inhomogeneous microstructure of weldment is a serious issue because it promotes the well-known Type IV cracking in P91 weldments. The present research work is focused on how the microstructure evolve in various zone of P91 pipe weldment during the sub-critical post weld heat treatment (PWHT) and normalized and tempered (N&T) heat treatment. The effect of PWHT and N&T heat treatment are also considered on tensile properties and hardness variation of P91 weldments. To characterize the sample scanning electron microscope (SEM), X-ray diffraction (XRD) and optical micrograph was used. It was observed that the N&T heat treatment provides the homogeneous microstructure compared to PWHT. The superior mechanical properties was also measured in N&T condition compared to PWHT. Study of fracture surface morphology of tensile tested specimen in different heat treatment condition is also presented.
67 citations
References
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TL;DR: In this article, the authors reviewed the creep deformation resistance and rupture life of high Cr ferritic steel with a tempered martensitic lath structure, and focused on the following three subjects: creep mechanism of the ferritic steels, its alloy design for further strengthening, and loss of its creep rupture strength after long-term use.
Abstract: 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.
610 citations
"Evolution of phases during temperin..." refers background in this paper
...Maruyama et al.(13) have been reported that high Cr steel is characterized by elongated subgrain with the high density of free dislocations within subgrains and grain boundaries....
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...Maruyama et al.13 have been reported that high Cr steel is characterized by elongated subgrain with the high density of free dislocations within subgrains and grain boundaries....
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TL;DR: In the 1970s, high chromium (9-12%Cr) ferritic/martensitic steels became candidates for elevated temperature applications in the core of fast reactors.
Abstract: In the 1970s, high chromium (9–12%Cr) ferritic/martensitic steels became candidates for elevated temperature applications in the core of fast reactors. Steels developed for conventional power plants, such as Sandvik HT9, a nominally Fe–12Cr–1Mo–0·5W–0·5Ni–0·25V–0·2C steel (composition in wt-%), were considered in the USA, Europe and Japan. Now, a new generation of fission reactors is in the planning stage, and ferritic, bainitic and martensitic steels are again candidates for in-core and out-of-core applications. Since the 1970s, advances have been made in developing steels with 2–12%Cr for conventional power plants that are significant improvements over steels originally considered. The present study will review the development of the new steels to illustrate the advantages they offer for the new reactor concepts. Elevated temperature mechanical properties will be emphasised. Effects of alloying additions on long-time thermal exposure with and without stress (creep) will be examined. Information ...
505 citations
"Evolution of phases during temperin..." refers background in this paper
...To avoid the creep failure in 12% Cr steels, the development of 9–10% Cr–Mo ferritic–martensitic steel have been continuing for decades, starting from P9, P91, and P92....
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...To avoid the creep failure in 12% Cr steels, the development of 9–10% Cr–Mo ferritic–martensitic steel have been continuing for decades, starting from P9, P91, and P92.(9) Cipolla et al....
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TL;DR: In this paper, a 12% Cr model steel was designed with the purpose of studying the nucleation and growth of modified Z-phase, Cr(V,Nb)N.
164 citations
"Evolution of phases during temperin..." refers background in this paper
...Cipolla et al.(10) have reported that the relatively low Cr content of 9% Cr alloys reduces the driving force for the precipitation of the Z-phase, which is detrimental to the creep strength....
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...9 Cipolla et al.10 have reported that the relatively low Cr content of 9% Cr alloys reduces the driving force for the precipitation of the Z-phase, which is detrimental to the creep strength....
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10 May 2016-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the evolution of phases in modified 9Cr-1Mo P91 steel and their effects on microstructural stability and mechanical properties have been studied for specimens that were subjected to different thermal heat treatment conditions.
Abstract: To achieve high thermal efficiency, modern day thermal power plants operate at higher operating temperature and pressure which necessitates use of steels with high creep rupture strength such as modified 9Cr-1Mo steels. In the present study, the evolution of phases in modified 9Cr-1Mo P91 steel and their effects on microstructural stability and mechanical properties have been studied for specimens that were subjected to different thermal heat treatment conditions. The main focus has been to study the effect of heat treatment temperature ranging from 623 K to 1033 K (350–760 °C) on P91 steel. Further, the effect of furnace cooling, water quenching, tempering at 1273 K (1000 °C) and austenitizing on the mechanical properties and microstructure has been studied. The techniques used for material characterization were scanning electron microscopy (SEM), optical microscopy (OM) and X-ray diffraction. For low tempering temperature, i.e. 623 K (350 °C), M 23 C 6 , M 3 C, M 7 C 3, and MX precipitates have been observed with high yield strength (YS), tensile strength (UTS), hardness and low toughness. In the high temperature range, 923–1033 K (650–760 °C), fine MX, M 7 C 3 , M 23 C 6 , M 2 X, and M 3 C precipitates have been observed with low YS, UTS, hardness and high toughness. The steel tempered at 1033 K (760 °C) was observed to be having best combination of YS, UTS, hardness, toughness and ductility.
160 citations
"Evolution of phases during temperin..." refers background in this paper
...In a previous work, Pandey et al.17 have reported that for P91 (X10CrMoVNNB9-1) steel, the optimum combination of mechanical properties and microstructural stability is obtained at the tempering temperature of 760 C....
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...In a previous work, Pandey et al.(17) have reported that for P91 (X10CrMoVNNB9-1) steel, the optimum combination of mechanical properties and microstructural stability is obtained at the tempering temperature of 760 C....
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TL;DR: In this article, the microstructural and microchemical analysis of the secondary phases were carried out using optical and electron microscopy techniques, supported by hardness measurements showed that the lath morphology of the tempered martensite was retained even after 10,000h of aging.
141 citations
"Evolution of phases during temperin..." refers methods in this paper
...The family of 9% Cr steels was firstly used in thermal power plants in 1970s and the continuous improvement in performance of the said group of steel has been achieved by optimizing chemical composition, solid solution strengthening by addition of Mo and W, addition of carbide and nitride forming elements such as V and Nb, addition of N and B in small amount, and substitution of Mo by W for microstructural stability and enhanced creep strength.(12) Over the years, improvements were incorporated in 9Cr–1Mo steel by the addition of strong carbide- and nitrideforming elements such as V and Nb with the controlled amount of N and the modified steel was designated as Grade 91 (X10CrMoVNb 9-1) steel, P91 for pipe, T91 for tube, and ASTM A335 for plate....
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