The morphology and ageing behaviour of δ-ferrite in a modified 9Cr-1Mo steel
TL;DR: In this paper, a dual phase (martensite + δ-ferrite) microstructures were developed in a modified 9Cr-1Mo steel, by austenitising at 1523-1623 K, followed by water-quenching.
About: This article is published in Journal of Nuclear Materials.The article was published on 1992-10-01. It has received 12 citations till now. The article focuses on the topics: Martensite & Laves phase.
Citations
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TL;DR: In this paper, the evolution of microstructures and mechanical properties of T91 steel were investigated in detail, and transition carbides were identified in water quenched T91 steels.
61 citations
TL;DR: In this article, the formation and microstructural evolution of delta ferrite phase in SAVE12 steel was studied under heat treatment and short-term creep and the results showed that most of the Delta ferrite can be dissolved by annealing in single phase austenitic region.
45 citations
TL;DR: In this article, the authors investigated the martensite formation kinetics in 9Cr 1W 0.23V 0.063Ta 0.09C 0.02N (wt.%) reduced activation steel.
38 citations
TL;DR: In this article, the microstructural and microchemical variations in a multipass Gas Tungsten Arc weld (GTAW) of modified 9Cr-1Mo steel are described.
Abstract: This paper presents the results of a study on the microstructural and microchemical variations in a multipass Gas Tungsten Arc weld (GTAW) of modified 9Cr-1Mo steel. The changes brought about in the steel due to the heating and cooling cycles during welding and the subsequent effects due to reheating effects during multipass welding are described. Detailed analytical transmission electron microscopy has been carried to study the type and composition of the primary and secondary phases in this steel. The systematic changes in microstructural parameters such as Prior Austenite Grain Size, martensite lath size, number density, size and microchemistry of carbides, have been understood based on the different transformations that the steel undergoes during the heating and cooling process. Based on the observed microstructure, an attempt has been made to identify distinct microstructural zones and possible thermal cycles experienced by different regions of the weldment.
35 citations
TL;DR: In this paper, the impact toughness of modified 9Cr-1Mo steel plates of 10 mm thickness have been fabricated by double side welding procedure employing A-TIG welding process.
Abstract: Modified 9Cr-1Mo steel plates of 10 mm thickness have been fabricated by double side welding procedure employing A-TIG welding process. Even after regular post weld heat treatment (PWHT), the impact toughness of A-TIG weld joint was found to be lower compared to that of conventional TIG weld joint. Therefore, post weld heat treatments of longer durations were considered for improving the toughness. Accordingly, in the present study, PWHT was carried out on A-TIG weld joints at 760 °C for 4, 6 and 8 h duration to optimize the tempering time for improving the toughness by careful study of the microstructures. It was observed that the A-TIG weld joint subjected to PWHT at 760 °C for 4 h exhibited higher hardness (410 VHN) and lower toughness (39 J) resulting from partial tempering of as-welded martensitic microstructure. The weld joint that was tempered at 760 °C for 6 h exhibited fully tempered martensite microstructure with extensive precipitation of M23C6 type carbide. The joint in this condition exhibits good impact toughness to a value of 96 J. After 8 h of tempering at 760 °C, the hardness decreased to a low value of 170 VHN and the toughness value increased beyond 200 J. It was attributed to over tempering of matensite resulting in coarsening of M23C6 precipitates and reduction in dislocation density. A-TIG weld joint with fully tempered martensite microstructure exhibit an average toughness value of 96 J and minimum single value of 75 J. Therefore, PWHT at 760 °C for 6 h was identified as the optimum tempering treatment for improving the impact toughness in mod. 9Cr-1Mo steel A-TIG weld joint.
21 citations
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TL;DR: In this article, the authors investigated the influence of trace amounts of V and Nb on the sequence of precipitation processes and identified the basis for the enhanced high-temperature strength compared to the standard 9Cr-lMo composition.
Abstract: The tempering and subsequent annealing of modified 9Cr-lMo steel have been investigated to determine the influence of trace amounts of V and Nb on the sequence of precipitation processes and to identify the basis for the enhanced high-temperature strength compared to the standard 9Cr-lMo composition. Air cooling (normalizing) from 1045 °C results in the precipitation of fine (Fe, Cr)3C particles within the martensite laths. Additional carbide precipitation and changes in the dislocation structure occur during the tempering of martensite at 700 °C and 760 °C after normalizing. The precipitation of M23C6 carbides occurs preferentially at lath interfaces and dislocations. The formation of Cr2C was detected during the first hour of tempering over the range of 650 °C to 760 °C but was replaced by V4C3 within 1 hour at 760 °C. During prolonged annealing at 550 °C to 650 °C, following tempering, the lath morphology remains relatively stable; partitioning of the laths into subgrains and some carbide coarsening are evident after 400 hours of annealing at 650 °C, but the lath morphology persists. The enhanced martensite lath stability is attributed primarily to the V4C3 precipitates distributed along the lath interfaces and is suggested as the basis for the improved performance of the modified 9Cr-lMo alloy under elevated temperature tensile and creep conditions.
166 citations
TL;DR: In this paper, the precipitation reactions in two ferritic steels, 9Cr-1Mo-V-Nb and 12Cr- 1MoV-W, were studied.
Abstract: The precipitation reactions in two ferritic steels, 9Cr-1Mo-V-Nb and 12Cr-1Mo-V-W, were studied. Analytical electron microscopy, optical microscopy, electrolytic extractions, and hardness measurements were used to determine the types, amounts, and effects of precipitates formed as a function of the heat treatment. The effect of variations in the austenitizing treatment was ascertained. In addition to variations in the austenitizing time and temperature, different cooling rates after austenitization were also used. Air cooling after austenitization (normalization) resulted in little precipitation in both alloys. Precipitation in the 12Cr-1Mo-V-W alloy after furnace cooling was found in all cases examined. Under certain conditions precipitation was also found after furnace cooling the 9Cr-1Mo-V-Nb alloy. However, when compared to the amount of precipitate in the fully tempered state, the 9Cr-1Mo-V-Nb showed a much greater variation in the degree of precipitation following furnace cooling. In addition, the matrix microstructure of the 9Cr-1Mo-V-Nb alloy was very sensitive to cooling rate. The precipitation reactions during tempering after a normalizing treatment were followed as a function of tempering treatment. Tempering temperatures were varied from 400 to 780 °C. The carbide precipitation was essentially complete after one hour at 650 °C for both alloys. Analytical microscopy was used to identify the precipitates. In the 9Cr-1Mo-V-Nb alloy, a combination of chromium-rich M23C6 and vanadium-niobium-rich MC carbides was found. The carbides in the 12Cr-1Mo-V-W alloy were identified as chromium-rich M23C6 and vanadium-rich MC. The results give an indication of the sensitivity of these alloys to heat treatment variations.
102 citations
TL;DR: In this article, the authors clarified the relationship between the toughness of a 9Cr-2Mo dual phase steel and precipitates formed during aging, with special attention to the Laves phase (Fe 2 Mo).
87 citations
25 citations
TL;DR: Several of the nuclear materials research and development programs that have involved ferrous metallurgy are described in this paper, including fabrication of first wall materials optimization and low activation materials development.
Abstract: This paper describes several of the nuclear materials research and development programs that have involved ferrous metallurgy. The research programs high-lighted are as follows: For light water reactors, corrections have been made for corrosion of coolant piping and irradiation embrittlement of pressure vessel steels. Gas-cooled reactor concerns have included breakaway oxidation of mild steel components, nitrided nitride strengthened cladding materials development, breakaway oxidation in martensitic steel and structural materials specifications for very high temperature. Programs on liquid metal reactors have included efforts on void swelling resistance, piping alloy optimization, and application of mechanically alloyed oxide dispersion strengthened steels. Fusion alloy development has considered first wall materials optimization and low activation materials development. Descriptions of the causes and needed corrections are given for each of these research and development programs.
16 citations