A roadmap for tailoring the strength and ductility of ferritic/martensitic T91 steel via thermo-mechanical treatment

Song, Miao; Sun, Cheng; Fan, Zhe; Chen, Youxing; Zhu, Ruixian; Kobayashi, Yu; Hartwig, K. T.; Wang, H.; Zhang, X.

doi:10.1016/j.actamat.2016.04.031

Cited by 86 publications

(24 citation statements)

References 74 publications

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“…Varios autores [11][12][13] reportaron austenita retenida con una morfología de película alargada sobre los bordes de listones. En particular, HURTADO-NOREÑA et al [11], la austenita retenida fue encontrada en un acero P91 similar al del presente trabajo, normalizado a 1050 ºC por 30 minutos y enfriado al aire.…”

Section: Discussionunclassified

Estudio de la microestructura de un cordón de soldadura de un acero P91 mediante microscopía electrónica de transmisión

et al. 2018

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RESUMENEn el presente trabajo se llevó a cabo la caracterización microestructural de un cordón de pasada simple de un acero 9Cr1MoVNb P91 obtenido por el proceso de soldadura semiautomática bajo protección gaseosa (FCAW), en la condición "as welding" mediante microscopía electrónica de transmisión.El acero P91 tiene una buena soldabilidad, pero las propiedades mecánicas de las uniones soldadas son inferiores a las del material base. La zona afectada por el calor (ZAC) de este tipo de aceros es de  4 mm lo que dificulta extraer réplicas y láminas delgadas para el estudio de las distintas microestructuras generadas en cada sub-zona de la ZAC: ZAC de grano grueso (ZACGG), ZAC de grano fino (ZACGF) y ZAC intercrítica (ZACIC). No obstante, fue posible extraer réplicas de cada región para identificar a los precipitados y por medio de la utilización de un haz de iones focalizados (FIB-SEM) se pudieron extraer láminas delgadas de un área específica para caracterizar la microestructura de la matriz. Se caracterizaron los precipitados presentes en cada sub-zona de la ZAC y cómo la disolución del M 23 C 6 afecta a la matriz que lo rodea. A bajas temperaturas pico y bajas velocidades de calentamiento/enfriamiento tales como las que caracterizan a las zonas de grano fino (ZACIC y ZACGF) se encontró austenita retenida en contacto de los carburos M 23 C 6 parcialmente disueltos. Por otra parte, en las zonas con más altas temperaturas pico y altas velocidades de calentamiento/enfriamiento (ZACGG y zona fundida) se encontraron pelícu-las finas de austenita retenida en los ex bordes de grano austenítico y en los listones de martensita. Palabras clave: acero 9Cr1Mo, cordón de soldadura, microscopía electrónica. ABSTRACTIn the present work the microstructural characterization of a single-pass weld of 9Cr1MoVNb P91 steel performed by the flux-cored arc welding (FCAW) process in the "as welding" condition has been carried out by means of transmission electron microscopy.P91 steel offers a good weldability, but the mechanical properties of the welded joints are found to be inferior compared to the base metal. The heat affected zone (HAZ) of these types of steels is  4 mm making it difficult to extract carbon replicas and thin foil to study the microstructure generated in each sub-zone of the ZAC: coarse grained ZAC (CGZAC), fine grained ZAC (FGZAC) and intercritical ZAC (ICZAC). Nevertheless, it was possible to extract replicas from each region to identify precipitates and using a focused ion beam (FIB-SEM), thin films could be extracted from a specific area to characterize the matrix microstructure.The precipitates present in each subzone of the ZAC were characterized as well as how the dissolution of M 23 C 6 affects the matrix. At low peak temperatures and low heating / cooling rates such as those characterizing the fine grain zones (ICHAZ and FGHAZ) the M 23 C 6 carbides were found to be partially dissolved and in contact with retained austenite. On the other hand, in the areas with the highest peak temperatures and high

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Section: Discussionunclassified

Estudio de la microestructura de un cordón de soldadura de un acero P91 mediante microscopía electrónica de transmisión

et al. 2018

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“…Thermomechanical processing of 9Cr FM steels has been revealed as a promising tool to promote a high number density of MX carbonitrides [30][31][32][33][34][35][36][37][38]. TMT involves different steps that need to be optimized to produce the most favorable precipitate microstructure for elevated-temperature strength.…”

Section: Creep and Microstructural Evolutionmentioning

confidence: 99%

High-Chromium (9-12Cr) Steels: Creep Enhancement by Conventional Thermomechanical Treatments

Vivas¹,

San-Martín²,

Caballero³

et al. 2021

Welding - Modern Topics

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There is a worldwide need to develop materials for advanced power plants with steam temperatures of 700°C and above which have the capacity to achieve high efficiency and low CO 2 emissions. This request involves the development of new grades of 9-12Cr heat-resistant steels, with a nanostructured martensite, mainly focusing on the long-term creep rupture strength of base metal and welded joints, creep-fatigue properties, and microstructure evolution during exposure at such elevated temperatures. The main shortcomings of actual 9-12Cr high-chromium steels are that the creep resistance is not enough to fulfill the engineering requirements at temperatures higher than 600°C and the material undergoes a cyclic softening. Creep strength at high temperature could be improved by a microstructural optimization through nano-precipitation, guided by computational thermodynamics, and thermomechanical control process optimization.

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“…Meanwhile, the TMCP principle to get fine microstructures has also been used for low and medium carbon bainitic steels, high strength bainitic steel, Dual Phase steel, precipitation hardened ferritic‐pearlitic steel, TRIP‐Steel, medium carbon steels, Spring steels, eutectoid and bearing steels, Mn‐Hadfield‐steel, over‐eutectoid steel, Creep resistant 9%Cr‐steel, and stainless steels . Automotive sheet metals are also TM‐rolled to obtain fine microstructures before cold rolling and annealing, but they will be treated in another paper of this issue.…”

Section: Successful Tmcp Applications For Flat Productsmentioning

confidence: 99%

Thermomechanical Treatment of Steels - A Real Disruptive Technology Since Decades

Buchmayr

2017

steel research int.

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The basic concept of thermomechanical treatment (TMT) or thermomechanical controlled processing (TMCP) is responsible for the development of many advanced steel grades with improved mechanical properties during the last 50 years. A retroperspective view, an explanation of the most important influencing factors and a presentation of the enormous benefits for the costumer are given in this review. A sound knowledge on the synergism of recrystallization, precipitation, and transformation phenomena forms the basis to produce fine, homogeneous microstructures with improved properties. Starting from structural steels, improvements can be achieved with respect to higher strength and toughness values combined with better weldability and formability, mainly based on reduction of carbon content and finer grain sizes. The benefits in the application areas are described in detail. TMCP is not only used for flat products, but also for long products and forgings of different steel grades. Physical simulation and modeling contribute significantly to these developments, which also form the basis for computer-aided control or real-time online-models. In the next years, a complete shift to cyber physical systems (CPS) is predicted, which needs an aligned education effort. REVIEW A Brief Historical ReviewSince the mid-sixties, steel mills began to produce fine grained structural steels by lowering the final rolling temperature. Based on fundamental research in Germany, USA, UK, Germany, and Japan, the fundamental understanding was further developed in metallurgical laboratories. Pioneers at that time were Haneke, [10] Schmidtmann, [11,12] Meyer, [13,14] Kaspar, [15][16][17][18][19][20][21][22][23][24] Streißelberger, [9,15,[25][26][27] DeArdo, [28,29] Jonas, [30][31][32][33] Sellars, [34][35][36][37] Hodgson, [38][39][40][41][42] Tamura und Tanaka, [43] Saito, [44] Ouchi, [45] Militzer, [46,47] and many others. The basic idea was to improve the strength and toughness behavior of structural steels by grain refining. Compared to conventional hot rolling at high rolling temperatures, the new steels were rolled at lower final rolling temperature. It was found that repeated recrystallization of the austenite structures leads to a decrease of grain size, but there is a limit, which is difficult to overcome. Deformation at temperatures, where no recrystallization takes place was successful in the conditioning of austenite having a dense population of glide planes, high dislocation density, and a high intrinsic energy, which provided a high density of nucleation sites for the transformation products of austenite.At the beginning, mainly ferrite plus pearlite microstructures were considered and later the role of rapid cooling became an additional opportunity to increase the strength level.Higher cooling rates or higher undercooling increase the driving force and with a lower diffusivity a finer microstructure like bainite and martensite can be reached.A comparison of the contributions of the strengthening mechanism in a commercial hot rolle...

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A roadmap for tailoring the strength and ductility of ferritic/martensitic T91 steel via thermo-mechanical treatment

Cited by 86 publications

References 74 publications

Estudio de la microestructura de un cordón de soldadura de un acero P91 mediante microscopía electrónica de transmisión

Estudio de la microestructura de un cordón de soldadura de un acero P91 mediante microscopía electrónica de transmisión

High-Chromium (9-12Cr) Steels: Creep Enhancement by Conventional Thermomechanical Treatments

Thermomechanical Treatment of Steels - A Real Disruptive Technology Since Decades

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