Microstructural zones in the primary solidification structure of weldment of 9Cr-1Mo steel

Vijayalakshmi, M.; Saroja, S.; Paul, V. Thomas; Mythili, R.; Raghunathan, V.S.

doi:10.1007/s11661-999-0204-8

Cited by 27 publications

(20 citation statements)

References 11 publications

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“…This suggests that some carbides could start to dissolve into austenite for higher peak temperatures. This result is consistent with literature data 29,30) obtained by TEM measurements of the carbide lattice parameters together with mass conservation, showing that in such thermal conditions, significant dissolution of carbides only starts for peak temperatures higher than 1 000°C. This slow dissolution of carbides is due to the fast heating and cooling rates in the weld thermal cycles and to carbon trapping in MX precipitates.…”

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confidence: 93%

High Temperature Creep Flow and Damage Properties of the Weakest Area of 9Cr1Mo-NbV Martensitic Steel Weldments

2005

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In the present study, creep flow and damage behaviour of modified P91 steel weldments are investigated. Premature creep failure of weldments (with respect to base metal) occurs in the intercritical heat affected zone (ICHAZ). This microstructure is reproduced by thermal simulation applied to blanks cut from the base metal. Metallurgical investigations of what happens during the welding cycle show that the weakest part of the heat affected zone is heated slightly below complete austenitisation, with little (if any) carbide dissolution. During the post-weld heat treatment, extensive recovery is allowed by carbide coarsening. The intrinsic creep behaviour of the resulting microstructure is experimentally determined under controlled constraint conditions. The welding cycle strongly decreases the creep strength by increasing the creep strain rate, but not necessarily by decreasing the ductility, at least for lifetimes up to 3 500 h.KEY WORDS: 9Cr1Mo-NbV martensitic steel; intercritical heat affected zone; Gleeble 1 500 thermalmechanical simulator; High temperature creep flow and damage.in the microstructure of interest was not known, just as for cross-weld specimens. The key point of the present study is thus to determine the properties of the weakest HAZ while eliminating, as much as possible, the constraint effects due to the surrounding materials. Material and Experimental Procedures MaterialsThe study focuses on a V-shaped, circumferentially welded joint of two pipes of 295 mm in outer diameter and 55 mm in thickness. It was fabricated by submerged metal arc welding in seventeen runs followed by a post weld heat treatment (PWHT) of 2 h at 760°C. The base metal is a tempered, modified P91 martensitic steel (see Table 1 for chemical composition). Its microstructure consists of lath martensite packets with M 23 C 6 (100 nm in mean size) and MX precipitates. The filler metal has nearly the same chemical composition as the base metal (Table 1). Simulation of Welding Thermal CyclesWelding thermal cycles were applied by using a Gleeble 1 500 thermal-mechanical simulator capable of heating specimens by Joule effect at very high heating rates, corresponding to those encountered in welding conditions (i.e. 100 to 250°C · s Ϫ1). The temperature is controlled by a thermocouple spot welded onto the specimen surface. Round bars of 5 mm in diameter were used to optimise the thermal cycle and 12 mm round blanks were treated and used to machine mechanical testing specimens respectively. For each of these two geometries, the closed-loop parameters of the Gleeble 1 500 simulator were carefully adjusted in order to ensure an uncertainty lower than 2°C for the value of T peak and smaller than 1 s for the value of the cooling parameter Dt 800→500 . For specimens of 5 mm in diameter, phase transformations were continuously monitored using in-situ dilatometric measurement of the specimen diameter. To prevent from extensive oxidation of the specimen, heat treatments were performed under primary vacuum (0.1 Pa). Phase transformations moni...

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Section: )supporting

confidence: 93%

High Temperature Creep Flow and Damage Properties of the Weakest Area of 9Cr1Mo-NbV Martensitic Steel Weldments

2005

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“…A medida que aumenta la distancia desde el MS las temperaturas alcanzadas son menores, de manera que en la ZACGF apenas es superada la temperatura de austenización y los precipitados no se disuelven completamente frenando el crecimiento de grano [2]. Luego del enfriamiento y posterior PWHT se obtuvo una estructura refinada de martensita revenida de una dureza menor a la de la ZACGG.…”

Section: Ms(v): Barrido Vertical Ms(h): Barrido Horizontalunclassified

“…Perfiles de microdureza de las juntas soldadas intercrítica (Ac 1 <T<Ac 3 ) se produce la transformación de la ZACIC, en la cual los precipitados no se disuelven pero pueden crecer y la estructura puede resultar con ferrita proeutectoide [2], producto de la transformación en la zona dúplex (austenita +ferrita) (Figura 1). En esta zona se obtuvieron las menores durezas de la ZAC, tanto para las probetas PMo como para las PMoW, siendo aún menores que las del metal base; este fenómeno se presentó para los dos PWHT con una leve tendencia a menores valores de dureza para el T2.…”

Section: Ms(v): Barrido Vertical Ms(h): Barrido Horizontalunclassified

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Caracterización de soldaduras circunferenciales de aceros avanzados 9Cr: parte 1

et al. 2014

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ResumoOs aços 9%Cr são amplamente utilizados à alta temperatura, principalmente em aplicações relacionadas à geração de energia. Ultimamente têm sido desenvolvidas variantes desses materiais incorporando B, W e Co, entre outros elementos, ao sistema de liga. Devido à escassez de informação sobre a influência do procedimento de soldagem sobre a junta soldada, neste trabalho se estudou o comportamento do metal base e do metal de solda em juntas circunferências soldadas com dois consumíveis diferentes pelo processo de soldagem semi-automático FCAW, sob proteção gasosa de Ar/20%CO 2 . Realizaram-se tratamentos térmicos pós-soldagem a 760°C durante 4 e 2 horas. Utilizaram-se dois arames tubulares de escória rutílica, ligados ao 9Cr1Mo e 9Cr0,5Mo1WCo. Analisou-se a microestrutura nas zonas do metal de solda, afetada pelo calor (zonas de grão grosso, grão fino, intercrítica e subcrítica) e metal base. Determinaram-se a composição química do metal de solda e as propriedades de tração transversal da junta, e realizaram levantamento do perfil de microdureza. Em todos os casos se observaram valores máximos de dureza na zona correspondente ao metal de soldadura e uma diminuição na zona afetada pelo calor desde a zona de grão grosso até o metal base, obtendo se valores mínimos na zona intercrítica, inferiores aos correspondentes ao aço base. Tanto a dureza como a resistência à tração aumentaram quando foi utilizado o arame 9Cr0,5Mo1W. O tratamento térmico mais curto permitiu alcançar maior resistência em todos os casos. Numa próxima etapa se fará as medições de tenacidade e de resistência ao creep. Palavras-chave: Aço 9Cr; Tratamento térmico pós-soldagem; Microestrutura; Junta soldada; Arames tubulares.Abstract: 9Cr steels are widely used for high temperature service, principally in applications related to energy generation. Lately several variants of these materials have been developed through the addition of B, W and Co, among others. Due to the fact that information on influence of welding procedure on the welded joint is scarce, the objective of this work was to study the behavior of both the base metal and the weld metal of circumferential weldments performed using semiautomatic welding process under gas mixture protection. Two FCAW rutilic slag wires, alloyed with 9Cr1Mo and 9Cr0.5Mo1W1Co respectively, were used under Ar/20%CO 2 gas shielding. Post weld heat treatments of 4 and 2 hours have been carried out. The microstructure was analyzed in the different zones: weld metal, heat affected (coarse and fine grain, intercritical and subcritical) and not affected base metal. Chemical composition of the weld metal, transversal tensile properties of the joint and microhardness along the weld transversal section were determined. In all cases it was obtained maximum hardness values in the weld metal and a decrease in this property in the heat affected zone from the coarse grain zone to the base metal one. The minimal hardness values were achieved in the intercritical zone, lower than those of the metal base. Hardness and tensi...

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“…[20] However, in fusion welding, the weldment would possess a highly heterogeneous microstructure depending on the distance of a region from the heat source and number of passes employed. [21,22] Since it is the microstructure that decides the response of a weldment to stresses subsequent to post-weld heat treatment or during long-term service exposures [23,24] many experimental studies focused on the change in structure and property of weld and HAZ upon varying the heat input and cooling rates during welding. [25,26] Recently, genetic algorithm-based computation was attempted for optimizing the chemistry of RAFM steels in order to achieve desired volume fraction and coarsening rate of M 23 C 6 carbides and Laves phase.…”

Section: Introductionmentioning

confidence: 99%

Influence of Alloy Content and Prior Microstructure on Evolution of Secondary Phases in Weldments of 9Cr-Reduced Activation Ferritic-Martensitic Steel

Paul

Sudha

Saroja

2015

Metall Mater Trans A

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9Cr-Reduced Activation Ferritic-Martensitic steels with 1 and 1.4 wt pct tungsten are materials of choice for the test blanket module in fusion reactors. The steels possess a tempered martensite microstructure with a decoration of inter-and intra-lath carbides, which undergoes extensive modification on application of heat. The change in substructure and precipitation behavior on welding and subsequent thermal exposure has been studied using both experimental and computational techniques. Changes i.e., formation of various phases, their volume fraction, size, and morphology in different regions of the weldment due to prolonged thermal exposure was influenced not only by the time and temperature of exposure but also the prior microstructure. Laves phase of type Fe 2 W was formed in the high tungsten steel, on aging the weldment at 823 K (550°C). It formed in the fine-grained heat-affected zone (HAZ) at much shorter durations than in the base metal. The accelerated kinetics has been understood in terms of enhanced precipitation of carbides at lath/grain boundaries during aging and the concomitant depletion of carbon and chromium and enrichment of tungsten in the vicinity of the carbides. Therefore, the fine-grained HAZ in the weldment was identified as a region susceptible for failure during service.

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Microstructural zones in the primary solidification structure of weldment of 9Cr-1Mo steel

Cited by 27 publications

References 11 publications

High Temperature Creep Flow and Damage Properties of the Weakest Area of 9Cr1Mo-NbV Martensitic Steel Weldments

High Temperature Creep Flow and Damage Properties of the Weakest Area of 9Cr1Mo-NbV Martensitic Steel Weldments

Caracterización de soldaduras circunferenciales de aceros avanzados 9Cr: parte 1

Influence of Alloy Content and Prior Microstructure on Evolution of Secondary Phases in Weldments of 9Cr-Reduced Activation Ferritic-Martensitic Steel

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