Počítačové simulace svarových spojů žárupevných ocelí

Computer Simulation of Heat-Resistant Steels Welds

conference paper

en

Structural stability is one of the substantial characteristics of materials that are used for long-term operation at elevated temperatures. It can be inferred from a comparison of an actual structural state with the equilibrium state. In the case of heat-resistant steels, the equilibrium state of their structure can be established via calculation using the CALPHAD method and a corresponding database, e.g. the Steel 13 database. Structural stability of heterogeneous weld joints can additionally be affected by redistribution, the redistribution of interstices in the first place. The Thermo-Calc and DICTRA program files provide for determining both the chemical composition profile across the weld joint and the phase composition profile. Knowing the evolution with time of the two above profiles enables judging the residual service life of weld joints and of whole structures and facilities. The paper gives the results of an experimental study (chemical composition profiles -of carbon in particular – established by the WDS method, and results of structural analyses in decarburized and carburized areas) of laboratory weld joints of the 6CrMoV 8-3-2 and X12CrMoVNb 10-1 steels annealed in a temperature interval from 500 to 900 C. A pronounced up-hill diffusion of carbon and the related decarburization of the 6CrMoV 8-3-2 steel and, conversely, the carburization of the X12CrMoVNb 10-1 steel have been confirmed also by calculation, which is in qualitative agreement with the structural changes observed.

Strukturní stabilita je velmi důležitou charakteristikou žárupevných ocelí pracujích při vysokoteplotní expozici. Strukturní stálost může být určena porovnáním aktuálního strukturního stavu se stavem v termodynamické rovnováze. V případě žárupevných ocelí ji lze určit výpočtem využitím metody CALPHAD a odpovídajících termodynamických a kinetických databází. Strukturní stabilita je velkou měrou ovlivňována redistribucí intersticiálních prvků, zejména redistribucí uhlíku. Pro tyto výpočty se využívá program DICTRA. Tento příspěvek popisuje porovnání experimentálního měření a modelových výpočtů redistribuce uhlíku a fázového složení ve svarových spojích nízkolegované oceli T25 a modifikované oceli P91 žíhaných od 500 do 900C.

Structural stability is one of the substantial characteristics of materials that are used for long-term operation at elevated temperatures. It can be inferred from a comparison of an actual structural state with the equilibrium state. In the case of heat-resistant steels, the equilibrium state of their structure can be established via calculation using the CALPHAD method and a corresponding database, e.g. the Steel 13 database. Structural stability of heterogeneous weld joints can additionally be affected by redistribution, the redistribution of interstices in the first place. The Thermo-Calc and DICTRA program files provide for determining both the chemical composition profile across the weld joint and the phase composition profile. Knowing the evolution with time of the two above profiles enables judging the residual service life of weld joints and of whole structures and facilities. The paper gives the results of an experimental study (chemical composition profiles -of carbon in particular – established by the WDS method, and results of structural analyses in decarburized and carburized areas) of laboratory weld joints of the 6CrMoV 8-3-2 and X12CrMoVNb 10-1 steels annealed in a temperature interval from 500 to 900 C. A pronounced up-hill diffusion of carbon and the related decarburization of the 6CrMoV 8-3-2 steel and, conversely, the carburization of the X12CrMoVNb 10-1 steel have been confirmed also by calculation, which is in qualitative agreement with the structural changes observed.

DICTRA, structural stability, simulation, phase profile

06.09.2004

DGM

Lausanne, Switzerland

JUNIOR EUROMAT 2004

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