Microstructure and creep characteristics of dissimilar T91/TP316H martensitic/austenitic welded joint with Ni-based weld metal

Journal Article · Mon Oct 15 04:00:00 EDT 2012 · Materials Characterization

DOI:https://doi.org/10.1016/J.MATCHAR.2012.06.014· OSTI ID:22163132

Falat, Ladislav ^[1]; Svoboda, Milan ^[2]; Vyrostkova, Anna; Petryshynets, Ivan; Sopko, Martin ^[1]

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1. Institute of Materials Research, Slovak Academy of Sciences, Watsonova 47, 040 01 Kosice (Slovakia)
2. Institute of Physics of Materials, Academy of Sciences of Czech Republic, Zizkova 22, 616 62 Brno (Czech Republic)

This paper deals with characterization of microstructure and creep behavior of dissimilar weldment between the tempered martensitic steel T91 and the non-stabilized austenitic steel TP316H with Ni-based weld metal (Ni WM). Microstructure analyses were performed using light microscopy, scanning and transmission electron microscopy and energy-dispersive X-ray spectroscopy. The martensitic part of the welded joint exhibited a wide heat-affected zone (HAZ) with typical microstructural gradient from its coarse-grained to the fine-grained/intercritical region. In contrast, the HAZ of austenitic steel was limited to only a narrow region with coarsened polygonal grains. The microstructure of Ni WM was found to be very heterogeneous with respect to the size, morphology and distribution of grain boundaries and MC-type precipitates as a result of strong weld metal dilution effects and fast non-equilibrium solidification. Cross-weld creep tests were carried out in a temperature range from 600 to 650 Degree-Sign C at applied stresses from 60 to 140 MPa. The obtained values of apparent stress exponents and creep activation energies indicate thermally activated dislocation glide to be the governing creep deformation mechanism within the range of used testing conditions. The creep samples ruptured in the T91 intercritical HAZ region by the 'type IV cracking' failure mode and the creep fracture mechanism was identified to be the intergranular dimple tearing by microvoid coalescence at grain boundaries. The TEM observations revealed pronounced microstructural differences between the critical HAZ region and the T91 base material before as well as after the creep exposure. - Highlights: Black-Right-Pointing-Pointer Phase transformations affect the microstructures of T91 and TP316H HAZ regions. Black-Right-Pointing-Pointer High weld metal dilution results in heterogeneous microstructure with MC carbides. Black-Right-Pointing-Pointer Creep behavior of the studied weldment is controlled by its martensitic T91 part. Black-Right-Pointing-Pointer The lowest hardness of T91 ICHAZ region corresponds with its lowest creep strength.

• OSTI ID: 22163132
• Journal Information: Materials Characterization, Journal Name: Materials Characterization Journal Issue: Complete Vol. 72; ISSN 1044-5803; ISSN MACHEX
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
AUSTENITIC STEELS
CREEP
DEFORMATION
FRACTURES
GRAIN BOUNDARIES
HEAT AFFECTED ZONE
MARTENSITIC STEELS
TRANSMISSION ELECTRON MICROSCOPY
WELDED JOINTS
X-RAY SPECTROSCOPY