The influence of hydrogen charging on the room-temperature tensile properties and fracture behaviour of two dissimilar weld joints has been investigated. The weld joints were either ferritic/ferritic ...(T91/STN15128) or ferritic/austenitic (T91/TP316H). The tensile tests were carried out using the samples with a circumferential notch. The position of notch was individually located in different weld joint regions, either in the heat-affected zones (HAZ) or weld metal (WM). The application of hydrogen charging had detrimental effect on strength and plasticity of the weld joint T91/STN15128. The most significant deterioration of the notch tensile properties was measured for the STN15128 HAZ. The hydrogen charging had only small influence on the strength of the weld joint T91/TP316H but remarkable detrimental effects on the plasticity. In the PWHT state (without hydrogen charging) all regions of the studied weld joints fractured by ductile dimple tearing. The failure initiated on the secondary phase particles and/or inclusions as well. In contrast, the failure after hydrogen charging initiated in the vicinity of sizeable particles and showed a transition from the ductile dimple tearing to the transgranular cleavage and/or quasi-cleavage fracture mode.
It has been shown that particles of M
6C in Cr–Mo–V low alloy steels can influence phosphorus grain boundary segregation in a similar manner to Laves phase particles in 12CrMoV steel. The influence ...of these particles arises from their ability to dissolve non- metallic elements such as phosphorus and silicon. As phosphorus is progressively segregated to the grain boundaries during prolonged ageing, the precipitation of M
6C particles leads to an anomalous decrease in the phosphorus grain boundary concentration as the ageing time is extended. This phenomenon originally observed for the Laves phase in long-term aged 12CrMoV steel at temperatures of 753, 773, and 803 K has now been observed for M
6C carbide in a 2.5Cr–0.4Mo–0.25V low alloy steel aged at 853 K.
The paper presents results of thermodynamic analysis of phosphorus grain boundary segregation in 17Cr12Ni austenitic steel annealed for 1000 h at 923, 973 and 1073 K. With respect to values of ...compensation temperature
τ
P=930 K and segregation enthalpy
ΔH
P
0=−14.1 kJ/mol the analyzed interfaces were considered to be special grain boundaries.
The phosphorus segregation at temperatures of 773 and 853
K has been studied in two low-alloy Cr–0.4 Mo–0.5 V steels with different chromium contents (0.85 and 2.5
mass%). Segregation of elements on ...grain boundaries was measured by means of Auger electron spectroscopy. Transmission electron microscopy techniques were used for the identification of secondary phases in the steels investigated. A significant influence of aging temperature on the kinetics and equilibrium value of phosphorus grain-boundary concentration was observed. Both lower temperature and higher bulk chromium content were found to increase the grain-boundary phosphorus segregation. This is in agreement with the Langmuir–McLean theory, the model of phosphorus–carbon site competition, and also confirms the significant effect of carbide formation on phosphorus segregation in steels.
Three austenitic steels (18Cr-8Ni, 18Cr-10Ni, and 21Cr-30Ni) exploited for long periods of time at temperatures between 600°C and 800°C were investigated. In the investigation, electrochemical ...potentiokinetic reactivation-double loop (EPR-DL) and oxalic acid etch corrosion tests, metallography, scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, and energy-dispersive x-ray spectroscopy were used. In the severe sensitized 18Cr-8Ni steel, small, densely arranged intergranular particles, mostly of M23C6, were found. The 18Cr-10Ni steel was classified as less-sensitized compared to the 18Cr-8Ni steel as a result of the presence of larger, discrete grain boundary particles in addition to small, densely arranged particles. In the unsensitized 21Cr-30Ni steel, huge, discrete clusters often exceeding 10 μm were observed at the grain boundaries. The clusters were found to consist of large Cr-rich M23C6 and small Ti-rich MC particles.
The paper deals with the fracture analysis of thermally exposed 9Cr–1Mo ferritic steel after tensile and impact testing at room temperature. The temperatures of the thermal expositions were 580, 620, ...and 650
°C, respectively. The duration of annealing experiments varied from 500 to 5000
h. The influence of thermal expositions on Vickers hardness as well as tensile properties was found to be negligible. On the other hand, remarkable effects of the annealing on room temperature impact toughness were observed. Fracture behaviour of the 9Cr–1Mo steel is strongly affected by the presence of precipitates of secondary phases. Fracture surfaces of tensile samples indicate mainly transgranular dimple fracture mechanism. By contrast, the fracture mode of the samples after impact testing is more complex. It shows both – ductile dimple tearing as well as inter-lath decohesion.
This paper deals with the characterization of creep cracking types occurring in similar T92/T92 and dissimilar T92/TP316H welded joints produced by tungsten inert gas (TIG) welding. Both ...martensitic/martensitic and martensitic/austenitic weldments types were post-weld heat treated by tempering at 760 degreesC. Moreover, one separate series of T92/TP316H weldments was subjected to re-quenching from 1060degreesC into water and subsequent tempering at 760 degreesC. Afterwards, all the weldments were subjected to creep testing at 625 degreesC and 650 degreesC using initial applied stresses ranging from 80 MPa to 160 MPa. Depending on PWHT and creep testing conditions used, several failure modes have been observed, including cracking in T92 base material (T92 BM), type IV cracking in fine-grained intercritical heat-affected zone (HAZ), type III cracking in the fusion zone at the interface between T92 steel and Nibased weld metal (Ni WM), over-load cracking at T92/Ni WM interface and cracking in over-tempered T92 BM relating to subcritical HAZ failure. Performed fracture path analyses combined with morphological observations of creep cracks and cavities in microstructures beneath fracture surfaces of creep-exposed specimens were essential for fracture mechanism determination.
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