Role of Long Term Ageing on the Creep Life of Type 316H Austenitic Stainless Steel Bifurcation Weldments

2016 ◽  
Author(s):  
Ana I. Martinez-Ubeda ◽  
Ian Griffiths ◽  
Oliver D. Payton ◽  
Charles M. Younes ◽  
Tom B. Scott ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Chemical Composition ◽  
Austenitic Stainless Steel ◽  
Grain Boundary ◽  
Creep Damage ◽  
M23c6 Carbide ◽  
Boiler Tube ◽  
Boundary Length

Intergranular creep cracks have been observed in the heat affected zone of the 316H austenitic stainless steel superheater boiler tube bifurcation weldments after long term service at temperature of ∼550°C. The cracking mechanism is believed to be creep dominated. Moreover, chemical composition of defective material compared with similar uncracked components suggests that composition influences susceptibility to creep cracking. A systematic characterization of ratios number of creep cavities/grain boundary length and inter-granular precipitation length/grain boundary length has been undertaken in HAZ of three samples extracted from plants with different specific compositions. Here, the role of precipitation on creep deformation and fracture is explored. Precipitates of both ferrite and M23C6 carbide arising from long term service and associated creep cavitation have been identified using transmission electron microscopy. The creep damage and cracking, and therefore overall service life creep, is discussed by consideration of susceptibility of creep cavity nucleation and subsequently growth arising from specific differences in the chemical composition of the three boiler tube bifurcations.

The Significance of Thermo-Mechanical Fabrication on Long Term Creep Life of Type 316H Austenitic Stainless Steel Components

2016 ◽  
Vol 853 ◽  
pp. 384-388
Author(s):  
Ana Isabel Martinez-Ubeda ◽  
Alexander D. Warren ◽  
Ian Griffiths ◽  
Peter E.J. Flewitt
Keyword(s):  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Nuclear Power ◽  
Energy Dispersive Spectrometer ◽  
Creep Damage ◽  
Ion Milling ◽  
Creep Life ◽  
Thin Foils ◽  
The Impact

The UK’s Advanced Gas Cooled Reactor (AGR) nuclear power generating plant operates at temperatures up to 550 °C, where creep life is important. We consider Type 316H austenitic stainless steel headers and tubes with thermo-mechanical fabrication histories that result in significantly different initial microstructures. The heat affected zone of weldments, in these thick section headers and thin walled boiler tubes, have been found to be susceptible to creep damage leading to cracking during service. In this work we explore these differences in the long term service aged microstructure and the link to overall creep life of these components. To achieve this, samples containing weldments have been removed from plant after extended periods of service. Specifically parent and HAZ regions have been examined to determine the types of precipitates arising from the long term ageing. In particular, thin foils have been examined in a JEOL ARM transmission electron microscope operating at 200KeV fitted with an Oxford Instruments energy dispersive spectrometer to allow comparison between high resolution images and chemical composition. The thin foils were removed from predetermined locations using gallium ion milling and finally thinned using a low ion current to minimise ion damage. Differences between the distributions and types of precipitates are considered in the context of the initial microstructure arising from the thermo-mechanical history on the loss of creep strength and initiation of creep cavities at grain boundaries. The impact on overall service life is addressed.

Sensitization control in AISI 316L(N) austenitic stainless steel: Defining the role of the nature of grain boundary

2009 ◽  
Vol 51 (9) ◽  
pp. 2144-2150 ◽  
Author(s):  
N. Parvathavarthini ◽  
S. Mulki ◽  
R.K. Dayal ◽  
I. Samajdar ◽  
K.V. Mani ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Grain Boundary ◽  
Aisi 316L

Origin and Role of Σ3 Boundaries during Thermo-Mechanical Processing of a Ti-Modified Austenitic Stainless Steel

2011 ◽  
Vol 702-703 ◽  
pp. 714-717 ◽  
Author(s):  
Sumantra Mandal ◽  
A.K. Bhaduri ◽  
V. Subramanya Sarma
Keyword(s):  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Grain Boundary ◽  
Hot Deformation ◽  
Cold Deformation ◽  
Grain Boundary Engineering ◽  
Annealing Twins ◽  
High Fraction ◽  
Deformation Tests

The origin and role of S3 boundaries during dynamic recrystallization (DRX) and grain boundary engineering (GBE) of a Ti-modified austenitic stainless steel (alloy D9) is studied. Hot deformation tests were carried out on solution-annealed (SA) specimens to study the DRX behavior whereas a series of cold deformation and annealing were performed on SA specimens to realize GBE microstructure. A linear relationship between the area fraction of DRX and the number fraction of Σ3 boundaries was observed during hot deformation. This high fraction of Σ3 boundaries could account for the formation of coherent annealing twins by “growth accidents” during DRX. For certain combinations of cold deformation and annealing, a significant increase in S3 boundaries was observed. In contrast to hot deformation, majority of these new S3 boundaries during cold deformation and annealing were formed by geometrical interactions between the pre-existing Σ3 boundaries. The role of the S3 boundaries during DRX and on tailoring microstructure through grain boundary engineering approach is discussed.

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