KMITL

Permanent URI for this communityhttps://dspace.kmitl.ac.th/handle/123456789/1

Browse

Search Results

Now showing 1 - 9 of 9

Some of the metrics are blocked by your
consent settings
Microstructure and high-temperature oxidation behaviour of AISI 304L stainless steel welds produced by gas tungsten arc welding using the Ar–N2–H2shielding gas
(2025-01-01)
Chueaprakha, Sompong
;
Thublaor, Thammaporn
;
Siripongsakul, Thamrongsin
;
Wiman, Panya
;
Chandra-Ambhorn, Walairat
In the present work, we added 1.5 and 5% v/v hydrogen gas to an Ar–7% N<inf>2</inf> shielding gas for the gas tungsten arc welding of AISI 304L stainless steel to investigate its effect on the weld microstructure and oxidation rate. By using Ar–7% N<inf>2</inf> as a shielding gas, the weld metal contained 2.1% of delta ferrite in an austenite matrix. The addition of 1.5 and 5% hydrogen gas in the shielding gas provided the welds with a higher ratio of delta ferrite to austenite matrix, ranging from 3.8 to 6.9%, thus helping reduce the risk of hot cracks. The weld metals were further subjected to an oxidation test in synthetic air at 700°C, and the parabolic oxidation kinetics were observed. The parabolic rate constant of the weld metal produced using the Ar–7% N<inf>2</inf> shielding gas was 5.44 × 10–13 g2 cm–4 s–1. When 1.5 and 5% hydrogen gas was added to the Ar–7% N<inf>2</inf> shielding gas, the rate constants were reduced to 64% and 24% of that of the weld produced using only Ar–7% N<inf>2</inf> shielding gas, indicating the promising role of the presence of hydrogen in the Ar–7% N<inf>2</inf> shielding gas on improving the weld metal oxidation resistance for high temperature services.
Some of the metrics are blocked by your
consent settings
Possibility of metallic cobalt formation in the oxide scale during high-temperature oxidation of Co-27Cr-6Mo alloy in air
(2023-01-01)
Wongpromrat, Patthranit
;
Tunthawiroon, Phacharaphon
;
Bumrungthaichaichan, Eakarach
;
Ponpo, Phisan
;
Nilsonthi, Thanasak
Co-based alloys are known to be high oxidation-resistant material and used in several high temperature applications. During high temperature oxidation, duplex oxides containing Co and Cr were formed. It was thermodynamically elucidated that when the growing scale was thick enough, the partial pressure of O<inf>2</inf> in the scale dropped. Then, the reduction of CoO occurred for promoting O<inf>2</inf> which was responsible for Cr<inf>2</inf>O<inf>3</inf> production. This work experimentally proved this point by in situ char-acterising Co-27Cr-6Mo at high temperatures in air by X-ray diffractometer in a grazing incident mode and metallic Co was confirmed to be formed by the reduction of CoO consistent with the image taken and analysed by field emission scanning electron microscope, energy-dispersive X-ray, and electron backscatter diffraction. Furthermore, the change in lattice parameter and the phase transition were observed when the temperature was altered.
Some of the metrics are blocked by your
consent settings
Effect of water vapour on the high temperature oxidation of stainless steels
(2020-01-01)
Chandra-Ambhorn, Somrerk
;
Wongpromrat, Patthranit
;
Thublaor, Thammaporn
;
Chandra-Ambhorn, Walairat
This chapter primarily reviews the nature of water vapour when it presents in bulk gas. The change in a ratio between water vapour and corresponding dissociated hydrogen, which determine the thermodynamic stability of the oxide formation, is analysed when the oxidation kinetics are linear and parabolic. When water vapour reaches the solid/gas interface, chromium species volatilisation and oxidation controlled by surface reaction can occur. The adsorbed water vapour can be further incorporated into the oxide possibly in the form of hydrogen defects. The role of these defects on altering the defect structure of the oxide is discussed. Finally, characteristics of the oxide scale on stainless steels formed in the atmosphere containing water vapour are reviewed.
Some of the metrics are blocked by your
consent settings
Development of sofc interconnect stainless steels
(2020-01-01)
Chevalier, Sébastien
;
Combemale, Lionel
;
Popa, Ioana
;
Chandra-Ambhorn, Somrerk
;
Chandra-Ambhorn, Walairat
The chapter introduces components and working principle of solid oxide fuel cells (SOFCs). It is followed by the explanation on the choices of materials focussing on ferritic stainless steels. The review is further made on the required properties of these steels, i.e. low oxidation rate, low chromium species volatilisation rate, high electrical conductivity and good scale adhesion. For the oxidation aspect, the behaviour of stainless steel interconnect in cathode, anode (hydrogen and biogas), and dual atmospheres are described. Surface modification by pre-oxidation and coatings to improve the oxide electrical conductivity and to reduce chromium species volatilisation is finally reviewed.
Some of the metrics are blocked by your
consent settings
High temperature oxidation of stainless steels
(2020-01-01)
Chandra-Ambhorn, Somrerk
;
Hayashi, Shigenari
;
Latu-Romain, Laurence
;
Wongpromrat, Patthranit
This chapter is dedicated to the description of high temperature oxidation of both chromia and alumina forming alloys. The defect structures of iron and chromium are firstly reviewed. The effects of elements on stainless steel oxidation behaviour are further addressed. For the chromia-forming stainless steel, the oxidation rate is reduced with the increased silicon content but not in a monotonic manner. Titanium and niobium can reduce breakaway oxidation of Fe–18Cr–10Ni austenitic stainless steel. Titanium can enhance the adhesion of scale to the Fe–18Cr by mechanical keying effect of TiO2 formed at the steel/scale interface. For the alumina-forming stainless steel, the formation of alumina and its transformation during oxidation are reviewed. Chromium can be added to reduce the critical aluminium content in the steels in order to form alumina at high temperatures. The addition of reactive elements with appropriate level can improve scale adhesion and reduce the steel oxidation rate. Refractory element like molybdenum can increase strength of material but also accelerate the oxidation rate of the steels containing reactive elements. The development of new alumina-forming austenitic alloy grades is finally described.
Some of the metrics are blocked by your
consent settings
High temperature corrosion behaviour of aluminide-coated cast iron for an exhaust manifold application
(2020-01-01)
Kerdbua, Panya
;
Bidabadi, Mohammad Hassan Shirani
;
Chandra-Ambhorn, Walairat
;
Chandra-Ambhorn, Somrerk
To reduce the pollution emission from vehicles, an improvement on the combustion process is expected, leading to increased exhaust gas temperature. As a result, the development of new materials for an exhaust manifold used at higher temperatures is required. A cost-effective cast iron exhaust manifold treated by aluminising pack cementation was developed in the present work to combat the high temperature corrosion. Its kinetics under cyclic oxidation in N<inf>2</inf>-12%O<inf>2</inf>-10%H<inf>2</inf>O at 850 °C was parabolic with the rate constant (kp) of 5.66 × 10-12 g2 cm-4 s-1, about two orders of magnitude lower than that of the bare cast iron, which indicated the protectiveness of the applied coating. These results relate to the protective alumina formation for the aluminised cast iron and the formation of the less protective iron oxides for the bare cast iron after oxidation, as evidenced by the XRD and Raman spectroscopy results. The addition of 10% water vapour to N2-12%O2 thickened the aluminide layer from 344 μm for the sample oxidised in dry atmosphere to 409 μm for the sample oxidised humidified one. It accelerated the oxidation rate of the aluminised cast iron as the kp value increased by 8.5 times, and also increased the hardness of the aluminised surface, as it was 364 HV for the sample exposed to dry atmosphere and 420 HV for the sample exposed to humidified one. The latter result implied the possibility of the hydrogen dissolution into the metal surface. The roles of hydroxyl ion and dissolved hydrogen on the oxidation and evolution of the aluminide layer after exposure to water vapour were proposed.
Some of the metrics are blocked by your
consent settings
Advanced microstructural investigations of AISI 441 early stage oxidation in wet atmosphere
(2017-01-01)
Wongpromrat, Wichitra
;
Parry, Valérie
;
Chandra-Ambhorn, Walairat
;
Chandra-Ambhorn, Somrerk
;
Galerie, Alain
AISI 441 ferritic stainless steel is a good candidate for metallic interconnects in solid oxide fuel cells (SOFCs). The minor elements Ti and Nb are used to stabilize the ferritic matrix and also to reduce creep by a combination of solid solution strengthening and precipitation of intermetallic Laves phase particles along the grain boundaries. However their influence on the oxidation behavior is not well understood. This study focuses on the early stages oxidation (from 4 to 24 h) at 800°C of AISI 441 under 5% H<inf>2</inf>O in O<inf>2</inf>. A relatively smooth micro-crystallized oxide scale and Ti, Nb containing nodules are observed. The internal microstructure of these objects is studied by FIB tomography which allows computing cross sectional views in any direction of interest. FIB study reveals a complex microstructure and a development strongly linked to the presence of niobium and/or titanium in the substrate.
Some of the metrics are blocked by your
consent settings
Chromium vaporisation from AISI 441 stainless steel oxidised in humidified oxygen
(2013-06-01)
Wongpromrat, Wichitra
;
Thaikan, Harit
;
Chandra-Ambhorn, Walairat
;
Chandra-Ambhorn, Somrerk
Chromium vaporisation from chromia-forming alloys when exposed to high temperatures can deteriorate the protective property of oxide scale. This problem affects the lifetime of solid oxide fuel cells and solid oxide electrolysers using chromia-forming alloys as interconnectors. In this work, AISI 441, a commercial grade stainless steel which chromium vaporisation investigation has not been reported so far, was chosen for study. Chromium vaporisation rates of bare AISI 441 and AISI 430 and AISI 441 and AISI 430 coated with Mn-Co spinel by electroplating method were measured in an atmosphere of 5 % H<inf>2</inf>O in O<inf>2</inf> over the temperature range of 650-900 C with the linear velocity of the humidified oxygen stream varied in the range of 0.8-3.0 cm s-1. For uncoated samples, AISI 441 showed a lower chromium vaporisation rate in comparison with that of AISI 430. Mn-Co spinel coating could reduce the chromium vaporisation rate from AISI 430 surface. However, on the contrary, the Mn-Co spinel coating could not only fail to suppress the chromium vaporisation, but it also promoted the chromium vaporisation from AISI 441 surface by 2 times. © 2013 Springer Science+Business Media New York.
Some of the metrics are blocked by your
consent settings
Characterisation and pickling behaviour of thermal oxide scale on low carbon steel produced from a thin slab
(2011-01-01)
Chandra-Ambhorn, Somrerk
;
Somphakdee, Tanongsak
;
Chandra-Ambhorn, Walairat
Thin slab interested in this work was the one with the thickness of ca. 50 mm and mainly made from recycled steel. Chemical composition of the studied steel strip produced from such slab was Fe with 0.077 wt% C, 0.233 wt% Mn, 0.191 wt% Si, 0.159 wt% Cu and 0.052 wt% Ni. Scale retained on that steel after hot rolling was studied. The hot-rolled sample was pickled in 10%v/v HCl aqueous solution at 80 °C. Weight loss and relative XRD peaks of hematite-per-iron and magnetite-per-iron were measured at different pickling periods of time. It was observed that the as-received scale was crack-free. Hematite-and-iron ratio approached zero at the pickling time of 3 seconds. Magnetite-per-iron ratio gradually decreased with increased pickling time and approached zero later. These results indicated that pickling solution attacked the outermost hematite layer resulting in removing of this layer first. Sublayers of scale consisting of magnetite were completely pickled later. Pickling behaviour was not merely volumetric since scale was crack-free. Mechanical adhesion of scale on steel substrate was additionally investigated by tensile test to help characterise the oxide scale. © (2011) Trans Tech Publications.

KMITL

Browse

Filters

Settings

Sort By

Results per page

Search Results