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The purpose of this investigation was to evaluate the performance of high velocity oxy fuel (HVOF) coated SS-310 samples in a carburizing environment.

The carburization behavior of metallic coatings with three different compositions was studied under isothermal carburizing exposure conditions at 900°C for 125 hours. The coatings were deposited on SS 310 substrates using the HVOF technique. The ASTM Standard method was used to evaluate coating adhesion. Scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, X-ray diffraction and weight gain were used to evaluate the surface morphology, microchemical composition, phase constitution and degree of environmental protection imparted by the coatings.

The experimental results indicate that Ni-rich coating offered better protection to SS 310 alloy compared to Co-rich coatings in carburizing environments. This was thought to be due to the formation of a continuous protective layer of Cr₂O₃ on the Ni-rich coating surface.

The study has direct practical relevance to the petrochemical industry, particularly for refinery applications. In refinery service, SS310 is used in header damper plates. The useful service life of such header plates can be extended by the use of high temperature corrosion resistant metallic coatings. The present investigation highlighted the protection offered by Ni-based HVOF coated SS-310 samples in carburizing environment.

THE problem of oxidation is one that is an ever‐present source of trouble to the welder. It is particularly the case in aircraft construction, where light‐gauge metals are most frequently employed. There is also the complementary, though less obstinate, problem of carburization. Elimination of these can be effected to a certain extent by one or more of several methods. However, before dealing with their cure, some notes on the nature of oxidation and carburization may lead to a better understanding of the processes.

The purpose of this study is to verify how the carbon doping of the WC-Co cemented carbide (CC) affected their structure before their processing by hot isostatic pressing (HIP) technology.

The samples for this experiment were fabricated by selective laser melting technology (SLM) using a YAG fiber laser with a power of P = 40 W and a scanning speed of 83 mm/s. The subsequent carbon doping process was performed in a chamber furnace at 900 0 C for 1, 4 and 12 h. The HIP was performed at 1,390°C and pressures of 40 MPa, 80 MPa and 120 MPa. The changes induced in the structures were evaluated using X-ray diffraction and various microscopic methods.

X-ray diffraction analysis showed that the structure of the samples after SLM consisted of WC, W₂C, Co₄W₂C and Co phases. As a result of the increase in the carbon content in the structure of the samples, the transition carbide W₂C and structural phase Co₄W₂C decayed. Their decay was manifested by the coarsening of the minor alpha phase (WC), which occurred both during the carburizing process and during the subsequent processing using HIP. In the samples in which the structure was carburized prior to HIP, only the structural phases WC and Co were observed in most cases.

The results confirm that it is possible to increase the homogeneity of the CC structure and thus its applicability in practice by additional carburization of the sample structure with subsequent processing by HIP technology.

This paper reviews some of the important processes underlying high temperature degradation of structural materials used in the petroleum and petrochemical industries. Particular emphasis is palced in degradation processes involving the interaction of structural metals and alloys with environments containing sulfidizing, carburizing, and halogenizing species. In addition the effect of gaseous hydrogen environments at elevated temperatures and pressures on the mechanical properties of steels will be discussed. The mechanism of attack and the effect of alloying elements in these phenomena will be described and discussed.

The purpose of this paper is to produce cobalt (Co)-based thin films by metalorganic chemical vapor deposition (CVD) technique and then to evaluate structural and mechanical integrity.

Co-based thin films were produced by metalorganic CVD technique. Boronizing, carburization and nitridation of the produced Co thin films were accomplished through a post-treatment stage of thermal diffusion into as-deposited Co thin films, in order to produce cobalt boride (Co₂B), cobalt carbide and cobalt nitride thin films in the surface layer of Co. The surface topography and the crystal structure of the produced thin films were evaluated through scanning electron microscopy and X-ray diffraction, respectively. The mechanical integrity of the produced thin films was evaluated through nanoindentation technique.

The obtained results indicate that Co₂B thin film exhibits the highest nanomechanical properties (i.e. H and E), while Co thin film has enhanced plasticity. The cobalt oxide thin film exhibits higher resistance to wear in comparison to the cobalt thin film, a fact that is confirmed by the nanoscratch analysis showing lower coefficient of friction for the oxide.

This work is original.

The purpose of this paper is to present a case study of unexpected sensitization to intergranular corrosion of highly resistant AISI 321 steel in petrochemical conditions, where it was subjected to the simultaneous influence of elevated temperature of ∼250°C and vapors from the asphalt production process.

Corrosion coupons were exposed in an installation carrying asphalt vapors. To identify the susceptibility to intergranular corrosion a standard Strauss test was performed. Scanning electron microscopy (SEM) micrographs show a degree of degradation as a result of local corrosion. Influence of the carburization process occurred during exposure and depletion of chromium in the passive layer and was evaluated using X-ray photoelectron spectroscopy (XPS) and X-ray spectroscopy (EDX) techniques.

The paper provides information on origin of corrosion of AISI 321 steel in a high-carbon-containing environment. It was found out that long-term exposure can lead to intergranular corrosion in temperatures that are much lower than those that have been considered to be required for sensitization of austenitic steels. The high concentration of carbon introduced during the exposure is stated to be responsible for this effect.

The formation of chromium carbides, leading to intergranular corrosion of the Type 321 stainless steel, is a major concern. The paper reports that in certain petrochemical environments, highly resistant stainless steels, such as AISI 321, can be susceptible to intergranular carbide degradation.

The presence of titanium is not sufficient to increase resistance in multiple environments and sensitization can occur even at relatively low temperatures of ∼250°C.

Inconel alloy 625 Inconel alloy 625 is a nickel‐chromium alloy strengthened by additions of molybdenum and niobium, with excellent high tensile, creep and rupture strength with good resistance to carburisation and oxidation, and is readily fabricated using normal industrial processes. It has a high resistance to a wide range of corrosive environments, particularly oxidising chlorides, is virtually immune to stress‐corrosion cracking and intergranular corrosion and can be used from cryogenic temperatures up to 1,100°C.

Other Industrial Gases All oxidising gases can lead to oxide formation on chromium steels at elevated temperatures and in some instances this can be associated with absorption of some other substance in the steel. Carbonaceous gases are a good example and whereas high‐alloy steels successfully resist flue gases even under conditions of considerable air deficiency, reduction of oxygen content eventually leads to conditions under which at a sufficiently high temperature considerable carburisation of the metal occurs. An example is the endothermic gases used as protective atmospheres for other metals which, at elevated temperature, can rapidly cause embrittlement of high‐alloy steel.

The paper summarises the merits and limitations of different methods used to determine the rejection criteria of the primary reformer tubes. It compares the microstructures as obtained on the outer surface of the reformer tubes with that observed in the transverse section in the regions of outer wall, midwall and inner surface. On the basis of these studies coupled with dimensional change measurements, the in situ metallographic technique has been used to monitor the condition of tubes in two reformation units and the tubes had given satisfactory service till the next turnaround as predicted.

The purpose of this paper is to investigate, the effects of residual stress and microstructure on the corrosion behaviour of carburised 18CrNiMo7-6 steel in a 3.5% NaCl aqueous solution.

The electrochemical tests were conducted using an electrochemical workstation with a three-electrode system in a 3.5% NaCl aqueous solution, the residual stress of each working face was measured by a high-speed residual stress analyser, and microstructure of different carburised layers were observed scanning electron microscopy. Finally, the effect of carbon content, microstructure and residual stress on the corrosion behaviour of the steel was discussed.

The results showed that the residual compressive stress in the carburised layer initially increased and subsequently decreased with increasing depth of the carburised layer, reaching stability in the matrix layer. The electrochemical tests before and after stress reduction showed that the electrochemical impedance and the electrochemical potential increased with the reduction of residual compressive stress.

The residual compressive stress in the carburised layer initially increases and subsequently decreases with increasing carburised layer depth. The electrochemical impedance and the electrochemical potential increased with the reduction of residual compressive stress. The general relationship between electrochemical potential and residual stress was established.