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The purpose of this paper is to clarify the destabilisation mechanism that occurs with two types of ferritic corrosion‐resistant steel during the welding cycle.

A series of experimental weld joints was made to verify the actual response of non‐stabilised corrosion‐resistant steel, and of the same steel that had been stabilised by added titanium. The character and extent of the ensuing structural changes were analysed. The essential characteristics of degradation in the heat‐affected zone are evaluated using optical and scanning electron microscopy; individual phases are identified by means of EDX microanalysis. The underlying mechanism for the loss of stability is induced experimentally in several stages; depending on the thermal doping level and interaction with the environment during the welding process, phases of various types are precipitated. These phases subsequently are studied in connection with the original microstructural characteristics of the steel and the induced grain boundary decohesion of the surface layer. The scope and character of the damage are analysed and the results verified by analysing the actual operating damage to the weldment.

A degradation mechanism of stabilised corrosion‐resistant steel 1.4510 is induced that is associated with destabilisation of titanium phases. The importance is demonstrated of ensuring that a protective atmosphere is maintained during welding, and various phase changes in the surface layers are identified that can delimit the use of appropriate post‐weld passivation procedures.

Identification of the mechanism underlying the damage to the surface layer in welded stabilised ferritic steel will find application in development of welding technology, specifically in designing a technology process and subsequent surface treatment.

The results bring new knowledge of material response of steel 1.4510 under specific material processing conditions; a destabilisation mechanism related to precipitation of several titanium‐containing phases is identified. The result enables the fatigue limit of the welded material as a function of the welding technology employed, which offers increased service life under specific application conditions.

The purpose of this paper is to verify the capability of pigmented coatings to mitigate the effects of thermal sensitisation of 430 stainless steel.

Experimental weld joints of non‐stabilised ferritic corrosion resistant steel type AISI 430 were prepared. Protective coatings in several variants were applied to a number of weldments, subsequently subject to corrosion tests in SO₂ and NaCl. The anticorrosive efficiency of the coatings was evaluated by means of normative visual assessment and metallographic analysis of the mechanism and depth of corrosion damage.

Anticorrosive efficiency of the tested coatings was experimentally established under conditions where differences were identified in structural changes caused by welding, or resulting from mechanical damage to the coating. Differences in the progress of corrosion damage caused by phase changes in the heat‐affected zone were established.

Tests of anticorrosive efficiency of coatings of selected types provided information about possible reduction in sensitisation of welded non‐stabilised steel. The effect of the investigated processes on degradation of anticorrosive resistance was identified.

A specific effect of phase changes accompanying welding on the corrosion mechanism was described and so were the reasons underlying development of corrosion damage at visually identical character of surface damage.

To evaluate the corrosion resistance of four different stainless steels often employed in hot end exhaust components.

This paper evaluated the outcomes of the hot salt test and the cyclic oxidation test on four different stainless steels, used as hot end exhaust components. The specimens were analyzed by means of SEM for surface changes and the weight loss was considered.

The general corrosion rate and pitting resistance under all the test conditions for hot end exhaust components indicated that 434 was by far the most corrosion resistant alloy, followed by 1.4509 and 321, and lastly 304 was the least corrosion resistant. In general, the ferritic stainless steels, especially 434, outperformed the austenitic ones under all the test conditions.

The comparison of the corrosion resistance and rate, between the frequently used ferritic and austenitic stainless steels used in the exhaust system, gave a clear indication that the ferritic steels will provide prolonged service and this could be beneficial information to the manufacturers.

A new approach to summarise the materials' behaviour and their relative performance in the tests performed was developed. This proposed summary of a number of corrosion indicators could serve as a relative guide to alloy selection for use in hot end automotive exhaust systems for both manufacturers and users.

1 Introduction Some interesting new developments have taken place in recent years in the field of ferritic stainless steel (1–16). As a material for chemical apparatus, the common highly alloyed chromium steels as listed in national standards (e.g. in the German Standard DIN 17440) have only found limited applications. The reasons are sensitivity of several of these chromium alloyed stainless steels to intergranular corrosion (especially after welding), lower corrosion resistance compared to austenitic stainless steels, and difficulties in fabricating (especially welding). It has been shown (1–16) that the intrinsic drawbacks of customary ferritics can be overcome by metallurgical measures, primarily keeping the amount of carbon and nitrogen extremely low. The solubility in the ferrite for these two elements in rather low, both occupying interstitial sites. Stainless steels of the type dealt with in this paper are therefore sometimes termed Extra Low Interstitial (ELI)‐ferritic stainless steels. At sufficiently low concentrations of carbon and nitrogen (and some other elements), the sensitivity of ferritic stainless steels to intergranular corrosion is definitely lowered, and their ductility at ambient temperature is increased, i.e. the transition temperature is lowered. An advantage of these steels is their resistance to stress corrosion cracking. They have, so far, shown no sensitivity against chloride stress corrosion cracking under realistic operating conditions. For this reason, cooling water systems using river water with a high chloride content represent a suitable field of application for these steels. They can be welded up to a wall thickness of 3mm without sensitisation and undue loss of impact strength so that tubes for heat exchangers can be made of these steels. Their development has led to alloys ranging from 18 Cr‐2 Mo‐0 Ni to about 28 Cr‐2 Mo‐4 Ni. The present paper will only deal with the 18 Cr‐2 Mo steel because this material can be compared in price and properties with the standard 18 Cr‐9 Ni‐2 Mo austenitic stainless steel. In addition, the material in question has now become available in the form of pipe and sheet.

This article presents the galvanostatic anodic oxidation of two types of stainless steel alloys, ferritic (15.03% Cr) and austenitic (20.45% Cr, 8.37% Ni), in molten NaNO₃‐KNO₃ eutectic mixture at different temperatures ranging from 673‐873K. At a temperature of 673K the shape of polarization curves for the alloys is complex, while at higher temperatures it is simple. The passivity potential range was calculated as the difference between the passivation potential, E_p, and the breakdown potential, E_b. The value of E_b – E_p decreases with the increase of temperature. The amount of iron, chromium and nickel dissolved in the melt was determined after each experiment using atomic absorption spectroscopy. The composition and structure of the corrosion products formed on the surface of electrodes were examined by X‐ray diffraction analysis. Corrosion parameters derived from the polarization curves are calculated; these are: polarization resistance at low current densities, R_p, exchange current density, i_o, corrosion current density, i_corr, passivation current density, i_p. It was found that the increase of temperature increases i_o, i_corr, and i_p while R_p, decreases. From these results it was found that, under the given conditions, the austenitic stainless steel alloy is more corrosion resistant than the ferritic one. The activation energy of corrosion was estimated for the two alloys.

Under severely aggressive conditions, such as those experienced in the chemical industry, there has been extensive use of stainless steels in order to reduce corrosion losses. The successful industrial use of stainless steels led to requests for information on the corrosion resistance of stainless steels and similar alloys in sea‐water. This paper was awarded a prize in the Essay competition organised by the Corrosion Group of the Society of Chemical Industry, 1959.

Stainless steel is rapidly achieving pre‐eminence as a favoured material of construction due, no doubt, to the fact that for many applications in chemical plant it is the only material that can fulfil the stringent requirements as well as ensuring minimum maintenance costs. This article describes the constitution of stainless steels and their physical, mechanical and corrosion properties. Finally, their importance to the chemical plant designer is surveyed.

Background An increasing number of requests from the engineering industry are being received by the author's company to advise on procedures for modern anti‐corrosive treatment and protection of valves, pumps, compressors, heat exchangers, filters etc.

Four thermal spray coatings were subjected to high temperature corrosive environments of oil‐fired boiler conditions to compare their corrosion protection under simulated conditions. The coatings included FeCrAl, Tafaloy 45CT, which were arc‐sprayed, 50Ni‐50Cr and Cr₃C₂‐NiCr, which were coated by high velocity oxy fuel spray (HVOF) method.

The coating substrates used were SA213TP 347H, SA213 T11 and SA213 T22 alloys that are widely used as boiler tube materials. Specimens were covered with a synthetic ash mixture of 70 per cent V₂O₅‐20 per cent Na₂SO₄‐10 per cent NaCl and exposed to 550°C and 650^oC°for 192 h (6 cycles). After high temperature corrosion tests, weight change curves were obtained; specimens were examined by metallographical techniques, scanning electron microscopy and EDX analyses.

Salt deposits attacked steels and coatings during the exposure. The corrosion rates were strongly affected by the composition of the scale formed adjacent to the steels and coatings surfaces. Austenitic steel was only bare material that experienced uniform corrosion in the tests. Ferritic steels were primarily attacked by grain boundary corrosion. Thermally sprayed coatings were mainly attached through oxides and voids at splat boundaries. FeCrAl and 50Ni‐50Cr were prone to spalling. Tafaloy 45CT is also a promising method for producing homogenous coatings. Cr₃C₂‐NiCr 80/20 coating remained mostly intact.

This paper provides useful information about corrosion behaviours of four coatings used for common boiler tubes. It shows with a practical explanation how the bare material and coatings react in corrosion simulated environments.

Several process stages in the pulp and paper industry are undergoing changes. This is done partly for optimization, and partly to discontinue the use of substances hazardous to the environment. A side effect of these measures is that the problem of corrosion has increased. Explains why certain environments in the pulp and paper industry represent corrosion risks, with some examples given of corrosion failures, and suggests appropriate materials for these process stages.