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Duplex stainless steels have become important competitors to austenitic stainless steels in many applications and a great deal of attention has focused on the welding aspects. The introduction of modern grades with improved properties and a competitive price level have increased their use in the offshore, petrochemical and shipbuilding industries, for example. In particular the newer grades, with their higher nitrogen content and improved weldability, have moved duplex stainless steels from a position as “interesting” materials to one of “useful in practice”. However, duplex stainless steels differ from austenitic grades in some respects, and know‐how combined with the use of appropriate welding procedures and consumables is therefore the key to successful welding.

States that duplex (austenitic/ferritic) stainless steels offer properties of interest and a cost‐effective material selection solution for plant and equipment in the pulp and paper industry. Reviews characteristics of duplex steels leading to successful long‐term applications of 22 Cr duplex and a copper containing 25 Cr super duplex stainless steel. Concludes that, applied correctly, two‐phase stainless steels can provide long‐term reliable maintenance‐free service in many pulp and paper plant environments.

The construction of the early platforms in the North Sea often stretched materials technology to its limits and sometimes beyond them. There are many instances where major pumps or piping systems have had to be replaced either because the original materials were not sufficient for the duty or because the process fluids have become more corrosive during the life of the oilfield. The paper reviews the considerable work that has been carried out in recent years specially directed at developing stainless steels capable of withstanding a number of the harsh corrosion environments met on off‐shore platforms. The latest stainless steels are able to withstand all the standard seawater duties without suffering from localised pitting or crevice corrosion. Their resistance to hydrogen sulphide stress corrosion means they can cope with the most sour process fluids at present met in the North Sea.

This paper aims to establish the microstructures and the process-structure relationships in duplex stainless steel powders consolidated by selective laser melting (SLM).

A priori data on energy density levels most appropriate to consolidation of duplex stainless steel powders through SLM served as the basis to converge on the laser settings. Experimental designs with varying laser power and scan speeds and test pieces generated allowed metallographic evaluations based on optical and scanning electron microscopy and electro backscatter diffraction analyses.

Duplex stainless steel powders are established for processing by SLM. However, the dynamic point heat source and associated transient thermal fields affect the microstructures to be predominantly ferritic, with grains elongated in the build direction. Austenite precipitated either at the grain boundaries or as Widmanstätten laths, whereas the crystallographic orientations and the grain growth are affected around the cavities. Considerable CrN precipitation is also evidenced.

Duplex stainless steels are relatively new candidates to be brought into the additive manufacturing realm. Considering the poor machinability and other difficulties, the overarching result indicating suitability of duplex powders by SLM is of considerable value to the industry. More significantly, the metallographic evaluation and results of the current research allowed further understanding of the material consolidation aspects and pave ways for fine tuning and establishment of the process-structure-property relationships for this important process-material combination.

A very wide variety of alloy types are available for selection to combat the potential corrosion problems posed in a diverse range of industries. Although in today's climate cost reduction is an important goal, the price of unexpected failure of equipment is often measured as risk to human life, and materials selection must always be given a prime place in design, engineering and construction. Material selection should not be based simply on low installed cost of equipment — the need to maintain safety standards and effective long‐term utilization of a production asset, with minimum costly maintenance and downtime, mandate the selection of materials which can be justified on the basis of life‐cycle cost and risk analysis. The material chosen should provide the lowest cost viable, and if possible, “fit and forget” solution. In the Offshore Oil and Gas industry in the North Sea the solution adopted would need to address the CRINE cost reduction strategy.

To find out the optimum heat treatments to recover the microstructural changes of stainless steel alloys.

A total of four alloys were used in this study: two duplex stainless steel (DSS) alloys type 2304 and 2205, super DSS (SDSS) type 2507 and austenitic stainless steel alloy type 316 L. The alloys were heated to different temperatures, 750, 850, 950 and 1,050°C, for three different times, 10 min, 1 and 4 h.

The microstructural investigations showed that 2205 and 2507 behaved similarly in recovering their microstructures, especially in terms of the ferrite:austenite ratio within specific heat treatments and changing the hardness values. The results indicated that the microstructure of both alloys started to change above 750°C, the largest changes were shown at 850 and 950°C as the lowest ferrite content (FC%) was recorded at 850°C for both alloys. However, the microstructures of both alloys started to recover at 1,050°C. The reduction in the hardness values was attributed to the formation of new ferrite grains, free of residual stresses. On the other hand, the microstructure of the alloy type 2304 was stable and did not show large changes due to the applied heat treatments, similarly for austenitic alloy except showing chromium (Cr) carbide precipitation.

Finding the exact heat treatments, temperature and time to recover the microstructural changes of DSS alloys.

Discusses some aspects of welding of FERRALIUM alloy SD40 and considers differences from the penultimate alloy refinement FERRALIUM alloy 255–3SF. Gives details relating to the metallurgy of FERRALIUM SD 40, noting that it has approximately equal amounts of ferrite and austenite. Reports on methods of achieving the optimum composition after hot working. Also notes methods of accomplishing welding of FERRALIUM alloy and parameters that must be adhered to.

The secondary phase decreased the corrosion resistance because of the segregation of Cr and Mo. Therefore, this paper aims to study the precipitation condition and the effect of secondary phase with volume fraction on corrosion behavior.

Secondary phase precipitated approximately from 375°C to 975°C because of saturated Cr and Mo at grain boundary by growth of austenite. Therefore, heat treatment from 800°C to 1,300°C was applied to start the precipitation of the secondary phase.

The secondary phase is precipitated at 1,020°C because of segregation by heterogeneous austenite. The growth of austenite at 1,000°C needs the time to saturate the Cr and Mo at grain boundary. When the volume fraction of austenite is 56 per cent (14 min at 1,000°C), the secondary phase is precipitated with grain boundary of austenite. The secondary phase increased the current density (corrosion rate) and decreased the passivation. That is checked to the critical pitting temperature (CPT) curves. The 1 per cent volume fraction of secondary phase decreased CPT to 60°C from 71°C.

The precipitation of secondary phase not wants anyone. Casted super-duplex stainless steel (SDSS) of big size precipitates the secondary phase. This study worked the precipitation condition and the suppression conditions of secondary phase.

Manufacturers need precipitation condition to make high-performance SDSS.

The corrosion resistance of SDSS is hard the optimization because SDSS is dual-phase stainless steel. The precipitation of the secondary phase must be controlled to optimize of the corrosion resistance of SDSS. Anyone not studied the precipitation condition of secondary phase and the effect of secondary phase with volume fraction on corrosion behavior of SDSS.

Considers the advantages of highly alloyed stainless steel such as duplex stainless steels or nickel‐based alloys in highly corrosive environments. Looks at corrosion rates for alloys in acetic acid and presents results of tests on the influence of contaminants in the acid. Gives practical applications. Concludes that duplex stainless steels demonstrate higher corrosion resistance than austenitic stainless steels and are often comparable to nickel base alloys.