Range Of Stainless Steels Research Articles

A Study of the Effect of Alloying Elements and Temperature on Nitrogen Solubility in Industrial Stainless Steelmaking

The role of nitrogen varies in different stainless steels from a harmful impurity to a valuable alloying element. Therefore, the strict control of nitrogen content is a very important issue in the steel making process. Better understanding about the thermodynamics of nitrogen solubility is the basis for this control. The aim of this study was to determine whether the nitrogen solubility at atmospheric pressure at any given composition and temperature in an Argon Oxygen Decarburization (AOD) converter could be reliably predicted. This was done by comparing different equations for nitrogen solubility to industrial measurements of several different steel grades with a wide range of compositions and temperatures. The test set consisted of 100 heats to ensure reproducibility and sufficient variability. The focus was on examining the effect of the main alloying elements (Cr, Ni, Mo, Mn) and temperature on nitrogen solubility. Nitrogen solubility is increased most by the chromium content, followed by manganese and molybdenum, whereas nickel decreases the solubility. The interaction effect of an alloying element on nitrogen declines at increasing temperatures, resulting in a negative temperature dependence, i.e., the maximum nitrogen solubility is obtained near the liquidus temperature. The study showed that most of the examined thermodynamic equations predicted the nitrogen solubility quite well in common stainless steels and even in high alloyed steels. On the other hand, clear discrepancies were observed for steels with a high manganese content as well as with strongly deviating temperatures. Therefore, based on the present measurements and the literature data, a new equation was developed for predicting the solubility of nitrogen in a wide range of stainless steels. This equation can be coupled with the existing process models to control the AOD process.

The relationship between alloying elements and biologically produced ennoblement in natural waters

A range of stainless steels, nickel–chromium and nickel–chromium–molybdenum alloys were exposed to coastal seawater from Mandapam (Indian Ocean) and freshwater from a perennial pond. Biofilms from both test waters produced an ennoblement of the open circuit potential (OCP) on all alloys as expected, which was slower but substantially larger in freshwater. In both waters an interesting relationship was perceived between the plateau OCP (Emax) and the mass percentage of the major alloying elements. In particular, iron exhibited strong positive correlations with Emax (r2 ≥ 0.77; p < 0.0005), while the sum of chromium, nickel and molybdenum presented significant negative correlations (r2 ≤ –0.81; p = 0.0002). Consistent with the regression analyses, Euclidean distance clustering yielded patterns where Inconel-600 and the nickel–chromium–molybdenum alloys had the smallest similarities of OCP with other alloys. The results emphatically reinforce a key role for surface passive films in the ennoblement phenomenon in natural waters.

Comparative study of erosion–corrosion performance on a range of stainless steels

Erosion–corrosion is one of the most severe types of material deterioration that occur in hydraulic machinery. Corrosion resistant alloys perform well in some marine applications. These materials do have their limitations, though, and for this reason a comparison of their performances is significant. This study focuses on the assessment of the relative behaviour of four different types of stainless steel (UNS S31600, UNS S32760, UNS S42000, and UNS S17400) in erosion–corrosion environments. The study was expanded to include a carbon steel (UNS G10400). Test pieces have been investigated in a submerged jet impingement apparatus in 3.5% NaCl solution with suspended solid particles at temperatures of 30–35°C. In situ corrosion monitoring was also undertaken and the influence of the application of cathodic protection was studied. This facilitated assessment of the relative roles of erosion, corrosion and synergy on the overall degradation processes. A variety of examination techniques were utilised (i.e. mass loss, surface profiling, microscopy) in order to obtain detailed information on those different modes of attack. Differences between stainless steels and carbon steel were observed and the superduplex stainless steel exhibited the best performance of the four types of stainless steel investigated herein.

Low-velocity impact performance of lattice structure core based sandwich panels

This paper outlines the findings of a study on a range of stainless steel and titanium alloy lattice structures manufactured using the selective laser melting technique. The effect of varying key manufacturing parameters on the properties of lattice strands was studied through a series of single-filament tensile tests. The resulting failure mechanisms were investigated using a scanning electron microscope. The resulting observations have shown that the properties of these lattice strands are determined by the laser energy during the manufacturing process, which in turn is controlled by the laser power and laser exposure time. The quasi-static and low-velocity penetration behaviour of lattice core-based sandwich panels has been examined, and an aluminium foam and an aluminium honeycomb were chosen to benchmark their performance. The impact resistance of the lattice core-based sandwich structures were shown to be dependent on both the manufacturing parameters and lattice unit-cell geometry of the lattice structure. The impact resistances were improved by increasing manufacturing laser energy and lattice core density. A series of drop-weight tests at velocities up to 6 m/s have shown that the penetration behaviour of the titanium alloy lattice cores and the aluminium honeycomb cores is similar.

Microbial Corrosion Resistance of Stainless Steels for Marine Energy Installations

A range of stainless steels has been investigated for resistance to microbiologically influenced corrosion in seawater. The corrosion potential was monitored for stainless steel coupons exposed to sterilized seawater and to microbiologically active seawater, which showed the effect of the growth of microorganisms. Cyclic potentiodynamic polarization scans confirmed that 13%Cr stainless steel is very susceptible to localized corrosion under these conditions. 316L stainless steel was also quite susceptible to localized corrosion, whereas 2205 duplex stainless displayed good resistance to localized corrosion. Naturally occurring microorganisms in the seawater were shown to exacerbate the localized corrosion.

Role of welding in an operating LNG manufacturing entity

AbstractWelding is not only a most important tool for nascent fabrication and erection of continuous process units but also in repair and maintenance, including for modifications and extensions. Liquefied natural gas (LNG), natural gas in liquid form that facilitates transport over large distances, is of large and growing importance for power generation. Though LNG plants are fairly simple from the process engineering point of view, the gamut of materials required is very wide. It is common to find many grades of carbon steel, high strength low alloy steels, elevated temperature resistant steels, high toughness steels for low temperature operation, high alloy steels, a broad range of stainless steels, aluminium and nickel alloys, copper and copper alloys, and titanium materials – in the forms of valves, equipment, tanks, structures, piping, etc. Case studies of the ways in which welding has contributed to the operational integrity of an LNG unit are presented. The role of welding in replacements and repai...

Electrochemical Evaluation of Crevice Corrosion in Stainless Steels

An electrochemical method for the evaluation of crevice corrosion in stainless steels is described. Specimens are carefully abraded in order to give a large number of microcrevices when the specimen is placed in contact with a rubber o-ring. Twelve specimens are tested simultaneously in a purpose-built electrochemical cell. A constant potential is applied to the specimens and the temperature automatically raised at intervals until a current increase indicates the onset of crevice corrosion and thereby defines the critical crevice corrosion temperature (CCT). Testing has been performed on a wide range of stainless steels in 3.5% NaCl at +700mV SCE. The temperature was raised by 5°C every 70 minutes. Results show good reproducibility with a typical standard deviation of below 5°C. There is also excellent agreement with the ranking of crevice corrosion resistance for different steel grades which is obtained by immersion testing in 6% FeCl 3 solution.

Room temperature stress corrosion cracking of stainless steels in indoor swimming pool atmospheres

AbstractWork undertaken to elucidate failures of standard austenitic stainless steels in indoor swimming pool atmospheres which have occurred in recent years in Europe and North America is described. The unusual feature of these failures is that they occurred by a stress corrosion cracking (SCC) mechanism at ambient temperature. Conditions which have given rise to room temperature SCC in laboratory tests are described and mechanisms which may give rise to such conditions in practice are postulated. The work described also involved a survey of conditions in indoor swimming pools as well as experimental work on a range of stainless steels in various environments.

Thick Film Screen Techniques

Basic properties of screen materials are defined, with a study of different mesh formations and coatings and their effect on the printed image. Detailed specifications are given for a range of stainless steel, polyester, and nylon fabrics. A table then summarises recommendations for specific thick film applications such as conductor tracks, fine line conductor tracks, resistors, solder paste deposition, dielectric layers, and overglazes. The requirements for the artwork and photopositive are examined, with recommended procedures for exposing and processing the mask. The survey concludes with notes on other factors which commonly influence quality at the print stage.

Properties of a new family of stainless steels without nickel

Many applications in which stainless steels are employed call for good corrosion resistance and, at the same time, for good weldability. The new family of stainless steels which we propose to describe is related by its structure to the steels of the ferritic group and by its properties,i.e., the ductility of its welds and its corrosion resistance, to the steels of the 18-8 austenitic group. One type of analyses will be examined in particular: C max 0.1, Mn 3-6, Si 1-2, Ni max 1, Cr 15-18, Mo 0.5-2. The carefully defined combination of the chromium, molybdenum, silicon and manganese concentrations ensures, on the one hand, a hot-state structure similar to that encountered in AISI 430 or AISI 434 ferritic steels and, on the other hand, eliminated the transformation to martensite of the austenite present at high temperatures; in other words, it conserves the advantages inherent in a two-phase structure as far as hot transformation is concerned (no abnormal increase in grain size), while at the same time avoiding the deleterious effects subsequently caused by the appearance of a brittle martensitic phase. Structural study of the phases formed in these new steels as a result of different heat treatments clearly shows their new and distinctive place in the range of stainless steels known to date. The fabricating of these steels raises no difficulties. Special attention will be given to welding, an area in which this new family of steels offers specific advantages, and a number of application examples will be described.