Constituents Of Steel Research Articles

Stainless steel for cost-competitive bipolar plates in PEMFCs

Bipolar plate materials for the PEM fuel cell (also known as the solid polymer fuel cell, SPFC) need to fulfil the following requirements in order to be applicable as an alternative to the presently used graphite: low in cost, easy to machine or to shape, lightweight and low volume, mechanically and sufficiently chemically stable, and with a low contact resistance. Stainless steel is a low-cost material, it is easy to shape and thin sheets can be used, yielding a low volume and weight. Several stainless steels have been tested here for their applicability. The compaction pressure has a significant influence on the contact resistance. The pre-treatment of the surface is another influence; this is a permanent effect. Stainless steel constituents slowly dissolve into the membrane electrode assembly (MEA). It has been found that the anode-side stainless steel flow plate is the main source of the contaminants. Direct contact between the stainless steel and the membrane greatly enhances the contaminant level. By using a proper pretreatment and a coating or gasket to prevent direct contact between the stainless steel and the membrane, we found one alloy that satisfies the requirements for use as a low-cost material for the flow plate of a PEMFC.

Transport and Deposition of Halide in Alkali Metal-Stainless Steel Systems, (IV). Measurement of Sodium Iodide Solubility in Sodium with Major Constituents of Stainless Steel and Oxide in Sodium.

Transport and Deposition of Halide in Alkali Metal-Stainless Steel Systems, (IV). Measurement of Sodium Iodide Solubility in Sodium with Major Constituents of Stainless Steel and Oxide in Sodium.

Effect of Nitrogen on Formation of Martensite-Austenite Constituent in Low Carbon Steels.

The effect of dissolved nitrogen on phase transformations and microstructural evolution in low-carbon high manganese silicon steel wire-rod was examined for varying nitrogen levels of 30, 70, and 100 ppm, while keeping the base composition constant. It was found that nitrogen suppresses the pearlite reaction start temperature by up to 30°C. A strong correlation was discovered between the nitrogen level and the formation of martensite-austenite microconstituent (MA phase). The possible mechanisms by which nitrogen causes the formation of MA phase are discussed. The main conclusion drawn from this study is that levels of nitrogen between 70 and 110 ppm can have a significant effect on microstructure, such that up to approximately 10vol% of MA phase is formed in these steels. Microstructural changes in titanium-microalloyed steels were also investigated - particularly changes in the development of the MA and pearlite phases. The pearlite content was up to double that found in a Ti-free alloy. Microalloying with titanium was found to be effective in completely eliminating MA phase.

Investigation of non-metallic impurities in High Speed Steel using SIMS imaging and scanning techniques

Non-metallic impurities or phases are often unintentional but important constituents in steel – they primarily influence the properties and behavior of the material by forming crystallization nuclei during the solidification process of the molten material. The kind, formation and spatial distribution of these inclusions has been investigated in this work by 2D SIMS, depth profiling and scanning SIMS. These non-metallic phases can be divided into oxides, nitrides, carbides, sulfides and gas bubbles. Probably the most important phase, the oxygenic, results from reactions of the molten bath with the ambient air and from the admixture of de-oxidation components. The investigated HSS specimen exhibits two different classes of inclusions. The first class mainly contains sulfide precipitates and differs widely from the second. The latter exhibits a spherical structure with the outer sphere combining the oxygenic precipitation and the core containing nitrides and sulfides. Due to the small size of the inclusions, they have been investigated by high resolution scanning SIMS to separate the different phases.

Effect of Hot Rolling Conditions on the Microstructure and Mechanical Properties of Fe-C-Mn-Si Multiphase Steels

There is a growing need for the high strength steels with high formability for many applications. Using the concept of transformation induced plasticity (TRIP) observed in austenitic steels, one can obtain the combination of high strength and high formability. However, these austenitic steels require a fairly large amount of alloying elements which impose several practical problems for their widespread applications. On the other hand, it has been shown that the dual phase steels possess the relatively good combination of strength and formability due to their characteristic microstructure. The major microstructural constituents of dual phase steels are soft ferrite and hard martensite/bainite with small amount of retained austenite. In recent years, the beneficial effect of retained austenite on the mechanical properties of dual phase steels have been re-recognized and accordingly, there have been several investigations on developing the so-called TRIP-aided dual phase steels having increased amount of retained austenite in the microstructure. Most investigations on these TRIP-aided dual phase steels have been concentrated on the effects of heat treatment conditions and alloying elements such as Si, Mn, C and P on the microstructure and mechanical properties of cold rolled sheet steels. There have also been a few studies on developing suchmore » steels by hot rolling, and the emphases of these studies are placed mostly on increasing the amount of retained austenite. However, the microstructure of these hot rolled steels is far from optimum, consisting of large packets of hard second phase particles. The main objective of the present study is to modify the microstructure of this class of steels by varying the hot rolling conditions. The steel used in the present study is Fe-0.2C-2Si-1.5Mn.« less

Application of total-reflection X-ray fluorescence spectrometry to the analysis of airborne particulate matter

Two fast and simple methods for the collection and characterization of airborne particulate matter were developed. Airborne dust was collected by filtration and by impaction with a six-stage Berner impactor. For both methods cellulose nitrate filters were used as collection media. The exposed parts of the filters were punched out and digested with a cool-plasma asher (CPA). After dissolving the residue with nitric acid and addition of an internal standard element, the analysis was carried out by total-reflection X-ray fluorescence spectrometry (TXRF). The collection time could be reduced to less than 1h and trace elements be determined in the range of ngm−3. The detection, however, was limited by blank values caused by the sampling devices, especially by the impactor made of stainless steel. High blank values of chromium, manganese, iron and nickel as typical constituents of stainless steel were found. To avoid these high blanks, a more suitable material was chosen for the construction of an impactor of the same type. Hereby the blank values could be reduced to below the detection limits of about 100pgm−3. © 1997 Elsevier Science B.V.

High temperature compression creep of aluminium nitride after immersion in molten stainless steel

The effect of immersion in molten steel on subsequent creep behaviour has been investigated in two AlN ceramics. Steady-state creep was not significantly affected but an enhanced initial creep rate was observed, especially when the surface layer had not been removed after immersion. In immersed samples, SEM revealed some open porosity and microcracks near the surface and particles containing steel constituents were found by TEM deep inside samples, in grain-boundary secondary phases.

Comparison of calculated helium production in stainless steel due to neutron irradiation with experiment

It is well known that helium produced during neutron irradiation through the (n, α) reaction affects the mechanical properties and the amount of void swelling in nuclear reactor materials. In order to estimate the amount of helium produced in a high alloy stainless steel, which is used in fast reactors and is appropriate to be used in future fusion reactor structural materials, calculations have been performed using the neutron interaction cross sections of the steel constituents. Two austenitic steel specimens of type 1.4970 with high and low boron content, respectively, for which some experimental results are available have been chosen for the present calculations. Predominant nuclear reactions like 10B(n, α) 7Li, and the two-step reaction viz. 58Ni(n, γ) 59Ni(n, α) 56Fe, and the details of the neutron spectrum are taken into account. The cross sections for 59Ni, the major contributor for higher irradiation times, are taken from the KEDAK-4 (German) and the most recent ENDF/B-VI (American) Evaluated Nuclear Data Libraries. The results show that the calculated and the measured estimates differ by a factor of 2 to 3. This difference may be due to uncertainties in the measurement as well as uncertainties in the reaction cross section, especially in the two-step reaction.

Complexing properties of the main organic acids used in decontamination solutions for nuclear power plants and reactions involved in their degradation or elimination

Deposited activity on PWR equipment and component surfaces sometimes has to be decontaminated. An appropriate method for the dissolution of contaminated chromium-rich grow-on oxides uses an alternation of oxidizing steps (generally alkaline permanganate) and a reducing step made of organic acids. These organic acids have simultaneously reducing and chelating properties. Then, chelates are destroyed on cation exchangers in the H + form and the resulting acids are oxidized with the permanganate of the first step. Basic information on chemical properties important in these three steps has been determined: acid-base properties of the considered organic acids, stability constants of the complexes formed between these acids and the metal cations originating from the stainless steel constituents (Fe, Ni, Cr, Co), ion exchange process, oxidation of the organic acids with emphasis on various products generated before the final products (CO 2, H 2O).

A solute drag treatment of the effects of alloying elements on the rate of the proeutectoid ferrite transformation in steels

The problem of diffusional growth of a proeutectoid constituent in a ternary steel is considered, taking into account the interfacial diffusion of a slow-diffusing substitutional solute, under conditions which do not permit its long-range redistribution between parent and daughter phases. It is assumed that the faster diffusing interstitial solute (carbon) controls the rate of the transformation. The substitutional solute profile within (across) the interface is estimated as a function of interface velocity; the interstitial chemical potential difference is allowed to vary with, and balance, the solute drag due to the substitutional component. A transition to paraequilibrium is found at high interface velocities, and a variety of behaviour is predicted for intermediate states, depending on the relative rates of diffusion of the two solutes and their energetic interactions with each other and with the interphase boundary.

Determination of chemical activities of Fe, Cr, Ni and Mn in stainless steel 316 by Knudsen effusion cell mass spectrometry

Cold-worked austenitic stainless steel of the type AISI 316 is being used as the cladding and wrapper materials in fast reactor fuel pins. Knowledge of the thermodynamic activities of the steel constituents is necessary to predict the possibility of fuel-cladding, coolant-cladding or fission product-cladding chemical reactions. The thermodynamic activities of Fe, Cr, Ni and Mn for stainless steel 316 were determined by measuring their partial pressures in the temperature range 1293–2120 K, using Knudsen effusion cell mass spectrometry. High purity Ag was used as an internal calibrant. The chemical activities of Fe (aFe), Cr (aCr), Ni (aNi) and Mn (aMn) were evaluated using literature data for the vapour pressures of pure metals.logaFe±0.18=−1.586+2074/T(T=1293−1872K)logaCr±0.30=−2.350+2612/T(T=1293−2120K)logaNi±0.20=−2.140+1794/T(T=1468−1974K)logaMn±0.23=−2.041+5478/T(T=1302−1874K)

The Influence of Plastic Deformation and Cooling Rates on the Microstructural Constituents of an Ultra-low Carbon Bainitic Steel.

An experimental ultra-low carbon bainitic steel was prepared to investigate the effect of a prior compressive deformation on the morphology of the transformation procuct during continuous cooling. It is found that at the higher cooling rate the deformed austenite tends to form the non-parallel plates of acicular ferrite, and that at the lower cooling rate the deformed austenite tends to form the parallel plates of bainitic ferrite. The orientation relationships between adjacent grains of acicular ferrite have been studied using the analysis of axis-angle pair. The result shows that the adjacent variants have nearly the same orientation in space, which is analogous to the case in alloy-steel weld metals. Furthermore, based on a thermodynamic analysis, it is indicated that acicular ferrite transformation (from deformed austenite) also exhibits the phenomenon of incomplete reaction, where the reaction ceases well before the residual austenite achieves its equilibrium carbon concentration.

Interaction of U-Pu-Zr alloys containing minor actinides and rare earths with stainless steel

Abstract Isothermal tests and tests in a thermal gradient have shown that U-Pu-Zr alloys containing 5% of minor actinides (Np and Am) and rare earths (Nd, Ce and Y) with the Fe and Ni constituents of stainless steel interact to form compounds that melt below 1000 K. U preferentially interacts with Fe, whereas the rare earths preferentially interact with Ni. In the absence of U, Fe interacts with the rare earths and in this case the Fe and Ni interaction compounds formed melt at a temperature around 890 K. Cr does not actively participate in the formation of low melting compounds. The melting temperatures were established by dilatometry and the phases formed in the reaction layers were determined by electron probe microanalysis.

Analytic investigation of the process of formation of a spatially inhomogeneous structural state in a steel plate subjected to rapid cooling

We analyze the process of formation of a spatially inhomogeneous phase composition of several types of steel in cooling with convective heat exchange with the environment. The principles of the classical theory of heat conduction and the theory of interpolational models of structural state formation in rapidly cooled steels are used for numerical prediction. On this basis, we develop a technique for the analysis of phase composition. It is shown that the percentage of the martensitic constituent in steels increases as the external heat removal becomes more intense; at the same time, the tendency to complete hardening in steel is intensified. These observations are in a good agreement with experiment.

Thermochemistry of transition metal tellurides of interest in nuclear technology

The binary systems of tellurium with the alloying constituents of stainless steel, viz. Fe, Cr, Ni, Mo and Mn, were investigated by using high temperature mass spectrometry. The partial pressures of Te 2 and Te, which were the only species detected in the vapour phase in all the cases except MnTe, were obtained as a function of temperature and composition. All the telluride phases were found to be nonstoichiometric and their homogeneity ranges broader than hitherto recognised. Thermodynamic parameters such as enthalpy of vaporisation, enthalpy of formation and Gibbs free energy of formation were deduced for various compositions. The threshold tellurium potential necessary for the corrosion of the clad was calculated for each alloying constituent, and this data was compared with the estimated tellurium potential in the fuel-clad gap of the fuel pins in fast breeder reactors. The role of fission product tellurium in the internal corrosion of the clad is discussed in the light of the above data.

Phase equilibrium studies in the Na-Fe-O system

In high temperature sodium-steel systems, the corrosion of structural steels by sodium is enhanced by the presence of dissolved oxygen. As iron is the major constituent in steel, the interaction between iron and sodium containing oxygen plays a decisive role in this corrosion process. A knowledge of the various phase relationships that exist in the Na-Fe-O system is essential to understand this phenomenon. In order to elucidate the equilibrium phase fields, various experiments such as in-sodium equilibrations, pseudo-isopiestic equilibrations, differential thermal analysis and solid state reactions between the oxides of iron and sodium of various compositions were carried out. On the basis of the results of these experiments an isothermal cross-section of the partial phase diagram of the Na-Fe-O system above 773 K is reported.

In situ investigation of sputter-deposited thin films by ion sputtering spectrometry

Low energy ion scattering spectrometry (ISS) was used to investigate thin films deposited by a sputtering process. Thin film deposited onto an aluminum substrate by Ar + ion sputtering of an AISI 304 stainless steel target was investigated in situ with alkali ions scattered from the deposited film during the process. Cobalt metal was used as a standard to calibrate the mass position of the IS spectrum by Li + ion scattering with different energies. Auger electron spectroscopy and depth profiling of the deposited films were carried out to compare with the ISS results. The sputtering rate was determined by measuring the thickness of the deposited film with an ellipsometer and was checked by depth profiling of the film. The ISS results show that as the deposited film reached an average thickness of 4.0 nm, only the iron peak of the major constituents of the stainless steel and the aluminum peak of the substrate were present in the IS spectrum. As the thickness approached 8.0 nm, the IS spectrum showed peaks of all constituents of the stainless steel without the aluminum peak.

Tribological and microstructural studies of oxygen-implanted ferrite and austenite

Ferrite (pure α-Fe) and austenite (AISI 304 stainless steel) discs were implanted to doses ranging from 1 × 10 17 to 1 × 10 18 O 2 cm -2 at temperatures ranging from 90 to 500 °C and tested using an oscillating pin-on-disc wear tester. Mössbauer spectroscopy, X-ray diffraction and Auger electron spectroscopy were used to characterize the microstructures and compositions of the implanted layers. Although oxygen implantation reduces the wear rates of both steel constituents at all implantation doses and temperatures, the lowest wear rates are observed in the α-Fe implanted at the lower doses and temperatures and in the stainless steel implanted at elevated temperatures. Ranked from most to least wear resistant, the oxides observed in ferrite are FeO, Fe 2O 3 and Fe 3O 4. When discs of austenite are implanted, hematite-like oxide is formed at all temperatures and a magnetite-like oxide begins to appear in addition at elevated temperatures (500 °C at 4 × 10 17 O 2 cm -2 and 430 °C at 1 × 10 18 O 2 cm -2). The hematite-like oxide formed when 4 × 10 17 O 2 cm -2 is implanted at 400 °C induces the greatest load for the transition from mild to severe adhesive wear (approximately 300 times the load for unimplanted discs).

Oxygen in the Liquid-Metal Fusion Reactor Blanket and Its Possible Influence on the Compatibility with Materials

Electrochemical oxygen meters with yttrium-doped thoria, yttrium-stabilized zirconia, and calcium-stabilized zirconia solid electrolytes are tested for the measurement of oxygen activity in Pb-17Li eutectic alloy. The proposed breeder blanket fluid for fusion reactors. In this paper the oxygen potentials of the alloy measured by these three meters are compared with the oxygen potentials of the alloy after the addition of lithium oxide and with theoretical values. Zirconium and yttrium metal foils are tested for gettering oxygen from the alloy. The compatibility of the three ceramic materials in the liquid alloy and the stability of the meters for prolonged use are discussed. The influence of oxygen on the corrosion of steels in Pb-17Li is reviewed in light of the oxygen potentials of the alloy compared to thermodynamic data of the ternary oxides of the metal constituents of steels. The possibility of using the oxygen meters to measure the lithium activity of the alloy is also indicated.

Determination of stainless steel constituents in plastics

Instrumental neutron activation analysis (INAA), atomic absorption spectrometry (AAS), and X-ray fluorescence analysis (XRF) were tested for the determination of the abrasion effect in plastics processing equipment. As optimal solution measurement of Fe by XRF in cylindrical samples was found.