Investigations on the Corrosion Behaviour and Structural Characteristics of Low Temperature Nitrided and Carburised Austenitic Stainless Steel

The wear resistance of austenitic stainless steels can be improved by thermo-chemical surface treatment with nitrogen and carbon. However, it is possible that the corrosion resistance will be impaired by the precipitation of chromiumnitrid or -carbide. The present contribution deals with investigations of the corrosion behaviour and structural characteristics of a low temperature nitrided and carburised austenitic stainless steel. The material investigated was AISI 316L (X2CrNiMol7-12-2) austenitic stainless steel. A commercial plasma-nitriding unit (pulsed dc) was used for the nitriding and carburising process. Additional samples were treated by the gasoxinitriding process for a comparison between plasma- and gasoxinitriding. The nitrided and carburised layer of austenitic stainless steel consists of the nitrogen or carbon S-phase (expanded austenite), respectively. X-ray diffraction investigations show the typical shift of the peaks to lower angles, indicating expansion of the fee lattice. Also the X-ray diffraction technique was employed to study the residual stresses in the nitrogen and carbon S-phase. The corrosion behaviour of surface engineered samples was investigated with electrochemical methods. Anodic potentiodynamic polarisation curves were recorded for testing the resistance against general corrosion (in H2SO4) and pitting corrosion (in NaCl).

Self-glazing SiC-andalusite Refractories for High Temperature Gasification Applications

The combination of SiC and andalusite with calcium aluminate binder for castables in high corrosive gasifying environments is a promising alternative refractory system for many different slag systems. After sintering,a glassy protective layer has been identified. Beside the interactions of the refractories with intermediate slag also the thermomechanical properties,the thermal shock performance and the microstructure have been evaluated as a function of different binder systems.

Analytical and Numerical Modeling of Flow in a Fractured Gneiss Aquifer

Investigating and modeling fluid flow in fractured aquifers is a challenge. This study presents the results of a series of packer tests conducted in a fractured aquifer in Freiberg, Germany, where gneiss is the dominant rock type. Two methods were applied to acquire hydraulic properties from the packer tests: analytical and numerical modeling. MLU (Multi-Layer Unsteady state) for Windows is the analytical model that was applied. ANSYS-FLOTRAN was used to build a two-dimensional numerical model of the geometry of the layered aquifer. A reasonable match between experimental data and simulated data was achieved with the 2D numerical model while the solution from the analytical model revealed significant deviations with respect to direction.

Improvement of the Corrosion Resistance of High Alloyed Austenitic Cr-Ni-Mo Stainless Steels by Solution Nitriding

Characteristic features of austenitic steel grades combine a good corrosion resistance with a low hardness, wear resistance and scratch resistance. An interesting possibility for improving the wear behaviour of these steels without loss of their corrosion resistance lies in enriching the near surface region with nitrogen. The process of a solution nitriding allows the rise of the solution of nitrogen in the solid phase. On this state nitrogen increases the corrosion resistance and the tribilogical load-bearing capacity. The aim of the study was, to investigate the improvement of the pitting corrosion behaviour by solution nitriding. A special topic was to observe the effect of nitrogen by different molybdenum content. So austenitic stainless steels (18% Cr, 12% Ni, Mo gradation between 0.06 to 3.6%) had been solution nitrided. The samples could be prepared with various surface content of nitrogen from 0.04 to 0.45% with a step-by-step grinding. The susceptibility against pitting corrosion of these samples had been tested by determination of the stable pitting potential in 0.5M and 1M NaCl at 25°C. For the investigated steel composition and the used corrosion system there is no influence of molybdenum on the effectiveness of nitrogen. The influence of nitrogen to all of the determined parameters can be described well by PRE = Cr + 3,3 * Mo + 25 *N. XPS analysis of the sample surfaces support the results of the pitting corrosion tests.Additionally surface investigations with an acid elektolyte (0,1M HC1 + 0,4M NaCl) were performed. In this case the passivation effective nitrogen content increases markedly with rising molybdenum concentration of the steel. Obviously an interaction of Mo and N is connected with a strongly acid electrolyte.

Hydro-mechanical fault reactivation modeling based on elasto-plasticity with embedded weakness planes

In this paper,an elasto-plastic constitutive model is employed to capture the shear failure that may occur in a rock mass presenting mechanical discontinuities,such as faults,fractures,bedding planes or other planar weak structures.The failure may occur in two modes:a sliding failure on the weak plane or an intrinsic failure of the rock mass.The rock matrix is expected to behave elastically or fail in a brittle manner,being represented by a non-associated Mohr-Coulomb behavior,while the sliding failure is represented by the evaluation of the Coulomb criterion on an explicitly defined plane.Failure may furthermore affect the hydraulic properties of the rock mass:the shearing of the weakness plane may create a transmissive fluid pathway.Verification of the mechanical submodel is conducted by comparison with an analytical solution,while the coupled hydro-mechanical behavior is validated with field data and will be applied within a model and code validation initiative.The work presented here aims at documenting the progress in code development,while accurate match of the field data with the numerical results is current work in progress.

Corrosion of Alumina and Mullite Based Refractories by an Ingot Casting Steel

The corrosion of refractory crucibles by a highly cor- rosive steel （18CrNiMo7-6） with a high aluminum con- tent and casting temperature of 1 580℃ was investiga- ted. The tested refractories were alumina, muUite and alumina doped with zirconia and titania （ AZT）. The samples were decreasingly attacked in the sequence AZT, alumina and mullite with corrosion layers of about 14, 6 and 1 mm, respectively. In the alumina and AZT, compositions corresponding to manganese aluminates and subsequently manganese aluminosilicates formed with manganese and silicon from the steel. In the mullite cru- cible, compositions corresponding to manganese aluminosilicates formed directly with manganese from the steel giving a highly viscous interfacial melt which retarded the further corrosion.

Interpretation of Groundwater Flow into Fractured Aquifer

The region of investigation is part of the western desert of Iraq covering an area of about 12,400 km2, this region includes several large wadis discharging to the Euphrates River. Since the Tectonic features in particular fault zones play a significant role with respect to groundwater flow in hard rock terrains. The present research is focus on investigate lineaments that have been classified as suspected faults by means of remote sensing techniques and digital terrain evaluation in combination with interpolating groundwater heads and MLU pumping tests model in a fractured rock aquifer, Lineaments extraction approach is illustrated a fare matching with suspected faults, moreover these lineaments conducted an elevated permeability zone.

Cracking Phenomenon in Spot Welded Joints of Austenitic Stainless Steel

The spot welds nugget cracking of austenitic stainless steel at temperatures between 700°C - 1010°C was investigated. Traditionally, the cracks have been observed around the spot nugget in welded temperature. Actually, these cracks are developed due to incomplete melting and inappropriate electrode pressure, which causes an expulsion of molten metal. These cracks start to grow and cause either the interface or plug fracture according to the loading type. In this work, the micro-cracks in the weld nugget were indicated for this type of steel at elevated temperature. Cracks appear in a certain range of temperature;about 700°C - 750°C. The cracks like defect and cavitations were presented. According to the fracture mechanics point of view, these cracks reduce the mechanical strength. Therefore, these cracks have to be taken into account with a certain precaution. Moreover, considering the working temperature and reducing the element may develop ferrite particles.

Abiotic Sponge Ecology Conditions,Limski Kanal and Northern Adriatic Sea,Croatia

The Limski kanal, a semi-closed inlet (channel-like bay) located on the western coast of Istria (Croatia), is an extraordinary sponge habitat. Research on the marine ecosystem has been conducted there for more than 100 years. Today, 42 valid Porifera species are described. 139 species are listed for the area around Rovinj and 159 species for the northern Adriatic Sea. While several scientists described the sponge fauna, information on the abiotic situation or an explanation for the diversity differences is missing. This study interprets physicochemical and ecological parameters including depth profiles (temperature, salinity, pH-value, oxygen, water current velocity, photosynthetically active radiation [PAR], water transparency and nutrients). Their variances are linked with the distribution patterns of the prevailing sponge fauna. The channel is characterised as predominantly marine habitat. Although a shallow sediment barrier and a headland reduce the impact of the northern Adriatic Sea, differences between the channel and the open sea seem to be limited. Compared to the more homogenous water body of the Adriatic sampling locations, the channel shows variations and gradients of ecological parameters between different locations (e.g., due to freshwater influx: nutrients, temperature, oxygen content, salinity and water current velocity) – this offering habitat diversity. The sponge fauna changes along those ecological gradients. It is dominated by the photophilic species Aplysina aerophoba and Chondrilla nucula, but sciaphilic species such as Dysidea avara, Axinella polypoides and Aplysina cavernicola can be found, too. Some specialised species (e.g., Geodia cydonium, Tethya aurantium) even populate the muddy bottom of the channel.