Thermal analysis of the chip formation in austenitic stainless steel

The most important property of austenitic stainless steels is corrosion resistance. In these steels, the transition between paramagnetic and ferromagnetic conditions occurs at low temperatures. Therefore, the use of austenitic stainless steels in conditions in which ferromagnetism absence is important can be considered. On the other hand, the formation of strain-induced martensite is detected when austenitic stainless steels are deformed as well as machined. The strain-induced martensite formed especially in the machining process is not uniform through the chip and its formation can also be related to the Md temperature. Therefore, both the temperature distribution and the gradient during the cutting and chip formation are important to identify regions in which martensite formation is propitiated. The main objective here is evaluate the strain-induced martensite formation throughout machining by observing microstructural features and comparing these to thermal results obtained through finite element method analysis. Results show that thermal analysis can give support to the martensite identified in the microstructural analysis.

Corrosion behaviour of new duplex stainless steel reinforcements embedded in chloride contaminated concrete

The use of reinforcing stainless steels (SS) in concrete have proved to be one of the most effective methods to guarantee the passivity of reinforced concrete structures exposed to chloride contaminated environment. The present research studies the corrosion behaviour of a new duplex SS reinforcements with low nickel content (LND) (more economicaly compatible) is compared with the conventional austenitic AISI 304 SS and duplex AISI 2304 SS. Corrosion behaviour of ribbed SS reinforcements was studied in mortars with chloride content (0, 0.4, 2 and 4% Cl ⎯ ) using linear polarization resistance and potentiostatic pulses technique, Ecorr and Rp values were monitored over the exposure time. The obtained icorr data for the new duplex stainless steel LND no afforded passivity breakdown after one year exposure

Pitting Corrosion in Austenitic Stainless Steel Water Tanks of Hotel Trains

The water storage tanks of hotel trains suffered pitting corrosion. To identify the cause, the tanks were subjected to a detailed metallographic study and the chemical composition of the austenitic stainless steels used in their construction was determined. Both the tank water and the corrosion products were further examined by physicochemical and microbiological testing. Corrosion was shown to be related to an incompatibility between the chloride content of the water and the base and filler metals of the tanks. These findings formed the basis of recommendations aimed at the prevention and control of corrosion in such tanks. Se han detectado problemas de corrosión por picaduras en los depósitos de agua de trenes hotel. Para identificar las causas se llevó a cabo un detallado estudio metalográfico así como de la composición química de los aceros inoxidables austeníticos utilizados en su construcción. También se realizaron estudios fisicoquímicos y microbiológicos de los productos de corrosión. Se ha encontrado que los problemas de corrosión están relacionados con la incompatibilidad entre el contenido en cloruros del agua y los metales base y de aporte de la soldadura de los tanques. En base a estos hallazgos se proponen una serie de recomendaciones encaminadas a la prevención y control de la corrosión de dichos depósitos.

Elemental partitioning and microstructural development in duplex stainless steel weld metal

A thermodynamic analysis which is capable of estimating the austenite/ferrite equilibria in duplex stainless steels has been carried out using the sublattice thermodynamic model. The partitioning of alloying elements between the austenite and ferrite phases has been calculated as a function of temperature. The results showed that chromium partitioning was not influenced significantly by the temperature. The molybdenum, on the other hand, was found to partition preferentially into ferrite phase as the temperature decreases. A strong partitioning of nickel into the austenite was observed to decrease gradually with increasing temperature. Among the alloying elements, average nitrogen concentration was found to have the most profound effect on the phase balance and the partitioning of nitrogen into the austenite. The partitioning coefficient of nitrogen (the ratio of the mole fraction of nitrogen in the austenite to that in the ferrite) was found to be as high as 7.0 around 1300 K. Consequently, the volume fraction of austenite was influenced by relatively small additions of nitrogen. The results are compared with the experimentally observed data in a duplex stainless steel weld metal in conjunction with the solid state δ → δ + γ phase transformation. Particular attention was given to the morphological instability of grain boundary austenite allotriomorphs. A compariso between the experimental results and calculations indicated that the instability associated with irregular austenite perturbations results from the high degree of undercooling. The results suggest that the model can be used successfully to understand the development of the microstructure in duplex stainless steel weld metals.

Corrosion of stainless steel components in seawater reverse osmosis desalination plants-investigations on adapted internal cathodic protection

Stainless steel is widely used in seawater reverse osmosis units (SWRO) for both good mechanical and corrosion resistance properties. However, many corrosion failures of stainless steel in SWRO desalination units have been reported. These failures may often be attributed to un-adapted stainless steel grade selection and/or to the particular aggressive seawater conditions in "warm" regions (high ambient temperature, severe biofouling, etc.). Cathodic protection (CP) is a well-known efficient system to prevent corrosion of metallic materials in seawater. It is successfully used in the oil and gas industry to protect carbon steel structures exposed in open-sea. However, the specific service conditions of SWRO units may seriously affect the efficiency of such anti-corrosion system (high flow rates, large stainless steel surfaces affected by biofouling, confinement limiting protective cathodic current flow, etc.). Hence, CP in SWRO units should be considered with special care and modeling appears as useful tool to assess an appropriate CP design. However, there is a clear lack of CP data that could be transposed to SWRO service conditions (i.e. stainless steel, effect of biofouling, high flow rate, etc.). From this background a Join Industry Program was initiated including laboratory exposures, field measurements in a full scale SWRO desalination plant, and modeling work using PROCOR software. The present paper reviews the main parameters affecting corrosion of stainless steel alloys in seawater reverse osmosis units. CP on specific stainless steel devices was investigated in order to assess its actual efficiency for SWRO units. Severe environmental conditions were intentionally used to promote corrosion on the tested stainless steel products in order to evaluate the efficiency of CP. The study includes a modeling work aiming at predicting and designing adapted CP protection to modeled stainless steel units. An excellent correlation between modeling work and field measurements was found.