Application of Mossbauer spectroscopy to the study of corrosion resistance in NaCl solution of plasma nitrided AISI 316L stainless steel

Corrosion research in steels is one of the areas in which Mossbauer spectroscopy has become a required analytical technique, since it is a powerful tool for both identifying and quantifying distinctive phases (which contain Fe) with accuracy. In this manuscript, this technique was used to the study of corrosion resistance of plasma nitrided AISI 316L samples in the presence of chloride anions. Plasma nitriding has been carried out using dc glow-discharge, nitriding treatments, in medium of 80 vol.% H-2 and 20 vol.% N-2, at 673 K, and at different time intervals: 2, 4, and 7 h. Treated samples were characterized by means of phase composition and morphological analysis, and electrochemical tests in NaCl aerated solution in order to investigate the influence of treatment time on the microstructure and the corrosion resistance, proved by conversion electron Mossbauer spectroscopy (CEMS), glancing angle X-ray diffraction (GAXRD), scanning electron microscopy (SEM) and potentiodynamic polarization. A modified layer of about 8 gin was observed for all the nitrided samples, independently of the nitriding time. A metastable phase, S phase or gamma(N), was produced. It seems to be correlated with gamma`-Fe-4 N phase. If the gamma(N) fraction decreases, the gamma` fraction increases. The gamma(N) magnetic nature was analyzed. When the nitriding time increases, the results indicate that there is a significant reduction in the relative fraction of the magnetic gamma(N) (in) phase. In contrast, the paramagnetic gamma(N) (p) phase increases. The GAXRD analysis confirms the Mossbauer results, and it also indicates CrN traces for the sample nitrided for 7 h. Corrosion results demonstrate that time in the plasma nitriding treatment plays an important role for the corrosion resistance. The sample treated for 4 h showed the best result of corrosion resistance. It seems that the epsilon/gamma` fraction ratio plays an important role in thin corrosion resistance since this sample shows the maximum value for this ratio. (c) 2008 Published by Elsevier B.V.

Wear and corrosion resistance of pack chromised carbon steel

Pack chromising treatment is an environmentally friendly alternative to hard chromium to form wear and corrosion resistant surface layers. In this work, samples of AISI 1060 steel were pack chromised for 6 and 9 h at 1000 and 1050 degrees C using different activator concentrations. Wear tests were performed in dry conditions and corrosion tests in natural sea water for the pack chromised samples and hard chromium. Pack chromising yielded the formation of layers with high chromium concentrations, high hardness and wear resistance. Increasing activator concentration causes no significant change on the morphology and thickness of the layers. The layers produced at 1050 degrees C yielded only a (Cr,Fe)(2)N1-x phase, and those obtained at 1000 degrees C are composed of a carbide mixture with (Cr,Fe)(2)N1-x. The sample treated at 1050 degrees C for 9 h resulted in an optimum condition by means of better wear resistance and corrosion properties, which were close to that exhibited by the hard chrome, indicating that pack chromising is a promising alternative.

Effect of cold-working process on corrosion behavior of copper

The microstructure, microhardness, texture and corrosion resistance of cold-swaged and cold-wiredrawn copper rods were evaluated. Elongated grains along the deformation direction were observed for both materials and the width of these grains decreased with the increase of reduction in area. Wiredrawn copper rods have higher microhardness than the swaged rods for the same reduction in area. The copper grains in both cold-worked rods presented a preferential orientation in the [1 1 0] crystallographic direction but this trend was more pronounced for swaged rods. The corrosion resistance of wiredrawn copper rods investigated in H(2)SO(4) solutions was lower than that of swaged rods, and for both deformed materials the corrosion resistance decreased with the deformation degree. (C) 2011 Elsevier Ltd. All rights reserved.

Nanosized precipitates in H13 tool steel low temperature plasma nitriding

A comprehensive study of pulsed nitriding in AISI H13 tool steel at low temperature (400 degrees C) is reported for several durations. X-ray diffraction results reveal that a nitrogen enriched compound (epsilon-Fe2-3N, iron nitride) builds up on the surface within the first process hour despite the low process temperature. Beneath the surface, X-ray Wavelength Dispersive Spectroscopy (WDS) in a Scanning Electron Microscope (SEM) indicates relatively higher nitrogen concentrations (up to 12 at.%) within the diffusion layer while microscopic nitrides are not formed and existing carbides are not dissolved. Moreover, in the diffusion layer, nitrogen is found to be dispersed in the matrix and forming nanosized precipitates. The small coherent precipitates are observed by High-Resolution Transmission Electron Microscopy (HR-TEM) while the presence of nitrogen is confirmed by electron energy loss spectroscopy (EELS). Hardness tests show that the material hardness increases linearly with the nitrogen concentration, reaching up to 14.5 GPa in the surface while the Young Modulus remains essentially unaffected. Indeed, the original steel microstructure is well preserved even in the nitrogen diffusion layer. Nitrogen profiles show a case depth of about similar to 43 mu m after nine hours of nitriding process. These results indicate that pulsed plasma nitriding is highly efficient even at such low temperatures and that at this process temperature it is possible to form thick and hard nitrided layers with satisfactory mechanical properties. This process can be particularly interesting to enhance the surface hardness of tool steels without exposing the workpiece to high temperatures and altering its bulk microstructure. (c) 2012 Elsevier B.V. All rights reserved.

Niobium Effects on the Recrystallization Behavior on a Full Austenitic 15Cr-15Ni Stainless Steel Investigated Using Adaptive Neural Networks (ANN)

A new series of austenitic stainless steels-Nb stabilized, without Mo additions, non-susceptible to delta ferrite formation and devoid of intemetallic phases (sigma and chi), without deformation induced martensite is being developed, aiming at high temperature applications as well as for corrosive environments. The base steel composition is a 15Cr-15Ni with normal additions of Nb of 0.5, 1.0 and 2 wt%. Mechanical properties, oxidation and corrosion resistance already have been invetigated in previous papers. In this paper, the effects of Nb on the SFE, strain hardening and recrystallization resistance are evaluated with the help of Adaptive Neural Networks (ANN).

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.