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This contribution reports on an experimental polishing procedure, that is comprised of early grinding in Al2O3 slurries and late polishing in colloidal silica, which is used for preparing the nitrided region of a plasma nitrided austenitic stainless steel, for crystallographic analysis via electron backscatter diffraction (EBSD). The suitability of the polished surfaces for conducting EBSD characterization was assessed through an analysis of both the surface roughness (appraised by atomic force microscopy) and the quality of the Kikuchi diffraction patterns. We observed that as-nitrided virgin surfaces were not suitable for EBSD characterization, due to intense surface roughening, which was induced by the nitriding process itself. At the subsurface region, exposed by on-top mechanical polishing, the flatter nature of the polished surfaces allowed the acquisition of EBSD patterns with enough quality for microtexture analysis. A resolution of 100 nm in the total removed layer was attainable via careful control of the polishing parameters. Close parallelism between the polished and original surfaces was verified.

Stainless steel films were obtained from an 316L target onto steel substrates by pulsed-DC magnetron sputtering, varying the pulse frequency from non-pulsed (conventional DC) up to 350 kHz. Experiments were carried out with a substrate temperature of 673 K and time-averaged electrical power density of 15.3 W cm−2. Stabilization of the face-centered cubic, but not the body-centered cubic phase was observed under pulsed-DC compared to conventional DC. This was attributed to increased average adatom energy under pulsed-DC.

This contribution presents a theoretical discussion on phase hierarchy stability between face-centered cubic (FCC), austenite, and body-centered cubic (BCC), ferrite, lattice structures of stainless steel (SS) films that are sputter-deposited from austenitic targets under non-reactive atmospheres. Data published in literature on both phase characterization and chemical composition of diverse SS films are interpreted anew in this contribution in the light of lattice stability thermodynamic simulations. For films obtained from 304 and 316 steel targets, thermodynamic simulations predict that the ferrite phase is more stable than the austenite phase at low thermal energies. In contrast, simulations forecast thermodynamic stability at low thermal energies of the austenite phase in films that are sputtered from 330 steel targets. The criterion of lattice stability reveals that structures observed in the experiments cannot be described comprehensively by thermodynamic states where either full atomic partitioning among phases is established or zero atomic partitioning takes place. Thereby, a description of an equilibrium with incomplete atomic partitioning is proposed here, with the aim of depicting the structures reported in the literature. Such an equilibrium with incomplete atomic partitioning adequately describes the gradual destabilization of ferrite and the increased fraction of austenite (up to fully austenitic structures), when either the substrate heating is intensified, or the Ni content of the alloy is increased, with an 73Fe18Cr9Ni, wt%, initial alloy as a basis.

In this study, we report on phase fractions and nitrogen distribution among structure components of stainless steel films that are sputter-deposited from an 316L target under Ar + N 2 atmospheres. As N 2 flow rate was increased were obtained samples with the following structures: BCC (N-lean), BCC plus FCC (between 2.0 and 6.0 N at.%), and fully FCC (11.5 N at.% and higher N-contents). Experiments under two different sets of deposition conditions were carried out, where the actual relationship between phase fractions and N 2 flow rate showed differences among the two experimental sets of samples. N-content in the FCC phase in duplex structures varied between 3 and 9 at.%. An equilibrium with constrained atomic partitioning of substitutional species and full atomic partitioning of nitrogen was proposed, with the aim of depicting the structures observed.

UNS S31603 stainless steel (SS) substrates were covered by reactive magnetron-sputtering with protective SS coatings of the same steel specification. A mechanical characterization study (through nano-, micro- and macro-hardness tests) of samples obtained under two different sputtering conditions and varying the N2 gas flow rate was carried out. This contribution aimed at appraising the effects of varying the nitrogen flow rate on hardness, elastic modulus, and susceptibility to indentation-induced crack formation of the coated SSs. Nitrogen-free samples displayed body-centered cubic (BCC) films with 9.0-9.4 GPa hardness and 203-206 GPa elastic modulus, while their susceptibility to indentation-induced cracking varied between superior and moderated among the two sets of sputtering conditions studied. Samples alloyed with 4-6 N at-% displayed a predominantly face-centered cubic (FCC) structure, 9.4 GPa hardness, 196-218 GPa elastic modulus, and superior resistance to crack formation. Samples with 11.5-22.0 N at-% were fully composed of the FCC structure, displayed 12.4-15.2 GPa hardness, 188-193 GPa elastic modulus, and moderated resistance to indentation-induced crack formation. Samples with 47.0 N at-% displayed FCC compound nitride structure, for which hardness and elastic modulus were 8.1 GPa and 139 GPa, respectively. These samples displayed low resistance to crack formation.

The stacking fault energy (SFE) in a set of experimental Ni–Cr–Fe alloys was determined using line profile analysis on synchrotron X-ray diffraction measurements. The methodology used here is supported by the Warren–Averbach calculations and the relationships among the stacking fault probability ( α ) and the mean-square microstrain ( e 2 L >). These parameters were obtained experimentally from cold-worked and annealed specimens extracted from the set of studied Ni-alloys. The obtained results show that the SFE in these alloys is strongly influenced by the kind and quantity of addition elements. Different effects due to the action of carbide-forming elements and the solid solution hardening elements on the SFE are discussed here. The simultaneous addition of Nb, Hf, and, Mo, in the studied Ni–Cr–Fe alloys have generated the stronger decreasing of the SFE. The relationships between SFE and the contributions on electronic structure from each element of additions were established.

UNS S31803 duplex stainless steel specimens, 1.5 mm in thick, were high temperature gas nitrided (HTGN) in order to obtain a 0.9 wt% N, through the thickness fully austenitic microstructure with increased cavitation-erosion (CE) resistance. The microstructure of the as received UNS S31803 duplex stainless steel consists of ferrite + austenite stringers (50% α + 50% γ). HTGN was performed at 1200 °C for 8 h, in a 0.1 MPa N2 atmosphere, followed by direct quench in water. A fully austenitic microstructure, 330 HV 0.1 hard, containing 0.9 wt% N in solid solution, was obtained. Part of the specimens were 30% cold rolled and part of the specimens were annealed after cold-working, obtaining cold worked and recrystallized specimens. All the specimens, including the as received UNS 31803 duplex steel, were tested in a 20 kHz vibratory cavitation erosion testing equipment. The HTGN specimens showed lower CE wear rates and higher incubation times, when compared to the as received condition. The 30% cold worked HTGN specimens showed the greatest increase in incubation times and greatest decrease of cavitation wear rates. The recrystallized specimens showed lower CE resistance when compared to HTGN samples. The difference was attributed to development of a sharp {1 0 1}//surface texture during HTGN, which was weakened after recrystallization. The mechanisms responsible for the improvement of CE performance are discussed.

Wrought material as well as physically simulated welding heat affected zone (HAZ) samples of an UNS S32304 duplex stainless steel were subjected to electrochemical corrosion tests and electron microscopy characterization. An impaired corrosion resistance of the HAZ microstructures compared to the wrought material microstructure was observed. Calphad-based numerical simulation of phase transformations and solute redistribution taking place during welding provided an explanation of the observed corrosion behavior. The poor corrosion resistance of the HAZ microstructures studied was mainly attributed to a decrease in corrosion resistance of ferritic grains after welding, which exhibited lower chromium content than ferritic grains in the wrought material.

An approach for numerically simulating in a one-dimensional system the three-dimensional process of atomic diffusion in multiphase microstructures of multicomponent systems is proposed. This numerical approach is based in the Calphad method and the multicomponent diffusion formalism. A numerical algorithm for implementing the proposed approach was build up by generalizing the previous model by Engstrom et al.(2) with new features that allow to compute transient states during diffusion when atomic partitioning between matrix phase and dispersed phases is far from the local equilibrium condition. After describing the algorithm, it is applied to an experimental case of nitrogen diffusion in stainless steel with chromium nitride precipitation during high temperature gas nitriding. The main characteristics of the proposed approach, their advantages and their restrictions, are discussed in depth using the case study.

An electron back scattering diffraction characterization analysis of a high temperature gas nitrided UNS S31803 duplex stainless steel was performed. Nitriding treatments were carried out between 1423 and 1473 K, for times varying between 0.18 and 86.4 ks, under nitrogen partial pressures varying between 0.03 and 0.15 MPa. Upon investigation, these samples displayed a fully austenitic surface layer on a ferritic–austenitic duplex core. The grain boundary character distribution of surface austenitic layers strongly varied as the nitriding parameters were varied; low- Σ CSL grain boundary fractions between 0.35 and 0.65 were obtained. Conversely, the microtexture mainly depended on nitriding time, being only slightly affected by nitrogen partial pressure or temperature changes. At the earliest stages of nitriding, austenitic cases displayed an intense microtexture with two major texture components, {0 0 1}〈1 0 0〉 and {0 1 1}〈2 1 1〉, which weakened as nitriding time was increased.

High nitrogen stainless steels (HNSS) are being considered a new promising class of engineering materials. When nitrogen is added to austenitic steels it can simultaneously improve fatigue life, strength and wear and localized corrosion resistance. In this work, a single pass pendulum scratch test was used to study the effect of nitrogen on the scratch resistance of an UNS S30403 austenitic stainless steel. Samples with increasing nitrogen contents at the surface were obtained through high temperature gas nitriding. The thermochemical treatments were performed at 1473 K in (N2CAr) gas atmospheres for 36.0 ks, obtaining fully austenitic cases (surface nitrogen contents up to 0.5 wt%) ca. 1.5 mm in depth. The scratch tests were performed in a single-pass pendulum, equipped with strain gages to measure normal and tangential forces during scratching. The specific absorbed energy was calculated as the ratio between the measured absorbed energy and the amount of mass removed from the specimen. An increase of the specific absorbed energy with increasing nitrogen content was observed. The results of the scratch tests were analyzed taking into account the stress–strain behavior during depth sensing indentation tests and the energy absorbed during Charpy impact tests. The improvement in scratch resistance due to nitrogen alloying was attributed to the strong hardening effect of nitrogen in solid solution, which does not affect significantly work hardening and toughness. A comparison between the scratch resistance and the cavitation-erosion resistance, measured in previous work, was made too. q 2005 Elsevier Ltd. All rights reserved.

The cavitation erosion (CE) resistance of a high temperature gas nitrided (HTGN) UNS S31803 duplex stainless steel (DSS), in substitute ocean water, was evaluated. The CE tests were performed in a vibratory cavitation testing equipment according to ASTM G32-92. For comparison purposes, solution treated samples of the same DSS, as well as of an austenitic UNS S30403 stainless steel (SS), were also studied. After high temperature gas nitriding (HTGN), the duplex stainless steel showed an austenitic surface layer, containing high nitrogen content in solid solution. Five sets of specimens with similar (0.8 wt%) nitrogen contents at the surface, but different grain diameters and increasing texture intensities, were investigated. Three sets of samples with similar grain size and texture but increasing nitrogen contents, between 0.65 and 1.15 wt%, were also studied. The CE mass loss rate of the nitrided samples decreased from 8 to 23 times as compared to the DSS solution treated samples. It was observed that the CE mass loss rate decreased with decreasing grain size, increasing the texture components sharpness or with increasing nitrogen content. The HTGN treatment allowed obtaining samples with CE resistance similar to the cobalt base Ireca and Stellite hard facing alloys. The results of CE tests were analyzed taking into account the major damaging mechanisms, which were examined by scanning electron microscopy observations of eroded surfaces.

Interstitially dissolved nitrogen improves the corrosion and wear resistance as well as the mechanical properties of stainless steels (SS) [1–5]. Production routes of High Nitrogen Stainless Steels (HNSS) by alloying, pressure metallurgy, powder metallurgy, and solid-state diffusion have been studied [6–10]. In the production route, which involves solid-state diffusion, the steel surface and near surface regions are alloyed with nitrogen through chemical, implantation, plasma, or laser techniques [9, 10]. Recently, a chemical solid-state nitrogen alloying technique was developed [10–14], consisting in annealing SS in a N2-containing gas atmosphere in the range 1273–1473 K. In this High Temperature Gas Nitriding treatment (HTGN), atomic nitrogen is absorbed at the surface of the steel and then diffuses into the near surface region. Case-depths from 0.5 to 2.0 mm and nitrogen contents in solid solution at the surface from 0.5–1.0 wt% can be obtained after 18 to 45 ks heat-treatments. HTGN has been successfully used to improve the surface properties of martensitic, austenitic, ferriticaustenitic and martensitic-ferritic SS [7, 10–13, 15]. Particularly, when ferritic-austenitic duplex stainless steels (DSS) are nitrided austenitic cases of higher wear and corrosion resistances are formed, on high strength DSS ferritic-austenitic cores. Due to both high temperatures and long nitriding times: (i) the austenitic cases grow forming coarse columnar grains [10–13], and (ii) the maximum attainable nitrogen content in precipitatefree cases corresponds to the nitrogen solubility limit at that temperature. The solubility limit in austenite, relative to nitride precipitation, increases with temperature; however the amount of ferrite in the dual-phase non-nitrided core increases with temperature too. Thus the optimum nitriding temperature for DSS is between 1423 and 1448 K. In the present work, a novel nitriding cycle that avoids formation of coarse grains in the austenitic case, inhibits nitride precipitation and leads to sharp textures is proposed. It consists on cycling the specimen between two different N2 partial pressures, PN2, (Fig. 1): a high-pressure stage (sorption stage) and a vacuum one (desorption stage). The high nitrogen pressure stage is a long term one where nitrogen is introduced in the specimen. It is followed by a short vacuum period (PN2 ∼ 0) where nitrogen desorption occurs and ferrite

A dual phase ferritic – martensitic AISI 410S stainless steel was nitrided in high purity N2 atmosphere between 1373 and 1473 K. After this treatment a high nitrogen martensitic case, free of precipitates, was formed. The growth kinetics of these fully martensitic cases during high temperature gas nitriding is studied with the aim of predicting martensitic case depths as functions of nitriding times, temperatures and N2 partial pressures. Thermocalc and Dictra software were used to calculate the equilibrium conditions and to solve the diffusion equations respectively. The results showed that the growth rate of the martensitic case is diffusion controlled and it can be calculated assuming local equilibrium. For the nitriding conditions used in this paper, the martensitic case depth is proportional to the square root of the nitriding time t1/2 proportional to the nitriding temperature and roughly proportional to the logarithm of the N2 partial pressure.

El acero inoxidable UNS S31600 fue recubierto con películas de la aleación Ti6Al4V, por medio de la técnica pulverización catódica magnetrón rf. La superficie de los materiales obtenidos se sometió a ensayos de macroindentación, de acuerdo con el procedimiento VDI 3198, para caracterizar la adherencia película-sustrato. Se realizaron experimentos de depósito variando tanto la presión del gas al interior de la cámara de depósito como la potencia aplicada al blanco. La adherencia película-sustrato varío no monotónicamente con la presión y la potencia; la menor adherencia se observó para las presiones y las potencias intermedias. En términos generales se observó una excelente adherencia película-sustrato, la cual se atribuyó principalmente al carácter nanométrico de los cristalitos de las películas (diámetro promedio alrededor de 20 ± 10 nm), a su carácter monofásico y a su elevado grado de uniformidad tanto química como morfológica.

Previous research has suggested that significant improvement in ductility-dip cracking resistance of ERNiCrFe-7 weld metal can be obtained if sec-ond phase precipitation during welding is optimized with some carbide and nitride forming element additions. Therefore, a theoretical and experimen-tal work has been conducted to address the effect of Nb and Ti additions to the precipitation of second-phase particles during welding of a ERNiCrFe-7-like alloy. The critical precipitation temperatures, phase fractions and atomic partitioning in the microstructure were among the factors analyzed in the light of DDC resistance improvement.

Os aços inoxidáveis de alto teor de nitrogênio constituem hoje uma classe promissora de materiais de engenharia. Quando se adiciona nitrogênio aos aços austeníticos, consegue-se aumentar, simultaneamente, a vida em fadiga, a resistência mecânica, a resistência ao desgaste e à corrosão. Nesse trabalho, estudam-se a resistência ao desgaste e a usinabilidade de um aço inoxidável austenítico UNS S30403 nitretado em alta temperatura. A nitretação gasosa em alta temperatura (1200ºC) em atmosferas (N2+Ar) foi realizada para obter amostras com teores crescentes de nitrogênio na superfície, desde 0,05 até aproximadamente 0,45% em peso. Os ensaios de esclerometria foram realizados em um pêndulo instrumentado de um único passe, com possibilidade de medir as forças normais e tangenciais durante o ensaio. A energia específica absorvida foi calculada através da relação entre a energia absorvida no ensaio e a perda de massa observada no ensaio. Observou-se que o aumento do teor de nitrogênio causou um aumento da energia específica absorvida. Os resultados dos ensaios foram analisados levando em consideração o comportamento da curva tensão deformação desses aços, inferida a partir de ensaios de indentação instrumentada, e da energia absorvida em ensaios de impacto Charpy. O aumento da resistência ao risco e a diminuição da usinabilidade devida à adição de nitrogênio foram atribuídos ao forte efeito endurecedor do nitrogênio em solução sólida, sem afetar, significativamente, a taxa de encruamento e a tenacidade. High nitrogen stainless steels (HNSS) are being considered a new promising class of engineering materials. When nitrogen is added to austenitic steels it can simultaneously improve fatigue life, strength and wear and localized corrosion resistance. In this work, a single pass pendulum scratch test was used to study the effect of nitrogen on the scratch resistance and on the machinability of an UNS S30403 austenitic stainless steel. Samples with increasing nitrogen contents at the surface were obtained through high temperature gas nitriding. The thermochemical treatments were performed at 1473 K in (N2+Ar) gas atmospheres for 36.0 ks, obtaining fully austenitic cases (surface nitrogen contents up to 0.5 wt%) ca. 1.5 mm in depth. The scratch tests were performed in a single-pass pendulum, equipped with strain gages to measure normal and tangential forces during scratching. The specific absorbed energy was calculated as the ratio between the measured absorbed energy and the amount of mass removed from the specimen. An increase of the specific absorbed energy with increasing nitrogen content was observed. The results of the scratch tests were analyzed taking into account the stress-strain behavior during depth sensing indentation tests and the energy absorbed during Charpy impact tests. The improvement in scratch resistance due to nitrogen alloying was attributed to the strong hardening effect of nitrogen in solid solution, which does not affect significantly foundry hardening and toughness. A comparison between the scratch resistance and the pitting-erosion resistance, measured in previous work, was made too.

High nitrogen stainless steels (HNSS) are being considered a new promising class of engineering materials. When nitrogen is added to austenitic steels it can simultaneously improve fatigue life, strength and wear and localized corrosion resistance. In this work a single pass pendulum scratch test was used to study the effect of nitrogen on the scratch resistance of an UNS S30403 austenitic stainless steel. Samples with increasing nitrogen contents at the surface were obtained trough high temperature gas nitriding. The thermo-chemical treatments were performed at 1473 K in (N2 + Ar) gas atmospheres for 10 hrs, obtaining fully austenitic cases (surface nitrogen contents up to 0.5 wt-%) circa 1.5 mm in depth. The scratch tests were performed in a single-pass pendulum, equipped with strain gages to measure normal and tangential forces during scratching. The specific absorbed energy was calculated as the ratio between the measured absorbed energy and the amount of mass removed from the specimen. An increase of the specific absorbed energy with increasing nitrogen content was observed. The results of the scratch tests were analyzed taking into account the stress – strain behavior during depth sensing indentation tests and the energy absorbed during Charpy impact tests. The improvement in scratch resistance due to nitrogen alloying was attributed to the strong hardening effect of nitrogen in solid solution, which does not affect significantly work hardening and toughness. A comparison between the scratch resistance and the cavitation-erosion resistance, measured in previous work, was made too.

Ti"6Al"4V thin films were grown by magnetron sputtering on a conventional austenitic stainless steel. Five deposition conditions varying both the deposition chamber pressure and the plasma power were studied. Highly textured thin films were obtained, their crystallite size being around 10-30nm and their hardness being around 10GPa.