Showing papers on "Austenitic stainless steel published in 1988"

Welding Metallurgy of Stainless Steels

Abstract: Contents: Significance of Constitution Diagrams for the Understanding of Welding Phenomena * Metallurgical Processes During Solidification and Cooling in Stainless Steel Weld Metal * Metallurgical Phenomena in Secondary Crystallization of Stainless Steels and Weld Metals * Precipitation Phenomena in Stainless Steel and Weld Metals * Hot Cracking Resistance During the Welding of Austenitic Stainless Steels * Welding Metallurgy of Ferritic Stainless Chromium Steels with Carbon Contents Below 0.15 per cent * Welding Metallurgy of Low Carbon Chromium-Nickel Martensitic Stainless Steels (Soft Martensitic Steels) * Welding Metallurgy of Duplex Austenitic-Ferritic Stainless Steels * Welding Metallurgy of Austenitic Stainless Steels * General Instructions for the Welding and Post-Weld Surface Treatments of Fabrications and Welded Components Made from Austenitic Stainless Steel * Welding Metallurgy of Heat Resisting Steels * Welding Metallurgy of Austenitic-Ferritic Dissimilar Joints * Appendix: Abbreviations and Short Designations * References * Author Index * Subject Index.

Nitrogen implantation of AISI 304 stainless steel with a coaxial plasma gun

Abstract: The application of a plasma focus (PF) device operated at 1 kJ and 25 kV as a pulsed ion implanter is described. Samples of AISI 304 stainless steel implanted with nitrogen with this device show a reduction of wear of 42 times with respect to the implanted ones, with a reduction, at the same time of the friction coefficient. X‐ray diffraction and x‐ray photoelectron spectroscopy analyses of nitrided samples show the Fe2N precipitate formation, in an almost homogeneous ∼0.4‐μm‐thick superficial layer. The feasibility of the use of the PF as an implanter arises from these results as well as the possibility of designing and constructing similar systems that could perform the whole process (e.g., nitriding) in short time intervals (∼10 s).

Thermal conductivity and thermal expansion of stainless steels D9 and HT9

Abstract: Renewed interest in the use of metallic fuel in a liquid-metal fast breeder reactor has prompted study of the thermodynamic and transport properties of fuel and cladding materials. Two stainless steels are of particular interest because of their good performance under irradiation. These are D9, an austenitic steel, and HT9, a ferritic steel. Thermal conductivity and thermal expansion data for these cladding alloys are of particular interest in assessing in-reactor behavior. These two properties were measured for the two steels at temperatures to 1200 K. Of particular interest is the influence on these properties of a phase transition in HT9.

Sensitization Development in Austenitic Stainless Steel: Correlation between STEM-EDS and EPR Measurements

Abstract: Direct measurements of grain boundary chromium depletion by energy dispersive x-ray spectroscopy (EDS) in a scanning transmission electron microscope (STEM) are compared to measurements of the degree of sensitization (DOS) using the electrochemical potentiokinetic reactivation (EPR) test technique. Results indicate that the EPR test attacks chromium-depleted regions in austenitic stainless steels (SSs) that contain less than about 12.5 to 13.5 wt% chromium. The amount of attack depends on the width and on the depth of the depleted region. Correlations are presented between STEM-EDS and EPR-DOS measurements and discussed based on the width and volume of chromium-depleted material in both AISI 304 and 316 SSs. Implications of such correlations on the ability to quantitatively model sensitization development are also discussed.

Simultaneous chromizing-aluminizing coating of austenitic stainless steels

Abstract: Chromium and aluminum were simultaneously codeposited by diffusion into austenitic stainless steel substrates, by a single step pack cementation process. The mechanism for the formation of diffusion-coated products on 304 and 316 stainless steels and on Incoloy 800 are discussed. The morphologies of the phases formed at the surface, namely, and external beta layer and an underlying multiphase interdiffusion zone, are presented. The formation of the brittle beta outer layer was minimized by variations in the pack composition and activator. The coated 304 and 316 steels exhibited excellent scaling resistance upon oxidation in air at 1000 C.

Microbiologically influenced corrosion failures of austenitic stainless steel welds

Abstract: The study described examined the microstructure, ferrite content and sensitization of the heat affected zones of twelve austenitic stainless-steel weldments with reported pitting corrosion. Eleven of the welds exhibited microbiologically influenced corrosion (MIC) or MIC chloride-assisted pitting attack.

Oxidation of high-aluminum austenitic stainless steels

Abstract: The cyclical oxidation behavior of an austenitic stainless steel (24% Ni, 10% Cr, 5% Al, and balance Fe) has been evaluated in the temperature range 800–1300°C. The effects of trace elements such as S, Y, Zr, and Ti on the oxidation of the austenitic stainless steel have also been evaluated. The results indicate that Fe-Ni-Cr-Al stainless steels exhibit superior oxidation resistance up to 1300°C due to the formation of a very adherent and thin film of α-Al2O3.

Microstructural transformations in austenitic-ferritic transition joints

Abstract: The relatively complex microstructures developed at the interface between ferritic steel and weld metal on austenitic-ferritic transition joints have been examined by metallographic observation and by hardness tests in the as-welded condition and in the as-welded-and-tempered condition. Both austenitic stainless steel and nickel-based filler metals were used in welds. On as-welded specimens a sharp change of hardness in low-alloy steel has been measured, with increasing distance from weld metal; the hardness values have been related to the observed metallographic constituents. On post-weld heat treated specimens, the behaviour is different according to the composition of filler material, either austenitic steel or nickel-based alloy. In the case of austenitic filler material, a dark-etching narrow diffusion region of carbon toward weld metal is formed, with an adjacent markedly decarburized zone, exhibiting the minimum microhardness values in a narrow band of about 60 micrometres. Since this sharp structural variation is recorded just in the zone where often failures occur, the final post-weld heat treatment appears to be proposed with due caution. In the case of nickel-based filler material, carbon diffusion is inhibited by the precipitation of alloy carbides at the weld interface. This determines a more homogeneous heat affected zone (HAZ) in the ferritic steel and a reduced decarburization near the fusion line after a post-weld heat treatment, confirming the reasons of the preference recognized to this filler material, especially when service temperature is elevated and submitted to frequent changes, or whenever a post-welded heat treatment is required.

Process for preparation of austenitic stainless steel having excellent seawater resistance

Abstract: In a continuously cast piece of austenitic stainless steel having a large amount of Mo, segregation of alloy elements such as Mo and Cr is caused at the center part in the thickness direction of the slab, and the σ-phase is precipitated during the step of cooling the cast piece. When a heavy plate or hot coil is prepared from this cast piece as the starting material, cracking occurs in the hot-working step and the corrosion resistance of the final product is degraded. According to the present invention, at the cast piece-­forming step, the super-heating degree of the molten steel is controlled to at least 25°C, whereby the isometric ratio is controlled to below 25%. When the heating times at the soaking and hot rolling treatments and the conditions for annealing the obtained steel sheet are controlled, the pitting resistance of the steel plate is greatly improved and cracking is prevented at the hot-working step.

Sensitization Development in Austenitic Stainless Steel — Measurement and Prediction of Thermomechanical History Effects

Abstract: The effects of thermal and thermomechanical treatments on sensitization development in AISI 304 and 316 stainless steels (SSs) have been measured and compared to model predictions. Sensitization development resulting from isothermal, continuous cooling, and pipe welding treatments has been evaluated. An empirically modified, theoretically based model is shown to accurately predict material degree of sensitization (DOS) as expressed by the electrochemical potentiokinetic reactivation (EPR) test after both simple and complex treatments.

High frequency stage I corrosion fatigue of austenitic stainless steel (316L)

Abstract: High frequency (123 Hz) fatigue crack propagation studies were conducted under rising ΔK conditions (R-ratio = 0.22) on single edge notch specimens of austenitic stainless steel (type 316L) that contained an annealed precrack. Tests were conducted in near neutral (pH 5.5) solutions of 1 M NaCl and 1 M NaCl + 0.01 M Na2S2O3 under potentiostatically controlled conditions and in desiccated air. Attention was directed primarily to the near threshold behavior and the stage I (crystallographic) region of cracking. Good mixing between the crack solution and bulk solution was obtained and crack retardation and arrest effects, due to surface roughness induced closure, were minimized at high anodic potentials by electrochemical erosion. Thermodynamic considerations showed that hydrogen played no role in fatigue crack propagation. Analysis of the results in terms of the estimated effective cyclic stress intensity, ΔK eff, showed a systematic effect of potential on the average crack growth increment per cycle,da/dN. Anodic dissolution processes were considered to make an insignificant contribution toda/dN. A model was proposed for stage I fatigue cracking based on the effect of oxide nucleation rate on restricted slip reversal. The essential features of the model were considered to be relevant to cracking in aqueous environments and in desiccated air.

The effects of nitrogen content and twin boundaries on the yield strength of various commercial heats of type 316 austenitic stainless steel

Abstract: The applicability of the Pickering and Norstrom equations for yield strength predictions in austenitic stainless steel has been evaluated for several commercial heats of type 316 austenitic stainless steel. Steel with various nitrogen contents and ultrafine grain structure have been investigated. It is shown that the Norstrom equation provides a better estimation of the σ 0 and k parameters in the Hall-Petch relationship for various commercial type 316 austenitic steels than the Pickering equation. The effect of the increasing number of coherent twin boundaries on the yield strength in type 316 austenitic steels has also been studied. It is shown that the number of twin boundaries per grain has no effect on 0.2% proof stress. It has also been shown that doping of type 316 steel with 30 ppm of boron increases the k parameter in the Hall-Petch relationship by about 50% in coarse-grained alloys (grain size about 0.2 mm).

The effect of grain size on the bulk formability and tensile properties of austenitic stainless steel types 304 and 316

Abstract: The formabilities and tensile properties of stainless steel types 304 and 316 of various grain sizes were measured by means of tensile and compression tests. It was found that variation in grain size had no significant effect on formability, but that the tensile properties of the materials varied slightly. The stress-strain relation for the two steels is described by the Ludwigson equation in a modified form.

Stage I corrosion fatigue crack crystallography in austenitic stainless steel (316L)

Abstract: The crystallographic and fractographic aspects of stage I corrosion fatigue of SS 316L have been studied with the aid of etch pitting techniques. Single edge notch specimens were fatigued at 123 Hz in desiccated air and near neutral (pH 5.5) aqueous environments of 1 M NaCl and 1 M NaCl + 0.01 M Na2S2O3. The fractographic features were found to be independent of the testing conditions. The orientation of primary facets and the crystallographic directions of crack propagation were identified. Six combinations of crack plane and direction were observed with primary facet orientations of {111}, {110}, and {001}. The primary facet crystallography was shown to arise from microscale propagation along a single variant of {111} or alternating periods of microscale propagation along a conjugate pair of {111} variants. The mechanism of cracking was discussed and shown to be consistent with a model of restricted slip reversibility (RSR), where environmental interactions with emergent slip steps influence the amount of slip reversibility.

Mapping of low cycle fatigue mechanisms at elevated temperatures for an austenitic stainless steel. Discussion

Abstract: Mapping of low cycle fatigue mechanisms at elevated temperatures is attempted for a better understanding of the elevated temperature, low cycle fatigue behavior of an austenitic stainless steel. Results of strain-controlled, uniaxial low cycle fatigue tests on a solution-treated Type 310 stainless steel were used in the analysis. The experiments were performed at 15 temperatures that ranged from room temperature to 800°C and under four strain rate conditions that ranged from 6.7 X 10 - 3 s - 1 to 6.7 X 10 - 6 s - 1 . Modes of variation, both in stress amplitude and in fatigue life, are classified and plotted against temperature-strain rate coordinates. By superposing the two maps, one can easily find the principal factors that govern the fatigue life for any given conditions of temperature and strain rate. The proposed idea of mapping is believed to have wide applicability (e.g., for selecting materials and predicting fatigue behavior under service conditions).

Austenitic stainless steel combining strength and resistance to intergranular corrosion

Abstract: A nonmagnetic austenitic stainless steel and articles such as drill collars or boat shafts fabricated therefrom, the steel having a 2% yield strength of at least 10 ksi (689 N/mm²), improved resistance to inter­granular stress corrosion, good ductility, good corrosion resistance and low magnetic permeability, and consisting essentially of, in weight percent, from greater than 0.05% to about 0.10% carbon, greater than 14% to about 18% manganese, about 15% to about 20% chromium, about 1% to about 3.5% nickel, about 0.3% to about 0.55% nitrogen, about 0.10% to about 0.5% vanadium, about 1.0% maximum copper, about 1.0% maximum molybdenum, about 1.0% maximum silicon, about 0.04% maximum phosphorus, about 0.03% maximum sulfur, and balance essentially iron.