Showing papers on "Austenitic stainless steel published in 1971"

Intergranular Corrosion of Austenitic Stainless Steel

Abstract: The well‐known susceptibility of austenitic stainless steels to intergranular corrosion after heat‐treatment in the temperature range of 550°–800°C (i.e., "sensitization") has long been attributed to depletion of Cr from regions of the alloy matrix adjacent to grain boundaries in which had precipitated. Those regions of the steel in which the local Cr composition falls below about 12% have a diminished ability to form a passive film and hence corrode preferentially.We have made thermodynamic calculations of the equilibria in and near grain boundaries in order to determine the chromium content in the vicinity of carbide particles. The calculations show that the equilibrium chromium content is a strong function of the temperature and of the carbon and alloy content of the steel. It is inferred from the analysis that variations in the susceptibility to intergranular attack are determined primarily by changes in the equilibrium chromium content near the carbides and not by changes in the number and distribution of particles. For instance, above 800°C the chromium content near the carbides is high enough to produce passivity, and the alloy is immune not because of the absence of carbides but because chromium depletion is not severe. Experimental studies of rates of grain boundary attack as functions of temperature and composition have confirmed the predictions of the analysis.A further factor of less importance is the distribution of carbides in the grain boundary. Calculations were made to determine the Cr concentration gradient within the boundary between carbide particles as a function of temperature and composition as well as the Cr gradient normal to the boundary. These calculations predict a strong interdependence between susceptibility to intergranular corrosion, carbide particle spacing, and sensitizing temperature. Experimental results on thinned samples of sensitized material corroded in a Strauss solution and examined by electron microscopy are in good agreement with predicted effects.

Measurements of the temperature rise ahead of a fatigue crack

Abstract: The temperature rise ahead of a fatigue crack has been measured using a Thermovision camera. Observations were made on three kinds of polymer and an austenitic stainless steel. The maximum temperature difference in macro-scale between the zone ahead of the crack and the bulk of the material was found to be, for the polymers, about 30°C at 725 N/min and amplitude o.1–0.8 kp/mm2 and, for the steel, 14°C at 6000 N/min and amplitude 3.0–24.0 kp/mm2.

Observation of partial dislocations on a coherent twin boundary

Abstract: Dislocations observed on a coherent twin boundary in an austenitic stainless steel are shown to be pairs of the Shockley partial α/6 ⟨ 211 ⟩ type. The twin boundary stacking-fault energy is measure...

Nickel aluminide coated low alloy stainless steel

Abstract: Low alloy austenitic stainless steel is protected from oxidative corrosion and erosion at high temperatures in the presence of exhaust gases from internal combustion engines by flame-spraying a layer between about 0.003 inches and about 0.007 inches thick of an alloy of 80 percent nickel and 20 percent chromium on the steel base, and thereafter converting the layer to an intermetallic chromium containing nickel aluminide coating by a low temperature aluminum cementation process. A cementation pack comprising 96 percent aluminum oxide, 2 percent aluminum, 1 percent sodium chloride, and 1 percent ammonium bifluoride is placed on the nickel-chromium layer in an inert atmosphere for a period between four hours and 24 hours at 1400*F to 1600*F to form an intermetallic chromium containing nickel aluminide coating containing 40 to 60 atomic percent aluminum. The coated steel is highly resistant to oxidation corrosion and erosion by high temperature exhaust gases from internal combustion engines. It is particularly useful in the construction of thermal reactors for exhaust systems in automobiles for the control of pollution from exhausts.

Shielded arc welding with austenitic stainless steel

Abstract: An austenitic stainless steel which is suitable for use as a filler metal in gas shielded arc welding and a gas shielded arc welding process employing said steel as a filler metal. The steel consists essentially of, in weight percent, up to 0.1 percent carbon, 7.5 - 16.0 percent manganese, up to 1.0 percent silicon, 17.5 - 26.0 percent chromium, 5.0 - 17.0 percent nickel, 0.75 4.0 percent molybdenum, 0.2 - 0.38 percent nitrogen, balance iron and incidental impurities, and is additionally limited as follows: 1. The ratio of austenitizing elements to ferritizing elements is greater than 1 in accordance with the following expression:

Elevated temperature mechanical properties of shock-strengthened austenitic stainless steel

Abstract: The mechanical properties of explosively shock-strenghened (320 kbar) Type 304 stain-less steel were investigated. Tensile tests were performed on the shock-strengthened material at temperatures ranging from room temperature to 650°C. The shock hardening caused large increases in yield strength, moderate increases in ultimate strength, and reductions in ductility. Annealing studies on the shock-strengthened stainless steel indicated that considerable amount of the shock-induced strength stainless steel indicated that considerable amount of the shock-induced strength increase is retained after long time anneals at 700 and 750°C. However, metallographic studies on the annealed material indicated the presence of fine carbide particles which may partly account for the strength of the material. Creep studies indicated that the minimum creep rate at 650°C was reduced by a factor of 1000 due to shock strengthening.

Irradiation-produced defects in austenitic stainless steel.

Abstract: The microstructure of annealed AISI Type 304 and type 316 stainless steels has been characterized by transmission electron microscopy as a function of fast reactor irradiation at fluence levels from 4×1021 to 7×1022 n per sq cm (E>0.1 mev) and at irradiation temperatures from 370° to 700°C. Several irradiation produced defect types where found: voids, Frank faulted loops, perfect loops, dislocation networks, and precipitates. Void number density obeys a power law relationship to fluence, wherein the exponent increases with increasing temperature from 0.8 to 1.4 over the irradiation temperatures investigated. The void size is nearly independent of fluence and increases with increasing temperature. The upper limit irradiation temperature for void formation is about 650° to 700°C. The density and size of Frank faulted loops followed trends similar to those found for voids to temperatures of ∼550°C where unfaulted loops, perfect loops, and dislocation networks coexist. These experimental results do not confirm predictions of recently acvanced models of void formation. The major deficiency of these models appears to be the nucleation rate. Accordingly, empirical nucleation rates were used to formulate a diffusion-controlled void growth model. This model was found to closely describe experimentally determined void growth kinetics.

Chromium-nickel-manganese-nitrogen austenitic stainless steel

Abstract: An austenitic stainless steel having good austenite stability, a very low work hardening rate and excellent weld ability by fillerless fusion welding techniques comprising from 17 to 19 percent chromium, from 4 to 10 percent nickel, from 11 to 13 percent manganese, from 0.01 to 0.16 percent nitrogen, 0.06 maximum carbon, up to 1 percent silicon, up to 2 percent molybdenum, up to 1.5 percent copper, and remainder iron except for incidental impurities. The 0.2 percent yield strength of the steel in the annealed condition ranges from about 172.5 to 345 MN/m2 (25 to 50 ksi). The alloys have particular utility in applications involving cold heading.

Cyclic Stress-Strain Behavior of Two Alloys at High Temperature

Abstract: The cyclic stress-strain curve is useful in the design of structural components that are subjected to cyclic plastic deformation. Since the incremental step test has been used successfully to approximate cyclic stress-strain curves of metals at room temperature, the objective of this study is to evaluate its usefulness in describing the cyclic deformation behavior of two alloys at elevated temperature. Constant strain rate incremental step tests were conducted on nickel-iron-chromium Alloy 800 and Type 304 austenitic stainless steel in air at temperatures between 70 and 1400 F. This experimental technique provided a useful method of determining cyclic stress-strain curves for these two alloys over that temperature range. Alloy 800 cyclically hardened by factors between 2 and 5, with a maximum amount of hardening at 1200 F. Type 304 stainless steel cyclically hardened by factors between 2 and 3, with a maximum amount of cyclic hardening at 1000 F. Strain rate and maximum strain range were shown to influence cyclic hardening of the Type 304 stainless steel at both 1000 and 1200 F. Results indicated that the cyclic stress-strain curve obtained from an incremental step test is most useful for estimating the cyclic stress-strain response of a material under variable-amplitude loading.

Freeze seal for sodium valves

Abstract: A freeze seal for a valve having an elongated stuffing box and a longitudinally movable valve stem extending through the box. A plurality of metallic packings separated by metallic rings are disposed in the box around the valve stem to maintain sodium in the frozen state within the box. Each packing is formed of nickel, nickel base alloy, austenitic stainless steel, aluminum or aluminum base alloy in the form of a thin wire, wool, thin sheet, foil or combinations thereof. It can include two coaxial layers of metallic wool, a metallic foil interposed between them and an outer sheath made of a braid of thin metallic wire.

Potentiostatic Study of the Corrosion Behaviour of Austenitic Stainless Steel Weld Metal

Abstract: The corrosion behaviour of austenitic stainless steel weld metals has been studied potentiostatically with particular reference to marginally and moderately oxidising conditions. Sample welds cover...

Densification of Stainless Steel Powder Compacts During Sintering

Abstract: Densification characteristics of stainless steel compacts having various compositions in α, γ and γ+e phases were examined by dilatometry. Results obtained are summerized as follows:1) The linear shrinkage (ΔL/L0) at the initial stage of the isothermal densification is given as a function of porosity (e), particle size (r) and sintering time (t):ΔL/L0≅K0-m⋅(e/e0)⋅tn, where e0 is the maximum porosity, and K0 a constant, m and n depend on the phase during sintering, e.g. m=1.5, n=0.5 in α and γ+δ phase region, and m=1.2, n=0.4 in γ phase.2) Activation energy for α phase of 410L was 53, 500 cal/mol, and for γ phase of 347, 53, 600 cal/mol and 96, 000 cal/mol below and above 1300°C respectively.3) Sintering of austenitic stainless steel powder is promoted by the presence of δ-phase in γ matrix. Activation energy calculated from the dimensional change was 70, 600-76, 500 cal/mol.

Process for preparing vinyl acetate

Abstract: PROCESS FOR PRODUCING VINYL ACETATE WHICH COMPRISES SUBJECTING A FEED-STOCK CONSISTING ESSENTIALLY OF ETHYLENE GLYCOL DIACETATE TO VAPOR PHASE PYROLYSIS WITHIN A PYROLYSIS ZONE HAVING SURFACES IN DIRECT CONTACT WITH THE REACTION MIXTURE DURING THE PYROLYSIS CONSISTING ESSENTIALLY OF AN AUSTENITIC STAINLESS STEEL.

A Metallurgical Study on Postheat Treatment of Overlaid Austenitic Weld Metals

Abstract: Overlaid weld metals of austenitic stainless steel in a pressure vessel of power reactor are usually postheated for a long period of time after welding. The heat treatment is considered a kind of sensitizing and it is important to check the soundness of the weld metal after heat treatment, especially about the precipitation of carbides.Investigation was made about the distribution of delta ferrite and its change by reheating, precipitation of carbides and their identifications, and sigma phase. The main conclusions reached from this study are as follows:(1) Precipitation of delta ferrite from molten weld metal depends on solidification phenomenon. There was a small amount of ferrite near the bond or toe in which the local solidification time was short, comparing with other parts of weld metal. At no specific location ferrite was found due to macrosegregation or extremely rapid solidification.(2) Shape and amount of ferrite were changed by reheating after solidification. Ferrite was extremely grown after heating at 1350°C for 15 sec. It was spheroidized by heating at 1200°C.(3) There were five types of carbides developed after postheating: a) dot-shaped carbide, b) massive carbide, c) precipitated carbide mostly due to diffusion of carbon from base metal, d) lamellar carbide by eutectic reaction, and e) precipitated carbide due to tempering of martensite.(4) The first two types of carbides were M23C6 type except for a relatively intense postheating of 700°C. A M6C carbide was detected with M23C6 carbide after postheating at 700°C. It should be noticed that dot-shaped carbides were linked to each other on an austenite grain boundary when there was no ferrite, and massive carbides co-existed sometimes with sigma phase.(5) The fourth one, lamellar carbide, which had not been pointed out in previous study, precipitated on an austenite grain boundary near base metal after a fairly large extent of carbon diffusion from base metal. The eutectic phase was very soft and it would be a cause of trouble in a side bend test which is required as part of the procedure test of power reactor.

Austenitic stainless steels

Abstract: An austenitic stainless steel alloy consisting of essentially less than 0.07% carbon, less than 0.05% manganese, 0.25-0.75% silicon, 24-26% nickel, 19-21% chromium, up to 0.75% niobium remainder iron and incidental impurities, the percentage being by weight. Optionally the steel may include yttrium or gadolinium within the range 0.025-1 weight percent.

Friction and Wear of Ball Bearings in Liquid Sodium

Abstract: An experimental study on the friction and wear properties of ball bearings has been conducted in liquid sodium at 400°C. Out of a number of materials compatible with sodium, Stellite 6, Hastelloy C and austenitic stainless steel (AISI 316) were chosen. A medium size, single-row, deep groove, radial type ball bearing was selected for the form of test bearings. The following conclusions were obtained from this study: (1) Of the three materials, the hardest material (Stellite 6) showed the highest resistance against wear, and the greatest recovery effect from friction. (2) Liquid sodium appears to contribute little as lubricant, due to its low viscosity and extremely high chemical activity. No tendency toward self-welding was, however, observed at temperatures up to 400°C, despite the mean compression stress applied having been over three times the yield strength. (3) The wear of ball bearings in liquid sodium is considered to be caused by local sliding friction. The wear rate is higher the softer the materi...

Welded joint for multi-wall container

Abstract: Welding-seam chamfers of a multi-wall container consist of a Cr-Mo steel containing 1-6% Cr and 0.3-1.3% Mo or of a Mo steel containing 0.3-0.7% Mo, and are coated with a built-up welded layer (3) of Cr-Mo steel, resistant to embrittlement by H2, and not hardening through welding heat and containing 4-7 times Ti content or 8-14 times Nb content, calcd. on C content, or having a Ti-Nb content corresponding to eqn. Nb + 2Ti = (8-14) x C. The container parts are then subjected to a standardisation annealing. The welding seam part situated within internal cylinder (1) range is welded with a material similar to layer (3) or austenitic stainless steel in thickness equal to at least the thickness of internal cylinder (1), (the filler layer 4), and the remaining part of the welding seam is welded with a metal hardening only just below welding heat (filler layers 5).

Initiation of Chloride-Pitting Corrosion of Austenitic Stainless Steel in Sulphate Solution

Abstract: The solution pH does not affect the initiation of pits in neutral solution but appears to affect in acid solution; the apparent effect in acid solution may be ascribed to the degree of association of SO42and H+ which decreases with pH. The Tafel line of the pit initiation differes between the passive passive potential region and the trans-passive potential region, though its slope remains constant; in the latter potential region the pit-initiation is hindered by CrO42ion produced by trans-passive dissolution of the alloy. From these results it is concluded that it is co-existing anions rather than hydrogen ion which determines the chloride-breakdown of the passivity of stainless steel. The initiation of pits also appears to depend on the aging or thickness of the passivation film, its rate decreasing with extending the time of passivation.