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At least 451 records · Page 25

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NASA NTRS1976

Rolling-element fatigue lives of AISI 52100 steel balls with several synthetic lubricants

Rolling-element fatigue tests were run with three synthetic lubricants with and without antiwear additives and with a paraffinic mineral oil at race temperatures of 336 to 353 K (146 146 to 175 F). The five-ball fatigue tester was used with steel balls to evaluate the relative fatigue lives with each of six lubricant-additive combinations. The tests were run at 5,520 MPa (800,000psi) maximum Hertz stress, 10,000 rpm shaft speed, and 30 deg contact angle. The lubricants tested have similar kinetic viscosities at 372 K (210 F) ranging from 0.034 to 0.089 sq cm/sec (3.4 to 8.9 cS). At these conditions, the mode of failure in the five-ball fatigue tester was classical subsurface rolling-element fatigue. The baseline for comparison of fatigue life was the paraffinic mineral oil without additives. The effects of the synthetic lubricants and their additives, which are useful for boundary lubrication, oxidation or foam inhibition, were evaluated.

Parker, R. J.↗

NASA NTRS1976

Sulfidation of 310 stainless steel at sulfur potentials encountered in coal conversion systems

The sulfidation of SAE 310 stainless steel was carried out in gas mixtures of hydrogen and hydrogen sulfide over a range of sulfur potentials anticipated in advanced coal gasification processes. The kinetics, composition, and morphology of sulfide scale formation were studied at a fixed temperature of 1,065 K over a range of sulfur potentials from .00015 Nm to the -2nd power to 900 Nm to the -2nd power. At all sulfur potentials investigated, the sulfide scales were found to be multilayered. The relative thickness of the individual layers as well as the composition was found to depend on the sulfur potential. The reaction was found to obey the parabolic rate law after an initial transient period. Considerably longer transient periods were found to be due to unsteady state conditions resulting from compositional variations in the spinel layer. The sulfur pressure dependence on the parabolic rate constant was found to best fit the equation K sub p equals const. (P sub S2) to the 1/nth power, where n equals 3.7. The growth of the outer layers was found to be primarily due to the diffusion of metal ions, iron being the predominant species. The inner layer growth was due to the dissociation of the primary product at the alloy scale interface and depended on the activity of chromium.

Rao, D. B.↗

NASA NTRS1976

Hydrogen-induced slow crack growth of a plain carbon pipeline steel under conditions of cyclic loading

The investigation described was aimed at establishing the degree of compatibility between a plain carbon pipeline-type steel and hydrogen and also hydrogen-rich environments containing small additions of H2S, O2, H2O, CO, CO2, CH4, and natural gas at pressures near 1 atm. Test were carried out under conditions of static and cyclic loading; the subcritical crack growth was monitored. The rates of crack growth observed in the hydrogen and hydrogen-rich environments are compared with the crack rate observed in a natural gas environment to determine the compatibility of the present natural gas transmission system with gaseous hydrogen transport.

Nelson, H. G.↗

NASA NTRS1976

Application of strainrange partitioning to the prediction of MPC creep-fatigue data for 2 1/4 Cr-1Mo steel

Strainrange partitioning is used to predict the long time cyclic lives of the metal properties council (MPC) creep-fatigue interspersion and cyclic creep-rupture tests conducted with annealed 2 1/4 Cr-1Mo steel. Observed lives agree with predicted lives within factors of two. The strainrange partitioning life relations used for the long time predictions were established from short time creep-fatigue data generated at NASA-Lewis on the same heat of material.

Saltsman, J. F.↗

NASA NTRS1977

X-ray photoelectron spectroscopic study of surface chemistry of dibenzyl-disulfide on steel under mild and severe wear conditions

Wear tests were performed on 304 stainless steel lubricated with pure mineral oil with and without dibenzyl-disulfide. Both mild and severe wear were observed. The type of wear was distinguished by a marked change in wear rate, friction coefficient, and wear scar appearance. The chemical composition of the wear scar surface was examined with X-ray photoelectron spectroscopy in conjunction with argon ion sputter etching. In severe wear scars, a sulfide was formed at the expense of the normal oxide layer. In mild wear scars, there were only superficial sulfur compounds, but there was a substantial increase in the oxide thickness.

Wheeler, D. R.↗

NASA NTRS1977

Influence of temperature and the role of chromium on the kinetics of sulfidation of 310 stainless steel

The sulfidation of 310 stainless steel was studied over the temperature range from 910 K to 1285 K. By adjusting the ratio of hydrogen sulfide, variations in sulfur potential were obtained. The effect of temperature on sulfidation was determined at three different sulfur potentials: 39/sqNm, 0.014/sqNm, and 0.00015/sqNm. All sulfide scales contained one or two surface layers in addition to a subscale. The second outer layer (OL-II), furthest from the alloy, contained primarily Fe-Ni-S. The first outer layer (OL-I), nearest the subscale, contained FE-Cr-S. The subscale consisted of sulfide inclusions in the metal matrix. At a given temperature and sulfur potential, the weight gain data obeyed the parabolic rate law after an initial transient period. The parabolic rate constants obtained at the sulfur potential of 39/sqNm did not show a break when the logarithm of the rate constant was plotted as a function of the inverse of absolute temperature. Sulfidation carried out at sulfur potentials below 0.02/sqNm, however, did show a break at 1145 K, which is termed as the transition temperature. This break was found to be associated with the changes which had occurred in the Fe:Cr ratio of OL-I. Below the transition temperature the activation energy was found to be approximately 125 kj/mole. Above the transition temperature the rate of sulfidation decreased with temperature but dependent on the Fe:Cr ratio in the iron-chromium-sulfide layers of the OL-I. A reaction mechanism consistent with the experimental results has been proposed.

Rao, D. B.↗

NASA NTRS1977

Experimental and Analytical Load-Life Relation for AISI 9310 Steel Spur Gears

Life tests were conducted at three different loads with three groups of 8.9 cm pitch diameter spur gears made of vacuum arc remelted VAR AISI 9310 steel. Life was found to vary inversely with load to the 4.3 and 5.1 power at the L10 sub and L50 sub life levels, respectively. The Weibull slope varied linearly with maximum Hertz contact stress, having an average value of 2.5. The test data when compared to AGMA standards showed a steeper slope for the load-life diagram.

Townsend, D. P.↗

NASA NTRS1976

Aqueous stress-corrosion cracking of high-toughness D6AC steel

The crack growth behavior of D6AC steel as a function of stress intensity, stress and corrosion history, and test technique, under sustained load in filtered natural seawater, 3.3 per cent sodium chloride solution, and distilled water, was investigated. Reported investigations of D6AC were considered in terms of the present study with emphasis on thermal treatment, specimen configuration, fracture toughness, crack-growth rates, initiation period, and threshold. Both threshold and growth kinetics were found to be relatively insensitive to these test parameters. The apparent incubation period was dependent on technique, both detection sensitivity and precracking stress intensity level.

Gilbreath, W. P.↗

NASA NTRS1977

Application of Strainrange Partitioning to the prediction of creep-fatigue lives of AISI Types 304 and 316 stainless steel

As a demonstration of the predictive capabilities of the method of Strainrange Partitioning, published high-temperature, low cycle, creep-fatigue test results on AISI Types 304 and 316 stainless steel were analyzed and calculated cyclic lives compared with observed lives. Predicted lives agreed with observed lives within factors of two for 76 percent, factors of three for 93 percent, and factors of four for 98 percent of the laboratory tests analyzed. Agreement between observed and predicted lives is judged satisfactory considering that the data are associated with a number of variables (two alloys, several heats and heat treatments, a range of temperatures, different testing techniques, etc.) that are not directly accounted for in the calculations.

Saltsman, J. F.↗

NASA NTRS1976

Sulfidation of 310 stainless steel at sulfur potentials encountered in coal conversion systems

Rao, D. B.↗

NASA NTRS1977

Gaseous hydrogen embrittlement of high strength steels

The effects of temperature, hydrogen pressure, stress intensity, and yield strength on the kinetics of gaseous hydrogen assisted crack propagation in 18Ni maraging steels were investigated experimentally. It was found that crack growth rate as a function of stress intensity was characterized by an apparent threshold for crack growth, a stage where the growth rate increased sharply, and a stage where the growth rate was unchanged over a significant range of stress intensity. Cracking proceeded on load application with little or no detectable incubation period. Gaseous hydrogen embrittlement susceptibility increased with increasing yield strength.

Gangloff, R. P.↗

NASA NTRS1976

Application of strainrange partitioning to the prediction of MPC creep-fatigue data for 2 1/4 Cr-1 Mo steel

Creep-fatigue tests were conducted on annealed 2.25Cr-1Mo steel in air at 538 C involving interspersion of rapid strain cycles (0 to 22 cycles) between constant tensile stress-hold periods (23 or 47 hours). Life predictions were made on the basis of the strain range-life relations obtained from short-time material characterization tests on tubular specimens taken from the same heat as the specimens for the creep-fatigue tests. The creep-fatigue tests lasted from about 500 to 5000 hours, while the short-time tests used as the prediction basis lasted from 0.1 to 100 hours. By partitioning the creep and plastic strains within every cycle and summing the damage on a cycle-by-cycle basis, the predicted lives agreed with the observed ones within factors of two.

Saltsman, J. F.↗

NASA NTRS1976

Nickel-free Fe-12Mn-0.2Ti alloy steel for cryogenic applications

A nickel-free Fe-12Mn-0.2Ti alloy steel was investigated for cryogenic applications. The systematic control of the grain size and the microstructural distribution of the retained gamma phase was made through alpha plus gamma heat treatments in combination with mechanical working. Substantial improvements of important low temperature mechanical properties were obtained by these processings.

Hwang, S.↗

NASA NTRS1976

Thermal energy storage using large hollow steel ingots

High temperature thermal energy storage (to 500 C = 930 F) using hollow steel ingots is investigated. Preliminary studies indicate that the system should be reliable, be characterized by low operation and maintenance costs, and be associated with low development risk. The estimated installed system energy unit storage cost is $13.50/kWh-t.

Turner, R. H.↗

NASA NTRS1978

Mechanical properties of 18-2 Mn stainless steel

Report details experimental data from behavioral studies of mechanical properties of 18-2 Mn (Nitronic 32) stainless steel obtained under cryogenic temperatures and stress-corrosion conditions.

Montano, J. W.↗

NASA NTRS1979

Processing high-strength steel alloys

Four-part report describes processing procedures for high-strength alloy steel suitable for use in pistons, piston rods, cylinder barrels, and other critical applications.

Mcknight, L. E.↗

NASA NTRS1979

Durable nonslip stainless-steel drivebelts

Two toothed stainless-steel drive belt retains its strength and flexibility in extreme heat or cold, intense radiation, or under high loading. Belt does not stretch or slip and is particularly suited to machinery for which replacement is difficult or impossible.

Bahiman, H.↗

NASA NTRS1977

Room temperature crack growth rates and -20 deg F fracture toughness of welded 1 1/4 inch A-285 steel plate

Data are presented which were developed in support of a structural assessment of NASA-LEWIS' 10-foot by 10-foot supersonic wind tunnel, critical portions of which are fabricated from rolled and welded 1 1/4 inch thick A-285 steel plate. Test material was flame cut from the tunnel wall and included longitudinal and circumferential weld joints. Parent metal, welds, and weld heat affected zone were tested. Tensile strength and fracture toughness were determined at -20 F, the estimated lowest tunnel operating temperature. Crack growth rates were measured at room temperature, where growth rates in service are expected to be highest.

Shannon, J. L., Jr.↗