Showing papers on "Maraging steel published in 1976"

Hydrogen enhanced crack growth in 18 Ni maraging steels

Abstract: The kinetics of sustained-load subcritical crack growth for 18 Ni maraging steels in high purity hydrogen are examined using crack-tip stress intensity,K, as a measure of crack driving force. Crack growth rate as a function of stress intensity exhibited a clearly definedK-independent stage (Stage II). Crack growth rates in an 18 Ni (250) maraging steel are examined for temperatures from -60°C to 100°C. A critical temperature was observed above which crack growth rates became diminishingly small. At lower temperatures the activation energy for Stage II crack growth was found to be 16.7 ± 3.3 kJ/mole. Temperature and hydrogen partial pressure are shown to interact in a complex manner to determine the apparentK th and the crack growth behavior. Comparison of results on ‘250’ and ‘300’ grades of 18 Ni maraging steel indicate a significant influence of alloy composition and/or strength level on the crack growth behavior. These phenomenological observations are discussed in terms of possible underlying controlling processes.

Precipitation of TiC in thermally embrittled maraging steels

Abstract: It is shown that maraging steels can be embrittled by the precipitation of TiC during slow cooling and/or intermediate annealing in the austenite temperature range. An important aspect in this embrittlement is the occurrence of lamellar precipitation of TiC at the austenite grain boundaries, generating a cellular structure of large fern leaf-like carbides. Within the austenite grains a nonuniform distribution of irregularly plate-shaped TiC particles are formed with (100) austenite habit orientation. Quenching to martensite, prior to any intermediate anneals, changes the carbide distribution upon subsequent annealing treatments into a fine dispersion of TiC particles. The embrittlement resulting from the various isothermal annealing treatments in the austenite temperature region could all be directly related to the carbide distribution in the prior austenite grain boundary region.

Structure and properties of a microduplex maraging steel

Abstract: A simple two-step thermal processing technique was devised to impart a microduplex structure in a high strength 250 grade commercial maraging steel. A martensite grain size of approximately 1 μm was obtained with interspersed islands of retained austenite whose volume fraction and mechanical stability could be controlled by varying the thermal processing conditions. The microstructure and mechanical properties of the microduplex structure were compared to those of the alloy in the maraged, martensitic condition. Due to the presence of the austenite phase, the microduplex structure showed a much smaller temperature and strain rate dependence of deformation than the martensitic structure. A remarkable increase in uniform elongation was observed below theMd temperature of retained austenite. The microduplex structure did not show any significant advantage in fracture toughness over the martensitic structure when compared at similar strength levels. By suitably adjusting austenitic stability a deformation-induced phase transformation (TRIP) of the retained austenite in the microduplex structure could be made to occur; however, the transformation did not lead to any evident increase in toughness. The micro-duplex structure exhibited a slight improvement in fracture toughness at high strain rate in contrast to the martensitic structure in which the rate effect significantly reduced the toughness.

High strength diffusion welding of silver coated base metals

Abstract: Al, Be, maraging steels, and a variety of dissimilar alloys were bonded using Ag as an intermediate layer. Effects of diffusion welding parameters on the Ag solid state joint were studied on maraging steel. Tensile strengths as high as 97 ksi were achieved with electrodeposited Ag surfaces. (DLC)

18% Ni-Mo-Co maraging steel having improved toughness and its method of manufacture

Abstract: An 18% Ni-Mo-Co maraging steel is processed to substantially increase its toughness (Charpy V-Notch) by heating the alloy in particle form to at least the solution treatment temperature thereof, quenching said alloy particles, compacting, and consolidating the quenched particles at a temperature within the recrystallization range of the alloy to form a consolidated product and aging the consolidated product.

Structure and properties of a microduplex maraging steel. [Fe--18 Ni--8 Co--5 Mo]

Abstract: A simple two-step thermal processing technique was devised to impart a microduplex structure in a high-strength 250-grade commercial maraging steel. A martensite grain size of approximately 1 ..mu..m was obtained with interspersed islands of retained austenite whose volume fraction and mechanical stability could be controlled by varying the thermal processing conditions. The microstructure and mechanical properties of the microduplex structure were compared to those of the alloy in the maraged, martensitic condition. Due to the presence of the austenite phase, the microduplex structure showed a much smaller temperature and strain rate dependence of deformation than the martensitic structure. A remarkable increase in uniform elongation was observed below the M/sub d/ temperature of retained austenite. The microduplex structure did not show any significant advantage in fracture toughness over the martensitic structure when compared at similar strength levels. By suitably adjusting austenitic stability a deformation-induced phase transformation (TRIP) of the retained austenite in the microduplex structure could be made to occur; however, the transformation did not lead to any evident increase in toughness. The microduplex structure exhibited a slight improvement in fracture toughness at high strain rate, in contrast to the martensitic structure in which the rate effect significantly reduced the toughness.more » 10 figures, 3 tables.« less

Increasing the fracture toughness of a maraging steel type alloy

Abstract: Mechanisms associated with fracture toughness of maraging steels aged at 550 to 600/sup 0/C are described. A correlation is observed between aging temperature and fracture toughness; this aging temperature is optimum for improved fracture toughness. It is shown that this aging temperature range improves the toughness by reducing the tendency for grain (or lath) boundary cracking, i.e., by reducing the amount of and/or by changing the morphology of the grain (or lath) boundary precipitate. It is suggested that there is an interaction between the formation of austenite and the formation of precipitate on the prior austenite and the lath boundaries, and that if austenite forms sufficiently early in the aging process boundary precipitation may be largely inhibited. This interaction is believed to account for the improved toughness at these aging temperatures. It should be noted that this interaction is independent of the presence of retained austenite after aging and that retained austenite is not responsible for the improved properties since no retained austenite was observed. This explanation for the improved toughness is supported by indirect evidence consisting largely of the relationship between the rate of formation of austenite and the rate of formation Ni/sub 3/Ti as a function of agingmore » temperature.« less

Strengthening and Toughening of 280kg/mm2 Grade Maraging Steel through Control of Microstructure

Abstract: Synopsis: In order to strengthen and toughen 280kg/mmm2 grade maraging steels, the effects of solution and aging treatments on the microstructure, tensile properties and fracture toughness have been investigated, and metallurgical factors affecting the strength-toughnesss balance have been discussed. Tensile ductility is strongly dependent upon prior ƒÁ grain size. Unstable fracture under low stresses occurs due to the decrease in ductility above a critical grain size, which depends on the strength level and fracture toughness of the steel. On the other hand, the fracture toughness is independent upon prior ƒÁ grain size but strongly dependent upon undissolved precipitates. The presence of undissolved precipitates can greatly lower the fracture toughness. Therefore, a simultaneous improvement of ductility and toughness would be obtained in the fine grained martensite structure without undissolved precipitates. Three special treatments, which consist of complete solution treatment of undissolved precipitates and grain refinement, have been proposed by utilizing the difference of metallurgical factors affecting the ductility and toughness respectively. Simultaneous improvements of the ductility and toughness for the higher strength level of 13 Ni-15 Co-10 Mo steel are obtained by a special thermomechanical treatment.

Fracture characteristics of a ductile-matrix/brittle-fiber composite

Abstract: A metallic composite consisting of a 304 stainless steel matrix reinforced with unidirectional 300 grade maraging steel wires has been studied with respect to (1) production method, (2) effect of wire diameter on the toughness at constant volume fraction, and (3) effect of changing volume fraction at constant wire diameter. Wire diameters of 0.508, 1.016 and 1.524 mm, and wire volume fractions of 0.3, 0.4 and 0.5 were used. It was found that by combining the brittle wires with the ductile matrix one obtained a simultaneous increase in strength and toughness. The toughness of the composite calculated on initial crack length and maximum load was higher than that of either of the two components individually at volume fractions above 0.4. Furthermore, one also found that Compact Tension (CT) specimens having continuous wires running the whole height of the specimen gave the same results as those having a composite section sandwiched between two solid blocks of maraging steel. The wires were oriented perpendicular to the crack in all cases.

The fracture toughness of a ferrous maraging alloy containing manganese

Abstract: A Fe-20 pet Co-15 pet Mn-5 pet Mo maraging alloy has been found to exhibit low toughness and brittle fracture throughout its response to age-hardening. Inter granular embrittlement associated with segregation of manganese and with residual oxygen (15 to 300 ppm) in the early stages of aging was replaced by brittle inter-lath separation as aging progressed, the latter mode being associated with intermetallic precipitation and, possibly, the presence of finely-dispersed austenite.

Steel alloy rotor for fast hysteresis motor - has steel alloy of specified composition to give desired properties

Abstract: The rotor for a fast hysteresis motor, is made of maraging steel contg. 16 to 20% Ni and has a coervice force of is not 40 Oe, a residual magnetisation of is not 5.0 kG and a yield point is not 100 kg/mm2. The steel contains specified amounts of C, Mn, Si, P, S, Ni, Co, Mo, Ti and Al. The steel finally treated at 600-725 degrees C.

Effect of titanium on the mechanical properties of sintered N14K7M5T maraging steel

Abstract: 1. The titanium content of sintered N14K7M5T maraging steel can be raised as high as 2%. The increase in the strength of such a steel brought about by heat treatment is not accompanied by a significant decrease in its resistance to crack propagation. 2. In the assessment of the service performance of a sintered MA steel it is necessary to supplement standard mechanical tests by evaluating parameters characterizing its resistance to crack propagation.

Environmental cracking of welded maraging steel in hydrogen sulphide.

Abstract: A comprehensive survey of the literature concerning environmental cracking in maraging steels has been carried out, with particular reference to the behaviour of welded joints. The major part of the present experimental work was centred on the performance of submerged-arc welded plate in aqueous hydrogen sulphide. By using pre-craclced specimens, stress-intensity/endurance relationships were determined for weld and parent metals together with mixed structure material from two positions within the heat-affected-zone.From these data, estimated threshold stress-intensities 3/2 of 20-30 MN/m showed little difference between materials from any of the four positions. Endurances themselves, however, were generally lower for weld metal than for parent material. Stage II crack propagation occurred at rates of the order of 10-4 - 10-3 mm/sec, predominantly along prior-austenite grain boundaries. An unusual feature of many tests was an apparent drop in propogation rate after growth was initiated. There followed growth at more or less constant rates before final acceleration just prior to fracture. Fractography showed preferential cracking along specimen edges ahead of the main crack front. This suggested either faster growth under plane stress conditions or a diffusion barrier affecting hydrogen ingress. Scanning electron microscopy confirmed the purely intergranular nature of cracking, and the presence of stretch zones.