Showing papers on "Maraging steel published in 1998"

Effect of aging on microstructure and mechanical properties of cobalt free 18%Ni (250 grade) maraging steel

Abstract: The influence of aging on the microstructure, tensile properties, fracture toughness, and fractographic features of a cobalt free 18%Ni 250 grade maraging steel has been investigated. This steel, designated as T250 steel, with 17.1%Ni, 2.25%Mo, and 1.39%Ti as the main alloying elements, contains no cobalt and less molybdenum than the widely used 18Ni-8Co-5Mo type 250 maraging steel (M250). The present investigation shows that tensile properties as well as plane strain fracture toughness values comparable with those of M250 can be obtained in the T250 steel with marginal change in aging cycle. The Ni3 Ti phase precipitating in the present steel has been found to have excellent resistance to coarsening at the normal aging temperatures. The condition for maximum yield and tensile strengths is also the one that gives peak values of toughness. While a low value of toughness in the underaged condition is attributed to the planar slip mode of deformation, the formation of reverted austenite and coarsenin...

The creep problem in the VIRGO suspensions: a possible solution using Maraging steel

Abstract: Each optical component of the interferometric gravitational wave detector VIRGO is suspended from a cascade of mechanical filters designed to suppress the transmission of seismic vibrations. Each mechanical filter supports the weight of the filters below it by means of a set of steel cantilever blade springs. The stress from the load acting on the blades was found to induce a drooping of the blade tips of several microns per day due to a series of microscopic yielding events (micro-creep). This process induces a mechanical displacement shot-noise on the optical component which can dominate the small displacements produced by gravitational waves. The use of a special precipitation hardened steel (Maraging C250), instead of common spring steel, allows the construction of blades that show an acceptable stability under stress.

Mo precipitation in a 12Cr–9Ni–4Mo–2Cu maraging steel

Abstract: A new maraging steel 1RK91, with the composition 12Cr–9Ni–4Mo–2Cu (wt.%) was investigated after heat treatments at 475°C up to 400 h using atom probe field ion microscopy (APFIM) and tomographic atom probe (TAP). According to the analytical microscopy investigations preceding this study, the high strength of the material was attributed to a new Mo-rich quasicrystalline R′ phase. Therefore the present study concerned evolution of Mo-rich precipitates. The investigation revealed that nucleation of a Mo-rich phase starts between 1 and 2 h of aging at the matrix near the Ni-rich precipitates that form earlier and at the martensite lath boundaries. Compositional changes of these two types of precipitates with aging time were followed. After 400 h of aging only a few small matrix precipitates were observed. Their structure could not be easily determined using electron diffraction because of their small size. The influence of Mo precipitates on the mechanical properties of the material is discussed.

The formation of reverted austenite in 18% Ni 350 grade maraging steel

Abstract: Austenite reversion was studied in 18% Ni 350 grade maraging steel. The samples were heat treated from room temperature to the austenite phase field and, without holding, they were cooled again to ambient temperature. The reverted austenite which was retained after this heat treatment was examined using a scanning transmission electron microscope equipped with an energy dispersive spectroscopic system. Two morphologies of the austenite were observed. The first forms at the martensite lath boundaries and the other nucleates inside the martensite laths in the form of Widmanstatten plates. These Widmanstatten plates mostly appear as coupled twins. The coupled twins have a distinct midrib which was found parallel to (1 1 1)γ and (1 1 0)α planes. The latter morphology of austenite appeared only after the formation of Ni3Ti precipitates. Growth of Fe2Mo precipitates was not observed in this heat-treatment cycle. Both Nishyama–Wassermann and Kurdjumo–Sachs orientation relationships were found between the austenite and martensite phases. On the basis of these results, it can be suggested that intra-lath-reverted austenite is formed on or by the local dissolution of Ni3Ti precipitates. © 1998 Kluwer Academic Publishers

Nitriding method for maraging steel and maraging steel product obtained thereby

Abstract: PROBLEM TO BE SOLVED: To obtain steel having high fatigue strength and wear resistance by previously forming a fluoride film by reaction gas contg. fluorine on the surface of steel and thereafter forming a nitrided hardened layer in a nitriding atmosphere in which the concn. of NH3 and temp. are specified. SOLUTION: At the time of forming a hard nitrided hardened layer on the surface of maraging steel, maraging steel is previously heated and held at about 300 to 400°C for about 5 to 30 min in an atmosphere of reaction gas contg. fluorine, e.g. a fluorine compd. such as NF3, BF3, CF4, HE, F2, or the like to form a fluoride film on the surface. Next, this maraging steel is treated at 400 to 500°C for about 15 min to 5 hr, preferably, in a nitriding atmosphere in which the concn. of NH3 lies in the range of 5 to 30 vol.% to the whole, on the surface, a nitride layer composed of nitride only is uniformly formed at a thickness of ≤1 μm, and, on the lower layer thereof, a diffused layer is formed. COPYRIGHT: (C)2000,JPO

Quantitative Evaluation of Effect of Artificial Small Defects on Torsional Fatigue Strength

Abstract: In order to investigate the effect of artificial small defects on torsional fatigue strength of high strength steel, fatigue tests for a maraging steel (HVc740) containing a small hole of diameter=100, 200, and 500μm were carried out. Torsional fatigue limit of the maraging steel was determined by the threshold condition of non-propagating cracks emanating either at the edge of hole or the smooth part of the specimens depending on the diameter of hole. The critical diameter of hole (dc) which does not influence torsional fatigue strength for several materials is between 100μm and 200μm regardless of hardness. Prediction equation for bending fatigue limit (σω) by the √(area) parameter model was extendedly applied to predict torsional fatigue limit (τω) for both smooth and holed specimens. The fatigue limits predicted by these method were in good agreement with the experimental results.

Effect of Repeated Thermal Cycling on the Formation of Retained Austenite in 18%Ni 350 Grade Maraging Steel

Abstract: Samples of 18%Ni 350 grade maraging steel were repeatedly thermal-cycled between ambient temperature and 800°C (above the austenizing finish temperature, A f ). This heat treatment produced retained austenite in the microstructure, the volume fraction of which increased and decreased alternatively in relation to the number of thermal cycles. It was observed that the retained austenite (γ), after having grown to a certain extent transformed back to the martensite phase (α 2 ) and had the following orientation relationship with the parent martensite matrix (α 1 ): (110) α1 //(110) α2 (112) α1 //(110) α2 . This may be explained on the basis of the Nishiyama-Wassermann (N-W) and Kudjumov-Sachs (K-S) orientation relationships between austenite (γ) and martensite (α) phases.

Maraging steel strip

Abstract: PROBLEM TO BE SOLVED: To provide a maraging steel strip excellent in fatigue strength with the acceptance of the presence of inclusions to some degree. SOLUTION: In the case the diameter of a circle outwardly connected with Ti series inclusions observed in the cross section of the structure is defined as Dmax and the diameter of a circle inwardly connected with them is defined as Dmin, Dmax is regulated to ≤8 μm, and as for the existing Ti series inclusions of 8 to 2 μm Dmax, the ratio of Dmin/Dmax is regulated to ≥0.75. Preferably, the content of N is regulated to ≤13 ppm, and the content of C is regulated to ≤0.01%, and more preferably, the content of N is regulated to ≤9 ppm, and the content of C is regulated to ≤0.006%. COPYRIGHT: (C)1999,JPO

The effects of various heat treating parameters on the hardness and microstructures of the experimental 18% nickel maraging steels

Abstract: The effect of the parameters of heat treatment on the experimental 18% maraging steels was studied using hardness tester, optical, scanning electron and transmission electron microscopy and X-ray metallography techniques. The specimens were solution treated at 815, 900, 1000, 1060°C for periods between 1 and 4 h. After air-cooling to room temperature, a bcc martensitic structure was obtained. The higher temperature (1060°C) and longer time (4 h) of the solution treatment caused essentially homogeneous, massive martensitic structure. The aging of the steels was studied between 240 and 480°C from 1 to 41 h. As indicated by the results, the hardness vs. aging time curves show a rapid rate of hardening at 480°C while the response at 240 to 320°C is slower. The time required to reach peak hardness increases with decreasing temperature. The increase in hardness during aging can be explained by the precipitation of hardening phases. So, it is necessary to use a high temperature solution treatment to obtain a better alloy distribution and a tough martensitic structure, and an aging treatment at 480 °C between 4 and 10 h to achieve the desired properties.

Hard cement material, and tool for metallizing and machine parts using the same

Abstract: PROBLEM TO BE SOLVED: To produce a hard cermet material free from deterioration in hardness even if the ratio of bonding metallic phases increase and to produce a tool for metallizing and machine parts free form wear, chipping and breaking and excellent in wear resistance. SOLUTION: In this hard cermet material consisting of metallic bonding phases having heat treatability of a martensitic stainless, a precipitation hardening type stainless steel, a maraging steel or the like and ceramics phases in which molybdenum carbide enters into solid solution in the surface of the crystal particles of the carbides, nitrides or carbon nitrides of the group IVa, Va or VIa elements, the ratio of the bonding metallic phases is regulated to 5 to 40wt.%. The tool for metallizing and machine parts are produced by the hard cermet material.

Manufacture of maraging steel

Abstract: PROBLEM TO BE SOLVED: To provide a method for manufacturing a maraging steel excellent in strength, toughness and ductility by producing a steel ingot by a mass- production process of an electric furnace melting - ladle refining - RH degassing - ingot-making instead of a VAR method. SOLUTION: The steel consisting by wt. the max cross sectional area, 2.0-4.0 ratio (ratio of height and width) of the height and the average width or the average diameter of the steel ingot and <=6t wt. Since micro-segregation is little, the maraging steel excellent in strength, toughness and ductility, is manufactured.

High strength steel excellent in delayed fracture resistance

Abstract: PROBLEM TO BE SOLVED: To provide a steel which is a high strength steel for bolt or steel for machine structural use, having >=1400N/mm tensile strength and excellent in delayed fracture resistance, and requires no long-time aging treatment after hardening, unlike in the case of maraging steel, and further is reduced in manufacturing costs and capable of production on an industrial scale. SOLUTION: This steel has a composition consisting of, by weight, 0.2-0.35% C, <=0.1% Si, <=0.1% Mn, <=0.01% P, 0.015-0.055% Ti, 0.0005-0.003% B, 7-12% Ni, 0.01-0.1% sol.Al, <=0.008% N, and the balance Fe with inevitable impurities.

Duplex antiabrasive coatings (Fe-based alloy-tin) produced by impulse plasma deposition

Abstract: TiN-type antiabrasive coatings are commonly produced by various PVD-CVD methods. It is known that the multilayer coatings are better than monolayer coatings because of the possibility of controlling the stress level, in particular, in interfaces, and as a result in the whole coating. In this paper, phase composition, morphology, anticorrosive (tightness) and antiabrasive properties of the duplex (Fe-based alloy-tin) coatings produced by impulse plasma deposition were examined and compared with the single-layer TiN ones. The very good mechanic and plastic properties of Fe-Ni-Mo-Al-Ti alloys (maraging steel) which were used seem to predestine this alloy as a metallic bond layer in multilayer antiabrasive coatings.

Experimental Observations and Theoretical Modelling of Equilibrium Quasicrystalline Phase in A Commercial Maraging Steel

Abstract: A recently developed maraging steel of type 12%Cr-9%Ni-4%Mo-2%Cu-l%Ti in which precipitation strengthening is caused by quasicrystalline precipitates is presented. the steel is used in its tempered condition as surgical instruments such as surgical needles and dental reamers. the high strength and the resistance to tempering induced softening is in part attributable to the formation of quasicrystalline precipitates of icosahedral symmetry. Profuse nucleation in combination with slow coarsening of precipitates are explicable in terms of a low surface energy associated with quasicrystallinity. There is experimental evidence supporting the conclusion that the quasicrystalline precipitates in the present material are formed under thermal equilibrium conditions. To rationalise this conclusion, we compare it with the thermodynamics and kinetic properties of an equilibrium quasicrystalline phase simulated by molecular dynamics. the simulation has demonstrated that the stability of this quasicrystal with respect to the crystalline ground state may be attributed to the large configurational entropy arising from the thermally activated phason dynamics. We argue that this mechanism, suggested by the random tiling model, may account for the observed equilibrium quasicrystalline precipitates in metallic alloys.

AR-aging as a new approach for enhanced results

Abstract: MAR-aging steels have earned a niche in the metal market arena, especially where aerospace and outerspace applications are concerned. MAR-aging steels owe their high strength, excellent fracture toughness, and good ductility to a precipitation-hardening (aging) mechanism that has been debated by scientists for several years. Because of today’s trend toward more demanding design requirements and a continuing need to better understand the MAR-aging family of materials, six different alloys (C-200, C-250, C-300, C-350, T-250, and T-300) were selected for study using a singular processing treatment: a hot-wall zone-gradient furnace. These alloys were evaluated for the effects of a specific thermal gradient (°C/cm) from 1231 °C (2250 °F) at the hot-wall limit to about 260 °C (500 °F) at the opposite end, the cold wall. All six alloys were evaluated in terms of their microstructure, microhardness, composition, and associated properties as a result of this specific thermal processing method. In this paper, detailed observations on the C-350 alloy are presented, and the results are interpreted in terms of a new heat treatment cycle called AR-aging.

Strain hardening of structural metals with metastable structure under complex loading

Abstract: We investigated distinctive features of strain hardening under complex loading for quenched and low-tempered steels of ferritic-pearlitic (40KhN), martensitic (30Kh3NSMV), and maraging (Kh16N5D3) types and an Al-4Cu age-hardening alloy whose matrix phase is characterized by the metastable structure corresponding to supersaturated interstitial and substitutional solid solutions susceptible to disintegration in the process of plastic deformation. We analyzed structural indicators of the depletion of the matrix phase of supersaturating alloying elements forming carbides and intermetallic compounds and the mechanisms of hardening and softening influence of preliminary deformation (within reasonable ranges of its variation) on the value of the yield limit when repeated loading changes its sign. It is shown that, for the investigated type of metastable materials, in the analyzed range of preliminary deformations governed by alloying, the application of repeated biaxial tension leads to a uniform extension of the limiting yield curves. As the degree of supersaturation decreases (in the process of thermal treatment) and we observe the formation of equilibrium solid solutions of the matrix phase, the character of strain hardening evidently changes from predominantly isotropic to kinematic.