Showing papers on "Maraging steel published in 1997"
TL;DR: The microstructure of oxides formed on 250 maraging steel in steam at elevated temperatures was established as discussed by the authors, which consisted of at least two sub-layers, an innermost layer of austenitic phase and a layer of magnetite Fe 3 O 4.
36 citations
TL;DR: The aging behavior of an Fe-19.5Ni-5Mn alloy has been studied in detail as discussed by the authors, and a substantial maraging-hardening response was obtained upon aging at between 300-550°C, and it displayed classical hardening behavior.
26 citations
TL;DR: In this article, the authors compared the oxides formed on 250 maraging steel in steam at elevated temperatures to standard phosphating treatment and found that the advantage of these oxides over phosphating was due to the austenitic sub-layer.
21 citations
TL;DR: In this article, the effects of strain rate and environmental hydrogen concentration on the tensile properties of various aged T-250 specimens were investigated, and the most resistant to hydrogen embrittlement of the underaged specimens are characterized by a more brittle fracture appearance, that is, intergranular fracture, under a low strain rate or in the gaseous hydrogen environment.
Abstract: Constant extension-rate tensile tests are performed to investigate the effects of strain rate and environmental hydrogen concentration on the tensile properties of various aged T-250 specimens. The 426 °C (800 °F) underaged specimens are very sensitive to strain rate; the 482 °C (900 °F) peak-aged specimens exhibit a reduced ductility under low strain rates; and the 593 °C (1100 °F) overaged specimens are insensitive to strain rate when tested in air. The excellent resistance to embrittlement of the overaged specimens in gaseous hydrogen could be associated with the extensive formation of reverted austenite and the incoherent Ni3Ti precipitates. The tensile-fractured surfaces of such specimens reveal a ductile dimple fracture. However, the peak-aged specimens are susceptible to gaseous hydrogen embrittlement, and the embrittled region shows a primary fracture mode of quasi-cleavage. The least resistant to hydrogen embrittlement of the underaged specimens is characterized by a more brittle fracture appearance, that is, intergranular fracture, under a low strain rate or in the gaseous hydrogen environment.
20 citations
TL;DR: In this paper, the formation of banded structure in high-strength maraging steels was investigated and it was found that titanium and molybdenum were the primary cause of banding structure formation.
Abstract: Chemical inhomogeneity results in the formation of banded structure in high-strength maraging steels. Segregation of titanium and molybdenum was found to be the primary cause of banded structure formation. When the concentrations of these elements increased beyond certain critical levels, bands comprising different grain sizes formed. The inclusions existed preferentially along the interface of the bands. A high-temperature homogenization treatment substantially reduced or eliminated the banded structure. The large grain size resulting from the homogenization treatment was subsequently reduced by a grain refinement treatment. The mechanical properties of the steel substantially improved following homogenization and grain refinement.
12 citations
TL;DR: In this article, the effects of environmental hydrogen content on fatigue crack growth rates (FCGRs) in T-250 maraging steel plates and laser welds were investigated and the influence of ageing treatments on fatigue characteristics of the alloy was also studied.
Abstract: — The effects of environmental hydrogen content on fatigue crack growth rates (FCGRs) in T-250 maraging steel plates and laser welds were investigated. The influence of ageing treatments on fatigue characteristics of the alloy was also studied. Experimental results revealed that the accelerated FCGRs in the presence of hydrogen were always associated with changes in fracture modes that appear in compact-tension specimens. Even for overaged specimens with excellent resistance to gaseous hydrogen embrittlement, such an acceleration of crack growth in hydrogen could not be avoided. The crack path of underaged specimens in hydrogen was found mainly along prior austenite boundaries for steel plates and along coarse columnar boundaries for welds. In gaseous hydrogen, peak-aged welds exhibited intergranular and quasi-cleavage mixed fracture modes, compared to mainly quasi-clevage for similar aged steel plates. Hence, the enhancement of crack growth in hydrogen was more pronounced for the welds. Overaged welds showed higher FCGRs than the same aged steel plates only in hydrogen and for ΔK values greater than 20MPa√m.
10 citations
TL;DR: In this paper, the tensile properties of laser-welded T-250 maraging steel are measured, with attention paid to the influence of strain rate and gaseous hydrogen on the fracture behavior of welded specimens.
Abstract: The tensile properties of laser-welded T-250 maraging steel are measured, with attention paid to the influence of strain rate and gaseous hydrogen on the fracture behavior of welded specimens. Post-weld heat treatments are performed on laser-welded specimens to obtain underaged (WU), peak-aged (WP), and overaged (WO) specimens. Hydrogen embrittlement (HE) affects the tensile fracture behavior of the welded specimens; HE changes not only the fracture mode but also the fracture location. Without the influence of hydrogen, the fracture location is at the softest region, the weld metal (WM), and the fracture appearance reveals a ductile dimple fracture. For welds sensitive to HE, the fracture is initiated at the heat-affected zone (HAZ) with coarse grain size, and the associated fracture surface exhibits intergranular and quasi-cleavage fractures that are brittle in nature. In addition, the HAZ with coarse grain size is more prone to HE, as compared to other regions in the welded specimens. The WU specimens are susceptible to HE in air under a low strain rate, while the WP specimens are only susceptible to gaseous hydrogen embrittlement (GHE). However, the WO specimens are immune to GHE and insensitive to strain rate.
8 citations
30 Apr 1997-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the ageing behavior of spray-deposited 18Ni(250) maraging steel+10 vol.% Al2O3 particulate-reinforced metal matrix composites (MMCs) was investigated by microhardness and nanoindentation techniques.
Abstract: The ageing behaviour of spray-deposited 18Ni(250) maraging steel+10 vol.% Al2O3 particulate-reinforced metal matrix composites (MMCs) was investigated by microhardness and nanoindentation techniques. Compared to the control steel, the composite material showed an accelerated ageing kinetics. Nanoindentation investigation revealed observable gradient distribution of elastic modulus and hardness around Al2O3 particulates inside the plastic zone in the matrix. Around a reinforcement particulate, the gradient distribution of the properties is steeper at the sharp corner than that at the flat interface. Theoretical Avrami-type precipitation model was successfully modified to calculate the distribution of precipitates around an Al2O3 particulate. The calculation results showed a gradient distribution of precipitates similar to the experimentally measured distribution of elastic modulus and hardness, which can attributed to the gradient distribution of dislocations within the plastic zones around the reinforcements.
6 citations
TL;DR: In this paper, Austenite and martensite textures were studied in 18 pct Ni 350-maraging steel as a function of various degrees of cold rolling, and its effect upon microstructure and hardness has been studied.
Abstract: Austenite and martensite textures were studied in 18 pct Ni 350-maraging steel as a function of various degrees of cold rolling. The austenite phase in the samples was produced by repeated thermal cycling between ambient and 800 °C. The austenite phase thus formed was mechanically unstable and transformed to the martensite phase after 30 pct cold rolling. The texture developed as a result of cold rolling, and its effect upon microstructure and hardness has been studied.
5 citations
TL;DR: In this article, the effect of the crystalline orientation of the tension axis on the rate of strain-hardening of the material was investigated. And the authors made a quantitative relation linking the strain components over the diameter and wall thickness of the tube during rolling and determined the volume fraction of crystallites that formed the secondary texture.
Abstract: Studies are made of the laws governing changes in the structure and crystallographic texture of tubes of austenitic (12Kh18N10T) and martensitic (38Kh5MSFA, 42Kh2N5SMA) steels that affect the anisotropy of the ultimate and yield strengths of these materials. These changes take place with a directional change in the strain characteristics of the rolled tubes. Features of transformation of the main components of texture in relation to initial structure and level and direction of plastic deformation are examined for rolled thin-walled tubes of austenitic and the same tubes when also heat-treated after rolling. The anisotropy of the strength properties is substantiated from the viewpoint of the effect of the crystalline orientation of the tension axis on the rate of strain-hardening of the material. For high-strength tubes made of martensitic steels, the measure of anisotropy of ultimate strength in longitudinal and transverse tension is determined to be dependent on the volume fraction of crystallites that form the secondary texture. The volume fraction of crystallites is determined by a quantitative relation linking the strain components over the diameter and wall thickness of the tube during rolling.
4 citations
TL;DR: In this article, the phase composition of added materials in welding high-strength steels for a new generation of aircraft is optimized for the effect of various embrittling factors and active media in addition to static and cyclic loads.
Abstract: A new generation of aircraft requires materials giving welded joints capable of operation under extreme conditions including the effect of various embrittling factors and active media in addition to static and cyclic loads. New steels have been developed and conventional steels have been modified with allowance for requirements on the base metal and the welded joints that would provide adaptability to different kinds of welding. The present work concerns the development of principles for alloying and optimizing the phase composition of added materials in welding high-strength steels for a new generation of aircraft. Corrosion-resistant steels and additives for parts operating under the effect of embrittling factors (cryogenic temperatures, temperature instability of the martensite matrix) and structural steels with elevated strength and reliability are considered.
Patent•
18 Mar 1997
TL;DR: In this article, an 18% Ni type maraging steel is irradiated with a high-density energy beam from an electron gun and subjected to the heat treatment to locally heat up and hold this part to and at a temp range from an austenitization temp of 500 to 800 degC to a m p of 1500 degC.
Abstract: PROBLEM TO BE SOLVED: To improve the fracture toughness of a welded joint part by subjecting the part near the welded joint of a welded structure consisting of maraging steel to a heat treatment to heat the part to a specific high temp then to cool the part, then subjecting this part to an aging treatment SOLUTION: The part near the welded joint part 2 of the welded structure 1 consisting of the 18% Ni type maraging steel is irradiated with a high-density energy beam 3 from an electron gun 4 and is subjected to the heat treatment to locally heat up and hold this part to and at a temp range from an austenitization temp of 500 to 800 degC to a m p of 1500 degC, by which the elements, such as Mo and Ti, solidified and segregated at the grain boundaries of weld zones are diffused and the segregation thereof is prevented Next, the part near the welded joint part is subjected to an aging heat treatment of once cooling this part then holding the part for one to two hours at 400 to 600 degC and to a soln heat treatment in a temp range of the austenitization temp to 900 degC The fracture toughness of the welded joint part 3 is improved and the reliability of the welded structure formed by using the maraging steel is improved
Journal Article•
TL;DR: In this paper, the influence of reversion austenite on the fatigue behavior of a maraging steel has been investigated by using 18%Ni-8%Co-5%Mo steel.
TL;DR: In this article, the dependence of microstructure and mechanical properties of maraging steel welded joints on both heat input and pre-weld heat treatment condition was investigated. And two different procedures were used for producing fully heat treated welded joint.
Abstract: This study is focused on the dependence of microstructure and mechanical properties of maraging steel welded joints on both heat input and pre-weld heat treatment condition. Two different procedures were used for producing fully heat treated welded joints. Procedure I included solution annealing before welding then, aging after welding. Procedure II included full heat treatment (solution annealing and aging) before welding then, aging after welding.It is found that optimizing heat input decreased austenite content and prevented coarsening of weld metal dendritic structure, HAZ grain size and grain boundary precipitates which in turn prevented softening of welded joints.Restoring properties in the HAZ and developing good strength in the weld metal are depended on pre-weld heat treatment condition. Optimum combination of tensile strength, elongation, toughness and structure of welded joints are attained using procedure I. This is due to forming of homogeneous microstructure consisting of fine weld metal dendrites, fine martensite and fine intermetallic compounds in addition to less retained austenite.However, satisfactory welded joints can be obtained using procedure II which should be applied in the case of manufacturing large-size welded assemblies since only the welding zone are treated locally after assembly.
Journal Article•
TL;DR: In this article, a Cr-Ni maraging steel is shown to have a structure consisting of martensite and reverted austenite, and an intense stress relaxation is caused by the development of isothermal martensitic transformation in this steel at -196°C.
Abstract: A Cr-Ni maraging steel heated into the intercritical temperature range and cooled to room temperature has a structure consisting of martensite and reverted austenite. An intense stress relaxation is caused by the development of isothermal martensitic transformation in this steel at -196°C. The stress relaxation predominantly occurs by a structural mechanism at -196°C and by a shear mechanism at room temperature.
Patent•
28 Apr 1997
TL;DR: In this article, a maraging steel for hot tool has a composition consisting of, by weight, 8 9.5-15% Co, 9 5.5% high temp, and Ti content is controlled to < 0.5%.
Abstract: PROBLEM TO BE SOLVED: To obtain the steel combining high temp. strength with toughness at high level by providing a composition in which the contents of Ni, Mo, Co, and Ti as essential elements are respectively specified. SOLUTION: This maraging steel for hot tool has a composition consisting of, by weight, 8 9.5-15% Co, 9.5% high temp., strength can be increased to a greater extent and also strength at room temp., decreased by the marked limitation of Ti content, can be effectively compensated. On the other hand, importance is given to toughness in the latter, and, when Ti content is controlled to <0.5%, toughness can be improved to a greater extent.