Results 1 - 10 of 373
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[en] By means of the neutron diffraction technique the texture of a maraging steel rolled sheet have been determined. The measurements were performed by using a neutron diffractometer installed at the IEA-PI Nuclear Research Reactor, in the beam-hole n0 6. To avoid corrections such as neutron absorption and sample luminosity the geometric form of the sample was approximated to spheric and its dimensions do not exceed that of neutron beam. The texture of the sample was analysed with help of a computer programm that analyses the intensity of the diffracted neutron beam and plot the pole figure. (author)
[pt]A tecnica da difracao de neutrons foi utilizada na determinacao da textura de uma chapa laminada de aco do tipo maraging. As medidas experimentais foram feitas em um difratometro de neutrons instalado junto ao reator nuclear de pesquisas IEA-R1, no canal de irradiacao n0 6. A amostra foi confeccionada no formato aproximado de uma esfera cuja dimensao nao excede a do feixe de neutrons que e extraido desse canal e dessa forma correcoes devido a variacao de atenuacao dos neutrons e de iluminacao da amostra sao evitadas. Um programa de computador analisa a intensidade do feixe de neutrons que e difratada pela amostra e gera figuras de polos atraves das quais sua textura e observada. (autor)
[en] Maraging steels show high mechanical strength and good fracture toughness. However, during thermal or thermal-mechanical treatments, these steels may become embrittled due to the precipitation of titanium carbonitrides films on the grain boundaries of previous austenite; as a consequence intergranular fracture takes place; The phenomenon is critically reviewed in this work and its effect in hot-processing of metals is emphasized. As example, initial experimental results are presented. (Author)
[pt]Os acos 'maraging' apresentam uma resistencia mecanica elevada aliada a uma boa tenacidade a fratura. Contudo, durante tratamento termico ou termo-mecanico estes acos podem se tornar frageis devido principalmente a precipitacao de carbo-hidretos de titanio nos contornos de grao da austenita primaria, apresentando entao fratura intergranular. Este fenomeno e aqui revisto criticamente e enfatizado o seu efeito em processos de conformacao a quente. Resultados experimentais preliminares sao apresentados como ilustracao do fenomeno. (Autor)
[en] Wire + arc additive manufacture (WAAM) is a new process for fabricating large-scale metallic components. In this paper, the use of cold metal transfer-based WAAM process for the production of maraging steel bulk material is reported. Process parameters were studied, and the effect of building strategies including oscillation, parallel and weaving on bead shape was investigated. The structural integrity of the WAAM bulk material regarding the surface finish, lack-of-fusion issue and microstructure was characterized. Results proved the feasibility of applying WAAM to producing maraging steel bulk material, and weaving was identified to be most recommended building strategy.
[en] Non-metallic inclusions in remelted maraging steel were investigated using optical and electron microscopy. The chemical composition of inclusions was determined by SEM equipped with EDS. The composition of metallic constituents was used to categorize the inclusions. The most frequently occurring inclusions were sulfides, oxy-sulfides, nitrides, carbonitrides and carbides of Ti and Mo. However, inclusions enriched in aluminium, calcium, magnesium and silicon were also observed. The level and nature of the inclusions were investigated and their possible sources were discussed. The information is used to modify the melting scheme of maraging steel. (author)
[en] Annealing after hot rolling or extrusion produces anisotropic shape changes in 18% Ni maraging steel. It has been observed that the material contracts along the longitudinal directions but expands perpendicular to it. This peculiar behavior has been studied in-situ by means of a dilatometer. The dimensional anisotropy (DA) was found to decrease with an increase in the annealing temperature. The metallographic investigations have led to the conclusion that DA is related to the presence of banding in the material. (author)
[en] Maraging steels are materials with very low contents of C and with Ni, Co, Mo and T1 additions, that can reach very high mechanical strength values by combinations of heat treatment operations. Three 18% Ni Maraging steels have had some aspects of their aging kinetics investigated by experimental procedures using electrical resistivity, internal friction and hardness measurement techniques, in samples aged from 30 seconds to several hours. Finally, it was verified that the techniques employed were very adequate to the purposes of the present kinetics studies. (author)
[en] The evolution of precipitates in PH13-8 Mo type stainless maraging steel alloyed with Cu was investigated during aging at 525 oC. Atom probe tomography was used to follow the evolution of precipitates with respect to type and chemical composition. It was found that Cu modifies the precipitation sequence in such alloys. Instead of Ni3(Ti,Al) and G-phase the formation of NiAl and G-phase occurred. The modification of the precipitation sequence is due to the incorporation of Cu in NiAl precipitates. However, both types of precipitates develop out of an undefined precursor phase, in contrast to other Cu-alloyed PH13-8 Mo maraging steel grades.
[en] A new approach for the development of medium Mn AHSS is proposed in this work. It exploits a fine scale (~ 100 nm) chemical patterning of Mn in austenite that may be obtained by the austenitisation of a pearlite structure formed under conditions with strong Mn partitioning between ferrite and cementite. The resulting ‘ghost pearlite’ ferrite/austenite can be subsequently treated to exhibit an interesting combination of ultimate tensile strength (UTS) (1600–2100 MPa) and ductility (7–10% elongation). The simple steel composition and very short processing provides a UTS-ductility combination similar to maraging steels and super bainitic steels.
[en] The excellent mechanical properties such as ultrahigh strength combined with good fracture toughness, hardness, ductility and corrosion resistance of maraging steels makes these steels the most preferred materials for nuclear power plants. The high strength and high fracture toughness of these maraging steels are characterised by intermetallic precipitation in iron-nickel martensite. The temperature dependent in-situ microstructural characterisation of maraging steel over wide range of temperatures is used to explore the microstructural changes in maraging steels during aging. An indigenous experimental set-up was used for in-situ measurements of ultrasonic longitudinal velocity (UL) over a wide range of temperatures from 300 to 1200 K at a heating rate of 1 K min"-"1. The measured UL as a function of temperature is represented. Zone A (300-735 K) shows a gradual decrease with an increase in temperature and Zone B (735-785 K) are attributed to recovery of martensite i.e., reduction in point defects induced by quenching process. Zone C (785-835 K) is attributed to nucleation and formation of Ni_3(Ti,Mo) coherent intermetallic precipitates. Coarsening and subsequent dissolution process of Ni_3(Ti,Mo) intermetallic precipitates with increase in temperature is observed from 835 to 905 K (Zone D). The coarsening and partial dissolution of globular precipitation of Fe_2Mo occurs during aging of maraging steel in the temperature region connecting to Zone E (905-1005 K). At 1005 K, the maraging steel gets transformed to austenite from martensite state, and hence, the velocity takes rapid decrease instead of taking a gradual decrease as marked by double dotted line. (author)