Browsing by Author "Pollock, JTA"

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    Creep properties at ambient temperature of some high strength steels
    (Australian Atomic Energy Commission, 1979-03) Pollock, JTA; Barton, SG
    Ambient temperature stress relaxation and creep data are reported at various stress levels for two grades of MAR300 steel, a MAR350 steel and a type 301 stainless steel. Analysis has shown that there is a linear relationship between the logarithm of time and relaxed stress, or creep strain. On the basis of this linear relationship, two parameters are calculated that are characteristic of the relaxation and creep behaviour at a given stress level. Using a conjugate relationship suggested by Felthat [1961 - Phil. Mat., 6:259; J. Inst. Met., 89:201], these characteristic parameters are compared to allow an assessment to be made of the possibility of deriving constant load creep characteristics from short-term stress relaxation data. Because of the difficulties in measuring some of the factors in this relationship, a large error band is associated with the derivation at stresses where the work hardening rate is very high. Nevertheless, in this difficult stress range, a working relationship is demonstrated which is sufficient to warrant the application of the approach if design information is required. At stresses in the range 1000-1500 N mm-2, creep increments per year of about 10-4 mm mm-1 were calculated from the experimental data for the maraging steels. In terms of creep increment per year, the type 301 stainless steel is roughly an order of magnitude inferior to the maraging steels over the same range of stress. At higher stresses in the range 1600-2150 N mm-2, which is beyond the applicability of the MAR300 steels or the type 301 stainless steel, an unchanged yearly creep increment of ~10-4 mm mm-1 was obtained with the MAR350 steel.
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    An electron microscopy study of the solution treatment of MAR 350 and MAR 400 maraging steels
    (Australian Atomic Energy Commission, 1980-12) Warren, RB; Pollock, JTA; Kelly, PM
    A study of the effect of solution treatment on the microstructure of types MAR 350 and MAR 400 maraging steels has been carried out using transmission electron microscopy (TEM). The aim of the study was to determine the heat treatments needed to produce fine-grained, single-phase microstructures which, after ageing at 500°C were likely to have acceptable combinations of strength, toughness and ductility. The main results are a series of fold out montages which present a detailed description of the microstructure.
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    High strength steels - stress relaxation and derived creep characteristics at room temperature
    (Australian Atomic Energy Commission, 1976-05) Pollock, JTA; Barton, SG
    The room temperature tensile strength and stress relaxation characteristics of 301 stainless, 431 stainless and Vascomax 300 maraging steels in the form of thin strip have been determined. On the basis of Ultimate Tensile Strength (UTS), the maraging and 431 steels (UTS ~ 1.8 GPa) are marginally superior to the 301 steel (UTS ~ 1.75 GPa). Relaxation data show that plastic deformation occurs at ~ 45% UTS in the 301 steel, ~ 60% UTS in the 431 steel and ~ 65% UTS in the 300 steel. These stresses, which define the lower limit above which creep will certainly occur, are significantly lower than 0.1% proof stresses measured directly from stress/strain data. The relaxation data were used to estimate logarithmic creep rates under constant load for these materials. There is a comparative superiority of the maraging steel over the two stainless steels in the range 80-90% UTS.
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    Optical metallography of some maraging steels
    (Australian Atomic Energy Commission, 1981-05) Meller, E; Pollock, JTA
    The structural features of maraging steels including those that impose limitations on strength and toughness are briefly reviewed. Phase relationships in the iron-nickel matrix system are introduced which in conjunction with alloy composition and heat treatment allow the interpretation of microstructure. Details are presented of methods for revealing the microstructure of maraging steels; the prior austenite grain size following a variety of heat treatments is of special interest since excessive grain size can lead to poor ductility. These methods are illustrated with micrographs of the microstructures of MAR 350 and MAR 400 steels in the cast solution-treated aged and cold-worked states.
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    Positron annihilation in neutron irradiated aluminium
    (International Institute of Welding, 1976-08-23) Pollock, JTA; Jostsons, A
    The angular correlation of positron annihilation radiation has been measured from a series of high purity, Polycrystalline, aluminium samples irradiated by neutrons to fluences in the range of 1023-1026 neutron m-2 (E . 0.1 MeV) at 55°. Changes in the annihilation characteristics are attributed primarily to voids formed as a result of irradiation. Data are presented for the sensitivity of angular correlation technique as a measure of the swelling which accompanies irradiation.
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    Work-hardening correction for stress relaxation derived creep properties
    (Australian Atomic Energy Commission, 1981-06) Pollock, JTA; Clissold, R
    A work-hardening correction has been added to a previously devised method for characterising the long-term deformation properties of metals and alloys by derivation from short-term relaxation data. The usefulness of this correction has been assessed by creep and stress relaxation measurements on titanium, copper and 70/30 brass. Within defined strain limits, good agreement is obtained between derived and directly measured creep parameters. The importance of the relaxation-system spring constant in determining the extent of the agreement is discussed.