Browsing by Author "Barton, SG"

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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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    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.