Fatigue strength of two heat treated carbon structural steel for low temperature service



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Quenched and tempered carbon steels are used in the construction of offshore platforms, refrigerated gas cargo tanks, storage tanks, pipelines, pressure vessels, and other structures which require a high degree of notch toughness at low temperatures or where the increased strength with minimized weight is the standpoint in design. These steels not only provide high static strength, good weldability and excellent notch toughness at low temperatures, but also high fatigue strength as reported in this thesis. The main objective of this thesis was to determine the fatigue strength of two different kinds of quenched and tempered structural steel: A-537B (Armco Super Lo-Temp) and CG-A-537M (Armco LTM-QT). The A-537B specimens were tested under bending and the CG-A-537M specimens were tested under both bending and axial loading. Both bending and axial-loading fatigue tests were performed at stress ratios of 0, 1/2, and -1 representing zero-to-tension, half-tension-to-tension, and tension-to-compression loading respectively. The experimental results are presented in conventional S-N curves. The highest stress for which no failure occurred in 2,000,000 cycles was chosen as the fatigue limit. The data from the tests for both steels at stress ratios of 0, 1/2, and -1 together with the static tensile strength (R = 1) were used to construct modified Goodman diagrams on which other stress ratios can be interpolated. [...]