In earlier N.P.L. work on the strength of carbon steels at high temperatures, steels showing ‘normal’ and ‘abnormal’ creep properties were assessed from tests extending to 1000 hours. Further results on the same steels indicate that the order of merit of these particular steels is not altered in tests extending to 100 000 hours.
The rupture properties of carbon steels are reviewed in the light of the N.P.L. results and other published data. A wide range of strength properties is shown to exist. The pattern of results, however, appears reasonably consistent. At the lower end of the strength scale are almost pure irons and at the upper end are steels of moderate carbon content and not low in manganese and silicon. Heavy deoxidation with aluminium of conventional carbon steels results in lower creep and rupture properties than are observed in similar steels deoxidized with silicon; the part played by nitrogen in this effect is considered.
The rupture ductility of carbon steels is discussed and in the types covered by the N.P.L. researches, low ductility in long-time service appears unlikely.
Further work required in this field is considered and the need for long-time, low-strain creep properties of mild steels for use in nuclear power plants is emphasized.
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