Abstract
Recently there has been an increasing use of liquidized gas in various industries, resulting in increases of the weight and wall thickness required for compressor casing, valve flange and other equipments for high pressure uses. A study was made to develop a new steel alloy for castings for such low-temperature services. Based upon the type SCS5 cast steel, the optimum chemistry was selected and the effect of heat treatment on notch impact properties was investigated. It was shown that toughness of the cast steel with the base composition of 12Cr-5Ni-0.5Mo was improved by increasing Ni and Mo content and by lowering C, Si, P and S. When this new alloy was normalized and tempered at around 600 degC, a superior low temperature toughness could be obtained. Toughness was further improved by adding a heating in the (α/γ) temperature range between the normalizing and tempering. It was shown that the low temperature toughness was dependent on hardness and the quantity of retained austenite. The newly developed steel possessed a good combination of tensile strength of more than 70 kgf/mm2 and fracture toughness of more than 300 kgf⋅mm-3/2.
