The development of precise data for the effect of chemistry and processing variables on the fracture toughness of low to medium carbon cast steels, is paramount to an increased understanding of the fracture behaviour of these important engineering materials. This knowledge would, in itself, lead to improvements in alloy development/selection rationale and increased cast steel usage, particularly in critical areas. / Toward this end, an investigation into the influence of Cr, Mn and Ni additions on the room temperature fracture toughness and flow properties of 0.30, 0.40 and 0.55 wt% C cast alloys was conducted. In order to avoid the chemical and processing complexity normally associated with commercial castings, the study was undertaken on heavy section castings produced in the laboratory from melts composed of commercial purity ingredients. Measurements were conducted on three-point bend test pieces machined from heat-treated castings. The fracture toughness techniques used included LEFM (K(,IC)), J integral and COD ((delta)(,c)). A potential drop method was employed to record crack initiation. / Very high room temperature fracture toughnesses were achieved in the majority of the alloys examined, with only three alloys having K(,IC) values of less than 150 MN.m('-3/2) or COD, (delta)(,c), values of less than 0.1 mm. Further, yield stress ((sigma)(,ys)) values were found to lie within 80-105% of those recorded for commercial castings of comparative composition. / At the 0.30 and 0.40 wt% C levels it was found that the room temperature fracture toughness of the alloys was relatively independent of the microstructure as well as the amount and particular addition element employed, although variations in the tensile properties were noted. / At the 0.55 wt% C level significant differences in the fracture behaviour were caused by the individual element additions. Manganese was found to improve the toughness of the high carbon alloys, while nickel produced little change and chromium had a negative effect on toughness. In each case the influence of these elements was manifested in microstructural differences. / The results of this study are reviewed in the light of the limited data available from commercial cast steels and the need for improved toughness performance without undue loss of yield strength and other properties. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI

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