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Published: 1990

Total Pages: 96

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This report describes research carried out to investigate the fracture of ultra-low-carbon bainitic steels. Eight materials have been evaluated using notched-bar bend tests, tensile strength tests and Charpy V- notch impact tests, which were performed over a range of temperatures from -1965 C to +1005 C. These tests measured the cleavage fracture strength and the ductility to brittleness transition temperature under impact loading. The materials evaluated had carbon levels of less than 0.03%, manganese level from 1% to 2%, and microalloys additions of niobium, titanium and boron. Some low alloy steels contained molybdenum and nickel. Some of the materials were subjected to simulated heat-affected-zone (HAZ) thermal cycle and other thermal- mechanical treatments. The fracture surfaces of the specimens were examined using the scanning electron microscope and energy dispersive x-ray analysis. The results of the fracture tests and analyses indicate that the cleavage fracture strength of these materials can vary from 1650 to 2300 MPa. High cleavage fracture strength may be achieved with either a polygonal ferrite or an acicular/bainitic structure, but the high cleavage fracture strength of the polygonal ferrite structure material was reduced of a simulated thermal HAZ cycle.