Fast Determination of the Critical Fracture Toughness (KIC) of the Rails U33 and UIC60 by the Charpy V-notch Test

Measurement the critical fracture toughness is one of the quality control parameters in rail manufacturing process. Critical fracture toughness value is needed for designing the rail lines, analysis of defects and other common prevalent works in mechanical engineering. The aim of this research is introducing a relation to measure the critical fracture toughness of the steel rail materials grade R260 by Charpy V-notch number. The fracture toughness of rail material has been determined by 3-point bending technique according to ASTM E399 and EN13674-1 at temperature range -20oC and +25oC. The fracture energies have been measured by the Charpy impact test and no significant change in the results have been observed over the tests temperature limit. Relations between the chemical analysis and mechanical properties have been studied and compared with the results of the other researches. To obtain the required data for calculating the critical fracture toughness the uniaxial tension test has been operated at ambient temperature and -20oC. Analysis of chemical composition, metallographic and hardness test have been carried out to better study of the process. Finally a relation to connect the Charpy V-notch number and fracture toughness has been introduced and the fracture toughness of the rail material over the impact test temperature limit has been calculated. Good agreement between the calculated results and result of 3-point bending fracture toughness test indicates appropriate accuracy of the introduced equation.