Cause Analysis on Fracture of Steel Bar in Nuclear Power Civil Construction Product Witness Samples during Bend Testing

Steel bar longitudinal fracture occured during bend testing for nuclear power civil construction product witness samples. Fracture reason of the steel bar was analyzed by chemical compositions analysis, hardness testing, metallographic examination and impact test. The results show that the heat produced by welding heated the steel bar to the temperature producing second category tempering brittleness, and the cooling rate was too slow, so impurity elements segregated at the grain boundary, and resulted in weakening of the brittle grain boundary. So the product witness sample fractured at the steel bar along the longitudind direction during bend testing.