Bending and Impact Tests on Various White Cast-Irons. (Studies on Alloy White Cast-Iron (6th Report))

Abstract

Bending and impact tests were carried out on sand-cast specimens and heat-treated ones of C 2∼4.2% white irons and C 3%, Ni 3.5∼4.5%, Cr 1∼2.5 alloy white irons. The results were as follows: (1) Some hair cracks were found in the eutectic cementite or along the boundaries, on the tension side of the bending test pieces, when the tensile strain became about 0.1∼0.5%. (2) When the cracks reached the primary crystals, they passed as transcrystalline (about 70%), or as intercrystalline cracks (about 30%). (3) As the hardness of the primary crystals or C% of the alloys increased, the flexture decreased from 5 to 1 mm, the fracture stress from 160 to 30 kg/mm², and the impact value from 30 to 10 kg·cm/cm². (4) The fracture stress in bending tests varied markedly. The factors causing this variation seemed to be S%, C%, the melting, the casting and the heat-treatment conditions of the alloys.