球状黒鉛鋳鉄材の延性に対する鋳肌の影響

抄録

  Spheroidal graphite iron has excellent ductility for a machined specimen, however a specimen with a cast surface shows very low ductility. This study reports how surface and heat-treatment in the production process affect the ductility of SG-iron with a cast surface. The factors examined are surface microstructures, heat treatment, shot blasting. The test method employed is three points bending tests for small test specimens in which observation and analysis on the initiation and propagation of cracks were made. Conclusions obtained are : (1) Ductility of specimen with a cast surface is much lower than one with a machined surface. The main reasons for this are pearlitic layer near surface in as-cast material and hardening effect by shot blasting in ferritized material. (2) Ductility of cast surface is improved by applying the combination treatment of shot blasting and low temperature annealing. (3) Ductility can be well evaluated by the parameter of growth rate of average crack length.