抄録
This investigation is concerned with the influence of C and Si on tensile strength, elongation, hardness and structure of gray iron cast into metal molds. The effect of variations in composition of C form 2.96 to 4.1% and Si from 1.56 to 3.6% were studied. Various mold ratio and melt treatments were employed to obtain two kinds of gray iron, one with pearlitic matrix and flake graphite structure, and the other with ferritic matrix and fine graphite which were obtained by annealing for either 2 or 3 hours at 900°C.
In the gray iron with pearlitic matrix and flake graphite, effect of the degree of saturation of saturation of carbon on tensile strength tended to be similar to iron cast into sand molds, but tensile strength of iron cast into metal molds was higher. Increase in the Si/C ratio increased slightiy the tensile strength. Tensile strength was not very much influenced by the area of pearlite occupied in the matrix. Tensile strength and elongation of iron with pearlite matrix and flake graphite were less than 30 kg/mm2 and about 0.4%, respectively.
In the gray iron with ferritic matrix and fine graphite, tensile strength was affected by Si/C ratio through the degree of saturation of carbon was almost the same. The relation between Si/C ratio and tensile strength tended to be similar to the case of pearlite and flake graphite iron but the rate of increase in tensile strength was about three times greater. Tensile strength and elongation of iron with ferritic matrix and fine graphite were about 48kg/mm2 and 1.0∼1.4% at Si/C≑1.21, respectively.
primary austenitic dendrite grew radially from the surface to the center of casting in all specimens. The size of fine graphite was less than 5 or 10μ, but the existence of larger graphite (30∼100μ) widened the dendrite spacing and decreased the tenshile strength.
