Abstract
he effects of O2, N2 and A on vacuum-melted cast inon and on hyper eutectoid carbon steel were investigated. 6 kinds of specimens of cast iron and steel with different % of C were vacuum-melted. The sample was cast after it had been held in O2, N2 or A gas with the pressure of 760mm Hg for 20 minutes. Then % of C, % of Si, microstructure and tensile strength were compared with those of vacuum-melted specimens having the same % of C respectively. The results obtained are summarized as follows.
The effects of O2 :
1) Decrease of % C is remarkable; the higher the melting temperature, the greater the decrease. Changes in % of Si were scarcely observed. 2) Structure of eutectic graphite in vacuum-melted cast iron, was the same as that of the cast iron melted under O2 atmosphere. But in the latter case, free cementite and pearlite appeared. In hyper eutectoid steel range, free cementite was added to the initial massive graphite+pearlite structure by melting in O2 atmosphere. 3) The values of tensile strength scattered greatly corresponding to the structural change in cast iron range, reaching to 50kg/mm2 in some case, while, in hyper eutectoid steels range, tensile strength always decreased greatly.
The effects. of N2:
Experiments were performed for 4 kinds of specimens whose % of C and % of Si are in the range of cast iron. 1) % of C, % of Si did not change. 2) Microstrucre change was not observed. 3) Tensile strength did not change.
The effects of A:
1) % of C, % of Si did not change. 2) Microstructure change was not observed. 3) Tensile strength did not change.
