Abstract
The influences of carburizing methods on the graphitization-rate of white irons and on the properties of the annealed irons have been studied. White irons containing about 2.6% C and 1.0% Si were prepared using various kinds of row iron made from steel scraps previously carburized with electrode carbon, charcoal, coke, coke plus calcium carbide, or with coke plus lime. The results thus obtained are as follows: (1) Carburizing efficiency was greatest with electrode carbon, followed by coke and charcoal, and was smallest in coke plus calcium carbide. (2) Malleable irons carburized with coke plus calcium carbide had high ductility as well as high strength after annealing. (3) The iron prepared with charcoal required the least time for the first graphitization and the one prepared with cock plus calcium carbide required the most. (4) In the irons cast with coke, coke plus calcium carbide and coke plus lime, considerable amounts of martensite and austenite were found in the structures during the heating. These white irons showed expansion, which was followed by contraction at 270∼450° due to the decompostion of austenite and martensite respectively. (5) Abnormal structures found in white irons made from various kinds of raw iron using coke, coke plus calcium carbide, or coke plus lime, were found to be mainly caused by the absorption of nitrogen into molten iron during the carburization of the steel scrap.
