A New Phenomenon concerning the Graphitization of White Cast Iron and its Application to the Manufacture of Black Heart Malleable Castings

Abstract

The results so far obtained may be summarised as follows : (1) It was found that the excessive continuation of the annealing of white cast iron, which was quenched before annealing, at the annealing temperature in the first stage has almost no effect upon the time required to complete the graphitization in the second stage. It is probably due to the fact that the temper carbon produced in the first stage of graphitization hardly diffuses in r-iron. (2) Some kinds of white cast iron castings were quenched in three kinds of quenching media, i.e., water, rape-seed oil and water covered with a rape-seed oil layer, and the safe quenching method was experimentally found in each case. White cast ir0n castings of a simple form can be safely quenched m water if they are slowly heated before quenching. They are also safely quenched in rape-seed oil or water covered with a rape-seed oil layer even if they are quickly heated before quenching. (3) The test bars which were quenched by the safe' method previously found were annealed in a far shorter time than that adopted in the present practice and then their tensile strength and elongation were compared with those of the test bars annealed in practical operation. The tensile strength of the former is greater than that of the latter but the elongation of the former is liable to be somewhat inferior to that of the latter. (4) From the economical standpoint, the merits of the new process of manufacturing black heart malleable castings were enumerated. (5) From all the results of the present investigation, the fact was confirmed that the new process can be applied to practice with a moderate economical profit.