Abstract:
Weldable and magnetic ferritic malleable iron castings having an improved abrasion resistant wear layer, and the method of forming such castings are described. The casing includes a body portion of full ferritic malleable iron which is covered with several zoned layers, viz., a pearlitic type matrix of broken spheroidized martensite which is partially depleted of carbon nodules, a decarburized wear layer of finely dispersed well distributed spheroidized carbides in a ferritic matrix which provides a good weld zone and an outer intergranular oxidation layer. In machining castings to be used for abrasion resistance the outer two layers and a portion of the wear layer are removed to expose the abrasion resistant wear layer. In the case of a casting to be welded, the outer layer and a portion of the weldable layer are removed. By controlling the structure of the casting between the fully ferritic body and the wear layer, high magnetic permeability and low magnetic remanance are obtained while providing a weldable casting. In forming such castings, white iron of malleable composition is annealed in a decarburizing atmosphere in which the ratio of carbon monoxide to carbon dioxide is closely controlled. The castings are heated to between 1800* F. and 1975* F. for a period of time sufficient to decompose the cementite followed by cooling to 1400* F. to 1650* F., and quenching or air colling, and tempering. Various details of the annealing and tempering cycles are described. rReference is made to U.S. application Ser. No. 605,955, filed Dec. 30, 1966, now U.S. Pat. No. 3,463,675 and assigned to the same assignee.