Abstract
The author presents an account of four years of research work undertaken for the American Malleable Castings Association as a plea for industrial research among manufacturers and as a striking example of what such research can accomplish. He sketches the organization and purpose of the Association and shows how the quality of the product of its members has steadily increased since the beginning of the research work. Malleable-iron castings, due to lack of uniformity and dependability, were rapidly being replaced by other materials. There were many fallacious ideas and theories regarding the physical properties of such castings and the methods of annealing them. Records of tests of 1-in. bars from seven different concerns made by the author in 1911 showed that the average ultimate strength was 39,882 lb. and the elongation under 5 per cent. A report dated March, 1919, to the members of the Association, each of whom regularly submits test bars from some one heat of each day’s runs, showed that 44 per cent of the test bars submitted during that month had an ultimate strength over 52,000 lb. and an elongation of 14.67 per cent, indicating the progress made since research work was undertaken.
It is further stated that the average of test bars of the Association from January 1, 1917, to March 31, 1919, has shown an ultimate strength of 51,000 lb. and an elongation 12.5 per cent. The records of tests show, contrary to generally accepted theory, that the elongation increases with the ultimate strength. The purpose of the Association, however, is not to increase ultimate strength and elongation but to increase the uniformity of a product upon which the engineer can rely, and this is being accomplished through exhaustive research and advice to members through the consulting engineer of the Association.
A description is given of the process of manufacturing malleable iron, of the air furnace, and of the annealing ovens and the annealing process. The structures of iron containing free carbon and iron containing combined carbon are shown by micrographs and the metallurgy of cast iron is carefully explained with abundant micrographs of typical structures.
The effects of the time element in cooling through the critical temperature, of successive anneals, of varying percentages of carbon, sulphur, silicon, phosphorus and manganese and of subsequent heating to high temperatures are clearly described and illustrated. Picture-frame fractures are also discussed.
