Effect of the rate of cooling on the magnetic and other properties of an annealed eutectoid carbon steel . ium tem-perature had been reached. 5. HARDNESS One end of each specimen was polished for the determinationof the scleroscope hardness, and the determinations were made bya self-recording Shore scleroscope. The size and form of thespecimens did not permit of Brinell hardness tests. 3 The heat treatment was carried out by Messrs. H. Scott and T. G. Digges, of the heat-treating laboratoryof the Bureau of Standards. Mr. Scott also gave the writers valuable assistance in selecting the mostsuit
Effect of the rate of cooling on the magnetic and other properties of an annealed eutectoid carbon steel . ium tem-perature had been reached. 5. HARDNESS One end of each specimen was polished for the determinationof the scleroscope hardness, and the determinations were made bya self-recording Shore scleroscope. The size and form of thespecimens did not permit of Brinell hardness tests. 3 The heat treatment was carried out by Messrs. H. Scott and T. G. Digges, of the heat-treating laboratoryof the Bureau of Standards. Mr. Scott also gave the writers valuable assistance in selecting the mostsuitable cooling rates for these experiments. 4C. W. Burrows, B. S. Sci. Papers, No. 117; 1909. 5 W. I,. Cheney, B. S. Sci. Papers, No. 361; 1920. 68 Scientific Papers of the Bureau of Standards [Vol. n III. OBSERVATIONS AND RESULTS 1. RATES OF COOLING Such rates of cooling were chosen as to cause a gradual varia-tion from an essentially sorbitic structure to one in which thematrix is essentially divorced pearlite. Specimen 16 was allowedto cool in air, and specimen 17 in lime, while specimens 18, 19, 20,. 90 m 150 780 2/0 Time > minutes I^G. 1.—Cooling curves for 4 specimens of annealed eutectoid carbon steel 270 and 21 were furnace cooled at various rates and under differentconditions. In Fig. i are plotted the time-temperature curvesfor the furnace-cooled specimens. In the case of specimen 18the current was cut off after the temperature had been held at8oo° C for 12 minutes, and the specimen was then allowed tocool with the furnace. Specimen ig was held for a time intervalof 13 minutes at a temperature of 8oo° C, and then slowly cooledby reducing the current, which was cut off when the temperature NusbaumlCheney J Magnetic Properties of Eutectoid Steel 69 had fallen to 5800 C; the specimen was then allowed to cool withthe furnace. Specimen 20 was held for a period of 20 minutes atthe initial temperature and allowed to cool in a definite manner bysuitable reductions of the
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