. Transactions of the Royal Society of New Zealand. ation—the Ar or carbon point, at 780° C.—and no separating-out offerrite crystals, the resulting steel being wholly the steel contains more than 9 per cent, of carbon, still fol-lowing the analogy of the salt-and-water solution, the carbideFe3C (cementite) first forms, then the pearlite, and the re-sulting steel consists of cementite in pearlite with no free ferrite-crystals. If a steel, instead of being slowly cooled, is quenched froma temperature the value of which is disputed, but which thewriter considers it rational to suppos
. Transactions of the Royal Society of New Zealand. ation—the Ar or carbon point, at 780° C.—and no separating-out offerrite crystals, the resulting steel being wholly the steel contains more than 9 per cent, of carbon, still fol-lowing the analogy of the salt-and-water solution, the carbideFe3C (cementite) first forms, then the pearlite, and the re-sulting steel consists of cementite in pearlite with no free ferrite-crystals. If a steel, instead of being slowly cooled, is quenched froma temperature the value of which is disputed, but which thewriter considers it rational to suppose should be just above theAr3 point, and hence dependent on the percentage of carbon,no time is given for the changes, indicated by the curves, tooccur, and the material is retained in practically the same stateas it was in at the quenching-temperature, the carbon remain-ing in its diffused or hardening condition. Steel so treated isfully hardened. To such quenched steel the name of martens-ite is given; if of eutectic proportions, S Ferrite 1*4 Carbon The diffusion of carbon in steel has never been better illus-trated than by an experiment performed last year by Mr. bars of varying carbon content were made coarsely crystal-line by very slowly cooling down in the heart of a ladle of molten 524 Transactions. blast-furnace slag. Then all of them were heated at one end toa little above 1,000° C. and kept comparatively cool at the otherextremity. The temperatures at equal intervals along the barswere measured by a Chatalier pyrometer. After heating untilthe temperatures were constant each bar was quenched in coldwater, ground bright, polished, and etched, and micro-photo-graphs prepared. Fig. 6 shows the result. In the case of No. 1 bar (pure iron) there is no apparentchange of structure until a temperature of 870° C. is reorganization is apparent, the crystals becoming smaller. No. 2 Bar (0-2 per cent, carbon).—In propo
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