The following phase transformations occur with iron-carbon alloys: Alloys, containing up to 0.51% of carbon, start solid

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The Following Phase Transformations Occur With Iron Carbon Alloys Alloys Containing Up To 0 51 Of Carbon Start Solid 1 (173.79 KiB) Viewed 48 times

The following phase transformations occur with iron-carbon alloys: Alloys, containing up to 0.51% of carbon, start solidification with formation of crystals of 8-ferrite. Carbon content in 8-ferrite increases up to 0.1% in course solidification, and at 1493ºC remaining liquid phase and 8-ferrite perform peritectic transformation, resulting in formation of austenite. In practice only hypoeutectic alloys are used. These alloys (carbon content from 2.1% to 4.3%) are called cast irons. When temperature of an alloy from this range reaches 1147 °C, it contains primary austenite crystals and some amount of the liquid phase. The latter decomposes by eutectic mechanism to a fine mixture of austenite and cementite, called ledeburite. All iron-carbon alloys (steels and cast irons) experience eutectoid transformation at 723ºC. The eutectoid concentration of carbon is 0.8%. When the temperature of an alloy reaches 723ºC, austenite transforms to pearlite (fine ferrite- cementite structure, forming as a result of decomposition of austenite at slow cooling conditions). Critical temperatures: Upper critical temperature (point) A3 is the temperature, below which ferrite starts to form as a result of rejection from austenite in the hypoeutectoid alloys. Upper critical temperature (point) ACM is the temperature, below which cementite starts to form as a result of rejection from austenite in the hypereutectoid alloys. Lower critical temperature (point) A1 the temperature of the austenite-to-pearlite eutectoid transformation. Below this temperature austenite does not exist. Magnetic transformation temperature A2 is the temperature below which a-ferrite is ferromagnetic. Task: OBSERVATION Theoretically draw the microstructures of Ferrite, Austenite, Hypo-eutectoid, Pearlite, Hyper-eutectoid steels. 1