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Bainite is a plate-like microstructure or phase morphology (not an equilibrium phase) that forms in steels at temperatures of 250–550 °C (depending on alloy content). First described by E. S. Davenport and Edgar Bain, it is one of the decomposition products that may form when austenite (the face centered cubic crystal structure of iron) is cooled past a critical temperature. This critical temperature is 1000K (727 °C, 1340 °F) in plain carbon steels. Davenport and Bain originally described the microstructure as being similar in appearance to tempered martensite. A fine non-lamellar structure, bainite commonly consists of cementite and dislocation-rich ferrite. The high concentration of dislocations in the ferrite present in bainite makes this ferrite harder than it normally would be. The temperature range for transformation to bainite (250–550 °C) is between those for pearlite and martensite. When formed during continuous cooling, the cooling rate to form bainite is more rapid than that required to form pearlite, but less rapid than is required to form martensite (in steels of the same composition). Most alloying elements will lower the temperature required for the maximum rate of formation of bainite, though carbon is the most effective in doing so.〔 The microstructures of martensite and bainite at first seem quite similar. This is a consequence of the two microstructures sharing many aspects of their transformation mechanisms. However, morphological differences do exist that require a TEM to see. Under a light microscope, the microstructure of bainite appears darker than martensite due to its low reflectivity. Bainite is an intermediate of pearlite and martensite in terms of hardness. For this reason, the bainitic microstructure becomes useful in that no additional heat treatments are required after initial cooling to achieve a hardness value between that of pearlitic and martensitic steels. ==History== In the 1920s Davenport and Bain discovered a new steel microstructure which they provisionally called martensite-troostite, due to it being intermediate between the already known low-temperature martensite phase and what was then known as troostite (now fine-pearlite). This microstructure was subsequently named bainite by Bain's colleagues at the United States Steel Corporation although it took some time for the name to be taken up by the scientific community with books as late as 1947 failing to mention bainite by name.〔 Bain and Davenport also noted the existence of two distinct forms: 'upper-range' bainite which formed at higher temperatures and 'lower-range' bainite which formed near the martensite start temperature (these forms are now known as upper- and lower-bainite respectively). The early terminology was further confused by the overlap, in some alloys, of the lower-range of the pearlite reaction and the upper-range of the bainite with the additional possibility of proeutectoid ferrite.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Bainite」の詳細全文を読む スポンサード リンク
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