铁需要从面心立方体奥氏体结构转变为体心立方体铁素体结构，但是铁素体只能容纳固溶体状态的0.02%的碳。

The iron wants to change from the FCC austenite structure to the BCC ferrite structure, but the ferrite can only contain 0.02% carbon in solid solution.

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论证了贝氏体铁素体在含碳量小于0.3％时为体心立方结构，碳量大于0.3％后呈体心正方结构。

The bainitic ferrite is BCC lattice when the carbon content in it is below 0.3% and it is BCT lattice when the carbon content is over 0.3%.

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