麻田散铁，另称马氏体，若母相元素为铁，则可称为麻田散铁。其为纯金属或合金从某一固相转变成另一固相时的产物；在转变过程中，原子不扩散，化学成分不改变，但晶格发生变化，同时新旧相间维持一定的位向关系并且具有切变共格的特征。

麻田散铁最先在淬火钢中发现，是由奥氏体转变成的，是碳在α铁中的过饱和固溶体。以德国冶金学家阿道夫·马登斯（A.Martens）的名字命名；现在麻田散铁型相变的产物统称为“麻田散铁”。

麻田散铁的开始和终止温度，分别称为M_始点和M_终点；钢中的麻田散铁在显微镜下常呈针状，并伴有未经转变的奥氏体（残留奥氏体）；钢中的麻田散铁的硬度随碳量增加而增高；高碳钢的麻田散铁的硬度高而脆，而低碳钢的麻田散铁具有较高的韧性。

Martensite, named after the German metallurgist Adolf Martens (1850–1914), most commonly refers to a very hard form of steel crystalline structure, but it can also refer to any crystal structure that is formed by diffusionless transformation. It includes a class of hard minerals occurring as lath- or plate-shaped crystal grains. When viewed in cross section, the lenticular (lens-shaped) crystal grains are sometimes incorrectly described as acicular (needle-shaped).