Which of the following describes martensite?

Martensite is a specific microstructure that forms when austenite is rapidly cooled, or quenched, from high temperatures. This quenching process results in a body-centered tetragonal (BCT) structure that is characterized by fine, needle-like grains. This unique arrangement contributes to the hardness and strength of steel, making martensite an important phase in the heat treatment of carbon steels.

The needle-like morphology of martensite provides significant mechanical properties, which is why it is often sought after in applications requiring high wear resistance. Understanding this microstructural development is vital for power engineers, particularly those dealing with materials that will be subjected to stress and elevated temperatures.

The other options do not accurately capture the essence of martensite. Soft, rounded grains indicate a softer and more ductile structure typically associated with other phases. A mixture of ferrite and cementite describes pearlite rather than martensite. Lastly, a combination of austenite and pearlite would not encompass the distinct needle-like structure that defines martensite.