2090 – 07 – Creating Martensite

1m

Once steel has been heated above the austenite phase and rapidly cooled back down to room temperature, it enters martensite phase. Quick cooling means carbon can’t precipitate from the steel. That’s why Martensite has no ferrite or cementite. Carbon gets stuck in the crystal structure even as the FCC structure changes to a BCC crystal structure. This causes the BCC structure to distort, creating a structure named a body-centered tetragonal structure. As heat escapes from steel in the Martensite phase, the steel expands a little bit. This type of stress can crack or distort the metal unless cooled the correct way.