21. The steel becomes more brittle ( martensite ) which leads to cavities forming in the wheel. 22. Martempering is used to produce martensite without developing the high stresses that usually accompany its formation. 23. By applying strain, the austenite undergoes a phase transition to martensite without the addition of heat. 24. When the edge cools fast a diffusionless transformation occurs, turning the austenite into very hard martensite . 25. For steel greater than 1 % carbon it will form a plate like structure called plate martensite . 26. However, greater undercooling by rapid quenching results in formation of martensite or bainite instead of pearlite. 27. Under a light microscope, the microstructure of bainite appears darker than martensite due to its low reflectivity. 28. Shape memory alloys also have surprising mechanical properties, that were eventually explained by an analogy to martensite . 29. Martensite is a highly strained and stressed, supersaturated form of carbon and iron and is exceedingly hard but brittle.30. In the third stage, ?-carbon precipitates into cementite, and the carbon content in the martensite decreases.
