During tempering, the microstructural changes in martensite undergoes several changes. Martensite is a high-strength and brittle phase that forms when austenite, a face-centered cubic crystal structure, is rapidly quenched to room temperature. Tempering is a heat treatment process that involves heating the martensite to a specific temperature and holding it there for a specific time, followed by cooling it to room temperature.
Firstly, tempering relieves the internal stresses present in the martensitic structure. This occurs through a process called subcritical annealing, where the iron atoms in the martensite move around and settle into a more relaxed configuration. This reduces the hardness and strength of the martensite, making it less brittle.
Secondly, tempering causes the formation of small carbide particles within the martensite. These carbide particles act as obstacles to the motion of dislocations, which are defects in the crystal structure that can cause deformation. This increases the toughness of the material, making it less prone to fracture.
Thirdly, tempering can lead to a reduction in the amount of retained austenite present in the martensite. Retained austenite is a metastable phase that can cause dimensional instability and reduced mechanical properties in the material. The reduction in retained austenite occurs because the carbon atoms in the martensite diffuse and combine with iron atoms to form carbides, which in turn, reduces the amount of carbon available to stabilize the austenite phase.
Overall, tempering transforms the high-strength, but brittle martensite into a material that has improved toughness, reduced internal stresses, and improved dimensional stability. The specific properties of the tempered martensite will depend on the temperature and time of the tempering process.
Ankit Sharma is the Chief Editor at Uptu Khabar. He is passionate about new age digital marketing tools and their integration with the AI.
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