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Martensite has a lower density than austenite, so that the martensitic transformation results in a relative change of volume. [4] Of considerably greater importance than the volume change is the shear strain, which has a magnitude of about 0.26 and which determines the shape of the plates of martensite. [5]
At high cooling rates, the material will transform from austenite to martensite which is much harder and will generate cracks at much lower strains. The volume change (martensite is less dense than austenite) [9] can generate stresses as well. The difference in strain rates of the inner and outer portion of the part may cause cracks to develop ...
The iron-carbon martensitic transformation generates an increase in hardness. The martensitic phase of the steel is supersaturated in carbon and thus undergoes solid solution strengthening. [6] Similar to work-hardened steels, defects prevent atoms from sliding past one another in an organized fashion, causing the material to become harder.
Bainite is a plate-like microstructure that forms in steels at temperatures of 125–550 °C (depending on alloy content). [1] First described by E. S. Davenport and Edgar Bain, [2] [3] it is one of the products that may form when austenite (the face-centered cubic crystal structure of iron) is cooled past a temperature where it is no longer thermodynamically stable with respect to ferrite ...
The large radius prevents the propagation of cracks in the material, further resulting in high ductility and good fatigue properties in the material. Some of the austenite phase mentioned above is mechanically metastable and will form martensite when subjected to high stress. The combination of hard, wear-resistant martensite with ausferrite ...
Aging followed by solution treatment of selective laser melted steels also reduces the amount of retained austenite in the martensitic matrix and lead to change in the grain orientation. [14] Aging can reduce the plastic anisotropy to some extent, but directionality of properties is largely influenced by its fabrication history. [15]
In steel it produces a bainite microstructure whereas in cast irons it produces a structure of acicular ferrite and high carbon, stabilized austenite known as ausferrite. It is primarily used to improve mechanical properties or reduce / eliminate distortion. Austempering is defined by both the process and the resultant microstructure.
However, greater undercooling by rapid quenching results in formation of martensite or bainite instead of pearlite. This is possible provided the cooling rate is such that the cooling curve intersects the martensite start temperature or the bainite start curve before intersecting the P s curve. The martensite transformation being a ...