Martensite start temperature

Magnetic effects on metastable transformations. The underlying factor in all the above effects is the magnitude of the ratio (G" /G ° ) and especially its variation with temperature. It follows that there can also be a substantial effect on the driving force for phase transformations, including shear transformations. Thus the martensite start temperature, in most Fe alloys is dominated by the... 

The temperature at which the transformation to martensite takes place is found to be composition-dependent. Martensite starts to form when the temperature reaches about 700 °C for the lowest-carbon-content steels but not until a temperature of about 200 °C for austenite with a carbon content of 1.2 wt%. The temperature at which the martensite starts to form is usually labelled Mg, the martensite start temperature, and the temperature at which the transformation is complete is labelled M(. the martensite hnish temperature. 

C, this structure orders to form the B2 (CsCl) stracture (Rgure 8.13). If this latter phase is quenched (cooled rapidly) to room temperature the structure transforms via a martensitic transformation into a monoclinic B19 type. On cooling, the transformation starts at a temperature designated Ms, the martensite start temperature, and is complete by a temperature M, the martensite finish temperature. For the alloy NiTi, Ms is 60 °C and Mf is 52 °C. 

Martensite is formed when steel with a carbon content above 0.2 % is rapidly cooled from the austenite temperature range to a temperature below the martensite starting temperature. Due to the prompt cooling, the carbon dissolved in austenite is forced to remain dissolved in the mixed crystal. Martensite has a fine-acicular, very hard, and brittle microstmcture which causes increased abrasive wear and high mechanical and thermal stresses during machining. 

Kun] Kunze, J., Beyer, B., Thermodynamical Calculation of Martensite Start Temperatures in the System FeCrMnNiC , Z Metallkd., 91(2), 106-113 (2000) (Phase Relations, Thermodyn., Calculation, 35)... 

Kun] Kunze, J., Beyer, B., Thermodynamical Calculation of Martensite Start Temperatures in the... 

Fig. 5.53 Plot of martensite start temperature, Mj, as a function of Zr02 volume concentration (for pure Zr02), determined from dilatometer studies [28], With kind permission of John Wiley and Sons...

The shape-memory effect is a complex function of composition, martensite start temperature Mg, stress, strain, microstructure, texture, and aging treatment. It consists essentially of a reversible transformation strain and the associated macroscopic shape change. At low numbers of transformation cycles (e g., up to 100), the... 

Fig. 3.1-89 Martensite start temperature Mg of the TiNi phase as a function of Ni content...

A NiTiNOL shape memory metal alloy can exist in two different temperature-dependent crystal structures or phases called martensite (i.e., lower-temperature phase) and austenite (i.e., higher-temperature or parent phase). Several properties of the austenite and martensite phases are notably different. When martensite is heated, it begins to change into austenite. The temperature at which this phenomenon starts is called the austenite start temperature A). The temperature at which the phenomenon is complete is called the austenite finish temperature (A). When austenite is cooled, it begins to change into martensite. The temperature at which this phenomenon starts is called the martensite start temperature (M ). The temperature at which martensite is again completely reverted is called the martensite finish temperature (Mj). Composition and metallurgical treatments have dramatic impacts on the above transition temperatures. From the point of view of practical applications, NiTiNOL can have three different forms ... 

For 12% Cr-steels, containing nitrogen it has been observed by [Pickering, 1988] that nitrogen lowers the martensite start temperature Ms 1 % nitrogen lowers Ms by 450 °C. 

Martensite-Start Temperature. Above a critical cooHng rate of 3000 °C/s (5400 °F/s), the (PTi) (aTi) transition is diffusionless (i.e., either martensitic or massive in mecheuiism). For unalloyed titaniiun, the martensite-start (Mg) temperature is influenced by ojtygen and iron contents (see table and figure). 

A metastable aggregate of ferrite and cementite resulting from the transformation of austenite at temperatures below the pearlite, but above the martensite start temperature. 

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