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# Phase Transformation Latent Heat Model
The phase transformation affects not only the thermal properties of the material, but also absorbs or releases heat. The latent heat may have a significant effect on the temperature distribution or further phase transformations if the part is bulky and the phase transformation rate is fast. The austenitizing is an endothermic process, and the austenite decomposing is an exothermic process. The amount latent heat is calculated from the phase transformation kinetics, and the defined latent heat amount for unit phase transformation using the key word **\*STEEL\_LHEAT** in the material data \*.THM file. The latent heat effect can be turned on or off according to the process or aspects of investigation.
```
*STEEL_LHEAT
** A-->F A-->P A-->UB A-->LB A-->M M-->TM (unit: kg/s^2/mm)
0.59, 0.59, 0.59, 0.59, 0.64, 0.00
```
Where the values represent the amount heat released with 100% transformation from austenite to ferrite (pearlite, bainite, and martensite). The amount of heat released from martensite to tempered martensite is set to 0.
Using a 40 mm radium cylinder as an example, the effects of latent heat during austenitizing and quenching on the temperature change are shown in the two figures below.
Time-temperature and simulated austenite phase fraction during heating process.
Time-temperature and simulated martensite phase fraction during quenching process. It is noted that the temperature is affected by latent heat released from its neighbor.