Heat distortion temperature (HDT) is the temperature at which a plastic material starts to deform under a specified load. It is an important property to consider in various applications, especially for thermoplastic components.

When a load of 0.45MPA is applied, the material's HDT is relatively low, indicating that it starts to deform at a lower temperature. This suggests that the material may not be suitable for high-stress applications where it is subjected to heavy loads or high temperatures.

On the other hand, when the load is increased to 1.8MPA, the material's HDT is higher, indicating that it can withstand a higher load without significant deformation. This suggests that the material is more suitable for applications where it needs to endure heavy loads or elevated temperatures.

Overall, the difference in heat distortion temperature between 0.45MPA and 1.8MPA reflects the material's ability to resist deformation under different load conditions. It is important to consider this difference when selecting a material for specific applications to ensure its optimal performance and durability.