Key Features:

• Phase Transformation: Marks the temperature range for steel changing from one crystal structure to another, e.g., ferrite to austenite.
• Heat Treatment Control: Very important for hardening, annealing, and tempering to obtain mechanical properties.
• Material-Specific Values: Different materials have different critical temperatures depending on composition and structure. 

The concept of critical temperature is significant in optimizing metals' mechanical properties. For example, in the metals industry, knowledge of the critical temperature of steel guarantees that the right heat treatment process is followed, impeding hardness and strength. In aerospace and automotive applications, strict control over temperature greatly improves durability and functionality of components. The continuing revolution in metallurgy aids in the advancement of heat treatment processes, thereby rendering products more efficient and reliable in modern applications.