What are differences between normalizing and annealing for 4140 steel?

Normalizing and Annealing process is quite commonly used in production for 4140 Steel.The main differences are as follows:

• Temperature: Normalizing (870-900℃) > Annealing (800-850℃).
• Cooling rate: Normalizing, air cooling, results in high hardness, while annealing, furnace cooling, results in low hardness.
• Microstructure and properties: Due to the difference in cooling rates, the microstructure after normalizing is finer than that after annealing, and its properties are improved.

For 4140 steel

• Normalizing: For better overall performance or as a pretreatment for subsequent strengthening processes.
• Annealing: For softening, stress relief, and improved machinability.