What is the main purpose of tempering steel after hardening?

Tempering steel after hardening is an essential process aimed at reducing brittleness. When steel is hardened, it undergoes a transformation in its microstructure that significantly increases its hardness but also makes it more brittle. This brittleness can lead to cracking or failure under stress or impact.

During the tempering process, the hardened steel is heated to a temperature below its critical point and then allowed to cool. This heating causes some of the hard microstructures, such as martensite, to transform into other structures that are tougher and less brittle, thus reducing the internal stresses within the material. As a result, the overall toughness and ductility of the steel improve, making it more suitable for practical applications where it may face dynamic loads or impact.

While other processes might improve attributes like tensile strength, the primary goal of tempering specifically addresses the issue of brittleness, ensuring that the steel maintains strength while also becoming more resilient and less susceptible to fracture during use.