spheroidize

Spheroidize is a heat treatment process applied to steel to soften it and improve its machinability. The primary goal is to alter the morphology of the carbide phases within the steel's microstructure. Typically, carbides exist in a lamellar or network form in steels that have undergone processes like annealing or normalizing. Spheroidizing transforms these elongated or plate-like carbide structures into small, discrete spherical particles dispersed within the ferrite matrix.

This transformation is achieved by heating the steel to a temperature just below or at its lower critical temperature (Ac1) and holding it there for an extended period, followed by slow cooling. Alternatively, it can be accomplished by cycling the temperature around the Ac1 temperature. The prolonged exposure to elevated temperatures allows the carbide particles to coalesce and minimize their surface area, naturally tending towards a spherical shape.

The benefits of spheroidizing are significant. The spherical carbides offer less resistance to deformation compared to lamellar structures, making the steel much softer and easier to cut, drill, and shape. This improved machinability can reduce tool wear and production time. Furthermore, spheroidized steel exhibits increased ductility and toughness, which can be advantageous for subsequent cold forming operations. While it reduces hardness and tensile strength, this is often a desired outcome for specific applications. Spheroidizing is a crucial step in the processing of many steels, particularly those intended for components requiring extensive machining or cold working.