An experimental investigation on pre-treatment-spheroidization effect on microstructure and tensile strength of AISI4140 steel

The purpose of heat treating steel components is significant, as it can impart essential properties to the material, enabling better service conditions and facilitating various manufacturing processes. Spheroidization is a specific type of heat treatment aimed at achieving a refined structure that enhances machinability. Therefore, it is important to study the effects of different room temperature structures on property enhancement, ensuring that the heat treatment yields the desired properties alongside structural changes. This research aims to connect preliminary room temperature structures—such as as-cast, normalized, and hardened—with the mechanical characteristics obtained after spheroidization, including hardness, tensile properties, and microstructure. The hardened structure exhibits a superior hardness distribution, along with enhanced tensile properties and a finer dispersion of carbides after spheroidization. In contrast, the normalized structure demonstrates moderate spheroidized properties, while the as-cast structure shows the lowest properties, characterized by coarser carbide globules. This work primarily focuses on relating the mechanical characteristics and resulting microstructure of spheroidized steel to the microstructure present before spheroidization.