Spheroidization and Heat Treatment of Carbon Steels
Summary
Spheroidization is a specialised heat-treatment technique applied to medium and high-carbon steels, designed to transform elongated cementite lamellae within a ferrite or martensite matrix into rounded, globular particles. By prolonging exposure at subcritical temperatures or by cycling through precise intercritical ranges, cementite dissolves and reprecipitates in a spheroidal morphology. This evolution of microstructure markedly reduces hardness, enhances ductility and improves formability and machinability. The process also refines grain size and alters diffusion pathways, enabling controlled austenitization and tempering sequences that tailor the balance of strength and toughness. Beyond conventional spheroidized annealing, modern approaches integrate cyclic heating, deformation-assisted transformation and diffusion-kinetics modelling to accelerate particle coarsening and enhance uniformity. Such advances underpin the manufacture of cold-formed components, bearing steels and high-strength rods, and hold global significance for sectors ranging from automotive and aerospace to fastener and spring production.
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Spheroidization and Heat Treatment of Carbon Steels publication trend
The graph below shows the total number of articles in spheroidization and heat treatment of carbon steels across all publications each year (not limited to Nature Index journals).
Technical terms
Spheroidization: Formation of rounded cementite particles within a ferritic or martensitic matrix to reduce hardness and enhance ductility.
Austenitization: Heating steel into the face-centred cubic phase (austenite) region to dissolve carbides and homogenise alloying elements.
Cementite: Iron carbide (Fe₃C), a hard, brittle phase that forms lamellae or spheroids in carbon steels.
Pearlite: A two-phase lamellar aggregate of ferrite and cementite formed during slow cooling of eutectoid steel.
Martensite: A hard, supersaturated body-centred tetragonal phase produced by rapid quenching of austenite.
Divorced Eutectoid Transformation: Partial decomposition of austenite into ferrite and cementite without forming a lamellar pearlite structure.
References
- Improvement of the Mechanical Properties of 1022 Carbon Steel Coil by Using the Taguchi Method to Optimize Spheroidized Annealing Conditions. Materials (2016).
- Study on Spheroidization and Related Heat Treatments of Medium Carbon Alloy Steels. MATEC Web of Conferences (2018).
- Obtaining ultrafine spheroidized carbides by combining warm deformation with divorced eutectoid transformation in GCr15 bearing steel. Materials Research Express (2020).
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