In modern steelmaking, controlling trace elements is essential for ensuring the quality of steel billets and the stability of subsequent rolling processes. Tin (Sn), a common impurity in scrap-based steel production, can severely reduce the hot ductility of steel when present in excessive amounts, leading to hot brittleness and cracking during billet heating or deformation.
1. Mechanisms of Hot Brittleness Caused by Tin
(1) Grain Boundary Segregation Weakens Cohesion
At high temperatures, tin tends to segregate along austenite grain boundaries. This segregation reduces the surface energy and cohesion between grains, accelerating the nucleation and growth of micro-voids. As a result, the billet becomes more prone to intergranular cracking during hot working.
(2) Suppression of Grain Boundary Migration and Dynamic Recrystallization
Tin hinders grain boundary migration and delays dynamic recrystallization—two processes that normally help eliminate voids and restore ductility. Experimental data show that low-tin steels can regain hot ductility at around 950°C, while high-tin steels require heating to about 1000°C due to the delayed recrystallization caused by tin segregation.
(3) Formation of Low-Melting Cu–Sn Alloys
Tin also reduces the solubility of copper in austenite. Both elements can segregate at the interface between the oxide scale and the steel matrix, forming low-melting Cu–Sn alloys. These liquid phases penetrate grain boundaries under stress, resulting in intergranular cracking and further deterioration of hot ductility.
2. Can Tin Be Removed in Electric Furnace Steelmaking?
Currently, neither basic oxygen furnace (BOF) nor electric arc furnace (EAF) steelmaking can effectively remove tin. Tin is thermodynamically stable and has a low vapor pressure, making it difficult to oxidize, volatilize, or transfer into slag at steelmaking temperatures.
Therefore, the most effective approach is raw material control — minimizing the use of high-tin scrap steel and optimizing scrap blending to prevent excessive tin accumulation during melting.
3. Conclusion
Excessive tin is a major factor causing hot brittleness in steel billets. Through grain boundary segregation, inhibition of recrystallization, and the formation of low-melting alloys, tin significantly reduces the high-temperature ductility of steel.
Since electric furnace steelmaking cannot remove tin effectively, strict control of raw materials and process parameters remains the key to ensuring billet quality and stable production performance.
