Grain Boundary Segregation of Phosphorus, Boron and Manganese in High Tensile Strength Steel Sheet

Abstract

Grain boundary segregation of Si, Mn, P and B was investigated by Anger electron spectroscopy (AES) in high tensile strength extra low C interstitial atom free steel sheet containing op to 0.7 mass% Si, 3 mass% Mn, 0.18 mass% P and 30 mass ppm B after annealing at 1153K. AES measurements were done for specimens cut from cup-shaped drawn sheets in order to induce intergranufar fracture and fractured by impact at about 153K. The segregation of Si and Mn was evaluated from their Anger peaks separated from overlap with the Fe peak by the Linear Least Square fitting method referring to pure materials. Mn, P and B segregate at the grain boundary, while segregation of Si is not recognized The grain boundary concentration of P decreases as that of B increases, indicating a site competition between the elements similar to that in extra low C steel sheet doped with P and B. The grain boundary concentration of Mn increases with increases in the bulk concentration of Mn, while that of P and B shows no appreciable relationship with the bulk concentration of Mn, probably due to differences in segregation sites at the grain boundary between these elements and Mn. The ductile-brittle transition temperature in secondary working has a linear relationship with the grain boundary concentration difference of ( Mn + P -B \It is concluded that the segregation of P and Mn degrades secondary miking embritfement of the steel sheet, while segregation of B improves it.