Application of Nickel Tablets in Hot-Dip Galvanizing for Silicon and Phosphorus Steel Reactivity Control

Abstract

Alloying zinc melt with nickel is used to control the thickness of the zinc coating on steels with different contents of silicon and phosphorus. Nickel is involved in the formation of iron-zinc phases in the coating and inhibits their growth. The use of zinc-nickel master alloys is well studied and has a significant disadvantage - the significant wastage of nickel in the bottom dross. The application of nickel tablets avoids wastage, because it allows us to distribute nickel evenly throughout the bath volume. The aim of this work was to determine the working concentration of nickel introduced into the melt from nickel tablets for a wide range of silicon-containing steels and for a galvanizing time of 2-5 minutes. It was found that the nickel concentration of 0.04% leads to the coating thickness decrease and normalization of the variation in coating thickness on steels with a silicon equivalent SiEV 0.12-0.28% at the galvanizing time of 2-5 minutes, and on high-silicon steel (SiEV 0.75%) at the holding time of 3 minutes. A nickel concentration of 0.03% is effective for SiEV steels 0.12-0.18% with a galvanizing time of 2-3 minutes. "Sandeline Peak" is completely smoothed out with a holding time of 3-5 minutes in the melt with a Ni content of 0.05%. The nickel presence in the zinc melt modifies the ζ-phase structure in the coating, making it more dense and uniform in thickness.