Title

Dissolution Kinetics of Iron-Based Intermetallic Compounds (τ5c IMCs) in a Commercial Steel Strip Metallic Alloy Coating Process

Publication Name

Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science

Abstract

The precipitation of discrete iron-based intermetallic compounds (τ IMCs) is an inevitable phenomenon in a steel strip coating pot due to the dissolution of iron from the steel strip surface and temperature perturbations in the pot. These τ IMC particles are a primary source of coating inclusions and bottom dross buildup in the coating pot. It has been hypothesized that they will re-dissolve into the pot during the heating cycle in the coating bath, but their dissolution kinetics remains largely unexplored. In this study, three forms of τ IMCs were used to investigate their dissolution kinetics: (i) τ -IMC disk samples (diameter: 14.88 mm) fabricated using a special approach; (ii) large τ IMCs (size: 1 to 10 mm) in the form of industrial mushy bottom dross (MBD); and (iii) fine suspended in-melt τ IMCs (size: < 50 μm). The driving force for dissolution is dictated by both the pre-existing iron content in solution in the AM alloy melt and the melt temperature. Experiments suggest that the dissolution kinetics of the τ IMCs in the forms of both τ -IMC disk and MBD is extremely slow (negligible) in the coating alloy at 595 °C. A mass transfer coefficient (k ) of 1.43 × 10 m/s is calculated in an iron-unsaturated AM alloy bath at 595 °C. Re-dissolution of fine suspended in-melt τ IMC particles (< 50 μm) occurs at the stirring rate of 220 mm/s and their dissolution rate is much faster than that of either the τ -IMC disk samples or the mushy bottom dross τ IMC particles. However, overall, their dissolution kinetics is still very slow so that their contribution as a source of Fe is practically negligible, considering that the heating time interval during a temperature perturbation cycle in an industrial coating pot is only about 7.5 minutes. This clarifies a long-standing unanswered important issue to the steel strip alloy coating process. Consequently, coating bath temperature control is important in minimizing the precipitation and growth of τ IMC particles in an industrial steel strip coating process, in addition to managing the source of iron from the highly active surface-deoxidized moving steel strip. 5c 5c 5c 5c 5c 5c 5c 5c m 5c 5c 5c 5c −6

Open Access Status

This publication is not available as open access

Volume

52

Issue

1

First Page

41

Last Page

50

Funding Number

IH130100017

Funding Sponsor

Australian Research Council

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Link to publisher version (DOI)

http://dx.doi.org/10.1007/s11663-020-01985-8