Liquid Metal Embrittlement of Steel with a Coating Obtained by Batch Hot Dip Method in a Zn + 2% Sn Bath

Abstract

The article presents investigation of steel subjected to external stress during hot-dip metallization. The results of experimental investigations of the LME phenomenon, reasons of its formation and influence of different parameters are described. Samples made of C70D steel subjected to various loads inducing tensile stress (400-800 MPa) during hot dip metallization ina zinc bath with 2% tin addition were investigated. The processes of hot dip metallization were carried out at 450°C temperature and immersion time of 180 s. It can be observed that the stress value can affect the behaviour of metal during the hot dip metallization process. Coated samples were analysed on a light microscope to specify the possibility of the occurrence of LME. These studies provided the basis for the selection of samples and areas for further quantitative andqualitative analysis on a scanning electron microscope (SEM) with a microanalysis system. The analysis of cracks in three microareas revealed that the tin content in the front of a fracture is twice as big as it is in other measuring points. It may be related to crack propagation due to the phenomenon of LME, by the accumulation of the initiating element atoms and those propagating the fracture.

Structural Aspects of Decreasing the Corrosion Resistance of Zinc Coating Obtained in Baths with Al, Ni, and Pb Additives

“…Bi and Sn additives, often used together, favorably affect the quality of the coating [4]; however, with the spread of these baths, many cases of steel structure cracking as a result of the phenomenon of liquid metal embrittlement (LME) have appeared [17]. Studies in this field have shown that the cause of structure's cracking in liquid zinc may be the presence of Bi [18] and Sn [19] in the bath. Hence, the restrictions on the amount of Sn added to 0.1 wt.% and a total Pb + 10 Bi addition of less than 1.5 wt.% [20].…”

Development of Bath Chemical Composition for Batch Hot-Dip Galvanizing—A Review

“…The use of multi-component baths containing Bi and Sn, however, has encountered new problems related to the increasingly common cracking of steel structures during galvanizing. The research conducted in this area allowed the identification of the phenomenon of Liquid Metal Embrittlement (LME) [68], and the content of Bi [69] and Sn [70] in the bath was indicated as one of the main reasons for the destructive impact of the galvanizing process on steel structures. Hence, it is recommended to limit the Bi and Sn content to 0.1 wt % Sn and total Pb + 10Bi addition of less than 1.5 wt % [71].…”

The synergistic effect of the optimal AlNi addition to the zinc bath as an alternative to the baths containing Pb, Bi and Sn

“…An alternative to the addition of lead is bismuth and tin which are not harmful to the environment. It was found, however, that Bi [8] and Sn [9] may contribute to cracking of the structure during galvanization as a result of the phenomenon of liquid metal embrittlement (LME). The German Directive DASt-Richtlinie 022 [10], which is applied in many countries, limits the content of Bi and Sn in the bath when galvanizing responsible building structures.…”