Relationship between Microstructure and Corrosion Behavior in Dual‐Phase Steels with Various Si Content

Abstract

The objective herein is to evaluate the effect of silicon on the corrosion behavior of dual‐phase steels. For this purpose, five different steels with various Si content ranging from 0.34 to 2.26 wt% are intercritically annealed at 780 °C for 15 min. It is clarified that the mechanism of the effect of Si on the corrosion behavior of dual‐phase steels is a mutual mechanism. The increase in Si content (from 0.34% to 0.91%) initially reduces corrosion resistance due to a decrease in the volume fraction of martensite. However, according to microcapillary studies, a further increase in Si content (from 0.91% to 2.26%) reduces the potential difference between ferrite and martensite and, as a result, reduces the galvanic couple between them. Therefore, corrosion resistance improves by increasing Si content in the range of 0.91%–2.26%. It is also shown that in the corroded surface of the low‐silicon sample, γ‐FeOOH is mainly formed, whereas with an increase in Si content, this compound reduces and α‐FeOOH rises. Also, β‐FeOOH, silicon oxide and Fe3O4 are formed in the high‐silicon sample. The study of the corroded surface topography depicts that surface roughness in a high‐Si sample is less than low‐Si sample.

Microstructural Characteristics and Strengthening Mechanisms of Ferritic–Martensitic Dual-Phase Steels: A Review

“…It has been confirmed that the silicon element can decrease and increase FGS [28,49]. Nouri et al [49,50] expressed that increasing the silicon content increased FGS. This more likely resulted from decreasing MVF (this reason will be discussed) and increasing the mobility of ferrite grain boundaries [49,50].…”

“…Increasing the silicon content decreases the carbon content of the eutectoid point [13]. Consequently, in a constant intercritical annealing temperature and time, the formed volume fraction of austenite, i.e., MVF, is reduced by increasing the silicon content [13,49,50]. M S is enhanced by an aluminum addition.…”

“…(15) Chemical composition: Chemical composition is one of the significant factors in grain refinement [95,99,100]. It has been confirmed that the silicon element can decrease and increase FGS [28,49]. Nouri et al [49,50] expressed that increasing the silicon content increased FGS.…”

“…Nouri et al [49,50] expressed that increasing the silicon content increased FGS. This more likely resulted from decreasing MVF (this reason will be discussed) and increasing the mobility of ferrite grain boundaries [49,50]. Zhou et al [28] showed that increasing the silicon content decreased FGS.…”

“…Due to the microstructure, desirable mechanical properties such as high strength, appropriate ductility, good formability, high strain hardening rate, great strength-ductility balance, high crash resistance, very good fracture toughness, and excellent weldability are obtained [13,[38][39][40][41][42][43][44][45][46]. The microstructural characteristics affect the behavior of ferritic-martensitic DP steels, such as mechanical performance, bake hardenability, weldability, corrosion, and wear properties [12,41,[47][48][49][50][51]. The main microstructural characteristics of these steels are ferrite grain size (FGS), martensite volume fraction (MVF), and martensite morphology (MM).…”