Abstract
Recent research efforts to develop advanced–/ultrahigh–strength medium-Mn steels have led to the development of a variety of alloying concepts, thermo-mechanical processing routes, and microstructural variants for these steel grades. However, certain grades of advanced–/ultrahigh–strength steels (A/UHSS) are known to be highly susceptible to hydrogen embrittlement, due to their high strength levels. Hydrogen embrittlement characteristics of medium–Mn steels are less understood compared to other classes of A/UHSS, such as high Mn twinning–induced plasticity steel, because of the relatively short history of the development of this steel class and the complex nature of multiphase, fine-grained microstructures that are present in medium–Mn steels. The motivation of this paper is to review the current understanding of the hydrogen embrittlement characteristics of medium or intermediate Mn (4 to 15 wt pct) multiphase steels and to address various alloying and processing strategies that are available to enhance the hydrogen-resistance of these steel grades.
Highlights
This review presents the current understanding of the relationships between processing, microstructure, and HE characteristics of medium or intermediate Mn (4 wt pct to 15 wt pct) steels with “ferrite–austenite”–based microstructures
The second soak is performed at a relatively high temperature in order to partially or fully replace intercritical ferrite with austenite that is converted to athermal martensite during quenching, and to create a higher-strength transformation-induced plasticity (TRIP)
H–resistant duplex or multiphase steel exists in quantifying or predicting the mechanical stability of the austenite in a multiphase microstructure, as the chemical composition of the austenite significantly varies depending on the processing history, phase fraction, and solute partitioning behavior
Summary
Advanced–/ultrahigh-strength medium-Mn steels are potentially susceptible to hydrogen (H) embrittlement as a consequence of their high strength levels; that is, H–. Substantial research efforts have been made to enhance the H-resistance of medium-Mn steel through a variety of alloying and processing strategies. This review presents the current understanding of the relationships between processing, microstructure, and HE characteristics of medium or intermediate Mn (4 wt pct to 15 wt pct) steels with “ferrite (or martensite)–austenite”–based microstructures. The literature review is intended to guide future design of alloy compositions and processes for H–resistant Mn–alloyed multiphase steels. The alloy and process designs are discussed in the context of the alloy– and process–dependent mechanical stability and stacking fault energy (SFE) of the austenite in Mn-alloyed steels
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