Abstract
Advanced high strength steels (AHSS) are developed to reduce vehicle weight without sacrificing passenger safety. The newly developed AHSS frequently incorporates the austenite as the intrinsic component with large amount and good stability, which is realized by carefully designed alloying elements and thermo-mechanical processing. To explore the great potential of austenite in enhancing the strain hardening behavior of AHSS, detailed information on the mechanical behavior of single austenite grain is a prerequisite, which can be collected by a small-scale test. The present work reviews the recent progress in understanding the nano/micro-mechanical behavior of austenite in varied AHSS. Three different plasticity modes including dislocation plasticity, martensitic transformation, and deformation twinning can be observed in the austenite grains during small-scale tests, given proper stacking fault energy and crystal orientation. The remaining issues concerned with the nano/micro-mechanical behavior of austenite are discussed. The present review advances the general understanding of the nano/micro-mechanical behavior of austenite grains in AHSS, which may shed light on the precise austenite engineering with the development of new AHSS, realizing the dream of high-performance steels at low cost.
Highlights
Continuous efforts in understanding the nano/micro-mechanical behavior of austenite are beneficial for the alloy design, service behavior of small-volume materials in the industry such as mechanical systems (MEMS), and the thorough capture of deformation mechanism of bulk materials
The engineering stress–strain curves of individual constituting phases in advanced high strength steels (AHSS) can be extracted from the single small-scale test based on the nanoindentation test combined with microhardness measurements using the inverse method or by numerical methods and finite element analyses, which properly compare with the mechanical response obtained from the tensile tests [154,155]
The cyclic nanoindentation test has been employed to investigate the mechanical behavior of the austenitic stainless steel [156,157,158], demonstrating an interesting reverse transformation that does not exist in the macroscopic tensile test
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. With a meticulous alloy design strategy associated with the precisely controlled thermomechanical processing, the mechanical property (strength and ductility) of 3rd generation of AHSS has reached a new high level in the recent decades, realizing the dream of highperformance steel at low cost [5,6]. It generally incorporates dual-phase microstructure including ferritic and austenitic phases, with typical steel grades known as carbide free bainitic (CFB) steel [7,8], medium Mn steel [9,10,11], and quenching and partitioning (Q&P).
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