Understanding Mechanical Properties of Nano-Grained Bainitic Steels from Multiscale Structural Analysis

Abstract

Steel components working in extreme conditions require materials presenting the highest performances. Nowadays, nanoengineering is being applied to the development of ultra-high strength steels as a key-enabling technology in the steel sector. The present article describes the multiscale structure of nano-grained steels designed using atomic transformation theory and processed by a simple heat treatment. Outstanding mechanical properties for these novel steels are reported, and strain-hardening mechanisms are discussed.

Controlling the Content and Morphology of Phase Constituents in Nanobainitic Steel Containing 0.6%C to Obtain the Required Ratio of Strength to Plasticity

“…Since nanobainitic ferrite is supersaturated in C, resulting in its tetragonality [19,20], part of the carbon in solid solution in the initial ferrite nanoplates could precipitate during isothermal holding. Observations of thin foils in TEM carried out by many researchers have not revealed any carbide particles but application of atom probe tomography resulted in identification of fine C-rich clusters and Fe-C plate-shaped carbides of several nm in thickness within the bainitic ferrite [10,12,16,21].…”

“…The proposals offered by Bhadeshia have been widely accepted but Caballero, Morales-Rivas, Garcia-Mateo, Sourmail et al have questioned them, based on the analysis of a large amount of experimental data on deformation mechanisms in nanobainitic steels [21,[25][26][27]. They have emphasized differences between characteristics of deformation mechanisms in classical TRIP-aided steels and in nanobainitic steels.…”

Advanced Heat Treatments and Complex Ferritic Structures for Bearing Steels

“…Moreover, cleanliness and thermal stability are vital in bearing steels due to the strict requirements in terms of fatigue resistance. Comparing the properties of nanostructured bainitic steels recently reviewed elsewhere [31] with the industrial specifications of commercial bearing steels (Table 1), a new alloy was designed applying displacive transformation fundaments to ensure low bainite reaction temperatures by using a high carbon content (1.0 wt.%), the prevention of cementite precipitation from austenite by high silicon additions (1.25 wt.%), and finally, improving hardenability and limited transformation times by an optimum combination of manganese and chromium additions, as Table 2 shows, together with the former alloying developments.…”

“…The complexity of nanostructured bainite has been recently reviewed elsewhere [31,33,34] showing the intricate phase distribution and carbon accumulation at the nearly atomic scale. The rationalization to their unprecedented mechanical performances was possible only after the comprehensive examination of the structure at several length scales using a wide variety of techniques, including scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), atom-probe tomography (APT), and electron backscatter diffraction (EBSD).…”

Welding Capabilities of Nanostructured Carbide-Free Bainite: Review of Welding Methods, Materials, Problems, and Perspectives

“…It has a film-like morphology and is characterized by a high carbon concentration and high dislocation density and stability in comparison to blocky austenite [5,7]. Such materials are called nanostructured bainitic (NB) steels without carbide precipitates (carbide-free bainite (CFB)) and their development continues to this day (among others, recently published [8][9][10]). The high mechanical properties of nanostructured carbide-free bainite create the possibility of a significant reduction in mass, and also increase the durability of structural parts in many branches of industry.…”