New Insights into the Microstructural Changes During the Processing of Dual-Phase Steels from Multiresolution Spherical Indentation Stress–Strain Protocols

Abstract

In this study, recently established multiresolution spherical indentation stress-strain protocols have been employed to derive new insights into the microstructural changes that occur during the processing of dual-phase (DP) steels. This is accomplished by utilizing indenter tips of different radii such that the mechanical responses can be evaluated both at the macroscale (reflecting the bulk properties of the sample) and at the microscale (reflecting the properties of the constituent phases). More specifically, nine different thermo-mechanical processing conditions involving different combinations of intercritical annealing temperatures and bake hardening after different amounts of cold work were studied. In addition to demonstrating the tremendous benefits of the indentation protocols for evaluating the variations within each sample and between the samples at different material length scales in a high throughput manner, the measurements provided several new insights into the microstructural changes occurring in the alloys during their processing. In particular, the indentation measurements indicated that the strength of the martensite phase reduces by about 37% when quenched from 810 • C compared to being quenched from 750 • C, while the strength of the ferrite phase remains about the same. In addition, during the 10% thickness reduction and bake hardening steps, the strength of the martensite phase shows a small decrease due to tempering, while the strength of the ferrite increases by about 50% by static aging.

Hydrogen suppression of dislocation cell formation in micro and nano indentation of pure iron single crystals

“…A spherical tungsten-carbide tip was used for all tests with a radius of 19 mm. The standard method for converting indentation load-displacement data into indentation stress-strain curves was followed [29,30]. Nanoindentation tests were carried out using a Bruker Hysitron TI Premier equipped with the continuous stiffness measurement with a 1 μm radius spherical diamond tip.…”

Influence of Heat Treatment on Microstructure and Mechanical Properties of Direct-Quenched Fe-0.06C-0.2Si-2.0Mn Steel

“…However, distinguishing between martensite and ferrite using EBSD is challenging because the accuracy of the IQ value is sensitive to the polishing conditions during the preparation step, and the crystal lattice parameters of ferrite and martensite become almost identical as the carbon content decreases. Hence, some researchers applied electron channeling contrast imaging (ECCI) and nanoindentation techniques based on the individual characteristics of ferrite and martensite [38][39][40]. Figure 5 shows the features of the ECCI technique for characterizing the defect structures of direct-quenched, tempered, and intercritically annealed microstructures of the investigated steels.…”

High-Strength Low-Alloy Steels

“…Guo et al [5] evaluated the casting process conditions on the mechanical properties of hot-rolled steel and studied the billet quality by developing and optimisation method. Khosravani et al [6] tackled the microstructural changes that occur during the processing of dual-phase steels by using multiresolution spherical indentation stress-strain tests. Dzioba et al [7] focused on the effect of temperature on fracture toughness and tensile strength properties of low-carbon high-strength steel.…”