Tailoring the Austenite Fraction of a Cu and Ni Containing Medium-Mn Steel via Warm Rolling

Developing medium-Mn steels (MMnS) demands a better understanding of the microstructure evolution during thermo-mechanical treatments (TMTs). This study demonstrates the relationship among processing, microstructure, and mechanical properties of a warm-rolled medium-Mn steel (MMnS) containing 1.5 wt. % Cu and 1.5 wt. % Ni. After short-time warm rolling (WR) in an intercritical temperature range, a significant quantity (40.6 vol.%) of austenite was reverted and retained after air cooling. The microstructure and tensile properties of the WR specimens were compared with two typical process routes, namely hot rolling+ cold rolling+ annealing+ tempering (CRAT) and warm rolling+ annealing+ tempering (WRAT). The WR specimen exhibited comparable tensile properties with the CRAT specimens (967 MPa yield strength, 1155 MPa tensile strength, 23% total elongation), with a remarkably shortened process route, which was derived from the dislocation accumulation and austenite reversion during rolling. The WR route stands out among the traditional CRAT and the extended WRAT routes for its excellent tensile properties and compact processing route

Austenite transformation and deformation behavior of a cold-rolled medium-Mn steel under different annealing temperatures

In this study, the austenite transformation in a cold-rolled medium-Mn steel (MMnS; 7 wt% Mn) was adjusted by inter-critical annealing (IA) at 680 °C (above the Ac1 temperature) and by partition annealing (PA) at 650 °C (below the Ac1 temperature). The deformation behavior associated with the microstructural evolution, and crystallographic changes were investigated using in situ synchrotron X-ray diffraction during tensile deformation. Electron backscatter diffraction was used to characterize the microstructure. A considerable amount of austenite (approximately 30 and 20 vol%) was promoted by reversion transformation during the IA and PA treatments, respectively. The difference in deformation behaviors between the IA and PA specimens was attributed to the different mechanical stabilities of the reverted austenite. The relatively low mechanical stability of retained austenite (RA), due to less Mn enrichment during IA, led to a pronounced activation of the transformation-induced plasticity effect, which improved the strain hardening capacity, the ultimate tensile strength, and total elongation. However, the low recovered/recrystallized fraction of the ferrite phase resulting from PA contributed to a significant increase in the yield strength. The current understanding of the characteristics and mechanical stability of RA induced by annealing at different temperatures below and above the Ac1 temperature will help in further optimizing annealing parameters to achieve better mechanical properties for MMnS

Austenite reversion and nano-precipitation during a compact two-step heat treatment of medium-Mn steel containing Cu and Ni

Breaking the strength-ductility paradox of very-low (0.05 wt.%)-C medium (3e12 wt.%)- Mn steels (MMnS) has been a hard-wired topic, since in these steels multi-step heattreatments are usually required to obtain austenite for improved ductility and precipitates for higher strength. In this study, a compact two-step heat treatment comprising short(2 min) annealing and tempering was developed to investigate the synergetic effect of austenite reversion and nano-precipitation on the tensile behavior of a very-low-C MMnScontaining 1.5 wt.% Cu and 1.5 wt.% Ni. The annealing step promoted considerable amount of reverted austenite (33 vol.%), and the annealing was short to prevent Cu and Ni from partitioning into austenite, since they were supposed to maintain in the ferrite phase and then promote the nano-precipitation in the subsequent tempering stage. During the subsequent tempering step, the nano-precipitates with Cu concentration of 20e50 at.% in the precipitation core and enriched with Cu, Ni, Al and Mn were observed in the ferrite phase. The volume fraction of reverted austenite reached 38.5 vol.% after tempering, which led to the ultimate tensile strength of 1222 MPa and total elongation of 29% by the transformation induced plasticity during plastic deformation. The current study demonstrates the beneficial influence of the compact two-step heat treatment on the austenite reversion and nano-precipitation behavior of very-low-C MMnS with the addition of Cu and Ni, which subsequently enables an enhanced strain hardening behavior, thereby improving the mechanical property profile of the MMnS

Recent Advances in Flexible Piezoresistive Arrays: Materials, Design, and Applications

Spatial distribution perception has become an important trend for flexible pressure sensors, which endows wearable health devices, bionic robots, and human–machine interactive interfaces (HMI) with more precise tactile perception capabilities. Flexible pressure sensor arrays can monitor and extract abundant health information to assist in medical detection and diagnosis. Bionic robots and HMI with higher tactile perception abilities will maximize the freedom of human hands. Flexible arrays based on piezoresistive mechanisms have been extensively researched due to the high performance of pressure-sensing properties and simple readout principles. This review summarizes multiple considerations in the design of flexible piezoresistive arrays and recent advances in their development. First, frequently used piezoresistive materials and microstructures are introduced in which various strategies to improve sensor performance are presented. Second, pressure sensor arrays with spatial distribution perception capability are discussed emphatically. Crosstalk is a particular concern for sensor arrays, where mechanical and electrical sources of crosstalk issues and the corresponding solutions are highlighted. Third, several processing methods are also introduced, classified as printing, field-assisted and laser-assisted fabrication. Next, the representative application works of flexible piezoresistive arrays are provided, including human-interactive systems, healthcare devices, and some other scenarios. Finally, outlooks on the development of piezoresistive arrays are given

Tailoring the Austenite Fraction of a Cu and Ni Containing Medium-Mn Steel via Warm Rolling

Developing medium-Mn steels (MMnS) demands a better understanding of the microstructure evolution during thermo-mechanical treatments (TMTs). This study demonstrates the relationship among processing, microstructure, and mechanical properties of a warm-rolled medium-Mn steel (MMnS) containing 1.5 wt. % Cu and 1.5 wt. % Ni. After short-time warm rolling (WR) in an intercritical temperature range, a significant quantity (40.6 vol.%) of austenite was reverted and retained after air cooling. The microstructure and tensile properties of the WR specimens were compared with two typical process routes, namely hot rolling+ cold rolling+ annealing+ tempering (CRAT) and warm rolling+ annealing+ tempering (WRAT). The WR specimen exhibited comparable tensile properties with the CRAT specimens (967 MPa yield strength, 1155 MPa tensile strength, 23% total elongation), with a remarkably shortened process route, which was derived from the dislocation accumulation and austenite reversion during rolling. The WR route stands out among the traditional CRAT and the extended WRAT routes for its excellent tensile properties and compact processing route