The structure–property relationship in 0.06C–5.5Mn steel subjected to different annealing temperatures and time was studied. Mn played a stronger effect on stabilizing austenite in comparison with Ni, and low-C medium-Mn steel possessed excellent hardenability. The reverse transformation of martensite to austenite occurred during intercritical annealing, and the volume fraction was first increased and then decreased on increasing annealing temperature or prolonging annealing time, indicative of change in thermal stability by element partitioning and coarsening of grain size. Correspondingly, the elongation was first increased and then decreased, consistent with the variation in the stability of reverted austenite. The yield strength was gradually decreased because of several factors, including recrystallization of α′ martensite, decreased stability of reverted austenite, and coarse grain size. The maximum product of strength and ductility was obtained on annealing at 650 °C for 10 min, which was attributed to the optimal stability of reverted austenite rather than the highest volume fraction, and tensile strength and elongation were 1120 MPa and 23.3%. The strain partitioning behavior of two phases was elucidated by analyzing Luders straining and continuous work hardening after yield point elongation, and the deformation mechanism was strongly related to the stability of reverted austenite.

High strength and ductility combination in nano-/ultrafine-grained medium-Mn steel by tuning the stability of reverted austenite involving intercritical annealing

Effect of Ti variation on microstructure evolution and mechanical properties of low carbon medium Mn heavy plate steel

During the past thirty years, two generations of low alloy steels (ferrite/pearlite followed by bainite/martensite) have been developed and widely used in structural applications. The third-generation of low alloy steels is expected to achieve high strength and improved ductility and toughness, while satisfying the new demands for weight reduction, greenness, and safety. This paper reviews recent progress in the development of third-generation low alloy steels with an M3 microstructure, namely, microstructures with multi-phase, meta-stable austenite, and multi-scale precipitates. The review summarizes the alloy designs and processing routes of microstructure control, and the mechanical properties of the alloys. The stabilization of retained austenite in low alloy steels is especially emphasized. Multi-scale nano-precipitates, including carbides of microal-loying elements and Cu-rich precipitates obtained in third-generation low alloy steels, are then introduced. The structure–property relationships of third-generation alloys are also discussed. Finally, the promises and challenges to future applications are explored.

Recent progress in third-generation low alloy steels developed under M 3 microstructure control

Hydrogen embrittlement behavior of high strength low carbon medium manganese steel under different heat treatments

A low-carbon Mn-Si-Cr alloyed steel was treated by two different heat treatment routes, quenching- partitioning- tempering (Q-P-T) and quenching- partitioning- cryogenic- tempering (Q-P-C-T). The strength and toughness were enhanced concurrently after Q-P-C-T treatment (i.e., ultimate tensile strength: 1236 MPa and the impact energy at 20 °C: ~ 113 J cm−2, respectively). Compared to the toughness of Q-P-T, the toughness of Q-P-C-T was improved by 23%. Microstructural characterization was carried out by conducting scanning electron microscopy, X-ray diffraction, electron backscatter diffraction and transmission electron microscopy. The enhanced toughness was attributed to the increasing high-angle boundary and newly formed martensite, which was caused by cryogenic treatment of Q-P-C-T. At last, a rational model was built to explain the toughening mechanism by microstructural evolution during Q-P-C-T. The work provides a meaningful idea that cryogenic treatment can cooperate with advanced heat treatment scientifically to acquire optimized performance of conventional steels.

Toughening optimization on a low carbon steel by a novel Quenching-Partitioning-Cryogenic-Tempering treatment

Ensuring combination of strength, ductility and toughness in medium-manganese steel through optimization of nano-scale metastable austenite

The invention discloses a Ti microalloyed medium-manganese steel medium-thickness plate for an ocean platform and a preparation method thereof The Ti microalloyed medium-manganese steel medium-thickness plate is characterized by comprising the following chemical components of, by weight, 003-01 % of C, 40- 80 % of Mn, 002-010 % of Ti, 010-040 % of Si, less than 0 005 % of S, less than 0005 % of P, 002-005 % of Al, 010-040 % of Cr, 010-030 % of Ni, 010-040 % of Mo, 010-030 % of Cu, the balance Fe and other inevitable impurities The preparation method comprises the following steps that 1, according to the Ti microalloyed medium-manganese steel medium-thickness plate for the ocean platform, alloy ingot is forged into a blank, heat preservation is carried out along with the heating of a furnace, and the heated blank is obtained; 2, multi-pass hot rolling is carried out on the heated blank to obtain a hot rolled plate, and then quenching is carried out; and 3, the quenched medium-thickness plate is put into the furnace for heating and preserving heat, the quenched medium-thickness plate is subjected to air-cooling to the room temperature to obtain the medium-manganese steel medium-thickness plate, and the structure of the medium-manganese steel medium-thickness plate is a tempered martensite and a fine inversion austenite dual-phase structure

Ti microalloyed medium-manganese steel medium-thickness plate for ocean platform and preparation method thereof

The invention discloses low-carbon V-N-Nb microalloying hot-rolled strip steel and a preparation method thereof, and belongs to the field of hot-rolled strip steel manufacturing. The low-carbon V-N-Nbmicroalloying hot-rolled strip steel comprises the following chemical components in percentage by weight: 0.06-0.15% of C, 1.5-2.2% of Mn, 0.10-0.50% of Si, S less than 0.005%, P less than 0.015%, 0.01-0.05% of Al, 0.06-0.15% of V, 0.008-0.020% of N, 0.03-0.06% of Nb, 0.01-0.02% of Ti, 0.20-0.50% of Cr, and the balance of Fe and inevitable impurities. The method comprises the following steps: 1)a steel blank is obtained by casting and forging after smelting according to the component ratios; 2) the steel blank is heated and insulated; 3) multi-pass rough rolling and finish rolling are performed on the steel blank to obtain a hot-rolled plate; and 4) the hot-rolled plate is cooled by water, and then, is cooled along with a furnace to reach the room temperature. The low-carbon component design is adopted, and the V-N-Nb microalloying is used as the core, VN educts are deformed and induced from austenite in the finish rolling process, so that the preparation cost is low, the structure performance is stable, and the industrial production is easily realized.

Liu Yujie

Papers

Ensuring combination of strength, ductility and toughness in medium-manganese steel through optimization of nano-scale metastable austenite

Ti microalloyed medium-manganese steel medium-thickness plate for ocean platform and preparation method thereof

Low-carbon V-N-Nb microalloying hot-rolled strip steel and preparation method thereof