In the current work, we design a novel medium Mn steel with a superior mechanical property and no Lüders band. For industrial applications, a “low Mn addition” chemical composition and two kinds of different annealing processes with various initial microstructures were introduced. Consequently, the sample subjected to full austenitized quenching plus intercritical annealing process exhibited an outstanding mechanical property without the Lüders band. The microstructural evolution and austenite reverted transformation behavior were discussed in detail. In addition, austenite stability was estimated by chemistry stability and mechanical stabilization. It seemed that the austenite stability was significantly influenced by the morphological component. Thus, the sample with single lath-like ferrite and austenite exhibited the most excellent mechanical property. Furthermore, the “Lüders band” phenomenon was considered to rely on the restriction of martensitic recovery and recrystallization by lath-like morphology. The occurrence of the Lüders band was attributed to the low work-hardening ability caused by dynamic recovery. The formation of lath-like morphology could prevent the occurrence and propagation of the Lüders band by increasing the dislocation density and active TRIP effect.

Based on the understanding that the essence of secondary recrystallization of Goss texture is to restrain the abnormal growth of {110}, {210} and partial Goss texture {110}, it was concluded that making sharp Goss grow up becomes the only choice. It was proposed that the abnormal growth mechanism of Goss texture was the result of selective generation, directed inheritance, and selective growth. The mechanism explained that the Goss texture was the most easily formed shear texture. In directed inheritance, the Goss texture was required to be highly compatible with the near-constant of the second-phase particle inhibition force, providing an optimal environment for the abnormal growth of the Goss texture by controlling the inhibition force near-constant. The control of the near-constant inhibition force provides an optimal environment for the abnormal growth of the Goss texture. Based on that, the process technology for producing low-temperature nitrided-oriented silicon steels and steel products was successfully developed.

This study evaluates the feasibility of producing high-strength low-alloy (HSLA) steel using advanced wire-fed laser additive manufacturing (LAM-W) and wire arc additive manufacturing (WAAM) technologies. Optimized parameters were independently developed for each heat source, utilizing a self-designed HSLA steel wire as the feedstock. Microstructural features and mechanical properties of the fabricated steels were characterized and compared, taking into account differences in heat input and cooling rates. LAM-W samples exhibited a finer columnar grain microstructure, while both LAM-W- and WAAM-produced steels predominantly showed lower bainite and granular bainite microstructures. LAM-W demonstrated higher strength and hardness, lower ductility, and comparable low-temperature toughness compared to WAAM. Both processes demonstrated an excellent balance between strength and ductility, with absorbed energy exceeding 100 J at −40 °C. The study confirms the feasibility of producing high-strength and tough HSLA steel parts using LAM-W and WAAM technologies, and compares the advantages and disadvantages of each method. These findings assist in selecting the most suitable wire-fed AM process for HSLA steel fabrication at high deposition rates.

1000 MPa grade low-carbon martensite press hardening steels (PHS) are widely used in energy-absorbing domains of automotive parts, such as the bottom of a B-pillar. To prevent oxide scale formation during hot forming, this PHS is often required to be protected by an additional Al–Si coating. In addition, although the low carbon martensitic microstructure grants it excellent bending toughness, the ductility tends to be limited. In this study, a novel 1000 MPa grade ultrafine-grained (UFG) martensite–ferrite (F–M) dual-phase (DP) PHS with superior oxidation resistance was designed using tailored additions of Cr, Mn, and Si, and refining the initial microstructure. Only 0.55 ± 0.18 μm thick oxide film is formed in the designed steel during austenitizing heating and stamping, which is significantly lower than the 24.6 ± 3.1 μm thick oxide film formed in conventional 1000 MPa grade low-carbon martensite PHS under the identical condition. The superior oxidation resistance of designed steel can be attributed to the rapid formation of the protective Si-rich, Cr-rich, and Mn-rich oxide layers during annealing. Moreover, due to the presence of ferrite and ultrafine microstructure, the designed steel also shows a significant improvement in ductility from 8.5% to 16.8% without sacrificing strength and bending toughness compared with conventional 1000 MPa grade low-carbon martensite PHS.

Generally, the addition of Chromium (Cr) into the dual-phase (DP) steels can suppress bainitic transformation. In this work, the continuous hot-dip galvanization of DP980 steel is thermally simulated with various Cr contents of 0/0.3/0.6 wt.%, and the effect of Cr on bainitic transformation and properties of steels is studied. The results indicate that the bainitic transformation is obviously inhibited. The fraction of bainite decreases with the increasing Cr content. The incubation time is prolonged in the 0.6Cr steel with a slower bainitic transformation rate. Compared to that of 0 and 0.3Cr steels, the 0.6Cr steel exhibits a high tensile strength of 1033 MPa and uniform elongation of 9.1% due to the rapid strain-hardening rate. As a result, the mechanical properties of 0.6Cr steel satisfy the requirements of hot-dip galvanized DP980 steel.

Here, a novel cryogenic rolling plus intercritical annealing process was applied to a transformation-induced plasticity (TRIP) steel with a low chemical composition of carbon and manganese. Compared with traditional cold rolling, obvious grain refinement was observed, due to a high amount of dislocations retained. In addition, austenite volume fraction was increased, because of a unique nucleation mechanism. Subjected to cryogenic rolling, strength and ductility were increased, due to the enhanced austenite stability, which provided continuous and active TRIP effect. Consequently, tensile strength was increased to 1030 MPa, and elongation was increased to 38.2%. Thus, a great mechanical combination was obtained in a steel with a relatively low chemical composition with carbon and manganese, only by cryogenic rolling process.