A low-alloy high-carbon martensite steel with 2.6 GPa tensile strength and good ductility

Medium Mn steels are promising candidates for the third-generation advanced high strength steels. However, it shows a distinct limit of mechanical property under conventional hot-rolling and intercritical annealing procedures. Aiming at improving the combination of strength, ductility and toughness, the present study proposed a multi-alloyed design principle together with a direct intercritical rolling process. The results show that the microstructure of the hot rolled steel consisted of wide delta ferrite, lath martensite, twinned-martensite and coarse retained austenite with a low stability, corresponding to a product of strength and elongation (PSE) of 24.0 GPa% and an impact toughness of 13.8 J/cm 2 at −40 °C. In contrast, the intercritical rolling produced a laminated microstructure containing thin delta ferrite, submicron recrystallized ferrite and retained austenite. The PSE and impact toughness at −40 °C simultaneously increased to 46.1 GPa% and 46.7 J/cm 2 , respectively, which was also much higher than the hot rolled steel subjected to low temperature and high temperature annealing. The significant enhancement of mechanical property was mainly attributed to the highest content and optimal stability of retained austenite caused by the submicron grain size, high density of dislocations, granular morphology, and elemental enrichment. The optimized austenite stability provided persistent transformation-induced plasticity (TRIP) effect for work hardening and damage resistance. Moreover, the nano-sized VC precipitates in the intercritical rolled steel played a significant role in reaching an ultrahigh yield strength of ∼1 GPa. This study not only provides a very simple pathway to improve the mechanical property of medium Mn steel, but also sheds light on the design and development of high-performance materials. 

Tailoring retained austenite and mechanical property improvement in Al–Si–V containing medium Mn steel via direct intercritical rolling

Effect of carbon content on microstructure, hardness and wear resistance of CoCrFeMnNiCx high-entropy alloys

Mechanically strong and ductile load–carrying materials are needed in all sectors, from transportation to lightweight design to safe infrastructure. Yet, a grand challenge is to unify both features in one material. We show that a plain medium-manganese steel can be processed to have a tensile strength >2.2 gigapascals at a uniform elongation >20%. This requires a combination of multiple transversal forging, cryogenic treatment, and tempering steps. A hierarchical microstructure that consists of laminated and twofold topologically aligned martensite with finely dispersed retained austenite simultaneously activates multiple micromechanisms to strengthen and ductilize the material. The dislocation slip in the well-organized martensite and the gradual deformation-stimulated phase transformation synergistically produce the high ductility. Our nanostructure design strategy produces 2 gigapascal–strength and yet ductile steels that have attractive composition and the potential to be produced at large industrial scales. Description Putting steel through the process High-strength steels with good ductility are attractive for a number of applications, but these alloys often require the use of expensive elements or complex processing methods. Li et al. found that a high-strength steel composed of iron, manganese, silicon, carbon, and vanadium can be made with a different processing strategy. A combination of forging, cryogenic treatment, and tempering creates an alloy with very high strength that also has good ductility and formability. The strategy should be an option for other compositions of steel. —BG A different processing strategy creates a high-strength steel with good ductility without expensive elements.

Ductile 2-GPa steels with hierarchical substructure

Carbide-facilitated nanocrystallization of martensitic laths and carbide deformation in AISI 420 stainless steel during laser shock peening

A lamellar structured ultrafine grain ferrite-martensite dual-phase steel and its resistance to hydrogen embrittlement

Grain refinement is one of the most effective methods for strengthening steels, but grain refinement to 1 µm or less deteriorates the ductility considerably. To evade the strength-ductility trade-off, a lamellar-structured (LS) ultrafine-grained (UFG) dual-phase (DP) ferrite/martensite (F/M) steel was produced by warm rolling an intercritical annealed low-carbon martensite and subsequent air cooling in this paper. The microstructure is similar to a short fiber reinforced composite, and the highest strength (1432 ± 15 MPa) combined with a decent ductility (16.5 ± 0.5% elongation) is achieved in DP steel. Compared with conventional equiaxed coarse-grained (CG) and UFG DP counterparts, the LS martensite in UFG DP steel can produce extra strengthening effect and is also beneficial to ductility. And the short fiber theory can predict the strength very well.

Ultrafine grained dual-phase martensite/ferrite steel strengthened and toughened by lamella structure

The effect of austenitizing and tempering temperature on the microstructure and mechanical properties of 65Mn spring steel refined by Tempforming (tempering and deforming of a quenched steel) process was investigated. The martensite substructure of ultrafine grain is composed of high density dislocations and a few twins, but the quantity of twins increases in normal grain martensite steel. Super strength (2220 MPa) and good ductility (8.6%) are achieved at grain size of 5.6 μm when austenitized at 790 °C and tempered at 250 °C. However, contrasted 65Mn steel with normal grain (18.7 μm) displayed almost no any ductility when processed at identical temperature parameters. Accordingly, the tempforming preprocessing contributes to the decrease in grain size and formation of crystallographic texture, which is beneficial for eventual grain refinement after subjected to reheat treatment. By appropriate quenching and tempering treatment after tempforming process, 65Mn spring steel achieved ultrafine grain and super strength and good ductility.

Super strength of 65Mn spring steel obtained by appropriate quenching and tempering in an ultrafine grain condition

The Enhanced Electrochemical Performance of Li1.2Ni0.2Mn0.6O2 through Coating MnF2 Nano Protective Layer

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