Porous high-N Ni-free austenitic stainless steel was fabricated by a powder metallurgical route. The microstructure and properties of the prepared porous austenitic stainless steel were studied. Results reveal that the duplex stainless steel transforms into austenitic stainless steel after nitridation sintering for 2 h. The prepared high-N stainless steel consists of γ-Fe matrix and FCC structured CrN. Worm-shaped and granular-shaped CrN precipitates were observed in the prepared materials. The orientation relationship between CrN and austenite matrix is [011]_CrN//[011]_γ and (-1-11)_CrN//(1-11)_γ. Results show that the as-fabricated porous high-nitrogen austenitic stainless steel features a higher mechanical property than common stainless steel foam. Both compressive strength and Young’s modulus decrease with an increase in porosity. The 3D morphology of the prepared porous materials presents good pore connectivity. The prepared porous high-N Ni-free austenitic stainless steel has superior pore connectivity, a good combination of compressive strength and ductility, and low elastic modulus, which makes this porous high-N Ni-free austenitic stainless steel very attractive for metal foam applications.

This study elucidates the influence of rapid heating (300 °C/s) on martensitic transformation pathways, crystallographic variant selection, and the resulting mechanical performance in a medium-carbon steel. Compared with conventional heating, rapid heating markedly refines the prior austenite grain (PAG) and martensitic substructures, reducing the mean PAG size from 16.08 μm to 5.06 μm and the martensitic block size from 4.24 μm to 2.41 μm. The accelerated austenitizing and quenching promote a higher density of high-angle grain boundaries (HAGBs) and favor variant selection dominated by the closely packed (CP) group. Σ3 twin boundaries are also found to assist variant nucleation and contribute to microstructural complexity. Despite a marginal decrease in tensile strength, rapid-heated steels exhibit significantly enhanced ductility and a 28.3% increase in the product of strength and elongation (PSE) compared to their conventionally treated counterparts. These findings demonstrate that rapid heating not only enables effective refinement of martensitic substructures but also offers a powerful means of controlling variant evolution, thereby achieving a superior strength–ductility synergy in martensitic steels.

The interaction between austenite static recrystallization and strain induced precipitation of a Ti microalloyed steel deformed in the non-recrystallization region was investigated by two-stage interrupted compression method and transmission electron microscopy (TEM). The softening rate curves of austenite were obtained by the true stress-strain curves of the two-pass of deformation. Results showed that the softening rates increased with increasing deformation temperatures. The softening rate curve exhibited a “S” shaped, and the static recrystallization was completed in 300 s when deformed at 1000°C, while deformed temperatures were lower than 950°C, the softening rates dropped sharply and increased very slowly as pass inter time increased. At 975°C or below, platforms appeared in softening curves, which implied strain-induced precipitates occurred during the isothermal process after the first deformation. The shortest incubation time of strain-induced precipitates was about 78 s when deformed at 925°C. Based on TEM results, strain-induced precipitates were found to be mainly distributed at dislocations and the diameters of the particles precipitated at dislocations were obviously larger than those of precipitated in other nucleation sites due to the effective route for the diffusion of Ti element. Evolution of austenite grains morphologies showed that the static recrystallization of deformed austenite was strongly inhibited by strain-induced precipitation and occurred again after the strain-induced precipitation finished.

Powder metallurgy is widely used to fabricate high-nitrogen, nickel-free austenitic stainless steel. However, after sintering and nitriding, additional solution treatment is typically required to achieve uniform nitrogen distribution and a homogeneous austenite phase. This work proposes a novel method to eliminate the need for lengthy and high-temperature solution treatment by switching the nitrogen atmosphere to argon during the cooling process. The effects of different N₂-Ar atmosphere-switching temperatures (750–1320 °C) on the phase composition, element distribution, microstructure, mechanical properties, and corrosion resistance of the studied steels were systematically investigated. Results show that cooling in the N₂ atmosphere initially transforms the matrix to a fully austenitic structure enriched with nitrogen. Excessive nitrogen infiltration leads to Cr₂N precipitation, inducing partial austenite decomposition and forming a multiphase structure comprising austenite, α-Fe, and Cr₂N. Strategic switching from N₂ to Ar reverses this reaction, yielding a high-nitrogen, chemically uniform austenitic structure. Specifically, switching at 1150 °C, the steel exhibits excellent mechanical properties and corrosion resistance, with a yield strength of 749 MPa, an ultimate tensile strength of 1030 MPa, an elongation of 38.7%, and a corrosion current of 0.06 mA/cm², outperforming the steels cooled solely in N₂ and subsequently solution-treated. This novel method offers advantages in cost reduction, energy saving, and operational effectiveness, highlighting its potential for broad industrial application.

A new composition steel was designed by adding 1wt.% Cu and 2wt.% Ni elements on the basis of low-carbon Ti-bearing microalloyed steel. The continuous cooling transition curve (CCT) is obtained by the phase transition curves, microstructure and hardness in the Gleeble3800 thermal simulation test machine. In order to further study the law of transformation and meet the needs of industrialized production, different cooling tests were carried out through industrialized trial production, and the corresponding organization and mechanical properties were analyzed. The results show that when the cooling rate increases, the microstructure transformation appears as granular bainite (GB) → granular bainite + lath bainite (GB+LB) → lath bainite (LB) → lath martensite (M). The mechanical properties increase with the increase of cooling rate, and the yield strength increases in a positive correlation trend. The results show that the steel can obtain good and stable comprehensive mechanical properties in a large cooling rate range without heat treatment. The best mechanical properties with a good combination of yield strength and impact performance are obtained under ultra-fast cooling conditions.