This paper investigated the response of carburized 20CrNi2MoV steel to cryogenic treatment including microstructure and wear resistance. Two cryogenic treatment methods including cryogenic treatment at −80 °C (CT) and deep cryogenic treatment at −196 °C (DCT) as well as conventional heat treatment (CHT) were carried out after carburizing process. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffractometry (XRD) were employed for microstructure characterization. The wear resistance was investigated by ball-on-disc sliding wear test on a multi-functional tribometer. The results show that the wear resistance of the experimental steel has been improved by 17% due to CT and by 25.5% due to DCT when compared to CHT. This significant improvement in wear resistance after cryogenic treatment is attributed to the microstructural changes including the finer martensitic structure, the reduction of retained austenite and the development of fine and more numerous carbides. Among these factors, the precipitation of fine carbides plays a more prominent role in enhancing wear resistance.

The evolution of microstructures during the hot working of metallic materials determines their workability and properties. Recrystallization is an important softening mechanism in material forming that has been extensively researched in recent decades. This paper comprehensively reviews the basic methods and their applications in numerical simulations of dynamic recrystallization (DRX). The advantages and shortcomings of simulation methods are evaluated. Mean field models are used to implicitly describe the DRX process and are embedded into a finite element (FE) program for forming. These models provide recrystallization volume fraction and average grain size in the FE results without requiring extra computational resources. However, they do not accurately describe the microphysical mechanism, leading to a lower simulation accuracy. On the other hand, full field methods explicitly predict grain topology on a mesoscopic scale, fully considering the microscopic physical mechanism. This enhances the simulation accuracy but requires a significant amount of computational resources. Recently, the coupling of full field methods with polycrystal plasticity models and precipitation models has rapidly developed, considering more influencing factors of recrystallization on a microscale. Furthermore, integration with evolving machine learning methods has the potential to significantly improve the accuracy and efficiency of recrystallization simulation.

Ni-Co/ZrO₂ composite coatings were fabricated by electrochemical deposition from sulfamate solutions containing zirconia nanoparticles. The main purpose of this research was to evaluate the effect of mechanical stirring and ultrasonic agitation in plating solutions on the structure and properties of Ni-Co/ZrO₂ composite coatings. The morphology, microstructure, microhardness, anti-corrosion and wear resistance of the composites were investigated via scanning electron microscopy, X-ray diffraction, Vickers microhardness testing, electrochemical workstation utilization and friction wear testing. The hardness, friction coefficient, wear loss, corrosion rate of the composite coating prepared with mechanical stirring, and ultrasonic agitation were 533 and 680 HV; 0.40 ± 0.02 and 0.35 ± 0.02; 2.15 × 10⁻⁵; 0.85 × 10⁻⁵ g·m⁻¹; and 0.36 and 0.07 mm/year, respectively. In comparison to mechanical stirring, ultrasonic agitation could more uniformly disperse the zirconia nanoparticles to obtain Ni-Co/ZrO₂ composite coatings, which has simplicity and compactness.

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.

Deoxidation of liquid steel is a key link that affects the quality of environmentally friendly free-cutting steel. The selection and addition sequence of deoxidizer affects the composition, size, distribution, and morphology of non-metallic inclusions, which ultimately affect the machinability of free-cutting steel. The effects of deoxidation processes on inclusions in environmentally friendly free-cutting steel were studied by high-temperature experiments and thermodynamic calculations. The content of total oxygen and inclusion characteristics in steel were analyzed by an oxygen and nitrogen analyzer, a metallographic microscope, a scanning electron microscope, and an energy spectrum analyzer. The results show that the inclusions in the process of an initial Si-Fe alloy addition followed by a manganese addition (H1) are mainly Al₂O₃-SiO₂-MnO composite inclusions in the liquid phase. In addition to the liquid phase Al₂O₃-SiO₂-MnO complex inclusions in the MnO-rich region, there are also some solid phase Al₂O₃-MnO inclusions with high Al₂O₃ content in the process of an initial manganese addition followed by a Si-Fe alloy addition (H2). In the two deoxidation experiments, Bi particles mainly exist in the form of adhesion to MnS inclusions. Referring to H2, the average value and median of the aspect ratio is larger and the number of sulfide inclusions with aspect ratio greater than 1.0 increases significantly in H1. In addition, the spheroidization degree of MnS inclusions in the H2 is relatively good.

To enhance the corrosion resistance of underground pipelines made of low carbon steel, nano-TiO₂-modified polyurea was applied to their surface. The anti-corrosion performance of these nano-TiO₂-modified coatings was tested by immersing them in a NACE (5 wt.% NaCl + 0.5 wt.% CH3COOH) solution under high temperatures and high CO₂ pressures. The mass variation, SEM morphology, and open-circuit potential were determined. EIS tests, neutral salt spray tests, and contact angle measurements were carried out to analyze the effect of nanoparticles on corrosion resistance. Within the same pressure range, the polyurea coating shows the highest corrosion resistance when 5% TiO₂ nanoparticles were added compared to that of polyurea coatings with 0%, 10%, and 15% TiO₂ added. Coatings with 5% TiO₂ nanoparticles showed rapid diffusion after being immersed for 96 h, indicating that the anti-corrosion performance of the coating weakened.