This paper studies the role of reversed austenite in martensitic stainless steels, summarizes the formation principles of reversed austenite in martensitic stainless steels and reviews elements influencing its formation. It also summarizes common heat treatment methods for obtaining reversed austenite in martensitic stainless steels and compares the advantages and disadvantages of various approaches. For example, layered quenching and tempering yield more reversed austenite compared to simple tempering, resulting in finer microstructures at room temperature. The paper analyzes how different reversed austenite contents affect the strength, ductility, and hardness of martensitic stainless steels, as well as the impact on pitting, intergranular, hydrogen, and stress corrosion. It finds that a higher amount of reversed austenite leads to a higher yield-to-tensile strength ratio, increased ductility, and lower hardness. While reversed austenite improves resistance to pitting, intergranular, and stress corrosion, its effect on hydrogen embrittlement remains debated. Additionally, the paper summarizes the formation principles of reversed austenite in martensitic stainless steels and reviews elements influencing its formation, aiming to identify optimal elements and heat treatment methods to increase reversed austenite content. This paper aims to make a summary of the research of experts and scholars in recent years, provide the knowledge foundation for the scholars who have just contacted, and give some reference for the future research direction.

This work investigates the effect of pre-nitriding treatment before vacuum carburizing on the carburizing efficiency of 20CrMnTi steel. The results show that pre-nitrocarburizing significantly enhances the vacuum carburizing efficiency of 20CrMnTi steel, refines the microstructure of the carburized layer’s martensite, and promotes the precipitation of carbides. At the same carburized layer depth, the hardness and carbon content of the pre-nitrocarburized samples are significantly higher than those of the samples without pre-nitriding. Specifically, the effective hardening depth and surface hardness increase by approximately 0.15 mm and 75 HV, respectively. These improvements are attributed to the formation of loose and porous nanoscale nitride particles on the surface during the pre-nitrocarburizing process, which significantly increases the surface roughness and porosity. This surface morphology facilitates the adsorption and inward diffusion of carbon atoms during the carburizing process. This study provides some inspiration for pretreatment techniques to improve the efficiency of vacuum carburizing.

Horizontal directional drilling is one of the most important processes in trenchless technology. Drill pipes are the most important tools for horizontal directional drilling, but can fail easily. Galling of rotary-shouldered thread connections is the usual failure style of drill pipe, which seriously threatens drilling process safety and leads to great economic losses. In the past several years, a lot of galling failure cases of drill pipes' rotary shouldered thread connections for horizontal directional drilling happened, which caused great economic losses and bad society influence. However, research on reasons for galling failure is rare at present, leading to a lack of prevention concepts for this failure style. In order to control the quantity of galling failure cases, we analyzed various factors affecting the galling failure process of rotary-shouldered thread connections based on typical failure cases, including: material chemical composition, mechanical properties, thread parameter size, thread compound, well trajectory, and field operation. Through the analysis, it was found that thread parameters, compound performance, drill string helical bucking and make-up torque have great effect on galling failure process of rotary shouldered thread connections. In order to control galling failure accidents, it is necessary to control compound quality and standard field operation.

The effect of a pre-nitriding treatment, applied prior to vacuum carburizing, on the carburizing efficiency of 20CrMnTi steel is investigated. The results demonstrate that pre-nitriding significantly enhances the vacuum carburizing efficiency of 20CrMnTi steel, refines the martensitic microstructure of the carburized layer, and promotes carbide precipitation. At the same carburized layer depth, the hardness and carbon content of the pre-nitriding samples are markedly higher than those of the without pre-nitriding samples. Specifically, the effective hardened depth and the surface hardness increase by approximately 0.15 mm and 75 HV500gf, respectively. These improvements are attributed to the formation of loose, porous nano-sized nitride particles on the surface during the pre-nitriding process, which substantially increases the surface roughness and pore volume. This surface morphology facilitates the adsorption and inward diffusion of carbon atoms during carburizing, and the presence of nitrogen in solid solution further enhances carbon diffusion.

With the increasing depth of oil and gas wells, the pressure of oil and gas reservoirs and the content of corrosive gases continue to rise, posing severe challenges to the service safety of oil and gas equipment. To develop material processes with excellent strength-toughness and H ₂ S corrosion resistance, this study systematically investigates the microstructure, strength, toughness, electrochemical corrosion, and hydrogen sulfide corrosion resistance of 13Cr super martensitic stainless steel (SMSS) under different processing conditions, combining intercritical quenching, conventional quenching, and double tempering processes. The results show that double tempering effectively refines the martensitic lath structure, significantly increases the content of reversed austenite (RA) in the material, reduces the self-corrosion current, enlarges the corrosion impedance arc radius, and enhances the corrosion resistance. Compared with the conventional quenching process, intercritical quenching combined with double tempering can produce more RA, reduce the yield-to-tensile ratio, improve low-temperature impact absorbed energy, and enhance corrosion resistance. As the double tempering temperature increases, the RA content gradually rises, while the yield strength first increases and then decreases, and the low-temperature impact absorbed energy first decreases and then increases. An optimized heat treatment process of intercritical quenching + double tempering was obtained, achieving a yield strength greater than 600 MPa with excellent strength-toughness and corrosion resistance. The material passed a 720-hour hydrogen sulfide stress corrosion cracking test.