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A systematic study was conducted on the influence of silicon on the microstructure, stress distribution, and martensitic nucleation and transformation of 301 metastable austenitic stainless steel during cold-rolling deformation. When the deformation amount of conventional 301 stainless steel is ≤20%, the amount of martensite transformation is very small. When the deformation amount is ≥30%, the amount of martensite transformation significantly increases. The introduction of Si significantly improves the amount of martensite transformation and the uniformity of deformation. 301Si-H has a significantly higher amount of martensite in the same deformation microstructure than conventional 301Si-L with a lower silicon content. Increasing the Si content decreases the stacking fault energy of 301 stainless steel. During deformation, Si tends to cluster at the grain boundaries, reducing stacking fault width and increasing dislocation density, creating sites for shear martensite nucleation at the grain boundaries. Simultaneously, significant deformation encourages the formation of deformation twins and facilitates martensite nucleation.

6Mo super austenitic stainless steel (SASS) with nitrogen contents of 0.2 and 0.4 (wt.%) was melted, and solution treatments at 1100, 1180, and 1250 °C for 30 min were performed. The effects of nitrogen on the microstructure and pitting resistance of the two steels that signed as 0.2N and 0.4N samples were investigated. At a heat-treatment temperature of 1180 °C, the alloy demonstrates the highest corrosion resistance, attributed to the combined effects of grain size and precipitates. The structure of the passivation film changes with increasing nitrogen content, with the Cr/Fe ratio is significantly higher in the 0.4N sample compared to the 0.2N sample. Moreover, the increase in nitrogen content results in thicker Cr and Mo oxide layers and higher levels of NH3 and NH4+, thereby improving the corrosion resistance of the stainless steel.

In austenitic steels, the co-segregation of C and Cr at grain boundaries can result in the formation of Cr23C6. However, the addition of B to steels can effectively reduce the amount of Cr23C6 formed and inhibit its ripening in experiments, simultaneously transforming it into Cr23(BC)6. Therefore, the effect of B on the co-segregation of C and Cr at the Σ5(210), Σ9(221) and Σ11(113) grain boundaries in austenitic steels was investigated using density functional theory. The results indicate that B, C, and Cr all tend to segregate at the three grain boundaries, with B and C showing a stronger segregation tendency. Furthermore, co-segregation of C and Cr with short distances occurs readily at the Σ5(210), Σ9(221) and Σ11(113) grain boundaries. The presence of B at grain boundaries can impede the segregation of Cr, particularly at the Σ9(221) and Σ11(113) grain boundaries. When B is pre-segregating at the Σ5(210) grain boundary, B, C, and Cr tend to co-segregate at the grain boundary. The grain boundary B hinders the accumulation of Cr near it for most grain boundaries, thereby inhibiting the co-segregation of Cr and C, making it difficult for B, C, and Cr to aggregate at most grain boundaries. This is beneficial for controlling the nucleation of Cr23(BC)6.

In order to reduce the segregation of Cr and Mo and inhibit the precipitates, we added a small amount of B and Ce to traditional S31254 steel. Using an air-cooling and low-temperature diffusion treatment, the purpose was to control B and Ce at the grain boundary. The heat-treatment process could prompt co-segregation of B, precipitate-forming elements, and Ce at the grain boundary at 950 °C. After aging at 950 °C for different amounts of time, the diffusion treatment had an obvious inhibitory effect on the precipitates that caused them to become discontinuous, fine, and serrated. The B-containing serrated precipitates were only rich in Mo, while Cr was homogeneously distributed in the probed volume. A uniform distribution of Cr reduced the Cr-depleted zone in the area adjacent to the phase interface. Ce was observed to be segregated at the grain boundary. This showed that Ce could inhibit the formation of precipitates at the grain boundary. The serrated precipitates had an obvious resistance to intergranular corrosion.

Focusing on the serious volatilization of MoO3 in super austenitic stainless steel with a high Mo content, the influence of B on the formation of oxide film and the distribution of Cr and Mo was investigated at 900 °C and 1000 °C. Without the addition of B, Mo tends to diffuse to the surface, forming porous Cr/Mo-rich oxides, causing the volatilization of Mo. The addition of B can inhibit the diffusion of Mo to the surface, facilitate the diffusion of Cr to the surface and combines with O, providing conditions for the nucleation of Cr2O3. A large amount of Cr2O3 accumulated on the surface to form a dense passive film, which inhibited the diffusion of Mo to the surface, reduced the loss of Mo, and formed Mo/Cr-rich precipitates at grain boundaries that are close to the surface. However, it was difficult to form Mo-rich precipitates at the grain boundaries of a sample without B, which aggravated the volatilization of Mo from grain boundary to surface. Therefore, the addition of B can improve the oxidation resistance of 254SMO and inhibit the volatilization of Mo.

S is a common corrosion medium for austenitic stainless steels. The severe intergranular fracture of austenitic stainless steels occurs in sulfur environments. In this paper, the permeation of S at different atomic positions for three symmetric tilt grain boundary types, i.e., Σ5(210), Σ5(310), and Σ9(114) have been computed using first-principles calculations. S has the strongest segregation tendency in the Σ5(210) grain boundary. A high content of S at the grain boundary indicates harm to the grain boundary. Sulfur segregation in the grain boundaries can weaken the strength of the metallic bond. When Mo and Cr are present at the Σ5(210) grain boundary, the sulfur-induced embrittlement is inhibited. With increased S concentration at the grain boundary, the coexistence of Mo and Cr can suppress the intergranular fracture of S on the grain boundary. The reason why high-Mo stainless steel has excellent sulfur-induced intergranular corrosion resistance is explained at the atomic level.

Sanicro 25 austenitic heat-resistant steel is expected to be used in superheaters and reheaters for ultra-supercritical power plants above 600 °C due to its excellent structural stability and high temperature mechanical properties. In this paper, the effects of Co and W on the structural stability, thermodynamic stability and mechanical properties of Sanicro 25 steel are analyzed by calculating the formation energy, binding energy, Gibbs free energy, elastic constant, Peierls stress and generalized stacking fault energy (GSFE) with first-principles calculation method. By calculating the formation energy, binding energy and Gibbs free energy, it concludes that alloying elements Co and W in Sanicro 25 steel can improve the structural stability and thermodynamic stability. It indicates that W and a small amount of Co can improve the plasticity and ductility of Sanicro 25 steel by calculating the bulk modulus (B), shear modulus (G), Young’s modulus (E), the B/G ratio, Poisson’s ratio and Peierls stress. It is found that when Co and W are far from the stacking fault region, it will promote the formation of partial dislocations and twins in the system, thereby improving its plastic deformation ability and mechanical properties.

The addition of B can inhibit the precipitation of σ phases at the grain boundary to improve the hot workability and corrosion resistance for super austenitic stainless steel with high Cr and Mo content. This study focused on the interaction between B and Mo at the Fe–Cr(111)/Cr2O3(0001) interface and its effect on interfacial adhesion by employing the first-principles method, especially the effect of B on the segregation behavior of Mo. The most stable O-terminated Fe/Cr2O3 interface was chosen as the basic configuration. The segregation energy and the work of separation were calculated for the metal/chromia interface with Fe–Cr as the substrate. It has been demonstrated that B can promote the diffusion of Mo atoms into the oxide layer to increase the content of Mo in the passive film. In addition, the interfacial adhesion is higher at the most segregated sites. However, it is more difficult for two or more Mo atoms than a single Mo atom to diffuse into the oxide part with the effect of B, indicating that B can only improve the Mo content of the passive film to a small extent. The electronic properties were also further discussed to analyze the interactions and the binding characters between doped atoms and their surrounding atoms and to explain the underlying reasons for the variation of interfacial adhesion.

In order to promote the development of ultra-supercritical technology, the optimum composition design of three new alumina-forming austenitic heat-resistant steels, based on Fe−22Cr−25Ni (wt. %), with low cost and excellent performance, and used for 700 °C ultra-supercritical unit was carried out using Thermo-Calc software. A comparison of the mechanical properties presented that with increasing Al content, the plasticity of the system was further improved. Based on the composition system, a systematic investigation regarding the structure stability, thermodynamic properties, and mechanical properties of these new steels was carried out to reveal possible strengthening and toughening mechanisms by employing the first-principles method. Calculation results showed that when Al existed in the Fe−Cr−Ni alloy system as a solid solution, the new structures were stable, especially under high temperature. The solution of Al and Al + Si could increase the value of B/G, namely improving the plasticity of the system, particularly in case of alloying with Al + Si. The inclusion of Si in the Fe−Cr−Ni−Al system was conducive to further improving the plasticity without affecting the strength, which provided references for the subsequent optimum composition design and performance regulation of alumina-forming austenitic heat-resistant steels.

Precipitate phases often play an important role on the corrosion resistance of 2205 Duplex stainless steels (DSS). In the present paper, the microstructure and the corrosion resistance of the hot-rolled and cold-rolled 2205 steels aged for different times at 850 °C was investigated through XRD, SEM, and potentiodynamic polarization. It was discovered that the Chi(χ) phase and Sigm(σ) phase were precipitated in turn following the aging treatment of the hot-rolled and cold-rolled steels, but the precipitate amount in the cold-rolled samples was significantly higher when compared to the hot-rolled samples. The corrosion resistance of the solution-annealed cold-rolled samples was similar to the hot-rolled samples, but the corrosion resistance of the cold-rolled sample with precipitate was weaker when compared to the hot-rolled sample following aging treatment. Pitting preferentially initiates in the Cr-depleted region from the σ phase in the aged hot-rolled 2205, becoming increasingly severe during aging for a long lime. Adversely, the initiation of pitting corrosion might occur at the phase boundary, defects, and martensite in the aged cold-rolled 2205. The σ phase was further selectively dissolved through the electrochemical method to investigate the difference in microstructure and corrosion behavior of the hot-rolled and cold-rolled 2205 duplex stainless steels.

To reduce the precipitation of σ phases and to improve the hot workability of S31254 steels, boron has been added into the composition of S31254 to a concentration of 40 ppm. The precipitation behavior was investigated before and after the addition of boron in different S31254 alloys during the compression deformation, and the nose temperature at 950 °C and the phase dissolution temperature at 1074 °C were selected as the measurement temperature. The result showed that more σ phases were precipitated at the grain boundary of S31254 alloys, compared to the boron-added alloy. Meanwhile, the addition of 40 ppm boron into the alloys has obviously prevented the σ phases from the austenitic matrix, and it takes longer time for the precipitation of σ phase at 950 °C. The specific influence factors of boron on the precipitation of σ phases were also further discussed.

Hot deformation behavior and microstructure evolution of 2707 hyper duplex stainless steel (HDSS) were investigated through hot compression tests in the temperature range of 900–1250 °C and strain rate range of 0.01–10 s−1. The results showed that the flow behavior strongly depended on strain rate and temperature, and flow stress increased with increasing strain rate and decreasing temperature. At lower temperatures, many precipitates appeared in ferrite and distributed along the deformation direction, which could restrain processing of discontinuous dynamic recrystallization (DRX) because of pinning grain boundaries. When the temperature increased to 1150 °C, the leading softening behaviors were dynamic recovery (DRV) in ferrite and discontinuous DRX in austenite. When the temperature reached 1250 °C, softening behavior was mainly DRV in ferrite. The increase of strain rate was conducive to the occurrence of discontinuous DRX in austenite. A constitutive equation at peak strain was established and the results indicated that 2707 HDSS had a higher Q value (569.279 kJ·mol−1) than other traditional duplex stainless steels due to higher content of Cr, Mo, Ni, and N. Constitutive modeling considering strain was developed to model the hot deformation behavior of 2707 HDSS more accurately, and the correlation coefficient and average absolute relative error were 0.992 and 5.22%, respectively.

This study investigated the structural stability and electrochemical properties of alloying additives M (M = Mn, V, Ti, Mo, or Ni) at the γ-Fe(111)/Cr2N(0001) interface by the first-principles method. Results indicated that V and Ti were easily segregated at the γ-Fe(111)/Cr2N(0001) interface and enhanced interfacial adhesive strength. By contrast, Ni and Mo were difficult to segregate at the γ-Fe(111)/Cr2N(0001) interface. Moreover, the results of the work function demonstrated that alloying additives Mn reduced local electrochemical corrosion behavior of the γ-Fe(111)/Cr2N(0001) interface by cutting down Volta potential difference (VPD) between clean γ-Fe(111) and Cr2N(0001), while alloying additives V, Ti, Mo, and Ni at the γ-Fe(111)/Cr2N(0001) interface magnified VPD between clean γ-Fe(111) and Cr2N(0001), which were low-potential sites that usually serve as local attack initiation points.