Epoxy coating is a commonly used anticorrosive coating on metal surfaces. Pseudomonas aeruginosa has been reported to be able to accelerate the corrosion of metal materials, but its effect on the corrosion resistance of epoxy coatings is rarely reported. In this work, the accelerated deterioration of epoxy coating on carbon steel caused by marine Pseudomonas aeruginosa was investigated. The immersion tests of epoxy coatings in the sterile and P. aeruginosa-inoculated culture media with 100%, 10%, and 0% nutrients were performed. When the nutrient concentration was reduced, the number of P. aeruginosa cells attached to the coating surface was improved, and the coatings suffered more degradation under starvation conditions. The results of electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements showed that the presence of P. aeruginosa promoted the degradation of epoxy coating, and the coating had lower low frequency impedance modulus and higher corrosion current density in the inoculated medium with starvation conditions. The results of Fourier transform infrared spectroscopy (FTIR) indicated that the peak intensities of C-O-C and C-O groups of coatings decreased as nutrient concentration dropped in the inoculated medium. It indicated that P. aeruginosa accelerated the degradation of epoxy coatings through destroying the C-O-C and C-O groups.

The microbiologically influenced corrosion of 201 stainless steel by Shewanella algae was investigated via modulating the concentration of fumarate (electron acceptor) in the medium and constructing mutant strains induced by ΔOmcA. The ICP-MS and electrochemical tests showed that the presence of S. algae enhanced the degradation of the passive film; the lack of an electron acceptor further aggravated the effect and mainly affected the early stage of MIC. The electrochemical tests and atomic force microscopy characterization revealed that the ability of ΔOmcA to transfer electrons to the passive film was significantly reduced in the absence of the c-type cytochrome OmcA related to EET progress, leading to the lower corrosion rate of the steel.

A novel plasma-pulsed GMAW hybrid welding (plasma-GMAW-P) process is proposed for joining 6061 aluminum and zinc-coated steel. The results show that the change in welding heat input has little effect on the microstructure of the joint and the composition of the intermetallic compounds (IMCs) but only changes the thickness of the reaction layer (increased from 5 μm to 12 μm). when the plasma arc current is 20 A and the MIG current is 80 A, the welded joint obtained has the highest tensile-shear force. With the optimal process parameters, the weld strength obtained by filling ER4043 welding wire is the highest, accounting for 65% of the tensile-shear force of the base material. The effect of the plasma arc acting on the joint properties is studied through the microstructure and a tensile-shearing test. The action position of the plasma arc plays a significant role in the Al/steel interface, which directly influences the strength of the welded joints. Regardless of the plasma-GMAW-P style used to obtain the joints, Fe-Al IMCs appear at the interface. When the plasma arc is in front of the welding direction and the GMAW-P arc is in the rear, the tensile-shear force reaches the maximum of 3322 N.

The short-chain forming process using rotary swaging (RS) is an important method of achieving the manufacturing of lightweight axles. Axle steel, like 42CrMo, is widely used in many types of axles and shafts; however, there is no existing research on rotary-swaged axle steel’s mechanical properties. It makes sense to carry out a comprehensive study on the effect of RS on the mechanical behaviors of axle steel rods. In this study, a 42CrMo steel rod was processed by RS through ten passes. The tensile properties, torsion properties, compression properties, and fatigue properties were tested. There was an overall improvement in the torsional and fatigue performance after RS. Combined with a finite element analysis (FEM), the uneven distribution of the dislocations and existence of the elongation material were inferred to have caused the different modes of the mechanical behaviors. Fracture surfaces were analyzed and the results showed that the fracture pattern had changed. There existed a competitive relation between the internal fatigue cracks and external cracks, which could be attributed to uneven strain hardening. This research proved the advantages of RS in the processing of axle parts, which mainly benefitted the torsional working conditions, and provided evidence for a new processing route for lightweight axles with RS.

The effect of Ti content on the microstructure and mechanical properties of 1Cr10Co6MoVNbN steel was systematically investigated by comparing a low-Ti steel (LTS, 0.0066 wt.%) with a high-Ti steel (HTS, 0.02 wt.%). Increasing the Ti content was found to markedly alter the precipitate distribution and, consequently, the creep and high-temperature tensile behavior. In HTS, the higher Ti level promoted the preferential formation of (Ti,Nb)N inclusions during solidification; EDS analyses indicated that the matrix of HTS was substantially depleted of Nb, N, Mo, and V relative to LTS, consistent with this preferential nitride formation. In the tempered state, HTS exhibited larger NbC particles that were frequently attached to (Ti,Nb)N inclusions, whereas LTS contained finer, more uniformly dispersed NbC and abundant needle-like Cr₂N precipitates within martensitic laths. These microstructural differences correlated with a substantially higher 100 h creep strain in HTS compared with LTS at 550 °C and 325 MPa, and with a 550 °C tensile strength in HTS that fell below the aerospace standard requirement. Post-creep examination further revealed void formation around (Ti,Nb)N inclusions in HTS, suggesting that these inclusions act as stress concentrators that reduce the effective load-bearing area during creep. The results indicate that strict control of Ti content is essential in Nb–N-strengthened martensitic steels to avoid excessive (Ti,Nb)N formation and the associated degradation of high-temperature mechanical performance.