Z3CN20.09M cast duplex stainless steel (CDSS) has been used for primary coolant water pipes in pressurized water reactors due to its excellent mechanical properties. Such pipes operate at an elevated service temperature (~320 °C) and experience issues of thermal aging embrittlement. In situ tensile tests were conducted to investigate the deformation mechanisms of Z3CN20.09M CDSS after long-term thermal aging at 475 °C for up to 2000 h in both optical microscope and scanning electron microscope at 320 °C. For the 320 °C tests, the tensile stress and other mechanical properties, e.g. the yield stress and the ultimate tensile strength, increase during the thermal aging process and recover to almost the same level as the unaged condition after annealing heat-treatment, which is caused by the formation and dissolution of precipitation during aging and anneal heat-treatment, respectively. For the slip mechanism, straight slip lines form first in the austenite phase. When these slip lines reach the austenite/ferrite interface, three kinds of slip systems are found in the ferrite phase. During the fracture process, the austenite phase is torn apart and the ferrite phase shows a significant elongation. The role of the ferrite phase is to hold the austenite matrix, thus increasing the tensile strength of this steel.

Investigation on the quasi-static residual stress relaxation is an important aspect of component design and life management. After taking into account the influence of transverse stress and strength distribution, this paper proposes a new criterion of residual stress relaxation under quasi-static load as follow: the surface residual stress tends to relax as long as the Mises effective stress anywhere exceeds the local yield point. In addition, by X-ray tensile test, a method of determining superficial yield strength based on the Von Mises hypothesis was applied at the shot-peened surface of a martensitic stainless steel 0Cr13Ni4Mo. The experimental results show that the yield strength of superficial layer is larger than that of core material. According to the experimental results, a simplified ladder-shaped model of the depth distribution of yield strength is proposed. On the basis of the above-mentioned relaxation criterion and the strength distribution model, a new method is presented to calculate the relaxation amount. The calculated results coincide with the experimental results.

A new method is applied to investigate the relationship between the yield strength and annealing temperature for a Cu film. By Ion Beam Assisted Magnetron Sputtering (IAMS), Cu film with 2.4 µm thickness was deposited on a strip of super high strength steel 37SiMnCrNiMoV, and the specimens were treated by vacuum-annealing at different temperature. The X-ray tensile test was used to measure the longitudinal and transverse stresses and applied strain for Cu film. Based on the experimental results, the equivalent stress s and the equivalent uniaxial strain t e can be obtained. According to the s- t e relation, the calculated proof stress is acquired. The results indicate that the proof stress of the film decreases with the increasing of annealing temperature. When annealing temperature rises from 150ı to 300ı, the decreasing amplitude of proof stress is the largest. The phenomenon can be explained by the recrystallization and microstructure evolution in Cu film during the annealing treatment.

The heat exchanger made up of several T-shaped joints is a critical component in energy equipment. A split induction coil was designed for T-shaped aluminum pipe brazing, and the Taguchi method was combined with multi-physical simulation to solve the multi-factor optimization of the split coil. The results showed that the multi-physical simulation model had high precision. The melting of filler metal was almost consistent with the spatial distribution of the temperature field, and the average simulation error was approximately 5.753 °C. The optimal coil parameters were obtained with a turn number of 3.5, a turn space of 7 mm, a heating distance of 15.6 mm, a coil diameter of 8 mm, and a coil length of 9 mm. Three well-formed T-shaped joints could be obtained at one time via the optimal split coil. During the induction brazing, the skin effects and the proximity effects induced a high magnetic field intensity around the joint, which had a significant relationship with the coil length and coil diameter. The high magnetic field intensity promoted a high eddy current density in this place, and as a result, the high Joule heat could be generated around the joint. In addition, the significant decrease in the heating rate at high temperatures promoted the homogenization of the temperature and the melting and filling of the filler metal as well as avoided local overheating.

The work hardening effect of the shot peening affected layer of hardened and low temperature tempered spring steel was investigated using the method for determining the yield strength of a metallic surface with biaxial residual stress. The results show that for the surface layer of the specimens, the microhardness and half-width values of X-ray diffraction lines is decreased, whereas the yield strength is increased during shot peening. Thus, shot peening leads the surface layer of steel in hard state to work hardening instead of work softening.