Z.-G. Yang

Effect of annealing temperature and time on microstructure evolution of 0·2C–5Mn steel during intercritical annealing process

Abstract Microstructure evolution of 0·2C–5Mn steel during the intercritical annealing at different temperatures was studied. It was found that the microstructure gradually evolved from martensite structure into a structure consisted of austenite and ferrite during the intercritical annealing process. The retained austenite volume fraction reached the maximum value of 36·5% after about 10 min annealing at 680°C. It was also found that carbides precipitated during initial annealing stage and gradually dissolved during following annealing process for all annealing temperatures; and interestingly, the fresh martensite was found, indicating that part of the newly forming austenite was unstable and would transform into martensite when quenching. Based on the microstructural analysis and the calculation by Thermo-Calc software, it was proposed that the different evolution behaviours of the microstructure during annealing were not only controlled by the thermal kinetics of the austenite, but also affected significantly by the thermal stability of the austenite.

Mechanical properties and microstructure of Al/Al laminated structure produced via ultrasonic consolidation process

Mechanical properties of a 2024 aluminium alloy laminated structure produced by the ultrasonic consolidation were investigated. In comparison with the monolithic aluminium alloy, the existence of laminated structure gave different fatigue and fracture mechanisms that associated with the layer interfaces. The Al/Al laminated specimens had the lower tensile strength but much higher fracture toughness than the monolithic Al specimens due to the exit of interface delaminations around the crack tip. The fatigue life of the laminated specimens was comparable to that of the monolithic Al specimens, though the initiation and propagation of the crack in the laminated specimens depended strongly on the microstructure of each material. The interface between layers could arrest the fatigue crack and impede the further propagation.

Variation of microstructure and mechanical properties of medium Mn steels with multiphase microstructure

Specimens of medium manganese steels with different manganese contents were austenised at 850°C for 30 min followed by intercritical annealing and water quenching at three different temperatures with different times. After heat treatments, mechanical properties were measured through tensile test. X-ray diffraction, electron back scattered diffraction and scanning electron microscopy examinations were also performed. Results indicate that annealing time, annealing temperature and manganese content all affect the final microstructure, which may consist of ferrite, retained austenite and fresh lath martensite, and variation of microstructure leads to different mechanical properties of steel.