The effect of Quenching-Partitioning-Tempering (Q-P-T) process on the microstructure and mechanical properties of 300M steel were investigated. X-ray diffraction, scanning electron microscopy and optical microscope were employed to characterize the evolution of microstructure as well as the volume fraction of retained austenite. The results showed that the samples treated by Q-P-T possess more retained austenite compared with traditional Quenching-Tempering process. After Q-P-T, the strength increased slightly, while the ductility and toughness improved markedly. Microstructure analysis indicated the difference between Q-T and Q-P-T process lies in the amount of the retained austenite as well as the size and size distribution of the martensite laths. The Q-T resulted in a little of thin film-like retained austenite in addition to wide martensite strip, while the Q-P-T resulted in large amount of thick-like austenite accompanying narrow martensite strip. Therefore, 300M steel with better ductility and toughness could be obtained by Q-P-T heat treatment.

An anti-corrosive primer was prepared with the epoxy resin modified with nanoparticles as its main film-formers.The influences of the ingredients, including the selection and proportion of epoxy resin modified with nanoparticles, curing agent,functional pigments and additives were studied in the present investigation.The results of performance test show that the epoxy resin modified with nanoparticles can enhance adhesion and flexibility of the coatings. Compared with the epoxy resin before modification, the film adhesion of the epoxy resin after modification increased by 3 times and flexibility changed from 30cm to 80cm. The resistance of salt fog and humid tropical condition of the coating were both more than 3000h. Meanwhile the coating has excellent comprehensive properties.