The air cooling rate of the Low Carbon Mn-Si-Cr steel bar with different diameter after austenitizing at 910oC and 960oC was simulated by Formaster-F Phase transforming instrument and Gleeble-1500 thermal /mechanical simulating machine. Microstructure of the specimen was observed by OLYMPUS PME3 optical microscope and FEI QUANTA200F scanning electron microscope. The hardness and impact toughness of the steel was tested by HBRV-187.5 hardness tester and JCSJ300-I instrumented Charpy impact tester. The experimental result showed that with the amount of CFB in CFB+M mixed microstructure increasing the combination of strength and toughness of the steel was improved. The higher the austenitizing temperature of the steel, the wider the air-cooling rate range obtaining CFB+M mixed microstructure. However, the steel produces mixed grain after austenitizing at 960 oC. For obtaining fine prior austenite grain size, Ti and Nb alloying element need to be added.

A new method, electro-thermal explosion ultra-high speed spraying, was utilized to produce the Mo-Si or Mo-Si-B coatings. Experimental results showed that submicron-grain pure MoSi2 phase coating and boron alloyed MoSi2-MoB2 multiphase coatings were in-situ synthesized on GH3039 nickel-based superalloy substrate. Erosion-resistance test of GH3039 nickel-based superalloy and MoSi2-based coatings were performed under high temperature(800°C) with GW/CS – MS erosion wear tester. Quartz sand was employed as erosive material. Experimental results showed that the erosion-resistance of the MoSi2-based coatings is better than that of the GH3039 nickel-based superalloy.

Intermetallic compound MoSi2 is useful for protective coatings against high-temperature oxidation. In this study, MoSi2-based coatings were prepared using electrothermal explosion ultra-high speed spraying methods. The spraying distance from electric exploding chamber to substrate are 5mm, 10mm, 15mm and 20mm, respectively. The microstructures, phase structures and hardness of the coatings were investigated by scanning electron microscope (SEM) equipped with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and Vickers hardness tester, respectively. The result indicates that MoSi2 primary phase is synthesized. When spraying distance is 10mm, the coatings have density microstructure, submicron grains and high microhardness. The bonding of coating-substrate is metallurgical. The oxidation resistance of Mo-Si-Al coating is higher than that of Mo-Si coating.