| Larger capability, higher parameter, higher efficiency and lower consumption of resource will be the development direction of ultra-supercritical steam turbine. In order to meet the electricity demand resulted from rapid growth of economy and catch up the advanced technology, it is necessary to accelerate the program of developing and manufacturing of the ultra-supercritical power equipment independently. Material is one of the key factor to develop ultra-supercritical power equipment, especially for the materials used in some parts at elevated temperature conditions. Rotor is one of the most important parts of steam turbine because of its severe operation conditions. Ferrite heat-resistant steel 9CrMoWVNb,12CrMoWVNb is used as material of rotor for their excellent properties and oxidation resistant at high temperature. However, the wearing behavior becomes bad because of raise of Cr content, for instance, adhesion or napping will occur at the bearing area, which will cause abnormal rotor vibration and would damage the whole system. Therefore, the technology of improving or preventing the bad wearing behavior becomes the key point.Improving the wearing behavior of 12CrMoWVNb rotor at bearing area is the target of this paper. In order to achieve the goal, we adopt submerged arc welding method to deposit Cr-Mo low-alloy metal on the surfaces of the rotor journal, by controlling welding parameters and rate of dilution, the layer with special chemical composition which would meet requirements is acquired. Samples taken from 12CrMoWV workpieces and simulated shaft welded with SAW build-up used for mechanical properties and metallographical analysis were made , through the laboratory tests, we will investigate the chemical composition changing trend, especially the Cr content varies with the continuous weld metal deposition, meanwhile, mechanical properties and metallurgical structure of layers subjected different welding thermal cycling will be analyzed.The result of chemical constitution of different layers is that the content of C, Cr, V, Mo etc. decrease with increasing of distance to base metal surface, especially Cr content decreases greatly. Cr content is lower than 2% at the distance 7mm～8mm to base metal surface which is near to original content of filler metal.Experiment results show tensile strength and hardness of build-up layer metal is lower than that of base metal because of carbon equivalent is lower than that of base metal, but ductility and toughness are higher than that of base metal, especially impact-toughness is better. Impact fracture characters of build-up layers is dimple fracture and impact fracture characters of base metal is stream cleavage fracture.Strengthening effectiveness of solid solution and diffusion strengthening of carbide particles increases with increasing of alloy content in build-up layers such as C, Cr, Mo, V etc., at the same time strength and hardness increase, ductility and toughness decrease. So the tensile strength, shearing strength and hardness decrease and impact toughness and ductility increase with the increasing of distance to base metal surface. And also shearing strength is much higher than the required maximum allowable shearing strength.The result of wearing experiments shows that the wearing capacity is smallest at distance of 7-8mm to surface of base metal which shows that the wearing resistance of the layer with Cr content lower than 2% is better than base metal. The microstructure of base metal is ferrite and Cr carbide which is coincident with prediction of chemical content. Martensite lath occurs at heat-affected zone, so hardness of HAZ is high and ductility is bad, especially impact toughness is worse. The study achievement of workpiece is used to build up welding rotor sample. The result of build-up welding rotor sample is coincident with that of build-up workpiece. The achievement of this paper could provide theory help and technical parameters for production of build-up welding on actual rotor of ultra-supercritical steam turbine.
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