【作者】 刘霞；

【导师】 姚舜； 沈红卫；

【作者基本信息】 上海交通大学 ， 材料加工工程， 2007， 硕士

【摘要】 超-超临界汽轮机组研制正向着大容量、高参数、高效率、低资源消耗方向发展。为了不断满足国民经济高速发展对电力的需求,赶超发达国家电站设备制造技术的先进水平,必须加速自主研发超-超临界发电设备。超-超临界发电设备开发的关键在于材料,特别是高中压部件的材料。从运行条件和工作状态来看,转子是汽轮机乃至整个发电机组设备中最关键的部件。汽轮机转子采用具有优良的高温性能和高温抗氧化性能的铁素体耐热钢锻件。但随着材料Cr含量的提高,转子轴颈与轴承之间的摩擦特性变差,容易发生粘着、“拉毛”的异常磨损问题,在转子和轴承合金表面形成深浅、宽窄不一的凹槽。轻则引起轴系异常震动,重则导致转子断裂。防止汽轮机转轴轴颈在高速旋转过程中发生不正常磨损,成为汽轮机正常运行的技术关键。本文任务是在X12CrMoWVNbN转子表面以低合金耐热钢2CrMo焊丝作填充金属,采用单丝埋弧堆焊方法在基体上堆焊一定厚度合金层,通过控制埋弧堆焊工艺规范和稀释率以期获得特定成分的合金层来改善转轴的抗粘着磨损性能;以解决12CrMoWVNb钢汽轮机轴颈部位摩擦性能恶化问题。本文通过在12CrMoWV钢试板和模拟件上进行埋弧堆焊试验,制备力学性能试验和金相分析试样;分析由于母材金属对堆焊填充金属的稀释造成的堆焊层金属化学成分的变化情况;通过力学性能试验,分析母材、堆焊层金属力学性能变化趋势;同时分析由于各堆焊层材料经受不同的焊接热循环所发生不同相变过程而得到不同的金相组织。通过不同堆焊层的主要化学成分分析,发现随着离开母材表面距离增加,堆焊层中C、Cr、V、Mo等含量逐渐下降,其中Cr含量下降显著,在离开母材表面7mm～8mm处,Cr含量已低于2%,已经接近堆焊填充金属的原始成分;由于堆焊层中的C当量低于母材,堆焊层金属的抗拉强度、硬度低于母材,但塑韧性高于母材,冲击韧性优于母材;堆焊层的冲击断口形貌多为韧窝状塑性断裂,而母材冲击断口形貌为河流状解理断裂。堆焊层中C、Cr、Mo、V等合金元素含量愈多,固溶强化和第二相弥散分布的碳化物粒子的弥散强化效果愈显著,材料强度值愈大,硬度愈高,塑性、韧性则下降;因此堆焊层拉伸强度、剪切强度和硬度随着与母材界面距离的增大而下降,而堆焊金属冲击韧性和塑性随着与母材界面距离的增大而增大;堆焊层的剪切强度也远高于转轴的最大允许剪切强度。磨损试验结果表明,距离熔合线7～8mm处的堆焊层其磨损量最少,这说明Cr含量低于2%堆焊层,其耐磨性能优于母材本身;堆焊层金属基本组织为铁素体+碳化物,金相观察的结果与成份分析推测组织结果相吻合;而在母材热影响区出现板条状马氏体,近缝区出现回火马氏体组织,因而热影响区硬度高,塑性差,尤其延伸率低;导致近缝区的冲击韧性最差,剪切强度低。将试板堆焊试验研究的结果用于指导转子模拟件轴径的堆焊试验,通过对转子模拟件堆焊层化学成分分析、剪切试验及磨损试验发现:转子模拟件堆焊试验结果与试板堆焊试验结果是一致的;论文研究结果为超-超临界汽轮机转子产品的轴径堆焊生产提供了可靠的理论指导和技术参数。更多还原

【Abstract】 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.更多还原