700℃超超临界蒸汽轮机叶片用Waspaloy合金组织与性能研究
发布时间：2018-09-08 17:01
【摘要】：发展高参数超超临界火电技术是符合我国国情的“洁净煤发电”首选技术。而随着蒸汽参数的提高,对耐热材料的要求也更加苛刻。叶片作为火电设备蒸汽轮机的关键部件,在蒸汽温度达到700℃时,叶片材料需要采用镍基耐热合金。Waspaloy合金是700-℃超超临界蒸汽轮机叶片的主要候选材料之一,本文利用光学显微镜、SEM、TEM、XRD等测试方法,对Waspaloy合金的热变形行为、热处理制度的影响、700-C长期时效过程中组织与性能变化、持久断裂寿命进行了系统研究；并对Waspaloy合金的成分进行了优化,同时进行一定的成分改进。取得的主要结果如下：研究了Waspaloy合金在0.01S-1-l0.0S-1及1000℃～1200℃变形条件下的热变形行为,建立了合金的热变形方程以及Z参数与峰值应力间的定量关系,求得了合金平均激活能为430.9kJ/mol。基于动态材料模型,建立了Waspaloy合金的热加工图,并确定了合金最佳的热加工工艺为：应变温度1050℃到1150℃,应变速率为O.O1s-1～0.1s-1时,在此条件下能量耗散率最高能达到45%,合金能获得均匀等轴的完全再结晶组织；而在应变温度1000℃～1050℃,应变速率为1.0 s-1～10.0 s-1加工时,会出现绝热变形带,发生流变失稳现象。研究了热处理制度对Waspaloy合金组织与性能的影响,随着固溶温度的升高,合金强度不断下降,晶粒尺寸不断长大：当固溶温度小于1080℃时,晶粒尺寸可以满足ASTM标准要求；固溶保温时间达到4h后,合金中仅有少量块状MC型碳化物未溶。在845℃进行高温时效时,合金强度达到最高,M23C6型碳化物大量析出,并沿晶界呈颗粒链状分布。合金在760℃时效16h时,合金的强度达到峰值。得到700℃叶片材料用Waspaloy合金的适宜热处理制度为1080℃保温4h,油冷+845℃保温4h,空冷+760℃保温16h,空冷。研究了Waspaloy合金在700℃条件下时效10000h过程中组织与性能变化。合金主要析出相为富Cr的M23C6型碳化物、富Ti的MC型碳化物和γ’相以及微量的M6C相,时效过程中没有其他相析出,合金表现出良好的组织稳定性。丫'相为球状颗粒在晶内弥散析出,颗粒大小符合正态分布规律；丫'相长大过程符合Ostward熟化规律,时效10000h后γ'相的平均尺寸长大并不明显。M23C6型碳化物主要沿晶界析出,随时效时间的延长,其形貌特征经历了由细小颗粒断续分布演变到长条状连续分布,并逐渐长大的演变过程。合金中一次MC相会与基体发生MC+γ→M23C6+γ'分解反应,但分解反应非常缓慢。在时效初期,持续析出丫'相的使得合金的强度明显提高；当时效时间超过2000h以后,丫'相的长大又会导致合金强度的缓慢下降。对合金中C、Ti元素含量进行了优化研究。合金中C元素的提高能有效增加合金中碳化物数量,增强碳化物对晶界钉扎作用,使得晶粒明显细化,但对碳化物种类、分布以及γ'相的形貌特征没有明显影响,不会改变Waspaloy合金中析出相的种类；当C含量取0.016%时,合金强度以及短时持久性能较低；当C取0.056%～0.096%时,合金具有较好的短时与外推长时持久性能。合金中Ti元素的提高不会引起Waspaloy合金中析出相种类的变化,能有效增加合金中γ'相的数量,改善合金强度和短时持久性能,但长时外推持久强度会有所降低；当Ti含量为3.18%,合金具有较好强度性能与较好的长时外推持久寿命。研究了W元素在Waspaloy合金中的作用。结果表明在合金中添加2%质量分数的W元素,能有效细化合金中γ'相的尺寸,显著降低γ'相的长大速率,改善合金的强度性能、冲击韧性以及持久性能,不会改变Waspaloy合金中析出相的种类,在长期时效过程中保持了良好的组织稳定性。W元素主要分布于基体和γ'相中,同时起到固溶强化和沉淀强化作用；添加到合金中的W元素,能够增加合金中重合位置点阵∑=3晶界数量,降低晶界界面能量,强化晶界,能同时改善合金的短时以及长时外推持久性能。700℃下10万小时持久强度外推值达到271MPa,比成分改进前的Waspaloy合金持久外推性能提高了14.0%。
[Abstract]:The development of ultra-supercritical thermal power technology with high parameters is the preferred technology for clean coal power generation in line with China's national conditions. With the improvement of steam parameters, the requirements for heat-resistant materials are more stringent. LOY alloy is one of the main candidates for ultra-supercritical steam turbine blades at 700-C. In this paper, the thermal deformation behavior of Waspaloy alloy, the effect of heat treatment regime, the change of microstructure and properties during long-term aging and the rupture life of Waspaloy alloy are studied systematically by means of optical microscope, SEM, TEM and XRD. The main results are as follows: The hot deformation behavior of Waspaloy alloy under deformation conditions of 0.01S-1-l0.0S-1 and 1000 ~1200 ~C was studied, the hot deformation equation and the quantitative relationship between Z parameter and peak stress were established, and the average activation of the alloy was obtained. Based on the dynamic material model, the hot working diagram of Waspaloy alloy is established. The optimum hot working process is determined as follows: when the strain temperature is 1050 1150 C and the strain rate is 0.O1s-1 0.1s-1, the maximum energy dissipation rate can reach 45%, and the homogeneous equiaxed fully recrystallized microstructure can be obtained. The effect of heat treatment on the microstructure and properties of Waspaloy alloy was studied. With the increase of solution temperature, the strength of Waspaloy alloy decreased and the grain size grew continuously. The strength of the alloy reaches its maximum at 845 C and M23C6 carbides precipitate in large quantities and distribute along the grain boundaries in a chain shape. The strength of the alloy reaches its peak at 760 C for 16 h. The optimum heat treatment regime of Waspaloy alloy for blade material at 700 C is 1080 C for 4 h, oil cooled 845 C for 4 h, air cooled 760 C for 16 h and air cooled. The microstructure and properties of Waspaloy alloy during aging at 700 C for 10000 h are studied. In addition, no other phases were precipitated in the aging process and the alloy exhibited good microstructure stability. The spherical particles in the Ya'phase dispersed in the grains and the size of the particles accorded with the normal distribution law. The growth process of the Ya'phase accorded with the Ostward aging law, and the average size of the gamma'phase did not grow up obviously after aging for 10000 hours. C-carbide precipitates mainly along grain boundaries, and the morphology of C-carbide evolves from discontinuous distribution of fine particles to continuous distribution of long strips and gradually grows up with the time of aging. The content of C and Ti in the alloy was optimized. The increase of C in the alloy can effectively increase the amount of carbide in the alloy, enhance the pinning effect of carbide on grain boundary and make the grain clear. The results show that the strength and short-term rupture properties of the alloy are lower when C content is 0.016%, and the alloy has better short-term and long-term rupture properties when C content is 0.056%-0.096%. The increase of Ti content will not cause the change of precipitated phase types in Waspaloy alloy. It can effectively increase the amount of gamma'phase in the alloy, improve the strength and short-term rupture properties of the alloy, but the long-term extrapolated rupture strength will be reduced. When the content of Ti is 3.18%, the alloy has better strength properties and long-term extrapolated rupture life. The results show that the addition of 2% W in the alloy can effectively refine the size of the gamma'phase, significantly reduce the growth rate of the gamma' phase, improve the strength, impact toughness and rupture properties of the alloy, and do not change the type of precipitates in the Waspaloy alloy, and maintain good properties during long-term aging. The W element mainly distributes in the matrix and the gamma'phase, and plays the role of solution strengthening and precipitation strengthening. The W element added to the alloy can increase the number of lattice_=3 grain boundaries in the overlapping position, reduce the energy of grain boundaries, strengthen grain boundaries, and improve the short-term and long-term extrapolated rupture properties of the alloy. The extrapolation value of tensile strength reached 271 MPa at 100 000 hours, which was 14.0% higher than that of Waspaloy alloy before composition improvement.
【学位授予单位】：昆明理工大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TM621;TG132.3
本文编号：2231132
[Abstract]:The development of ultra-supercritical thermal power technology with high parameters is the preferred technology for clean coal power generation in line with China's national conditions. With the improvement of steam parameters, the requirements for heat-resistant materials are more stringent. LOY alloy is one of the main candidates for ultra-supercritical steam turbine blades at 700-C. In this paper, the thermal deformation behavior of Waspaloy alloy, the effect of heat treatment regime, the change of microstructure and properties during long-term aging and the rupture life of Waspaloy alloy are studied systematically by means of optical microscope, SEM, TEM and XRD. The main results are as follows: The hot deformation behavior of Waspaloy alloy under deformation conditions of 0.01S-1-l0.0S-1 and 1000 ~1200 ~C was studied, the hot deformation equation and the quantitative relationship between Z parameter and peak stress were established, and the average activation of the alloy was obtained. Based on the dynamic material model, the hot working diagram of Waspaloy alloy is established. The optimum hot working process is determined as follows: when the strain temperature is 1050 1150 C and the strain rate is 0.O1s-1 0.1s-1, the maximum energy dissipation rate can reach 45%, and the homogeneous equiaxed fully recrystallized microstructure can be obtained. The effect of heat treatment on the microstructure and properties of Waspaloy alloy was studied. With the increase of solution temperature, the strength of Waspaloy alloy decreased and the grain size grew continuously. The strength of the alloy reaches its maximum at 845 C and M23C6 carbides precipitate in large quantities and distribute along the grain boundaries in a chain shape. The strength of the alloy reaches its peak at 760 C for 16 h. The optimum heat treatment regime of Waspaloy alloy for blade material at 700 C is 1080 C for 4 h, oil cooled 845 C for 4 h, air cooled 760 C for 16 h and air cooled. The microstructure and properties of Waspaloy alloy during aging at 700 C for 10000 h are studied. In addition, no other phases were precipitated in the aging process and the alloy exhibited good microstructure stability. The spherical particles in the Ya'phase dispersed in the grains and the size of the particles accorded with the normal distribution law. The growth process of the Ya'phase accorded with the Ostward aging law, and the average size of the gamma'phase did not grow up obviously after aging for 10000 hours. C-carbide precipitates mainly along grain boundaries, and the morphology of C-carbide evolves from discontinuous distribution of fine particles to continuous distribution of long strips and gradually grows up with the time of aging. The content of C and Ti in the alloy was optimized. The increase of C in the alloy can effectively increase the amount of carbide in the alloy, enhance the pinning effect of carbide on grain boundary and make the grain clear. The results show that the strength and short-term rupture properties of the alloy are lower when C content is 0.016%, and the alloy has better short-term and long-term rupture properties when C content is 0.056%-0.096%. The increase of Ti content will not cause the change of precipitated phase types in Waspaloy alloy. It can effectively increase the amount of gamma'phase in the alloy, improve the strength and short-term rupture properties of the alloy, but the long-term extrapolated rupture strength will be reduced. When the content of Ti is 3.18%, the alloy has better strength properties and long-term extrapolated rupture life. The results show that the addition of 2% W in the alloy can effectively refine the size of the gamma'phase, significantly reduce the growth rate of the gamma' phase, improve the strength, impact toughness and rupture properties of the alloy, and do not change the type of precipitates in the Waspaloy alloy, and maintain good properties during long-term aging. The W element mainly distributes in the matrix and the gamma'phase, and plays the role of solution strengthening and precipitation strengthening. The W element added to the alloy can increase the number of lattice_=3 grain boundaries in the overlapping position, reduce the energy of grain boundaries, strengthen grain boundaries, and improve the short-term and long-term extrapolated rupture properties of the alloy. The extrapolation value of tensile strength reached 271 MPa at 100 000 hours, which was 14.0% higher than that of Waspaloy alloy before composition improvement.
【学位授予单位】：昆明理工大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TM621;TG132.3
【参考文献】
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1 曹金荣;刘正东;程世长;杨钢;谢建新;;应变速率和变形温度对T122耐热钢流变应力和临界动态再结晶行为的影响[J];金属学报;2007年01期
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