P91耐热钢高温低应力下蠕变性能的研究

发布时间：2018-10-24 06:09

【摘要】：P91耐热钢由于突出的抗蠕变性能、良好的抗腐蚀性和高温抗氧化能力,成为火电、核电厂管道部件的主选或更新换代材料。工程上,将管道材料的持久蠕变寿命定义为在使用时间为105h时,形变量不超过2%。此时低应力下蠕变的应变率将会低于10-10ms-1,传统的单轴蠕变试验由于应变率低,不能满足此应变速率下蠕变性能研究的需求;另一面,P91耐热钢在服役过程中会产生组织退化,组织退化对高温低应力下的蠕变性能的影响仍未知。本研究的目的:采用具有高应变率的“螺旋弹簧蠕变试验法”调查不同条件的热时效处理后P91耐热钢在高温低应力下的蠕变性能,揭示了P91耐热钢高温低应力下的“组织退化因子”。通过ANSYS有限元仿真软件,对不同螺距的P91螺旋弹簧试样的力学场进行了分析,得到结论:当螺距的长度是螺旋段横截面长度的1-3倍时,“螺旋弹簧蠕变试验法”满足纯扭转变形。对不同热时效处理时间的试样分别进行X-rd和SEM微观组织分析,结果显示:1)析出相有M23C6、Laves相和MX相。2)MX相在热处理之后达到饱和状态,主要弥散析出在马氏体板条晶粒的内部。3)M23C6相沿马氏体板条晶界处和原奥氏体晶界析出,在时效700h达到饱和状态,之后发生粗化。4)Laves相在时效2100h沿马氏体板条边界和亚晶边界析出,且极易长大。对P91耐热钢在高温低应力下蠕变性能进行了研究,得出结论:1)“螺旋弹簧蠕变试验法”有效。2)Blackburn’s equation能够最好的描述实测蠕变数据。3)单轴蠕变试验法会过大的评测使用材料的剩余寿命。4)Laves相是影响P91耐热钢高温低应力下的蠕变性能的“组织退化因子”。本文从有限元分析、微观组织观察和高温低应力下的蠕变性能三个方面对P91耐热钢进行了研究,研究结果对下一步开展耐热钢改性提供了理论支持,高温、低应力下的蠕变数据为开展高铬耐热钢的服役安全性评价提供了数据支持。
[Abstract]:Due to its outstanding creep resistance, good corrosion resistance and high temperature oxidation resistance, P91 heat resistant steel has become the main selection or replacement material for pipeline components of thermal power plants and nuclear power plants. In engineering, the creep life of pipeline material is defined as that when the service time is 105 h, the shape variable is not more than 2. Under low stress, the strain rate of creep will be lower than 10-10ms-1. the traditional uniaxial creep test can not meet the need of creep property research at this strain rate because of its low strain rate, on the other hand, the microstructure of P91 heat-resistant steel will degenerate during service. The effect of microstructure degradation on creep properties at high temperature and low stress is still unknown. The purpose of this study is to investigate the creep properties of P91 heat-resistant steel under high temperature and low stress by means of "helical spring creep test method" with high strain rate. The microstructure degradation factor of P 91 heat resistant steel under high temperature and low stress was revealed. The mechanical field of P91 helical spring specimens with different pitch is analyzed by ANSYS finite element simulation software. It is concluded that when the length of pitch is 1-3 times of the length of cross section of spiral segment, The helical spring creep test method satisfies the pure torsional deformation. X-rd and SEM microstructures of samples with different thermal aging time were analyzed. The results showed that: 1) the precipitated phases were M23C6 Laves phase and MX phase. 2) the MX phase reached saturation state after heat treatment. The main dispersion precipitation occurs in the interior of martensite lath grain. 3) the M23C6 phase precipitates along the martensite lath grain boundary and the original austenite grain boundary, and reaches saturation state at 700h, then coarsens. 4) the Laves phase precipitates along martensite lath boundary and subcrystalline boundary at 2100h. And easy to grow up. The creep behavior of P91 heat resistant steel under high temperature and low stress was studied. The conclusions are as follows: 1) "helical spring creep test method" is effective. 2) Blackburn's equation can best describe the measured creep data. 3) uniaxial creep test method can evaluate the remaining life of used materials too large. 4) Laves phase affects the high temperature and low temperature of P91 heat-resistant steel. The "microstructure degradation factor" of creep properties under stress. In this paper, P91 heat resistant steel is studied from three aspects: finite element analysis, microstructure observation and creep property under high temperature and low stress. The results provide theoretical support for further modification of heat resistant steel at high temperature. The creep data under low stress provide data support for evaluating the service safety of high chromium heat resistant steel.
【学位授予单位】：天津理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG142.73

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