核电用不锈钢模拟工况热老化组织与性能研究

发布时间：2018-01-11 19:37

本文关键词：核电用不锈钢模拟工况热老化组织与性能研究　出处：《西安工业大学》2016年硕士论文　论文类型：学位论文

【摘要】：压水堆核电站一回路主管道用不锈钢在288～327℃,15.5 MPa高温高压水蒸气介质环境下长期服役后出现的热老化脆化现象,对核电站的安全运行和寿命构成了巨大的威胁,因此,研究该钢在该环境下长期服役后组织和性能的变化具有重要的实际意义。本文对国产离心铸造Z3CN20-09M奥氏体不锈钢分别在400℃空气介质和400℃硼酸水蒸气介质条件下进行了加速热老化试验,采用OM和TEM对不同状态下的金相组织和亚结构分别进行了观察与分析,测试了不同热老化时长下材料的维氏硬度和纳米压入硬度、微型杯突力学性能和冲击力学性能,利用SEM对微型杯突和冲击断口形貌进行了观察,并分析了其断裂机理。分析和对比了两种不同介质条件下热老化对该钢微观组织和力学性能的影响,探究了其在模拟工况环境下的热老化行为。在两种不同介质条件下,Z3CN20-09M钢的金相组织特点均为奥氏体基体上随机的分布着细针状、岛状和带有尖角的条带状铁素体相。随着热老化时间的增加,铁素体相的形态和尺寸并未发生明显变化,而奥氏体相内的位错和层错密度降低,且在老化300 h和1000 h时铁素体和奥氏体基体及位错线上均有细小的氮化物Cr2N析出；老化3000 h时,铁素体内发生调幅分解,出现黑白相间的斑点；随着老化延长到5000 h,铁素体相的调幅分解产物分布均匀,调幅分解接近平衡。对比两种不同介质条件下调幅分解产物的形貌发现：模拟工况老化3000 h时调幅分解产物的形貌与空气介质老化5000 h时相似,且模拟工况老化5000 h后调幅分解产物的边界较3000 h清晰,由此可知,相同热老化时长下,模拟工况条件下调幅分解的程度比空气介质条件下大。铁素体相的维氏硬度和纳米压入硬度,在两种不同介质条件下均随热老化时间的延长持续缓慢增大,而奥氏体相的硬度变化并不明显。统计学检验表明,模拟工况条件下的与空气介质下的热老化对铁素体硬度的影响差异显著。两种不同介质条件下的冲击吸收功Akv均随热老化时间的延长不断减小,其减小幅度均呈现出小范围波动性变化的特点,统计学检验表明,两种条件下热老化对冲击吸收功Akv的影响无显著差异。冲击断口分析表明：在两种不同介质条件下,随着热老化时间的延长,断裂机理都是由具有韧窝特征的微孔聚集型逐渐过渡为具有撕裂棱、解理台阶特征的解理型,断裂形式由韧性断裂转变为脆性断裂。微型杯突试验表明：Z3CN20-09M钢的比屈服和比强度在两种不同介质条件下均随热老化时间的延长而持续缓慢增大,而比断裂能均缓慢减小,模拟工况条件与空气介质条件下的热老化对材料微型杯突性能的改变有差异,但统计学检验表明差异并不显著。断口分析表明：空气介质条件下,断口微观形貌特征随着热老化的进行由韧窝过渡为撕裂棱；模拟工况条件下,其断裂机理由具有韧窝特征的微孔聚集型韧性断裂逐渐过渡为具有撕裂棱和解理台阶特征的脆性断裂。
[Abstract]:PWR primary pipe made of stainless steel in 288 ~ 327 DEG C, embrittlement of 15.5 MPa high temperature and high pressure water vapor medium environment after long term service of thermal aging, safe operation and service life of nuclear power plants pose a huge threat, therefore, it has important practical significance in research on the microstructure and properties of the steel in the environment after long-term service. Based on the domestic centrifugal casting of Z3CN20-09M austenitic stainless steel were accelerated aging test at 400 C and 400 C air medium boric acid water vapor medium conditions, using OM and TEM on the microstructure under different conditions and sub structure were observed and analyzed, different thermal aging when the length of materials under Vivtorinox hardness and nano indentation hardness test, mechanical properties and impact properties of micro cup on micro mechanics, cupping and impact fracture morphology was observed by SEM, and Analysis of the fracture mechanism. Analysis and comparison of the effects of aging on the microstructure and mechanical properties of steel two kinds of medium heat, explores its working conditions in the simulation of thermal aging behavior. In two different medium conditions, the microstructure characteristics of Z3CN20-09M steel is austenite matrix random the distribution of fine acicular, island and a sharp iron banded ferrite phase. With the increase of thermal aging time, the shape and size of the ferrite phase did not change significantly, while the density of dislocations and stacking faults in the austenite phase decreases, and in aging 300 h and 1000 h ferrite and austenitic matrix and dislocation line has fine nitride Cr2N precipitation; aging at 3000 h ferrite occurred spinodal decomposition, appear black and white spots; with aging increased to 5000 h, the ferrite am bulk decomposition products of uniform distribution, the spinodal decomposition Near equilibrium. Found morphology comparison of two different media under the condition of spinodal decomposition products: Simulation of aging at 3000 h similar spinodal decomposition products of medium morphology and air aging at 5000 h, and the simulation condition after 5000 h aging spinodal decomposition product range is 3000 h, the same thermal aging time. The simulated condition of spinodal decomposition degree than air medium. The ferrite phase of Vivtorinox hardness and nano indentation hardness, in two different media conditions, with the increase of aging time continues to increase slowly, while the hardness change of austenite phase is not obvious. The statistical test showed that the effect of aging on ferrite body hardness between the simulated condition and air medium heat significantly. Two different media under the condition of impact toughness of the Akv decreased with the increase of aging time decreases, the decrease rate Presents the characteristics of small changes in volatility, the statistical test showed that there was no significant difference between the two kinds of impact absorbing energy under the condition of Akv the influence of thermal aging. The impact fracture analysis showed that in two different media conditions, with the increase of aging time, the fracture mechanism is composed of microporous characteristic of dimple aggregation type with the gradual transition to the torn edges, the cleavage type cleavage characteristics of the fracture mode changes from ductile fracture to brittle fracture. It shows that the micro cup test: Z3CN20-09M steel than the yield and strength in two different medium conditions with the increase of aging time and continued to increase slowly, rather than fracture can decrease slowly under simulated conditions, and the air medium under the condition of heat aging on material micro Cup performance change is different, but the statistics test showed that the difference was not significant. The fracture analysis shows that the air medium. The fracture surface micro morphology features transition from dimple to tear edge with thermal aging. Under simulated working conditions, the fracture of microporous aggregates with fracture characteristics is gradually transformed into brittle fracture with tear edge and cleavage step characteristics.

【学位授予单位】：西安工业大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TM623.91

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