不同温度长时热老化对Z3CN20-09M钢组织和性能的影响

发布时间：2018-03-27 19:49

本文选题：Z3CN20-09M钢　切入点：模拟工况　出处：《西安工业大学》2017年硕士论文

【摘要】：铸造双相不锈钢(CDSSs)因兼具有高强度、优异的可铸造性和焊接性以及良好的抗应力腐蚀开裂等性能,而广泛用于制造核电站压水堆一回路主冷却剂管道等压力边界部件。但是在反应堆运行温度(一般范围为288~327℃)下长期工作,铸造双相不锈钢会产生热老化脆化,导致管道钢性能下降,进而威胁一回路压力边界的完整性和核电站的运行安全。因此,有必要对长时间热老化后的铸造双相不锈钢组织结构和力学性能进行研究,揭示其热老化机理,为核电站老化和寿命管理以及延寿工作提供技术支持。基于Z3CN20-09M铸造双相不锈钢的服役条件,本文在350℃和400℃两种温度及空气和模拟工况两种环境条件下对国产离心铸造Z3CN20-09M双相不锈钢进行了加速热老化试验,然后采用透射电镜、维氏硬度试验、微型杯突试验对不同时长热老化后Z3CN20-09M铸造双相不锈钢显微组织结构、显微硬度、室温(25℃)及高温(290℃)微型杯突力学性能进行了研究;通过扫描电镜对该钢的微型杯突试样的断口形貌进行观察,分析热老化对其断裂机理的影响。获得了以下主要结论:Z3CN20-09M钢长期热老化后奥氏体中全位错的密度大幅降低,全位错之间、扩展位错之间以及全位错和扩展位错之间会发生相互交割而形成位错网络、亚晶界和不可动位错,造成扩展位错的密度下降。350℃热老化1000h和400℃热老化300h后,在基体上有细小的颗粒状第二相析出;400℃热老化3000h后铁素体内可以观察到调幅分解产生的富Fe的α相及富Cr的α′相,随热老化时间的延长,双相不锈钢中的调幅分解程度逐渐增大,热老化10000h后,调幅分解逐渐达到平衡。显微维氏硬度测试表明:在不同的热老化环境与温度下,Z3CN20-09M钢奥氏体相的硬度值随热老化时间延长变化并不明显。350℃不同环境热老化,铁素体相硬度有少量的增长。在400℃不同环境热老化,铁素体相的硬度在2000h前增长缓慢,3000h后硬度值迅速增长。维氏硬度值变化与热老化温度及其热老化时长有关,统计学分析表明不同热老化环境对显微维氏硬度值影响不显著。室温(25℃)微型杯突试验表明:350℃两种不同环境条件下,随着热老化时间的延长,Z3CN20-09M钢的最大强度Pu/t02有小幅度的增加;比断裂能Esp有小幅度的减少,比屈服Py/t02均变化幅度不大。400℃两种不同环境条件下,随着热老化时间的延长,Z3CN20-09M钢的比强度Pu/t02和比屈服Py/t02均有少量增长,比断裂能Esp均持续减少。微型杯突力学性能数值变化与热老化温度及其热老化时长有关,热老化环境的对力学性能影响不显著。断口分析表明:微型杯突试验宏观断口没有明显的区别。在热老化初期材料的微型杯突断口主要以微孔聚集型断裂为主,表现为较好的韧性断裂;随着热老化时间延长,出现准解理断裂形式与微孔聚集型断裂的结合。随着热老化时间延长,材料的韧性下降,逐渐转化为脆性材料。高温(290℃)微型杯突试验表明:在不同的热老化温度和环境条件下,随着热老化时间的延长,Z3CN20-09M钢的最大强度和比屈服都有着小幅度的增加;比断裂能逐渐减少。高温微型杯突力学性能数值变化与热老化温度及其热老化时长有关,热老化环境对其的影响不显著。
[Abstract]:Casting Duplex Stainless Steel (CDSSs) by and has high strength, excellent castability and weldability and good resistance to stress corrosion cracking performance, and is widely used in the manufacture of nuclear power plant primary coolant piping in PWR pressure boundary components. But in the reactor operating temperature (generally in the range of 288~327 DEG C) under work for a long time, the casting will produce thermal aging embrittlement of duplex stainless steel, resulting in a decline in performance and threatens the safe operation of pipeline steel, a loop pressure boundary integrity and nuclear power plant. Therefore, it is necessary to study the long time after thermal aging of cast duplex stainless steel structure and mechanical properties, the thermal aging mechanism and provide technical support for the nuclear power plant aging and life management and life extension. The service condition of double phase stainless steel casting based on Z3CN20-09M, the 350 degrees and 400 degrees two kinds of temperature and air and simulated conditions The two conditions of domestic centrifugal casting of Z3CN20-09M duplex stainless steel was studied by accelerated thermal aging test, and then by transmission electron microscopy, Vivtorinox micro hardness test, Erichsen test on different time after thermal aging of Z3CN20-09M cast duplex stainless steel microstructure, hardness, room temperature (25 DEG C) and high temperature (290 DEG C) the mechanical properties of micro cup were studied; to observe fracture morphology of the steel micro cup samples by scanning electron microscopy, the effects of aging on the fracture mechanism of thermal analysis. The main conclusions are as follows: the aging of Z3CN20-09M steel after long term thermal austenite full dislocation density is greatly reduced, the dislocation between the expansion between and around the dislocation and dislocation of extended dislocations has formed the dislocation network delivery, subgrain boundaries and immobile dislocations, dislocation density decrease caused by expansion of.350 thermal aging and thermal 1000h 400 After aging for 300h, a small granular precipitated in the matrix; after aging 3000h ferrite can be observed spinodal decomposition and the resulting Fe rich 400 degrees heat alpha and alpha 'Cr rich phase, with the increase of aging time, duplex stainless steel in spinodal decomposition increases and thermal aging after 10000h, the spinodal decomposition gradually reached equilibrium. Vivtorinox micro hardness test show that the aging environment and temperature in different heat, the hardness of austenite of Z3CN20-09M steel phase value with aging time prolonged.350 did not change significantly at different thermal aging, the ferrite hardness has risen slightly. Aging 400 degrees in different environment the heat, the ferrite phase hardness in the 2000h before the slow growth of 3000h hardness increased rapidly. Vivtorinox change of hardness and thermal aging temperature and thermal aging time, the statistical analysis showed that the aging hardness on the microstructure of different heat environment of Vivtorinox The value is not significantly affected. At room temperature (25 DEG C) shows that the micro cup test: two different environmental conditions of 350 DEG C, with the increase of aging time, the maximum strength of Pu/t02 Z3CN20-09M steel has increased slightly; Esp has little scope to reduce the ratio of fracture energy, than the yield Py/t02 change of two kinds of different environmental conditions modest.400 DEG C, with the increase of aging time. Specific strength of Z3CN20-09M steel Pu/t02 and Py/t02 were less than the yield increase than the fracture energy Esp decreased continuously. The aging temperature and thermal time related numerical changes and thermal properties of micro cup mechanical aging, influence of thermal aging on the mechanical properties of the environment is not significant. Fracture analysis showed that the small punch test macro fracture has no obvious difference. In the beginning of thermal aging material micro cup fracture to microvoid accumulation fracture mainly exhibited ductile fracture with good heat ageing; The extension, combined with quasi cleavage fracture form and micropore aggregation fracture. With the extension of the thermal aging time, decrease the toughness of the material, gradually transformed into brittle materials. High temperature (290 DEG C) showed that the small punch test: aging temperature and environmental conditions in different heat, with the increase of aging time. The maximum intensity Z3CN20-09M steel and yield have a small increase; than fracture energy decreases gradually. The aging temperature and thermal time related numerical changes and thermal performance of high temperature micro cup mechanical aging, thermal aging environment is not significant for its impact.

【学位授予单位】：西安工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM623.91;TG142.1

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