本文關鍵詞：核電用不銹鋼模擬工況熱老化組織與性能研究　出處：《西安工業(yè)大學》2016年碩士論文　論文類型：學位論文

  更多相關文章： 模擬工況 Z3CN20-09M鋼 金相組織 亞結構 維氏硬度 納米硬度 微型杯突 沖擊吸收功

【摘要】：壓水堆核電站一回路主管道用不銹鋼在288～327℃,15.5 MPa高溫高壓水蒸氣介質環(huán)境下長期服役后出現的熱老化脆化現象,對核電站的安全運行和壽命構成了巨大的威脅,因此,研究該鋼在該環(huán)境下長期服役后組織和性能的變化具有重要的實際意義。本文對國產離心鑄造Z3CN20-09M奧氏體不銹鋼分別在400℃空氣介質和400℃硼酸水蒸氣介質條件下進行了加速熱老化試驗,采用OM和TEM對不同狀態(tài)下的金相組織和亞結構分別進行了觀察與分析,測試了不同熱老化時長下材料的維氏硬度和納米壓入硬度、微型杯突力學性能和沖擊力學性能,利用SEM對微型杯突和沖擊斷口形貌進行了觀察,并分析了其斷裂機理。分析和對比了兩種不同介質條件下熱老化對該鋼微觀組織和力學性能的影響,探究了其在模擬工況環(huán)境下的熱老化行為。在兩種不同介質條件下,Z3CN20-09M鋼的金相組織特點均為奧氏體基體上隨機的分布著細針狀、島狀和帶有尖角的條帶狀鐵素體相。隨著熱老化時間的增加,鐵素體相的形態(tài)和尺寸并未發(fā)生明顯變化,而奧氏體相內的位錯和層錯密度降低,且在老化300 h和1000 h時鐵素體和奧氏體基體及位錯線上均有細小的氮化物Cr2N析出；老化3000 h時,鐵素體內發(fā)生調幅分解,出現黑白相間的斑點；隨著老化延長到5000 h,鐵素體相的調幅分解產物分布均勻,調幅分解接近平衡。對比兩種不同介質條件下調幅分解產物的形貌發(fā)現：模擬工況老化3000 h時調幅分解產物的形貌與空氣介質老化5000 h時相似,且模擬工況老化5000 h后調幅分解產物的邊界較3000 h清晰,由此可知,相同熱老化時長下,模擬工況條件下調幅分解的程度比空氣介質條件下大。鐵素體相的維氏硬度和納米壓入硬度,在兩種不同介質條件下均隨熱老化時間的延長持續(xù)緩慢增大,而奧氏體相的硬度變化并不明顯。統(tǒng)計學檢驗表明,模擬工況條件下的與空氣介質下的熱老化對鐵素體硬度的影響差異顯著。兩種不同介質條件下的沖擊吸收功Akv均隨熱老化時間的延長不斷減小,其減小幅度均呈現出小范圍波動性變化的特點,統(tǒng)計學檢驗表明,兩種條件下熱老化對沖擊吸收功Akv的影響無顯著差異。沖擊斷口分析表明：在兩種不同介質條件下,隨著熱老化時間的延長,斷裂機理都是由具有韌窩特征的微孔聚集型逐漸過渡為具有撕裂棱、解理臺階特征的解理型,斷裂形式由韌性斷裂轉變?yōu)榇嘈詳嗔选Ｎ⑿捅辉囼灡砻鳎篫3CN20-09M鋼的比屈服和比強度在兩種不同介質條件下均隨熱老化時間的延長而持續(xù)緩慢增大,而比斷裂能均緩慢減小,模擬工況條件與空氣介質條件下的熱老化對材料微型杯突性能的改變有差異,但統(tǒng)計學檢驗表明差異并不顯著。斷口分析表明：空氣介質條件下,斷口微觀形貌特征隨著熱老化的進行由韌窩過渡為撕裂棱；模擬工況條件下,其斷裂機理由具有韌窩特征的微孔聚集型韌性斷裂逐漸過渡為具有撕裂棱和解理臺階特征的脆性斷裂。
[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.

【學位授予單位】：西安工業(yè)大學
【學位級別】：碩士
【學位授予年份】：2016
【分類號】：TM623.91

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