本文關(guān)鍵詞： 超超臨界高中壓轉(zhuǎn)子 X12CrMoWVNbN10-1-1鐵素體耐熱鋼 析出相 微觀組織表征 力學(xué)性能　出處：《上海交通大學(xué)》2015年博士論文　論文類型：學(xué)位論文

【摘要】：超超臨界汽輪機高中壓轉(zhuǎn)子是百萬千瓦超超臨界汽輪機組的關(guān)鍵部件,其服役蒸汽溫度達到600℃、蒸汽壓力達到30MPa。惡劣的工作環(huán)境要求轉(zhuǎn)子擁有良好的材料綜合性能,而材料的性能與微觀組織有著直接的聯(lián)系。因此研究轉(zhuǎn)子材料在熱處理過程中的微觀組織演變規(guī)律及其與力學(xué)性能的關(guān)系,對于制定合理的熱處理工藝以獲得所要求的性能具有極其重要的學(xué)術(shù)價值和工程意義。本文采用多種材料表征手段,如物理化學(xué)相分析、X射線衍射、背散射電子衍射、掃描電鏡、透射電鏡和力學(xué)性能測試等,以X12Cr Mo WVNb N10-1-1鋼為主要研究對象,探索其微觀組織演變規(guī)律及其對力學(xué)性能的影響,從而為制定合理的熱處理工藝,實現(xiàn)批量化生產(chǎn)中組織穩(wěn)定性和均勻性的控制提供技術(shù)支撐。首先,研究了X12Cr Mo WVNb N10-1-1鋼過冷奧氏體700℃(TTT圖鼻尖溫度)等溫分解的相變機制、特征和動力學(xué)等問題。研究發(fā)現(xiàn)等溫過程中所發(fā)生的擴散型相變產(chǎn)物主要為鐵素體基體、Cr-rich M23C6、少量Cr-rich M2N和Nb-rich MN。析出相首先在原奧氏體晶界處形核長大,隨著等溫時間的延長,以胞狀物的形式向奧氏體晶粒內(nèi)部析出,并伴有γ→α的轉(zhuǎn)變。以不同等溫時間轉(zhuǎn)變后所得到的微觀組織作為初始組織,對其再次進行奧氏體化加熱和晶粒尺寸的測定,結(jié)果發(fā)現(xiàn)隨著等溫時間的延長,奧氏體晶粒的細化效果越明顯,當?shù)葴貢r間長達120h后,其細化效果不再顯著增加。在此基礎(chǔ)上提出了通過等溫轉(zhuǎn)變的方法實現(xiàn)奧氏體晶粒細化的機制,認為殘余奧氏體含量是細化奧氏體晶粒的關(guān)鍵,并確定了該鋼有效細化奧氏體晶粒的殘余奧氏體臨界體積分數(shù)約為3.2%。其次,研究了不同奧氏體化條件下,碳氮化物的溶解規(guī)律與奧氏體晶粒長大的關(guān)系。結(jié)果表明,1070℃保溫60min后富Cr相全部溶解于基體中。Nb-rich MN相在1070℃奧氏體化過程中起初逐漸溶解,當保溫時間達到180min后不再繼續(xù)溶解。而在1010℃條件下,Nb-rich MN相沒有發(fā)生溶解。1200℃保溫90min之后,僅有少量的Nb-rich MN相存在。結(jié)合奧氏體晶粒長大規(guī)律,可發(fā)現(xiàn)Nb-rich MN相對奧氏體晶界有顯著的釘扎作用,起有效釘扎作用的Nb-rich MN顆粒的臨界直徑和體積分數(shù)分別約為117nm和3.1×10-4。同時還發(fā)現(xiàn),奧氏體晶粒的長大行為對后續(xù)冷卻過程中的馬氏體相變行為有顯著影響,即奧氏體晶粒異常長大現(xiàn)象的存在可能是引起馬氏體相變開始點分離的主要原因。再次,研究了不同淬火冷卻條件對X12Cr Mo WVNb N10-1-1鋼微觀組織與沖擊性能的影響。通過實驗觀察確定了鐵素體形成的臨界冷速在1~1.5℃/min之間,而抑制Cr-rich M2N和Fe-rich M3C析出的臨界冷速分別大于1.5℃/min和600℃/min。將不同冷速冷卻后的試樣進行700℃/24h回火并測試其沖擊性能。結(jié)果表明,水冷、空冷和爐冷后回火試樣的沖擊性能幾乎相同,約為33J;冷速降為1.5℃/min時,其回火試樣的沖擊性能下降至23.3J左右。隨著淬火冷速進一步下降,對應(yīng)的回火沖擊性能也隨之降低。結(jié)合不同條件下的微觀組織與沖擊性能的分析,認為冷速過低造成硬化相Cr-rich M2N的析出是沖擊性能降低的主要原因。最后,以1080℃/16h奧氏體化后爐冷得到的產(chǎn)物作為初始狀態(tài),系統(tǒng)地研究了回火溫度與時間對微觀組織演變規(guī)律和力學(xué)性能的影響。組織觀察表明,550℃以下回火18h,有Cr-rich M2N、Cr-rich M7C3和Nb-rich MN的析出。570℃回火10h后有Cr-rich M23C6的析出。隨著回火溫度的升高,Cr-rich M7C3逐漸減少,Cr-rich M23C6逐漸增多。此外,基于物理化學(xué)相分析方法測定了提取的析出相中所含元素含量,著重分析了不同回火條件下析出相的析出行為。在此基礎(chǔ)上確定了在回火過程中碳化物的析出序列為Fe-rich M3C→Cr-rich M7C3→Cr-rich M23C6。硬度測試顯示,550℃以下回火時析出相較少,大量合金元素在基體中仍起著固溶強化作用,其硬度值基本穩(wěn)定在430 HV10左右;550℃以上回火時,隨著回火溫度的升高,大量合金元素從飽和的基體中析出,削弱了固溶強化效果,硬度值逐漸降低。沖擊性能顯示,570℃以下回火時,由于大量Cr-rich M7C3的析出,在其周圍存在微應(yīng)力場,導(dǎo)致沖擊值約為7.5J左右;570~700℃之間回火時,亞穩(wěn)相Cr-rich M7C3逐漸向穩(wěn)定相Cr-rich M23C6轉(zhuǎn)變,微應(yīng)力逐漸被釋放,沖擊性能略有提高;700℃以上回火時,馬氏體基體發(fā)生回復(fù),生成大量亞晶,導(dǎo)致沖擊性能大幅度提高。
[Abstract]:Ultra supercritical steam turbine high pressure rotor is 1000MW ultra supercritical steam turbine is the key component of the service, the steam temperature reached 600 degrees, up to 30MPa. bad working environment with good steam pressure rotor material properties, material properties and microstructure have direct contact. So studying the relationship of microstructure of rotor material in the heat treatment process of the evolution and mechanical properties, to make reasonable heat treatment process to obtain the required performance has important academic value and engineering significance. This paper uses various materials characterization techniques, such as physical and chemical analysis, X ray diffraction, electron backscatter diffraction, scanning electron microscopy, transmission SEM and mechanical property testing, with X12Cr Mo WVNb N10-1-1 steel as the main research object, explore the evolution of the microstructure and its effect on mechanical properties, In order to develop a reasonable heat treatment process, to achieve control of mass production stability and uniformity of the organization to provide technical support. First of all, on the X12Cr Mo WVNb N10-1-1 700 degrees of undercooling austenite (TTT tip temperature) phase transition mechanism of isothermal decomposition, and the characteristics of the problem. The study found that the dynamic diffusion transformation products what happened in isothermal process is mainly ferrite matrix, Cr-rich M23C6, Cr-rich M2N and Nb-rich MN., a small amount of precipitates firstly in austenite grain boundary nucleation and growth, with the increase of isothermal time, the austenite grains precipitated by internal cell like form, accompanied by gamma, alpha change. To change the different isothermal time after the microstructure as the initial organization, again to its determination of austenitizing and grain size, the results found that with the increase of isothermal time, the austenite grain refinement effect The more obvious, when the isothermal time up to 120h, the refinement effect is no longer significant increase. On the basis of this proposed mechanism of austenite grain refinement by isothermal transformation method, that is the key content of residual austenite austenite grain refinement, and to determine the critical volume fraction of retained austenite austenite grain size of the steel is about 3.2%. second refine the study, different austenitizing conditions, the relationship between dissolution of carbonitride and austenite grain growth. The results show that 1070 DEG C after 60min Cr rich phase dissolved in the matrix of.Nb-rich MN at 1070 DEG C austenitizing process initially gradually dissolved, when the holding time is up to 180min in 1010 and no longer continue to dissolve. C, Nb-rich MN had dissolved.1200 Deg. C for 90min, only a small amount of Nb-rich MN. Combined with the austenite grain growth law, Can be found in Nb-rich MN relative austenite grain boundary pinning effect, Nb-rich MN effective particle pinning effect of the critical diameter and volume fraction are about 117nm and 3.1 * 10-4. also found that the austenite grain growth behavior on the subsequent cooling process of martensite phase change behavior has a significant impact, there is austenite the abnormal grain growth phenomenon may be caused by the martensitic start point. The main reason for the separation again, the effects of different cooling conditions on the microstructure of N10-1-1 steel and X12Cr Mo impact WVNb performance. By experimental observations to determine the critical cooling rate of ferrite formation between 1~1.5 DEG /min, critical cooling and suppression Cr-rich M2N and Fe-rich M3C precipitation speed were greater than 1.5 DEG /min and 600 DEG /min. different cooling samples after cooling speed 700 DEG C /24h tempering and test its performance. The simulation results show that the impact of, The impact of water cooling, air cooling and furnace cooling performance after tempering is almost the same, about 33J; cold downhill 1.5 C /min, the impact toughness of tempering decreased to about 23.3J. With the quenching rate to decline further, tempering impact performance corresponding decreases. Combined with the analysis of microstructure and impact properties of different. Under the condition of the precipitation caused by the low speed that cold hardening phase Cr-rich M2N is the main reason for the impact of reduced performance. Finally, the product of 1080 DEG /16h after austenitizing furnace cooling are used as the initial condition, systematic study of the influence of tempering temperature and time on microstructure evolution and mechanical properties of the tissue were observed. Show that the 550 DEG Cr-rich tempering 18h, M2N, Cr-rich M7C3 and Nb-rich MN.570 C 10h after tempering precipitation precipitation of Cr-rich M23C6. With the increase of the tempering temperature of Cr-rich M7C3 decreased gradually, Cr-rich M23C6 Gradually increased. In addition, the phase analysis method based on physical and chemical extraction of precipitates containing elements were determined, focuses on the analysis of the precipitation phase under different tempering condition. The precipitation based on the precipitation sequence of carbides during tempering for Fe-rich M3C, Cr-rich M7C3, Cr-rich M23C6. hardness test showed that 550 DEG C during tempering with little, a lot of alloying elements in the matrix remains a solid solution strengthening effect, value basically stable at about 430 HV10 the hardness more than 550 DEG C; tempering, with the increase of the tempering temperature of alloy elements precipitated from the saturated matrix, weaken the effect of solid solution strengthening, hardness decreased. The impact of the performance shows that the 570 DEG C during tempering due to precipitate a large number of Cr-rich M7C3, the existence of micro stress field around it, resulting in impact value is about 7.5J between 570~700 degrees; tempering, metastable The phase Cr-rich M7C3 gradually changes to stable phase Cr-rich M23C6, and the micro stress is released gradually, and the impact properties increase slightly. When the temperature is over 700, the martensite matrix regenerates, resulting in a large number of sub crystals, resulting in a great improvement in impact properties.

【學(xué)位授予單位】：上海交通大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2015
【分類號】：TG142.1;TG161

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本文編號：1494662