本文選題：X12CrMoWVNbN10-1-1 + 組織均勻化和細化��； 參考：《上海交通大學(xué)》2015年博士論文

【摘要】：X12CrMoWVNbN10-1-1馬氏體不銹鋼由于具有優(yōu)良的高溫強度、抗腐蝕性能、抗疲勞性能以及低的熱膨脹系數(shù),被廣泛的用作超超臨界發(fā)電機組高中壓轉(zhuǎn)子材料。近年來,隨著人類能源需求的急劇增長,發(fā)電機組的裝機容量不斷提高,高中壓轉(zhuǎn)子的尺寸越來越大。盡管高中壓轉(zhuǎn)子尺寸的增大增加了電站運行的安全性,但是卻給制造帶來了巨大的困難。高中壓轉(zhuǎn)子的制造是一個融合了鑄造、機械加工、熱處理、無損檢測等多個工序的復(fù)雜過程,其中鑄造工序為后續(xù)加工提供原始坯料。因此為了保證高中壓轉(zhuǎn)子的質(zhì)量,首先必須生產(chǎn)出高質(zhì)量的大型鑄錠。本文以X12CrMoWVNbN10-1-1(以下簡稱X12)高中壓轉(zhuǎn)子鋼材料為研究對象,采用熱場控制法,分別從兩種不同的路徑(一是采用砂鑄型,通過熔體過熱處理,在慢的冷卻速度下,使鑄錠整體溫度場均勻分布、同時凝固;二是采用金屬型,通過消除固—液界面間隙,增強冷卻速度,使鑄錠迅速凝固)實現(xiàn)了X12鋼鑄錠組織均勻化和細化,并在此基礎(chǔ)上研究了不同工藝參數(shù)對鑄錠組織的影響機理。主要結(jié)論如下:研究了砂型鑄造過程中,不同工藝參數(shù)對X12鋼鑄錠宏觀組織和微觀組織的影響。在本實驗條件下,砂型鑄造的最佳工藝參數(shù)是:熔體過熱溫度1650°C,鑄型溫度800°C,熔體澆鑄溫度1600°C,在該條件下得到的鑄錠,宏觀組織幾乎全部由直徑1.1mm左右的等軸晶組成,微觀組織由馬氏體和δ鐵素體組成,且其δ鐵素體不超過2%。在砂型鑄造中,鑄型預(yù)熱溫度是影響宏觀組織中等軸晶比例的主要因素;熔體過熱溫度和熔體澆鑄溫度是影響晶粒大小的主要因素;熔體過熱溫度是影響δ鐵素體的主要因素;研究了不同熔體過熱溫度對X12鋼組織的影響,并對X12鋼的熔體過熱細化機理進行了探討。實驗發(fā)現(xiàn),經(jīng)過1650°C的熔體過熱處理后,X12鋼的凝固組織都是由細小的等軸晶組成,且冷卻速度對它的影響不大。通過對合金的微觀組織和XRD物相組成的分析,排除了由于熔體內(nèi)高熔點團簇分解增殖引發(fā)異質(zhì)形核作用增強而導(dǎo)致組織細化的可能性;通過對凝固過程中過冷度的比較,排除了由于熔體變均勻而引發(fā)均質(zhì)形核導(dǎo)致組織細化的可能性�？紤]到X12鋼凝固過程是包晶反應(yīng),在此基礎(chǔ)上提出了X12鋼熔體過熱細化機理。研究認為,FeC合金中的液—液相轉(zhuǎn)變在X12鋼熔體過熱細化中發(fā)揮著決定性的作用,當(dāng)熔體過熱溫度為1650°C時,X12鋼熔體正好處在液—液相轉(zhuǎn)變區(qū)域,它的液相結(jié)構(gòu)中既有類δ結(jié)構(gòu)的團簇,又有類γ結(jié)構(gòu)的團簇,類δ結(jié)構(gòu)的團簇為δ鐵素體的形核提供了更多的質(zhì)點,類γ結(jié)構(gòu)的團簇降低了包晶反應(yīng)進行所需要的動力,因此短時間內(nèi)在溶液中形成了大量的晶粒,從而得到了細小的鑄態(tài)組織。通過對傳統(tǒng)金屬鑄型的改造,提出了一種新的鑄造方法—無間隙金屬型鑄造,該方法的特點就是在原來的金屬鑄型內(nèi)側(cè)放置了一個薄壁的可熔金屬鑄型,該可熔鑄型是由低熔點的金屬制成。通過對傳統(tǒng)鑄型鑄造和無間隙金屬型鑄造的X12鋼鑄錠進行比較,發(fā)現(xiàn)新的凝固方法可以極大地提高整個凝固過程中的冷卻速度進而細化鑄錠組織。通過對凝固過程中可熔鑄型的溫度變化曲線的綜合分析并結(jié)合數(shù)值模擬,揭示了無間隙金屬鑄型提高冷卻速度的原因:當(dāng)金屬液被澆入到鑄型之后,在鑄型附近會立即形成一個凝固殼,此時熱量通過凝固殼傳遞到可熔鑄型,可熔鑄型受熱熔化成液體并填充在鑄型和鑄錠之間;在隨后的凝固過程中,金屬液始終保持液體狀態(tài)直到鑄錠的凝固徹底結(jié)束,這樣就消除了由于鑄錠凝固收縮和鑄型受熱膨脹所產(chǎn)生的空氣間隙,使得傳統(tǒng)鑄型凝固中的復(fù)雜的傳熱模式轉(zhuǎn)變成單一的熱傳導(dǎo),進而大大地提高了冷卻速度并細化了鑄錠組織。采用數(shù)值模擬,模擬了X12鋼無間隙金屬型鑄造過程中的鑄錠的溫度場和固相體積分數(shù)的變化,獲得了影響無間隙金屬型鑄造冷卻速度的主要因素以及無間隙金屬型鑄造的優(yōu)化工藝條件,并在該工藝條件下實現(xiàn)了X12鋼鑄錠組織的均勻化和細化。模擬結(jié)果表明,可熔鑄型材料的物理性質(zhì)對無間隙金屬型鑄造過程中的冷卻速度有著重要的影響。在其他性質(zhì)相同的情況下,可熔鑄型材料的熔點越低,熱導(dǎo)率越高,凝固過程中可熔鑄型的起始熔化時刻就越早;可熔鑄型材料的熔化潛熱越高,凝固過程中可熔鑄型從起始熔化到完全熔化所需要的時間就越久,在選擇可熔鑄型材料的時候應(yīng)該綜合考慮各種物理性能的影響。盡管較高的澆鑄溫度可以使可熔鑄型提前熔化,獲得較大的冷卻速度,但是由于系統(tǒng)內(nèi)引入的熱量過多,并不會使鑄錠的凝固速度加快,因此在澆鑄的時候應(yīng)該選取較低的澆鑄溫度。在本文所考察的范圍內(nèi),X12鋼的最佳鑄造工藝條件是:可熔鑄型材料為6061鋁合金,澆鑄溫度為1560°C。采用無間隙金屬型鑄造,在最佳工藝條件下對X12鋼進行鑄造,結(jié)果發(fā)現(xiàn)X12鋼鑄錠的宏觀組織全部是由均勻細小的等軸晶組成,從鑄錠表面到鑄錠中心,晶粒尺寸僅從80μm增大到110μm,微觀組織都是由馬氏體組成。
[Abstract]:X12CrMoWVNbN10-1-1 martensitic stainless steel is widely used as the high school pressure rotor material for super supercritical power generator because of its excellent high temperature strength, corrosion resistance, fatigue resistance and low coefficient of thermal expansion. In recent years, with the rapid growth of human energy demand, the installed capacity of the generator set is constantly improved, high school pressure rotor The size of the high - pressure rotor increases the safety of the power plant, but it has brought great difficulties to manufacturing. The manufacture of the high - pressure rotor is a complex process that combines casting, machining, heat treatment, nondestructive testing and many other processes, in which the casting process provides the original billet for subsequent processing. Therefore, in order to ensure the quality of the high pressure rotor, it is necessary to produce high quality large ingot. This paper uses X12CrMoWVNbN10-1-1 (hereinafter referred to as X12) high and high pressure rotor steel material as the research object, using the heat field control method, from two different paths (one is using sand casting, through melt superheat treatment, at slow cooling rate. " At the same time, the whole temperature field of the ingot is uniformly distributed and solidified. Two is the use of metal type, by eliminating the gap between the solid and liquid interface and strengthening the cooling speed, making the ingot solidified rapidly) to realize the homogenization and refinement of the ingot structure of X12 steel. On this basis, the influence mechanism of different process parameters on the ingot structure is studied. The main conclusions are as follows: In the sand mold casting process, the influence of different process parameters on the macro structure and microstructure of X12 steel ingot is made. Under this experimental condition, the optimum parameters of sand mold casting are as follows: melt superheating temperature 1650 C, casting temperature 800 C, melt casting temperature 1600 C, and the macroscopic microstructure of the cast ingot under this condition is almost entirely from the diameter 1.1mm left The microstructure of the right ISO axis is composed of martensite and delta ferrite, and the delta ferrite is not more than 2%. in sand casting. The preheating temperature of the mold is the main factor affecting the medium axis crystal proportion of macrostructures. The melt superheating temperature and the melt casting temperature are the main factors affecting the grain size, and the melt superheat temperature is the influence of the delta ferrite. The influence of different melt superheating temperature on the microstructure of X12 steel was studied. The mechanism of melt superheating refinement of X12 steel was discussed. The experiment found that after the melt superheat treatment of 1650 degree C, the solidification structure of X12 steel was made up of fine equiaxed grains, and the cooling rate had little effect on it. The analysis of the composition of tissue and XRD phase excludes the possibility of microstructure refinement due to the enhancement of the heterogeneous nucleation caused by the decomposition and proliferation of high melting point clusters in the melt. By comparing the supercooling degree of the solidification process, the possibility of microstructure refinement caused by the homogeneous nucleation caused by the melting of the melt is excluded. Considering the solidification of the X12 steel The process is a peritectic reaction. On this basis, the superheating refining mechanism of X12 steel is proposed. It is considered that the liquid liquid phase transition in the FeC alloy plays a decisive role in the melt superheating refinement of the X12 steel. When the melt superheating temperature is 1650 C, the melt of X12 steel is in the liquid liquid phase transition region, and the liquid phase structure of the molten steel has a delta junction. Clusters of structured clusters and clusters of gamma like structures and clusters of delta structures provide more particles for the nucleation of delta ferrite. Clusters of gamma like structures reduce the power needed for the peritectic reaction. Therefore, a large number of grains are formed in the solution in a short time, and thus the fine cast microstructure is obtained. A new casting method, non gap metal casting, was put forward, which was characterized by a thin wall of molten metal cast on the inside of the original metal mold, which was made of low melting metal. By comparing the X12 steel ingot of the traditional casting and the non gap metal casting, the new casting was found to be new. The solidification method can greatly improve the cooling rate of the whole solidification process and then refine the ingot structure. Through the comprehensive analysis of the temperature change curve of the molten casting type in the solidification process and the numerical simulation, it reveals the reason that no gap metal casting can improve the cooling speed: when the metal is poured into the mold, the mold is attached to the mold. In the near future a solidifying shell is formed, when the heat passes through the solidified shell to the molten cast mold, and the molten cast heat is melted into liquid and filled between the mold and the ingot; in the subsequent solidification the liquid keeps the liquid state until the solidification of the ingot is completely finished, thus eliminating the ingot solidification and shrinkage and the casting mold. The air gap produced by thermal expansion makes the complex heat transfer mode in the traditional casting solidification transform into a single heat conduction, and then greatly improves the cooling rate and refines the ingot structure. Numerical simulation is used to simulate the change of the temperature field and the solid volume fraction of the ingot in the X12 steel without gap metal casting. The main factors affecting the cooling rate of the non gap metal casting and the optimum technological conditions for the non gap metal casting have been achieved, and the homogenization and refinement of the X12 steel ingot are realized under the conditions. The simulation results show that the physical properties of the molten cast materials are important for the cooling rate in the process of non gap metal casting. The lower the melting point of the casting type material, the higher the thermal conductivity, the earlier the melting time of the melt cast type in the solidification process, the higher the melting latent heat of the casting type material, the longer the time it takes for the melting casting from the beginning melting to the complete melting in the solidification process, and the choice of melting casting in the choice of melting casting. The effect of various physical properties should be taken into consideration when the material is made. Although the high casting temperature can make the molten casting melt in advance and get a larger cooling rate, the casting temperature should not be accelerated because of the excessive heat introduced in the system, so the lower casting temperature should be selected in the casting. In the scope of the study, the optimum casting conditions for X12 steel are: the molten cast material is 6061 aluminum alloy and the casting temperature is 1560 C., the X12 steel is cast under the best technological conditions. The results show that the macroscopic microstructure of the X12 steel ingot is all composed of uniform and fine equiaxed grains, from the surface of the ingot. To the center of the ingot, the grain size increases from only 80 m to 110 m, and the microstructure is composed of martensite.
【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】：TG260

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