本文選題：COST-FB2鋼 + 淬火工藝　； 參考：《昆明理工大學(xué)》2017年碩士論文

【摘要】：燃煤發(fā)電在我國未來相當(dāng)長一段時期內(nèi)仍然是發(fā)電的主要形式,620℃超超臨界發(fā)電技術(shù)具有高效率低能耗的優(yōu)點,建設(shè)620℃超超臨界電站對于我國掌握先進發(fā)電技術(shù)、提高綜合國力具有重要的意義。我國現(xiàn)投入運營的620℃超超臨界電站均選用COST-FB2鋼作為汽輪機轉(zhuǎn)子材料,大型轉(zhuǎn)子鍛件均需進口購買,而我國對COST-FB2鋼的相關(guān)研究仍處在起步階段,尚不具有工業(yè)生產(chǎn)的能力。因此,通過系統(tǒng)的研究熱處理工藝和退火工藝對大型汽輪機轉(zhuǎn)子鍛件實際的生產(chǎn)具有一定的參考價值及指導(dǎo)意義。實驗借助OM、SEM、TEM、XRD和相分析等手段,研究了熱處理工藝對COST-FB2鋼組織和性能的影響和等溫退火過程對COST-FB2鋼組織均勻性的影響,探討COST-FB2鋼的強韌化機制,得出如下結(jié)論:(1)在1000℃-1200℃隨淬火溫度的提高,使鋼固溶態(tài)過飽和度提高,回火后析出碳化物數(shù)量增加,加強了沉淀強化的效果,同時晶粒發(fā)生粗化,導(dǎo)致細晶強化效果減弱。晶粒的粗化導(dǎo)致鋼沖擊韌性下降。(2)淬火冷卻速度降低至1℃/min開始發(fā)生鐵素體轉(zhuǎn)變,使材料強度硬度明顯下降,回火后晶界處碳化物數(shù)量較少,提高了材料的韌性;淬火冷卻速度降低至0.5℃/min獲得單一的鐵素體組織,強度硬度急劇下降,晶界處呈網(wǎng)狀的碳化物析出造成韌性的下降。(3)400℃-570℃回火,金相顯微組織差異不大,位錯密度較高,因此強度硬度較高;高于570℃回火,開始發(fā)生回復(fù),隨回火溫度的上升回復(fù)現(xiàn)象加劇,位錯密度降低,導(dǎo)致強度硬度下降,韌性提高。延長570℃回火時間,回火1h和2h差別不大,延長至4h碳化物開始在晶界處聚集,造成沖擊韌性的降低。700℃回火時,隨時間的延長,碳化物開始聚集長大,回復(fù)加劇,位錯密度降低,造成強度下降,沖擊值上升。(4)570℃和700℃兩步回火的冷卻速度主要影響碳化物析出過程中原子的擴散和聚集長大,冷卻速度快,原子擴散時間短,容易得到細小的碳化物;冷卻速度慢,原子擴散時間長,容易造成碳化物的聚集長大,得到大尺寸碳化物,降低力學(xué)性能。700℃回火時的冷卻速度對析出碳化物尺寸的影響更大。570℃和700℃兩步回火均采用空冷的冷卻方式可得到最佳的力學(xué)性能。(5)將COST-FB2鋼進行700℃或730℃等溫退火可發(fā)生完全的鐵素體轉(zhuǎn)變,將粗大晶粒分割為大量細小的鐵素體,同時析出碳化物在奧氏體化過程中可以阻礙奧氏體晶粒長大。等溫退火后直接最終熱處理或者進行預(yù)備熱處理與最終熱處理制度均會得到細小均勻的組織。730℃等溫退火效果優(yōu)于700℃。
[Abstract]:Coal-fired power generation in China for quite a long period of time is still the main form of power generation, has 620 degrees of ultra supercritical power generation technology with high efficiency and low energy consumption, the construction of 620 C ultra supercritical power plant for advanced power generation technology in China, has important significance to improve the comprehensive national strength. China is put into operation 620 C ultra supercritical power stations are used for COST-FB2 steel as the steam turbine rotor, large rotor forgings are required to purchase imported, and related research of COST-FB2 steel in China is still in the initial stage, there is no industrial production capacity. It has certain reference value and significance through the systematic study of heat treatment process and annealing the process of large steam turbine rotor forging production. The actual experiment by means of OM, SEM, TEM, XRD and phase analysis method, study the effect of heat treatment on the microstructure and mechanical properties of COST-FB2 steel and isothermal annealing The fire process on Microstructure of COST-FB2 steel inhomogeneity of COST-FB2 steel, toughening mechanism, draw the following conclusions: (1) at 1000 DEG -1200 DEG with increasing quenching temperature, the steel solid solution supersaturation increased after tempering, the carbide precipitation increased, strengthened the effect of strong precipitation, while grain coarse, lead to fine grain strengthening effect is weakened. The grain coarsening decreases the impact toughness of steel. (2) the cooling rate decreases to 1 DEG /min began the transformation of ferrite, the material strength and hardness decreased obviously after tempering, less grain boundary carbide quantity, improve the toughness of the material; the cooling rate decreases to 0.5 DEG /min to obtain a single ferrite, strength and hardness decreased rapidly, the grain boundary was caused by mesh carbide toughness decreased. (3) 400 DEG -570 DEG tempering, little difference in microstructure, higher dislocation density, so strong The degree of hardness higher than 570 DEG C; tempering, began to return, with the increase of tempering temperature recovery phenomenon intensified, the dislocation density decreased, resulting in decreased strength and hardness, toughness increased. 570 C prolonged tempering time, tempering little difference in 1H and 2H, extended to 4h carbide began gathering at the grain boundary, the impact toughness decreased tempering.700 C, with the extension of time, carbide begins to grow up, recovery intensifies, reduction of dislocation density, leads to the decrease of strength and impact value rise. (4) 570 degrees and 700 degrees two step tempering cooling rate mainly affects the precipitation of carbide in the process of atomic diffusion and coalescence, cooling speed, diffusion time is short and easy to get fine carbides; slow cooling rate, diffusion time is long, easy to cause the aggregation and growth of carbides, large size carbide, lower cooling rate and mechanical properties of.700 DEG C during tempering of precipitation Effect of carbide size and greater.570 degrees and 700 degrees two step cooled by air cooling and tempering are the best mechanical properties could be obtained. (5) the COST-FB2 steel was 700 degrees or 730 degrees Celsius isothermal annealing can occur completely ferrite transformation, will be divided into a large number of coarse grains of fine ferrite, at the same time in the process of precipitation of carbides in austenite can impede austenite grain growth. The isothermal annealing directly after final heat treatment or pre heat treatment and final heat treatment system will be better than.730 DEG C fine uniform isothermal annealing effect of 700 degrees.

【學(xué)位授予單位】：昆明理工大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TG142.1

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