發(fā)布時(shí)間：2018-06-06 17:45

  本文選題：蠕墨鑄鐵 + 凝固過程��； 參考：《西安工業(yè)大學(xué)》2017年碩士論文

【摘要】：蠕墨鑄鐵因其良好的綜合性能在高功率密度柴油機(jī)缸蓋上獲得了廣泛的應(yīng)用,然而隨著發(fā)動(dòng)機(jī)功率的增加,蠕墨鑄鐵的各項(xiàng)性能指標(biāo)也必須進(jìn)一步提升。材料的性能取決于其組織,而組織轉(zhuǎn)變?nèi)Q于凝固過程,因此就需要更加深入地了解蠕墨鑄鐵的凝固過程,以求更好地改善其性能。關(guān)于蠕墨鑄鐵的凝固過程,已經(jīng)有不少學(xué)者進(jìn)行過研究,但是其研究成果絕大多數(shù)是定性地描述,鮮有定量的描述。本文以高功率密度柴油機(jī)缸蓋用蠕墨鑄鐵為基礎(chǔ),采用液淬的方法獲得蠕墨鑄鐵凝固過程中不同時(shí)期的晶體組織狀態(tài),結(jié)合熱分析法分析蠕墨鑄鐵的組織轉(zhuǎn)變過程,在此基礎(chǔ)上研究了合金元素和蠕化劑加入量對(duì)蠕墨鑄鐵凝固過程的影響,總結(jié)了蠕墨鑄鐵的組織轉(zhuǎn)變規(guī)律,探索了蠕墨鑄鐵的蠕化機(jī)理。并且利用高分辨率X射線三維掃描成像技術(shù)分析了蠕蟲狀石墨三維形態(tài)的轉(zhuǎn)變過程,利用掃描電子顯微鏡分析了蠕蟲狀石墨的形核機(jī)制,利用DT2000專業(yè)金相分析軟件總結(jié)了蠕蟲狀石墨的形核和長(zhǎng)大規(guī)律,研究了蠕蟲狀石墨形核和結(jié)晶的動(dòng)力學(xué)。結(jié)果表明:(1)合金元素Cu、Mo、Sn對(duì)蠕墨鑄鐵的凝固曲線特征值、共晶組織轉(zhuǎn)變過程及石墨的長(zhǎng)度和含量均沒有明顯影響。(2)蠕化劑加入量對(duì)蠕墨鑄鐵的共晶組織轉(zhuǎn)變過程影響很大。蠕化劑加入量為0.2%時(shí),共晶奧氏體的生長(zhǎng)速度比畸變石墨慢,因此畸變石墨長(zhǎng)成片狀,且大范圍連通,共晶反應(yīng)結(jié)束時(shí)片狀石墨的連通率為88.87%。蠕化劑加入量為0.4%時(shí),共晶奧氏體的生長(zhǎng)速度比畸變石墨快,使畸變石墨不能大范圍連通,最終長(zhǎng)成蠕蟲狀。蠕化劑加入量為0.6%時(shí),共晶奧氏體的生長(zhǎng)速度更快,導(dǎo)致一些未畸變的球狀石墨被完全包裹住而不能畸變,因此蠕化率下降。(3)蠕墨鑄鐵中的石墨結(jié)晶時(shí),其最初形貌是球狀。共晶反應(yīng)開始后由于共晶奧氏體的析出,鐵液中的氧、硫含量富集到一定程度,導(dǎo)致和鐵液直接接觸的球狀石墨發(fā)生畸變,然后畸變石墨生長(zhǎng)連通在一起。由于共晶奧氏體的生長(zhǎng)速度比畸變石墨的生長(zhǎng)速度快,共晶奧氏體逐漸將畸變石墨包裹住,使畸變石墨只能在小范圍內(nèi)相互連通,最終長(zhǎng)成蠕蟲狀,蠕蟲狀石墨室溫下的連通率為32.5%。(4)蠕蟲狀石墨的異質(zhì)核心物質(zhì)有CeS、MgS、CaS、La_2S_3、FeS、A1203、TiC,石墨異質(zhì)核心是由其中的幾種物質(zhì)共同組成的,核心尺寸為12.5μm。過共晶蠕墨鑄鐵中的石墨主要在初生石墨階段形核,共晶反應(yīng)初期也有石墨形核,石墨形核速率不斷下降,形核數(shù)量 N 與時(shí)間 t 的關(guān)系為 N =-1.1 + 1.1sin[(t+5911.8)π/11929.4]。(5)共晶反應(yīng)階段是石墨生長(zhǎng)的主要階段,石墨結(jié)晶速率先增長(zhǎng)后降低,在共晶反應(yīng)開始70s時(shí),石墨結(jié)晶速率最快,此時(shí)石墨長(zhǎng)度增長(zhǎng)速率為1.33μm/s,石墨含量增長(zhǎng)速率為0.18%/s。石墨長(zhǎng)度L與時(shí)間t的關(guān)系為L(zhǎng) = 100.54-93.87(1+e~(（t-99.98)/16.98),石墨含量 C與時(shí)間 t 的關(guān)系為C = 9.02-8.64/(1 + e~((t-101.74)/9.54))。
[Abstract]:Vermicular graphite cast iron has been widely used in the cylinder head of high power density diesel engine because of its good comprehensive properties. However, with the increase of engine power, the performance indexes of vermicular graphite cast iron must be further improved. The properties of the materials depend on their microstructure, while the microstructure transformation depends on the solidification process. Therefore, it is necessary to better understand the solidification process of vermicular graphite cast iron in order to improve its properties. The solidification process of vermicular graphite cast iron has been studied by many scholars, but most of its research results are qualitative description, few quantitative description. Based on vermicular graphite cast iron used in cylinder head of high power density diesel engine, the crystal structure state of vermicular graphite cast iron during solidification process was obtained by liquid quenching method, and the microstructure transformation process of vermicular graphite cast iron was analyzed by means of thermal analysis. On this basis, the effect of alloy elements and vermicularizing agent on the solidification process of vermicular graphite cast iron was studied, the microstructure transformation law of vermicular graphite cast iron was summarized, and the compacted mechanism of vermicular graphite cast iron was explored. The transformation process of vermicular graphite 3D morphology was analyzed by high resolution X-ray 3D scanning imaging, and the nucleation mechanism of vermicular graphite was analyzed by scanning electron microscope (SEM). The nucleation and growth laws of vermicular graphite were summarized by using DT2000, and the kinetics of nucleation and crystallization of vermicular graphite was studied. The results show that the alloy element Cu-Mo-Sn has no obvious effect on the characteristic value of solidification curve, the process of eutectic structure transformation and the length and content of graphite. The addition of vermicularizing agent has great influence on the eutectic transformation process of vermicular graphite cast iron. The growth rate of eutectic austenite is slower than that of distorted graphite when the amount of vermicularizing agent is 0.2 / 0.2.Therefore, the distorted graphite grows into sheet and is connected in a wide range, and the connectivity rate of sheet graphite is 88.87 at the end of eutectic reaction. The growth rate of eutectic austenite is faster than that of distorted graphite when the amount of vermicularizing agent is 0.4, so that the distorted graphite can not be connected in a wide range and eventually grows into a worm. When the amount of vermicularizing agent is 0.6, the growth rate of eutectic austenite is faster, which leads to some undistorted spheroidal graphite being completely enveloped and unable to be distorted. Therefore, the vermicular rate of graphite in vermicular graphite cast iron is decreased. 3) when the graphite in vermicular graphite cast iron crystallizes, its initial morphology is spherical. At the beginning of eutectic reaction, due to the precipitation of eutectic austenite and the enrichment of oxygen and sulfur in molten iron to a certain extent, the nodular graphite in direct contact with molten iron is distorted, and then the distorted graphite grows and connects together. Because the growth rate of eutectic austenite is faster than that of distorted graphite, eutectic austenite is gradually wrapped in distorted graphite, so that the distorted graphite can only be connected to each other in a small range, and eventually grows into a worm. The connectivity of vermicular graphite at room temperature is 32.5 / 4) the heterogeneous core material of vermicular graphite is CeSmg / MgS / CaSU / La _ 2S _ 3 / FES _ (A1203) TiC. The graphite heterostructure core is composed of several kinds of substances and the size of the core is 12.5 渭 m. The nucleation of graphite in hypereutectic vermicular graphite cast iron is mainly in the primary graphite stage, and the nucleation rate of graphite is decreasing at the beginning of eutectic reaction. The relationship between nucleation number N and time t is N ~ (-1.1) 1.1sin [t _ (5911.8) 蟺 / 11929.4]. 5) the phase of eutectic reaction is the main stage of graphite growth. The crystallization rate of graphite increases first and then decreases, and the crystallization rate of graphite is the fastest at the beginning of eutectic reaction for 70s. The graphite length increases at a rate of 1.33 渭 m / s, and the graphite content increases at a rate of 0.18 / s. The relationship between graphite length L and time t is L = 100.54-93.871e1 / 99.98g / r 16.98g / t, and the relationship between graphite content and time t is C = 9.02-8.64 / t / 101.74 / 9.54 / m ~ (-1).
【學(xué)位授予單位】：西安工業(yè)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TG250

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