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  本文關(guān)鍵詞： 風(fēng)電用球鐵 石墨形態(tài) 隨流孕育 形核核心 球化率　出處：《湖南大學(xué)》2016年碩士論文　論文類型：學(xué)位論文

【摘要】：球墨鑄鐵鑄件具有性能和價格優(yōu)勢,在機床、核電、水電、風(fēng)電等行業(yè)具有廣泛應(yīng)用前景。球墨鑄鐵鑄件是國家重大技術(shù)裝備的重要基礎(chǔ)零部件,在國民經(jīng)濟(jì)中起著十分重要的作用,是衡量國家工業(yè)綜合實力的重要標(biāo)志,但生產(chǎn)風(fēng)電用球鐵鑄件時,易出現(xiàn)球化率低、石墨粗大、石墨畸變等組織缺陷,導(dǎo)致鑄件力學(xué)性能不穩(wěn)定,從而影響產(chǎn)品質(zhì)量。本文從公司生產(chǎn)實際出發(fā),采用電爐熔煉工藝生產(chǎn)風(fēng)電用球鐵鑄件,同時制備單鑄和本體試塊,借助光譜、光學(xué)金相顯微鏡、電子掃描顯微鏡(SEM)、低溫沖擊試驗儀以及微機控制電子萬能試驗機等手段,研究了孕育處理、合金化、球化后包內(nèi)保溫時間、鐵液爐內(nèi)靜置時間、冷卻速度等工藝因素對風(fēng)電用球鐵鑄件石墨形態(tài)和力學(xué)性能的影響,研究結(jié)果對制定風(fēng)電用球鐵鑄件生產(chǎn)方案控制其組織性能具有重要指導(dǎo)意義�；诮鹣嘟M織、力學(xué)性能、低溫沖擊性能、球化等級、石墨大小及圓整度,研究了合金元素銻(Sb)、爐內(nèi)高溫靜置時間、包內(nèi)保溫時間、冷鐵、鑄件壁厚等工藝因素對風(fēng)電用球鐵石墨形態(tài)的影響規(guī)律。發(fā)現(xiàn)球化時加入0.002%～0.01%銻合金,基體組織晶粒細(xì)小、石墨球數(shù)量多,直徑小,圓整度較好、球化等級提高;爐內(nèi)高溫靜置時間增加,石墨形核核心減少,球化率降低,石墨球數(shù)量減少;延長球化處理后鐵液在包內(nèi)保溫時間,球狀石墨衰退,石墨球數(shù)量減少,最后完全呈片狀形式;冷鐵可改善風(fēng)電用球鐵鑄件的冷卻條件,利于獲得規(guī)則的石墨球,提高球化等級和細(xì)化組織,同時避免石墨畸變和石墨漂浮現(xiàn)象。在上述工藝因素對風(fēng)電用球鐵石墨形態(tài)影響規(guī)律的基礎(chǔ)上,修正并完善試驗條件,研究了球化孕育處理對風(fēng)電用球鐵鑄件金相組織和力學(xué)性能的影響規(guī)律�；诶鞌嗫谔卣�、石墨結(jié)晶核心的分析,發(fā)現(xiàn)隨流孕育處理時,球化孕育衰退現(xiàn)象減慢,本體試塊球化率為2級,石墨球大小基本穩(wěn)定在7級水平,伸長率、抗拉強度和低溫沖擊性能等力學(xué)性能均提高;孕育劑C成分中含有均衡的鈣含量和鈰含量,能夠中和阻止石墨球形成的有害微量元素;含有少量的硫和氧,在加入鐵水過程中與鈣和鈰進(jìn)行反應(yīng)形成特殊成分,這些特殊成分在球墨鑄鐵中形成非常好的石墨結(jié)晶核心,核心質(zhì)點穩(wěn)定,殘留時間較長,具有較強的抗球化孕育衰退的能力,球化率高,石墨球的大小較穩(wěn)定,從而得到高密度的石墨球分布。孕育劑D作瞬時孕育劑,成分中Y元素的平均含量較高,加入鐵水中氧化成氧化釔,石墨以Y203為形核的核心生長,其在鐵水中的殘留時間較長,能起到有效的核心,具有一定的抗石墨衰退的能力,球化率高,獲得較好的石墨球分布。但在鐵液凝固后期,抗石墨衰退能力和形核能力不及孕育劑C,不能獲得高密度石墨球分布,對鐵素體基質(zhì)沒有影響,不能細(xì)化基質(zhì)晶粒和促使球墨鑄鐵中形成更多的鐵素體。
[Abstract]:Ductile iron castings are widely used in machine tools, nuclear power, hydropower, wind power and other industries because of their advantages in properties and prices. Ductile iron castings are important basic parts of national major technical equipment. It plays a very important role in the national economy and is an important symbol to measure the comprehensive strength of national industry. However, it is easy to produce ductile iron castings for wind power, such as low spheroidization rate, coarse graphite, graphite distortion and other structural defects. The mechanical properties of the castings are unstable, and the quality of the products is affected. In this paper, based on the production practice of the company, the ductile iron castings for wind power are produced by the electric furnace smelting process. At the same time, single casting and bulk test blocks are prepared, with the help of spectrum. The incubation treatment, alloying and spheroidizing time after inoculation, alloying and spheroidization were studied by means of optical metallographic microscope, electron scanning microscope, low temperature impact tester and microcomputer controlled electronic universal testing machine. The influence of the process factors such as the static time and cooling rate on the graphite morphology and mechanical properties of the ductile iron castings for wind power. The results of the study are of great significance in establishing a production plan for wind power ductile iron castings to control their microstructure and properties. Based on metallographic structure, mechanical properties, low temperature impact properties, spheroidizing grade, graphite size and roundness. The alloying element SB _ (B), the high temperature static time in the furnace, the holding time in the ladle and the cooling iron were studied. The influence of technological factors such as casting wall thickness on graphite morphology of ductile iron used in wind power was studied. It was found that the addition of 0.002% antimony alloy to nodular iron during spheroidization had fine grain size, large number of graphite spheres and small diameter. The degree of roundness is better and the grade of spheroidization is improved. With the increase of the high temperature static time in the furnace, the nucleation core of graphite decreases, the spheroidization rate decreases and the number of graphite nodule decreases. After prolonging the heat preservation time of molten iron in the ladle after spheroidizing treatment, the nodular graphite decays, the number of graphite nodule decreases, and finally it appears as a sheet form. Cold iron can improve the cooling conditions of ductile iron castings for wind power, which is conducive to obtaining regular graphite balls, improving the spheroidization grade and refining the microstructure. At the same time, the graphite distortion and graphite floatation were avoided. On the basis of the influence of the above technological factors on the graphite morphology of ductile iron for wind power, the test conditions were revised and improved. The effect of spheroidization inoculation on the metallographic structure and mechanical properties of ductile iron castings for wind power was studied. Based on the tensile fracture characteristics and the analysis of graphite crystal core, it was found that when inoculation was carried out with current. The spheroidization decay was slowed down, the spheroidization rate of the bulk sample was 2, and the graphite spheroidal size was stable at the level of 7. The mechanical properties such as elongation, tensile strength and low temperature impact properties were improved. The inoculant C contains a balanced content of calcium and cerium, which can neutralize the harmful trace elements that prevent the formation of graphite spheroids. It contains a small amount of sulfur and oxygen and reacts with calcium and cerium in the process of adding hot metal to form special components which form a very good graphite crystal core in ductile iron and the core particles are stable. The residual time is longer and has a strong ability to resist the spheroidization decay. The spheroidization rate is high and the size of the graphite spheroids is stable. Thus the high density graphite spheres are obtained. The inoculant D is used as the instantaneous inoculant. The average content of Y element in the composition is higher, adding in molten iron to form yttrium oxide, graphite nucleation with Y203 as the core growth, its residue time in molten iron is longer, can play an effective core. It has high spheroidization rate and good graphite spheroidal distribution. However, in the late solidification period of molten iron, the graphite decay resistance and nucleation ability are not as good as inoculant C. The high density graphite spheroids could not be obtained and had no effect on the ferrite matrix and could not refine the matrix grain and promote the formation of more ferrite in ductile iron.
【學(xué)位授予單位】：湖南大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2016
【分類號】：TG255

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