工艺因素对风电用球铁铸件石墨形态和力学性能的影响

发布时间：2018-01-27 17:31

本文关键词： 风电用球铁石墨形态随流孕育形核核心球化率　出处：《湖南大学》2016年硕士论文　论文类型：学位论文

【摘要】：球墨铸铁铸件具有性能和价格优势,在机床、核电、水电、风电等行业具有广泛应用前景。球墨铸铁铸件是国家重大技术装备的重要基础零部件,在国民经济中起着十分重要的作用,是衡量国家工业综合实力的重要标志,但生产风电用球铁铸件时,易出现球化率低、石墨粗大、石墨畸变等组织缺陷,导致铸件力学性能不稳定,从而影响产品质量。本文从公司生产实际出发,采用电炉熔炼工艺生产风电用球铁铸件,同时制备单铸和本体试块,借助光谱、光学金相显微镜、电子扫描显微镜(SEM)、低温冲击试验仪以及微机控制电子万能试验机等手段,研究了孕育处理、合金化、球化后包内保温时间、铁液炉内静置时间、冷却速度等工艺因素对风电用球铁铸件石墨形态和力学性能的影响,研究结果对制定风电用球铁铸件生产方案控制其组织性能具有重要指导意义。基于金相组织、力学性能、低温冲击性能、球化等级、石墨大小及圆整度,研究了合金元素锑(Sb)、炉内高温静置时间、包内保温时间、冷铁、铸件壁厚等工艺因素对风电用球铁石墨形态的影响规律。发现球化时加入0.002%～0.01%锑合金,基体组织晶粒细小、石墨球数量多,直径小,圆整度较好、球化等级提高;炉内高温静置时间增加,石墨形核核心减少,球化率降低,石墨球数量减少;延长球化处理后铁液在包内保温时间,球状石墨衰退,石墨球数量减少,最后完全呈片状形式;冷铁可改善风电用球铁铸件的冷却条件,利于获得规则的石墨球,提高球化等级和细化组织,同时避免石墨畸变和石墨漂浮现象。在上述工艺因素对风电用球铁石墨形态影响规律的基础上,修正并完善试验条件,研究了球化孕育处理对风电用球铁铸件金相组织和力学性能的影响规律。基于拉伸断口特征、石墨结晶核心的分析,发现随流孕育处理时,球化孕育衰退现象减慢,本体试块球化率为2级,石墨球大小基本稳定在7级水平,伸长率、抗拉强度和低温冲击性能等力学性能均提高;孕育剂C成分中含有均衡的钙含量和铈含量,能够中和阻止石墨球形成的有害微量元素;含有少量的硫和氧,在加入铁水过程中与钙和铈进行反应形成特殊成分,这些特殊成分在球墨铸铁中形成非常好的石墨结晶核心,核心质点稳定,残留时间较长,具有较强的抗球化孕育衰退的能力,球化率高,石墨球的大小较稳定,从而得到高密度的石墨球分布。孕育剂D作瞬时孕育剂,成分中Y元素的平均含量较高,加入铁水中氧化成氧化钇,石墨以Y203为形核的核心生长,其在铁水中的残留时间较长,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,获得较好的石墨球分布。但在铁液凝固后期,抗石墨衰退能力和形核能力不及孕育剂C,不能获得高密度石墨球分布,对铁素体基质没有影响,不能细化基质晶粒和促使球墨铸铁中形成更多的铁素体。
[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.
【学位授予单位】：湖南大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TG255

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