半固态高铬铸铁组织及性能研究

【作者】 王红超；

【导师】 游晓红；

【作者基本信息】 太原科技大学 ， 材料加工工程， 2010， 硕士

【摘要】 金属半固态成形技术是上世纪70年代开始兴起的一门新兴的成形技术。随着人们对半固态成形技术认识的加深及对其成形规律的研究。半固态成形技术在轻金属低熔点合金中得到了很好的商业应用,然而对高熔点的钢铁材料半固态成形工艺的研究尚处于起步阶段。本文以高熔点的高铬铸铁为研究对象,采用电磁搅拌的方法制备了半固态高铬铸铁坯料,研究了半固态成形制备的坯料和铸态高铬铸铁微观组织、力学性能,探索出一种制备高性能半固态高铬铸铁坯料的工方法,为高铬铸铁半固态成形技术的进一步发展提供理论和试验基础,加快半固态成形技术在高熔点材料领域的商业应用。试验中以搅拌时间和影响电磁搅拌程度主要因素的电压作为处理工艺参数变量,采用对比试验的方法,分别设置了输入电压为160v、180v、200v,搅拌时间为75s、90s、120s,研究了工艺参数对高铬铸铁组织性能的影响。试验结果表明：使用电磁搅拌制备高铬铸铁半固态坯料组织是有效的,可行的；高铬铸铁初生奥氏体由传统铸态下的粗大树枝晶转变为蔷薇状及近球状；平均等效直径大幅度下降,平均等效直径为49.9μm,最高下降幅度为67.6%,晶粒细化效果极其明显,细化程度及分布都比较均匀；形状因子也有了大幅度的提升,平均形状因子为0.709,最大提高幅度为83.2%,晶粒趋于椭圆、近球状；在同一输入电压下,初生奥氏体晶粒等效直径随着搅拌时间的增加在不断减小,其形状因子在不断上升,当搅拌时间达到某一数值后,其等效直径和形状因子趋于稳定；在不同输入电压下,初生奥氏体的等效直径随着输入电压的升高先降低而后略微上升,形状因子不断的提升后略微下降,表明输入电压并非越高越好,当其达到一定数值后,高铬铸铁组织变化趋于稳定,电磁搅拌对高铬铸铁组织影响力下降；半固态高铬铸铁试样的力学性能也有了大幅度提高,同一输入电压下,半固态高铬铸铁试样硬度随搅拌时间先升后降,韧性变化不大,在同一搅拌时间下,半固态高铬铸铁试样也有类似的变化趋势；磁场对高铬铸铁凝固曲线有散热、加热两个方面的影响,随着输入电压的不同,这两方面影响的主导地位不同,就得到不同的凝固曲线。本文还研究了经同一热处理工艺处理后组织性能。结果表明,经过电磁搅拌处理后试样的组织其残余奥氏体及马氏体组织更为明显,其中马氏体较为细小,二次碳化物分布弥散；材料性能有较大提高,未经热处理的半固态高铬铸铁试样较常规铸造试样及其热处理后的性能都有提高。因此,在同等条件下,获得同样性能的高铬铸铁试样,半固态成形方法可以省去热处理工艺,减少工业生产中的工序和生产成本,有很大的商业应用价值。在本试验中,确定了使用电磁搅拌方法制备半固态高铬铸铁的最佳工艺参数,即输入电压为180v,搅拌时间在90s左右,为高铬铸铁的半固态成形技术的进一步研究奠定了基础。更多还原

【Abstract】 Semi-solid metal forming is a new forming technology on the rise of the 70s.In recent years, it had a deep understanding and shaping the law of the Semi-solid forming. Semi-solid forming had got a good commercial applications in the low melting point alloy and the light metal, but in the high melting point semi-solid forming of steel materials, the process is still in the initial stage. In this paper, the high chromium cast iron with high melting point was chosen for the study, semi-solid billets of the high chromium cast iron were papered by electromagnetic stirring. Compared the performance of high chromium cast iron in different electromagnetic stirring process with the conventional high chromium cast iron, we hope that we can obtain the optimal process of high-chromium iron billets. And the optimal processing to prepare the semi-solid ingot of high-chromium cast iron has been explored, providing the basis for the further study on the semi-solid forming technology of high-chromium cast iron. The commercial application of Semi-solid forming technology can be speeded up in the high melting point material.In this experiment, we take the voltage of the main factors affecting the magnetic induction and the mixing time as a high-chromium cast iron melt variable process parameters, using comparative methods to study the process parameters on high-chromium cast iron performance. We set the input voltage at 160v、180v、200v,stirring time at 75s、90s、120s, The results showed that:the use of electromagnetic stirring semi-solid preparation of high chromium cast iron billet organization is effective and feasible; Primary austenite of the high-chromium alloy cast iron morphology changed from the traditional large-cast into a petal-shaped dendrite and agglomerate; The average equivalent diameter of primary austenite significant decline, the average equivalent diameter is 49.9μm, the largest average diameter of primary austenite decreased by 67.6%, Primary austenite become smaller and the distribution is more uniform; The shape factor of primary austenite was improved significant, the average shape factor is 0.709, the maximum increase rate of 83.2%. The primary austenite tends to elliptical and nearly spherical. In the same input voltage, the primary austenite grain equivalent diameter increases with the mixing time continuously decreased, the shape factor on the rise. When the mixing time to reach a certain value, its equivalent diameter and shape factor stabilized; in different input voltage, Increased with the input voltage intensity, the primary austenite equivalent diameter will be decreased firstly and then increased slightly, the shape factor will be decreased after upgrading continuously, which show that the input voltage is not as high as possible. The performance of semi-solid cast iron mechanical samples has also been greatly improved, When it reaches a certain value after the change of high chromium cast iron stabilized electromagnetic stirring on the influence of high chromium cast iron drop; Under the same magnetic flux density, hardness of semi-solid high-chromium cast iron will increase and the decrease with the adding mixing time, toughness changed little; under the same stirring time, the semi-solid high-chromium cast iron has the similar trend; There are two aspects on the solidification curve of the high-chromium cast iron in the magnetic field(heating、cooling), the dominant position of two aspects will be different with the different input voltage, and then we will get the different curves of solidification.This paper also studied the performance and structure of the high chromium cast iron under the same heat treatment. The results showed that the organization of the samples retained austenite and martensite is more obvious after the same heat treatment, in which martensite was relatively small, dispersed distribution of secondary carbides. Performance of the materials had a significant improvement. Performance of semi-solid without heat treatment will be better than both of the conventional high chromium cast iron sample and the sample with heat treatment. So, achieved the same performance of high chromium cast iron, prepared by semi-solid forming method eliminates the need for heat treatment process, which can reduce industrial production processes and production costs, It will have great commercial value.In my experiment, we get the best processing of the high chromium cast iron prepared by the semi-solid method of electromagnetic stirring (input voltage at 180v,stirring time at 90s),laying the foundation for the development of the semi-solid forming technology of high chromium cast iron.更多还原