碲、硼对高强韧性球墨铸铁组织和性能的影响

发布时间：2018-04-14 04:00

本文选题：铸态球墨铸铁 + 碲　；参考：《吉林大学》2017年硕士论文

【摘要】：球墨铸铁以其高强度、高韧性和低成本被广泛应用于机械、船舶、汽车等领域。随着汽车向着轻量化、高性能和低成本的方向不断发展,当前的球墨铸铁已逐渐不能满足行业的需求,对于像汽车曲轴这样的结构件不仅需要高的强度同时还要具备较高的韧性。目前,要想获得高强度高韧性的球墨铸铁主要是通过热处理实现,而这种方式成本高、工艺复杂、成品率低,因此,在铸态下生产高强度高韧性的球墨铸铁具有重大的现实意义。本文主要研究了微合金元素Te、B及其复合对球墨铸铁组织及力学性能的影响规律,优化出合适的微合金元素Te和B的加入量,初步实现了铸态球墨铸铁QT700-10的性能指标要求;在此基础上,进一步研究了合金元素Mo以及纳米TiC对铸态球墨铸铁组织与性能的影响,为实现稳定生产球墨铸铁QT700-10提供了实验基础。本文主要研究结果如下:1.研究了合金元素Te、B对球墨铸铁组织和性能的影响,发现:当Te含量不断增加时,球墨铸铁组织中石墨的球化率先增高后降低,珠光体含量呈逐步降低的趋势,相对应的球墨铸铁的抗拉强度变化趋势是先增加后降低,而延伸率则不断提高。优化出Te含量为0.0011wt.%时,球墨铸铁力学性能最好,抗拉强度为764MPa,延伸率为7.20%;在加入Te含量不变的条件下,加入不同含量的微合金元素B,随着B含量的增加,球墨铸铁组织中石墨的球化率先增大后降低,珠光体含量明显减少,球墨铸铁件抗拉强度不断降低,而延伸率则呈上升趋势,当B含量为0.001wt.%时,球墨铸铁的抗拉强度为711MPa,延伸率为12.28%。2.考察了纳米TiC对球墨铸铁组织与性能的影响。加入0.02wt.%TiC-Al中间合金时对石墨的影响不大,而使珠光体含量减少,抗拉强度降低,延伸率提高;加入0.02wt.%TiC-Cu中间合金时对石墨的影响不大,而珠光体含量增多,层片间距细小,抗拉强度及延伸率都有所提高。当加入0.02wt.%TiC-Cu中间合金时球墨铸铁的抗拉强度为715MPa,延伸率为10.6%,达到了球墨铸铁QT700-10的性能指标要求。3.通过研究球墨铸铁的拉伸性能和显微组织之间的关系,要实现球墨铸铁QT700-10的目标,其显微组织需满足下面几种情况:当球化等级在1级时,珠光体含量35%～45%,铁素体含量55%～65%,此时的珠光体层片间距240nm左右;当球化等级在2～3级时,珠光体含量在45%～55%,铁素体含量45%～55%,此时层片间距要220nm;当球化等级在4～5级时,珠光体含量在50%～65%,铁素体含量35%～50%,此时不仅珠光体的层片间距220nm,而且要结合珠光体的形态提高球墨铸铁的韧性。
[Abstract]:Ductile iron is widely used in machinery, ship, automobile and so on for its high strength, high toughness and low cost.As cars continue to develop in the direction of lightweight, high performance and low cost, the current nodular cast iron is no longer able to meet the needs of the industry.For a structure such as an automobile crankshaft, it needs not only high strength but also high toughness.At present, to obtain ductile iron with high strength and toughness is mainly achieved by heat treatment, which is of high cost, complex process and low yield.It is of great practical significance to produce ductile iron with high strength and toughness in the as-cast state.In this paper, the effect of microalloying element Teo B and its compound on the microstructure and mechanical properties of ductile iron was studied. The proper addition of Te and B elements was optimized, and the requirements of QT700-10 properties of as-cast ductile iron were preliminarily realized.On this basis, the effects of alloying element Mo and nanometer TiC on the microstructure and properties of as-cast ductile iron were further studied, which provided the experimental basis for the stable production of ductile iron QT700-10.The main results of this paper are as follows: 1: 1.The effect of the alloying element Teo B on the microstructure and properties of ductile cast iron was studied. It was found that with the increasing of Te content, the spheroidization of graphite in ductile cast iron first increased and then decreased, and the content of pearlite decreased gradually.The tensile strength of the corresponding ductile iron increased first and then decreased, while the elongation increased continuously.When the Te content is 0.0011wt.%, the ductile iron has the best mechanical properties, the tensile strength is 764MPa and the elongation is 7.20.The microalloying element Bwith different contents increases with the increase of the content of Te.The spheroidization of graphite in ductile iron increases first and then decreases, the content of pearlite decreases obviously, the tensile strength of ductile iron decreases continuously, and the elongation of ductile iron increases. When the content of B is 0.001wt.%,The tensile strength and elongation of ductile iron are 711 MPA and 12.28 MPA, respectively.The effect of nanometer TiC on the microstructure and properties of ductile iron was investigated.The addition of 0.02wt.%TiC-Al master alloy had little effect on graphite, but decreased the content of pearlite, decreased tensile strength and increased elongation, but the addition of 0.02wt.%TiC-Cu master alloy had little effect on graphite, but the content of pearlite increased and the interlaminar spacing was small.Tensile strength and elongation have been improved.When 0.02wt.%TiC-Cu master alloy was added, the tensile strength and elongation of ductile iron were 715 MPA and 10.6 respectively, which met the requirements of ductile iron QT700-10.By studying the relationship between tensile properties and microstructure of ductile iron, in order to achieve the goal of ductile iron QT700-10, the following conditions should be satisfied: when the spheroidization grade is in grade 1,The pearlite content is 35: 45 and the ferrite content is 5565. At this time, the distance between the pearlite layers is about 240nm; when the spheroidization grade is 2 or 3, the pearlite content is 45 / 55, the ferrite content is 45 / 55, and the lamellar spacing is 220 nm; when the spheroidization level is at 4 / 5,The content of pearlite is about 50% and the content of ferrite is 35%. At this time not only the interlaminar spacing of pearlite is 220 nm but also the toughness of nodular cast iron should be improved in combination with the morphology of pearlite.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG143.5

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