材料和工艺因素对蠕墨铸铁组织、加工性能的影响

发布时间：2018-09-13 09:40

【摘要】：蠕墨铸铁是一种综合性能十分优良的铸铁材料,不仅具有近似球铁的力学性能,同时具备近似灰铁的铸造、减震和导热等性能。近年来随着研究的不断深入,蠕墨铸铁在汽车等重工业行业有着不可替代的作用。但采用现有的灰铸铁加加工生产线对蠕墨铸铁件进行机加工时,出现了崩刃、打刀、加工精度不够等一系列的机加工问题,而目前国内外对蠕墨铸铁机加工困难的问题却没有很全面的研究。本课题是结合中国一拖集团有限公司在缸体用蠕墨铸铁材料的研究开发中所使用的炉料、可选择的蠕化剂种类、合金化元素等方面开展研究,试探索炉料、蠕化剂、合金元素和铁水过滤等对蠕墨铸铁加工性能的影响。本文主要研究在不同工艺条件下蠕墨铸铁的显微组织及加工性能,分为有无过滤对比、蠕化剂种类对比、时间静置对比、添加合金元素对比、不同炉料对比以及不同强度铸铁加工性能对比和相同强度不同种类铸铁加工性能对比。每组对比研究中都用万能拉伸试验机进行拉伸试验来测得其抗拉强度、屈服强度和延伸率。用布氏硬度计测得其布氏硬度。用光学显微镜并参照国标对石墨形态和珠光体含量进行评级。用扫描电镜来观测珠光体的片间距大小。用动静态应变仪来进行标定和切削力大小的测定。从而来分析蠕墨铸铁的材料及工艺因素对组织及切削加工性能的影响。试验结果表明:添加过滤网后,能显著提高蠕墨铸铁的蠕化率,优化组织。能有效提高以Z14铁为主要炉料的蠕墨铸铁的抗拉强度和布氏硬度,并减小断面敏感性,但切削力略微增大。而对以高纯生铁为主要炉料的蠕墨铸铁的性能基本上无影响。与蠕化剂FeSi RE15Mg3相比,使用蠕化剂FeSiRE6Mg6能获得更高的蠕化率和更小的断面敏感性。且以高纯生铁为主要炉料的蠕墨铸铁使用蠕化剂FeSiRE15Mg3,抗拉强度达到400 MPa,但蠕化率较低,而使用蠕化剂FeSiRE6Mg6不仅蠕化率高、断面敏感性小,抗拉强度也达到350 MPa。随着Cu、Sn合金元素的复合添加,铸铁的断面敏感性都明显降低。以高纯生铁为主要炉料的蠕墨铸铁能获得较高的蠕化率、珠光体含量、抗拉强度和布氏硬度,但切削力也显著增大。而以Z14铁为主要炉料的蠕墨铸铁非常容易灰铁化,因此不适宜采用复合添加Cu、Sn合金元素的方法来提高其力学性能。随着静置时间的延长,铸铁试样的断面敏感性会显著增高,而切削力都略微降低。以高纯生铁为主要炉料的蠕墨铸铁仍能保持80%以上的蠕化率、抗拉强度也在330 MPa。而以Z14铁为主要炉料的蠕墨铸铁易灰铁化。铸铁的抗拉强度和切削力没有严格的对应关系,铸铁的石墨形态和珠光体含量对抗拉强度和切削力都有一定的影响,但石墨形态对抗拉强度的影响更加显著,而基体中的珠光体含量对铸铁切削力的影响更加显著。珠光体含量和珠光体片间距决定了布氏硬度值大小,是影响铸铁材料切削力大小的主要因素,且对布氏硬度的影响与对切削力的影响具有相同的趋势。
[Abstract]:Vermicular graphite cast iron is a kind of cast iron with excellent comprehensive properties. It has not only similar mechanical properties to ductile iron, but also similar properties to gray iron, such as casting, shock absorption and thermal conductivity. When machining vermicular iron castings in the production line, a series of machining problems have appeared, such as edge breaking, knife cutting, inadequate machining accuracy and so on. At present, there is no comprehensive study on the problem of vermicular iron machining difficulties at home and abroad. In this paper, the effects of furnace charge, creeping agent, alloy element and hot metal filtration on the processing properties of vermicular graphite cast iron are studied. The microstructure and processing properties of vermicular graphite cast iron under different processing conditions are mainly studied. The tensile strength, yield strength and elongation were measured by universal tensile testing machine in each group of comparative studies. Graphite morphology and pearlite content were graded by optical microscope and reference standard. The spacing of pearlite was observed by scanning electron microscope. The dynamic and static strain gauge was used to calibrate and measure the cutting force. The microstructure and cutting process of vermicular graphite cast iron were analyzed. The experimental results show that the creep rate and microstructure of vermicular graphite cast iron can be significantly improved and the tensile strength and Brinell hardness of vermicular graphite cast iron with Z14 iron as the main burden can be effectively improved, and the section sensitivity can be reduced, but the cutting force is slightly increased. Comparing with the vermicularizing agent FeSiRE 15Mg3, the vermicularizing agent FeSiRE 6Mg6 can obtain higher vermicularizing rate and lower section sensitivity, and the vermicularizing agent FeSiRE 15Mg3 for the vermicular cast iron with high purity pig iron as the main burden can reach 400 MPa in tensile strength, but the vermicularizing rate is lower, while the vermicularizing agent FeSiRE 6Mg6 not only has higher vermicularizing rate. With the addition of Cu and Sn alloy elements, the cross-section sensitivity of the cast iron decreases obviously. The vermicular graphite cast iron with high purity pig iron as main burden can obtain higher vermicularity, pearlite content, tensile strength and Brinell hardness, but the cutting force also increases significantly. Vermicular graphite cast iron with high purity pig iron as main burden can still keep more than 80% vermicularity. The graphite morphology and pearlite content of the cast iron have certain influence on the tensile strength and cutting force, but the graphite morphology has more significant influence on the tensile strength and the matrix. The pearlite content and the distance between pearlite sheets determine the Brinell hardness, which is the main factor affecting the cutting force of cast iron, and the influence of pearlite content on Brinell hardness and cutting force has the same trend.
【学位授予单位】：河南科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG250

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