Mn对ADI组织及磨损性能的影响研究

发布时间：2018-03-26 17:58

  本文选题：Mn　切入点：等温淬火温度　出处：《武汉纺织大学》2017年硕士论文

【摘要】：ADI(Austempered Ductile Iron),即等温淬火球墨铸铁,因具有优良的力学性能和耐磨性能,已成为当今最热点的材料之一。该材料是球墨铸铁通过等温淬火处理得到的以针状铁素体和富碳奥氏体为主要基体的高性能铸造合金。本课题设计的Mn含量有三组,等温淬火工艺参数有4组,通过对不同的试样进行金相组织分析、X射线衍射分析、扫描电子显微镜分析、摩擦磨损试验、表面硬度测量、磨损形貌观察和能谱分析,研究了Mn及等温淬火温度对ADI组织与磨损性能的影响。ADI的铸态组织主要包括:石墨球、珠光体、碳化物及极少量的铁素体。Mn主要以碳化物的形式存在,Mn含量的多少对石墨球化作用影响不明显,都能使球化率达到2级,石墨球大小等级达到6级。但Mn能影响铸态组织中石墨球的均匀程度和珠光体、碳化物的体积分数,Mn含量越高,石墨球分布不均,珠光体和碳化物含量增多。ADI的基体组织主要由针状铁素体和富碳奥氏体组成。随着Mn含量的增加,组织中原有的针状铁素体逐渐粗化,数量增多。且组织中残余奥氏体的含量和奥氏体中碳含量随Mn的增加而增加,这使得高Mn量的ADI受应力作用时,发生加工硬化明显,表面硬度因Mn含量增加而增大,提高了材料的耐磨性。在所研究的等温淬火温度(280℃~370℃)范围内,等淬温度低的铁素体呈细针状,等淬温度高的铁素体呈粗针状。同一试样的表面硬度随磨损的进行逐渐增高;相同Mn含量,不同试样的表面硬度随等淬温度的升高而降低,总磨损量增多,但磨损中,磨损量的幅度逐渐变小;同一等淬温度,ADI的表面硬度随Mn量的增加而升高,总磨损量减小,耐磨性增强。通过扫描电镜观察磨损形貌组织发现等温淬火温度为280℃时,微切削磨损是其主要磨损机制,切削痕浅,耐磨性好;等温淬火温度为310℃和340℃时,微切削磨损是材料的主要磨损机制,表面存在少许犁沟,切削痕加深,磨损量增加,耐磨性降低;等温淬火温度为370℃时,材料磨损表面有明显深度的切削痕,伴随少量物料剥落,材料的磨损以犁沟为主,还有少量微观切削。相同等温淬火温度下的ADI,当Mn含量为0.2%~0.5%时,犁沟及微观剥落是材料的主要失效形式;当Mn含量为0.8%时,失效形式以犁沟及切削为主。通过对试样磨损后的物相分析发现,ADI在摩擦应力的作用下发生了加工硬化,残余奥氏体转变成了马氏体增加了表面硬度。能谱分析发现ADI组织中的石墨球会脱落到摩擦副表面,形成减磨层,提高ADI耐磨性。
[Abstract]:ADI(Austempered Ductile iron, or isothermal quenched ductile iron, has excellent mechanical properties and wear resistance. This material is a kind of high performance cast alloy with acicular ferrite and carbon-rich austenite as the main matrix, which is obtained by isothermal quenching of ductile iron. There are three groups of mn content designed in this paper. There are 4 groups of isothermal quenching process parameters. X-ray diffraction analysis, scanning electron microscope analysis, friction and wear test, surface hardness measurement, wear morphology observation and energy spectrum analysis were carried out on different samples. The effects of mn and isothermal quenching temperature on the microstructure and wear properties of ADI. The presence of carbides and ferrite. Mn mainly in the form of carbides has no obvious effect on the spheroidization of graphite, and the spheroidization rate can reach 2 order. However, mn can affect the homogeneity of graphite spheroids and pearlite in as-cast structure. The higher the content of mn in carbides is, the more uneven the distribution of graphite spheroids is. The matrix structure of pearlite and carbides increased. ADI was mainly composed of acicular ferrite and carbon-rich austenite. With the increase of mn content, the acicular ferrite in the microstructure gradually coarsened. The amount of residual austenite and the content of carbon in austenite increase with the increase of mn, which makes the ADI with high mn content work hardening obviously, and the surface hardness increases with the increase of mn content. The wear resistance of the material is improved. In the range of isothermal quenching temperature of 280 鈩，

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