固溶处理对锰镍系奥氏体球墨铸铁低温断裂特征的影响

发布时间：2018-02-02 00:33

  本文关键词： 锰元素 碳化物 固溶处理 冲击韧性 断裂机理　出处：《沈阳工业大学》2017年硕士论文　论文类型：学位论文

【摘要】：奥氏体球墨铸铁具有良好的机械性能和物理性能,自诞生起就被广泛应用于工业生产中。目前,大多数生产方式是通过添加大量镍和少量锰来得到奥氏体基体,且以常温和高温应用为主。为了探究高锰含量下,组织形貌和基体性能的变化及奥氏体球墨铸铁的低温性能,本研究通过不同含量的Mn对组织和性能造成的影响进行探究,并利用固溶处理,分析它们的断裂特征,找到一种性能上接近高镍奥氏体球墨铸铁的锰镍系奥氏体球墨铸铁。通过观察锰含量不同的奥氏体球墨铸铁的金相组织,能够发现,Mn虽然作为奥氏体化元素能够促进奥氏体形成,但对石墨的球化起抑制作用,并会加快铁液的冷却速度导致晶界上产生大量碳化物,这些碳化物会影响材料的力学性能。采用固溶处理能够使晶界碳化物溶解,提高奥氏体球墨铸铁的力学性能,但是对石墨的球化等级并无明显影响,这仍制约了性能的提高。在16Mn-8Ni、12Mn-8Ni、12Mn-10Ni和7Mn-10Ni四种种成分中,7Mn-10Ni的球化等级最高。通过观察裂纹的扩展路径,发现了断裂前后起裂区域V口附近形貌的变化,对比四组数据可以发现,16Mn-8Ni-2.3C-3Si、12Mn-8Ni-2.3C-3Si、12Mn-10Ni-2.3C-3Si和7Mn-10Ni-2.3C-3Si四种种成分的奥氏体球墨铸铁在铸态时,常温下断裂的裂纹都是在V口处的晶界碳化物上萌生并沿碳化物扩展的。但是,在固溶处理后,它们的裂纹变为在V口处的缺陷处萌生,沿石墨球扩展,这种变化与组织的力学性能发生变化有关。为了分析低温下7Mn-10Ni-2.3C-3Si奥氏体球墨铸铁的冲击韧性,选取-30℃、-60℃、-100℃和-196℃四种温度进行冲击试验。结果表明,铸态及固溶处理后的数值都随温度降低而降低,但固溶处理后性能较高。分析了低温冲击过程中屈服载荷Fy、最大载荷Fm和韧性断裂带Dmp1的变化。发现屈服载荷Fy不受固溶处理和温度的影响,韧性断裂带Dmp1和冲击韧性成正比。最大载荷Fm则表现出先增后减的变化趋势。通过分析断口形貌的改变,解释了7Mn-10Ni-2.3C-3Si奥氏体球墨铸铁的断裂机理。铸态时,7Mn-10Ni-2.3C-3Si奥氏体球墨铸铁在室温下的断裂表现出韧窝断裂与准解理断裂的混合断裂方式,在低温下的断裂则是由于晶界碳化物处产生的微裂纹扩展导致的。而在固溶处理后,7Mn-10Ni-2.3C-3Si奥氏体球墨铸铁在常温下表现出明显的韧窝断裂方式,准解理断裂形貌消失。随温度降低,会突然发生沿晶断裂,随着温度的降低,沿晶断裂面积增大,最终变为脆性断裂。
[Abstract]:Austenitic ductile iron has good mechanical and physical properties and has been widely used in industrial production since its birth. At present, most production methods are to obtain austenitic matrix by adding a large amount of nickel and a small amount of manganese. In order to study the changes of microstructure and matrix properties and the low temperature properties of austenitic ductile cast iron under high manganese content, the main applications were at room temperature and high temperature. In this study, the effects of different contents of mn on microstructure and properties were investigated, and their fracture characteristics were analyzed by solution treatment. An austenitic ductile iron of manganese and nickel series with similar properties to high nickel austenitic ductile iron was found. The metallographic structure of austenitic ductile iron with different manganese content was observed. Although mn as an austenitizing element can promote the formation of austenite, it can inhibit the spheroidization of graphite and accelerate the cooling rate of molten iron, resulting in a large number of carbides on grain boundaries. These carbides will affect the mechanical properties of the materials. The solution treatment can dissolve the carbide at grain boundary and improve the mechanical properties of austenitic ductile iron, but it has no obvious effect on the spheroidization grade of graphite. This still restricts the improvement of properties in the four compositions of 16Mn-8NiO12Mn-8NiO12Mn-10Ni and 7Mn-10Ni. 7Mn-10Ni has the highest spheroidization grade. By observing the crack propagation path, the changes of the morphology near the V mouth of the fracture initiation region are found, which can be found by comparing the four groups of data. 16Mn-8Ni-2.3C-3Si 12Mn-8Ni-2.3C-3Si. The austenitic ductile cast iron with 12Mn-10Ni-2.3C-3Si and 7Mn-10Ni-2.3C-3Si is in the as-cast state. The cracks of fracture at room temperature all germinate on the grain boundary carbides at the V mouth and propagate along the carbides. However, after the solution treatment, the cracks of the cracks begin to germinate at the defects at the V mouth and propagate along the graphite spheroids. In order to analyze the impact toughness of 7Mn-10Ni-2.3C-3Si austenitic ductile iron at low temperature, we select -30 鈩，

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