Metallographic Analysis on Fracture Surface of Spheroidal Graphite Cast Iron(Cast State, Tensile Test)
Abstract:
This paper mainly introduces the fracture surface of the spheroidal graphite cast iron sample under the tensile test. According to the microstructure and fracture morphological features of the sample, the strain of the sample and other related information are analyzed. Through macroscopical and microscopic observation, it can be found that the steels shrinkage cavity is quite micro or subtle, and its fracture surface is mostly composed of uniform dimple formed after high-energy plastic deformation. Outer curvature cracks are distributed at the edge of the dimple. The microstructure morphology of samples is mainly spheroidal graphite, obvious graphite covered the matrix in most area and the spheroidal graphite size is good. This study has provided some references for in-depth research and an understanding of the fracture process of spheroidal graphite cast iron subjected to tensile testing.
Key words: Spheroidal graphite Cast iron; Microstructure; fracture morphology; Tensile Test
1 Introduction
Spheroidal graphite cast iron is a type of casting material that contains graphite in nodular form, unlike gray cast iron. It is also known as nodular cast iron and spheroidal graphite for short. Sphere+calcined graphite+tempered graphite is the main component of spheroidal graphite cast iron. Its excellent combination of strength, ductility and resistance to wear, corrosion and heat make it the preferred material for many industrial applications [1], such as auto parts, agricultural parts, valve parts, pump parts and so on.
To study the tensile properties of spheroidal graphite cast iron, a tensile experiment was carried out and the corresponding metallographic examination was conducted. The paper introduces the microstructure and morphological features of the fracture surface of the sample, as well as the strain of the sample and other related information.
2 Materials and methods
2.1 Sample preparation
The tensile sample is prepared according to the corresponding standards. The surface of the sample was fulcised and the size of the specimen was 13mm×18mm×70mm.
2.2 Test simulation
The tensile test was performed in a universal testing machine (Electro 250KN)at room temperature and the speed of the test was 2mm/min.. The test force, displacement and strain were recorded.
2.3 Metallographic preparation
After the test was finished, a section was taken from the sample. The size of the sample is 16mm×9mm×2mm. After the sample was cut, it was mechanically polished and then the sample was washed and dried. Then the sample was etched in 10%HF reagent for 5sec, and then observed by optical microscope.
3 Results and discussion
3.1 Fracture surface morphology
The fracture surface of the sample was observed by optical microscope. Figure 1 shows the macroscopic morphology of the fracture surface. It can be seen that the fracture surface is relatively flat and the dimples are distributed in a regular manner, with a large number of small dimples formed by high-energy plastic deformation, and the outer curvature cracks distributed along the edge of the dimples. The fractographs indicate that the failure process is a ductile fracture process.
Fig.1. The macroscopic morphology of the fracture surface
The microstructure of Sample is observed by optical microscopy. Figure 2 shows the microstructure of sample. It can be seen that the microstructure morphology is mainly spheroidal graphite, and obvious graphite is in the matrix in most area and the spheroidal graphite size is good.
Fig.2. The microstructure of sample
3.2 Tensile properties
The information of the tensile test is showed in the Table 1. From the table, it can be seen that the maximum tensile strength of the specimen is 365.8MPa, the elongation at fracture is 8.50%, the reduction of area of the specimen is 82.2%.
Table 1. Tensile test result
4 Conclusions
The macrostructure and microstructure of the fracture surface of the spheroidal graphite cast iron sample were observed by optical microscopy and accompanied tension test. The results showed that:
(1) The fracture surface of the sample is composed of uniform dimples caused by high energy plastic deformation and outer curvature cracks are distributed at the edge of the dimple.
(2) The microstructure morphology of sample is mainly spheroidal graphite, obvious graphite covered the matrix in most area and the spheroidal graphite size is good.
(3) The maximum tensile strength of the specimen is 365.8MPa, the elongation at fracture is 8.50%, the reduction of area of the specimen is 82.2%.
This research provides an understanding of the fracture process of spheroidal graphite cast iron subjected to the tensile testing and related microstructural features.
