Three-Dimensional Characteristics and Morphological Evolution of Micro/Meso Pores inG20Mn5N Steel Castings
Huadong YAN,Hui JIN()
Jiangsu Key Laboratory of Engineering Mechanics, Department of Civil Engineering, Southeast University, Nanjing 211189, China
Cite this article:
Huadong YAN,Hui JIN. Three-Dimensional Characteristics and Morphological Evolution of Micro/Meso Pores inG20Mn5N Steel Castings. Acta Metall Sin, 2019, 55(3): 341-348.
Cast steel is an important metal material that is widely used in civil engineering due to its strength and ductility. However, a variety of casting defects such as micro/meso pores are usually present in the as-cast components and can lead to the degradation of mechanical properties. In this work, the initial micro/meso pores in the G20Mn5N low-alloy cast steel were investigated based on high resolution 3D X-ray tomography technology. Based on their formation mechanism and characteristics, pores were classified into gas, gas-shrinkage and shrinkage pores, and the parameters such as the number, size and sphericity of three types of pores have been counted and analyzed. Then the evolutionary behavior of micro/meso pores in G20Mn5N low-alloy cast steel specimens under monotonic tensile loading has also been studied. The results showed that the volume of gas pore was small and its sphericity coefficients were high. Compared with the gas pore, the shrinkage pore had large volume and more complex shape in space. The volume and sphericity coefficients of gas-shrinkage pore were between the gas pore and the shrinkage. Damage evolution to metallic materials can be divided into void nucleation, growth and coalescence. The void nucleation and growth law were investigated by statistical analysis, which showed that the evolution of the void density could be modeled by an empirical function, and the evolution of void average radius was not only related to void growth but also affected by void nucleation.
Fund: National Key Research and Development Program of China(2017YFC0805100);National Natural Science Foundation of China(51578137);Open Research Fund Program of Jiangsu Key Laboratory of Engineering Mechanics;Priority Academic Program Development of the Jiangsu Higher Education Institutions
Fig.1 Shape and dimension of notched specimen (unit: mm)
Fig.2 Average load-displacement curve of notched specimens and loading or unloading paths
Fig.3 Pores inspected with 3D X-ray tomography technology in the specimen gauge section(a) specimen 4 (b) specimen 5 (c) specimen 6 (d) specimen 7
Specimen
Pore type
Number
Voxel
Surface area / mm2
Sphericity
No.
Max.
Min.
Mean
Max.
Min.
Mean
Max.
Min.
Mean
4
Gas pore
98
159
20
50.66
0.08
0.02
0.03
0.70
0.51
0.56
Gas-shrinkage pore
84
678
24
89.74
0.23
0.02
0.05
0.50
0.41
0.47
Shrinkage pore
8
7315
212
1676.25
2.12
0.14
0.55
0.38
0.24
0.34
5
Gas pore
86
540
20
59.62
0.15
0.04
0.04
0.64
0.51
0.55
Gas-shrinkage pore
88
454
20
76.41
0.19
0.02
0.05
0.50
0.40
0.47
Shrinkage pore
10
779
38
289.90
0.32
0.04
0.15
0.39
0.33
0.37
6
Gas pore
102
210
20
52.04
0.09
0.02
0.03
0.66
0.51
0.55
Gas-shrinkage pore
87
622
20
115.61
0.23
0.02
0.07
0.50
0.41
0.46
Shrinkage pore
3
751
37
341.00
0.39
0.04
0.19
0.39
0.28
0.35
7
Gas pore
68
186
20
51.49
0.08
0.02
0.03
0.65
0.51
0.54
Gas-shrinkage pore
72
424
20
84.18
0.18
0.02
0.05
0.50
0.40
0.45
Shrinkage pore
11
1280
224
682.09
0.56
0.12
0.30
0.39
0.28
0.34
Table 1 Characterization informations of initial gas, gas-shrinkage and shrinkage pores in specimens 4~7
Fig.4 Morphologies and characteristics of representative micro/meso pores in G20Mn5N cast steel(a~c) gas pore (d~f) gas-shrinkage pore (g~i) shrinkage pore
Fig.5 Measured and fitted void density (N) in specimen 4 under the uniaxial tensile loading (εAxial—axial strain)
Fig.6 Evolution of average radius (Rarv) for different numbers of examined pores in the gauge section of specimen 4 during the uniaxial tensile loading
Fig.7 Scanning slices of the specimen 4 gauge section during the uniaxial tensile loading(a) εAxial=0.214 (b) εAxial=0.343 (c) εAxial=0.422 (d) εAxial=0.460
Fig.8 Pores inspected with 3D X-ray tomography technology in the gauge section of specimen 4 during the uniaxial tensile loading(a) εAxial=0.214 (b) εAxial=0.343 (c) εAxial=0.422 (d) εAxial=0.460
Fig.9 Low (a) and high (b) magnified fractured surface SEM image of specimen 4
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