PSI - Issue 13

Alan Vaško et al. / Procedia Structural Integrity 13 (2018) 1527–1532 Alan Vaško/ Structural Integrity Procedia 00 (2018) 000–000

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3

Melting was realised in an electric induction furnace at the Department of Foundry Engineering at Brno University of Technology, Czech Republic. Charge composition of the melts is given in Table 1. The basic charge of the melts was made up of 60 % of steel and 40 % of pig iron with additives for regulation of the chemical composition, i.e. carburizer, ferrosilicon FeSi75, ferromolybdenum FeMo65 or copper. The content of those additives was chosen to achieve required chemical composition of the melts and eutectic degree approximately S C  1.0. For modification the FeSiMg7 modifier was used and for inoculation the FeSi75 inoculant was used.

Table 1. Charge composition of the melts. Melt

Charging raw materials ( kg ) steel pig iron

carburizer FeSi75

FeMo65

Cu

modifier FeSiMg7

inoculant FeSi75

cover sheet

GJS-SiMo GJS-SiCu

27 27

20 20

1.2 1.1

2.1 2.1

1.1

0.5 0.5

0.4 0.4

3 3

0.7

Both types of nodular cast irons were cast into sand molds in the shape of the Y blocks. The resultant chemical composition of the melts is given in Table 2. Test specimens for structural analysis, mechanical tests and fatigue tests were machined from the Y blocks.

Table 2. Chemical composition of the melts. Melt

Content of chemical elements ( weight % ) C Si Mn P S

Cr

Mo

Cu

Ni

Al

Mg

S C

GJS-SiMo GJS-SiCu

3.021 3.281

4.094 4.156

0.376 0.363

0.026 0.028

0.032 0.037

0.084 0.072

0.938 0.009

0.115 1.394

0.059 0.055

0.027 0.031

0.039 0.049

1.002 1.096

The metallographic analysis of the specimens was done by the light metallographic microscope Neophot 32. The specimens for metallographic analysis were prepared by usual metallographic procedure. Microstructure of the specimens was evaluated according to STN EN ISO 945 (STN 42 0461) and by automatic image analysis (using the NIS Elements software) (Skočovský 2007, Belan 2014). The subject of image analysis was evaluation of the shape factor, equivalent diameter of graphite, count of graphitic nodules per unit area and content of ferrite. The tensile test was performed according to STN EN ISO 6892-1 by means of the testing equipment Instron 5985 with a loading range F = 0 to 50 kN. For the tensile test, cylindrical test specimens with diameter d 0 = 10 mm and measured length l 0 = 50 mm were used. The impact bending test was executed according to STN EN ISO 148-1 by means of the Charpy hammer PSW 300 with a nominal energy of 300 J. For the impact bending test, test specimens of square cross-section with a width a 0 = 10 mm and length l 0 = 55 mm were used. The Brinell hardness test was done according to STN EN ISO 6506-1 by means of the testing equipment CV-3000 LDB with a hard-metal ball of diameter D = 10 mm forced into specimens under the load F = 29 430 N (3000 kp) (Kopas 2014). The values of mechanical properties were determined as an average of three measurements. The fatigue tests were carried out according to STN 42 0362 at low frequency sinusoidal cyclic push-pull loading (stress ratio R = –1) at ambient temperature (T = 20  5 °C). They were realised in the high cycle fatigue region (from 10 5 to 10 7 cycles) at frequency f  75 Hz using the fatigue experimental machine Zwick/Roell Amsler 150HFP 5100 (Fig. 1 a,b). For the fatigue tests, specimens of circular cross-section with a diameter d 0 = 8 mm were used. Shape and parameters of the specimens for the fatigue tests are shown in Fig. 1c; 15 specimens from both melts were used to determine the fatigue characteristics (relationship between the amplitude of stress σ a and number of cycles to failure N f , as well as the fatigue strength) (Trško 2018).