PSI - Issue 13

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

1531

5

Table 3. Microstructure of the specimens. Melt Microstructure

Content of ferrite ( % )

Shape factor

Equivalent diameter of graphite ( μ m )

Count of graphitic nodules ( mm -2 )

(according to STN EN ISO 945)

GJS-SiMo GJS-SiCu

90%VI6 + 10%V6 – Fe80 90%VI6/7 + 10%V6 – Fe15

0.88 0.84

31.2 24.3

122.8 172.4

59.4 19.7

Results of mechanical tests (tensile test, impact bending test and Brinell hardness test) are given in Table 4. The specimen of GJS-SiCu has higher yield strength R p0,2 , tensile strength R m and Brinell hardness HBW, but lower elongation A and absorbed energy K0 than the specimen of GJS-SiMo. That is related to the microstructure of the specimens, especially to the character of matrix (content of ferrite and pearlite) and also to the size of graphite and count of graphitic nodules.

Table 4. Mechanical properties of the specimens. Melt R p0,2 ( MPa ) R m ( MPa )

A ( % )

K0 ( J )

HBW 10/3000/10

GJS-SiMo GJS-SiCu

515.3 631.1

573.9 652.7

1.4 0.7

11.3

213.7 247.3

8.0

For the fatigue tests, 15 specimens from both melts were used to obtain Wöhler fatigue curves σ a = f(N) and determine the fatigue strength σ c for N = 10 7 cycles. Results of fatigue tests (relationship between stress amplitude σ a and number of cycles to failure N f ), obtained at low frequency cyclic loading (f  75 Hz), are shown in Fig. 3. The number of cycles to failure increases with a decreasing stress amplitude. The values of fatigue strength σ c , determined for N = 10 7 cycles, in comparison to tensile strength R m are given in Table 5. The specimen of GJS-SiCu has higher tensile strength R m , as well as fatigue strength σ c , than the specimen of GJS-SiMo. Results of experiments have shown that the fatigue strength of nodular cast irons increases with an increasing tensile strength what corresponds to previous study (Vaško 2017).

a

b

Fig. 3. Wöhler curves σ a = f(N); (a) GJS-SiMo, σ c = 210 MPa; (b) GJS-SiCu, σ c = 270 MPa.

In comparison to unalloyed types of nodular cast irons (Vaško 2017), the specimen of GJS-SiCu has higher tensile strength and fatigue strength than the specimens of non-alloyed nodular cast irons (the difference is more than 10%). The specimen of GJS-SiMo has higher tensile strength but a slightly lower fatigue strength than the specimens of non-alloyed nodular cast irons.