PSI - Issue 58

Alan Vaško et al. / Procedia Structural Integrity 58 (2024) 48–53

51

4

A. Vaško et al. / Structural Integrity Procedia 00 (2019) 000–000

a

b

Fig. 1. Microstructure of selected austenitic nodular cast irons; (a) NiMn-NCI, etched by Kallins 2; (b) NiCr-NCI, etched by Marble.

Table 2. Microstructural parameters of selected austenitic nodular cast irons. NCI STN EN ISO 945 Shape factor of graphite

Content of graphite ( % )

Equivalent diameter of graphite ( μ m )

Count of graphitic nodules ( mm -2 )

NiMn NiCr

80%VI6 + 20%V6 80%VI6 + 20%V6

0.72 0.60

36.3 26.0

78.1

9.4 7.7

132.9

The mechanical properties of chosen austenitic nodular cast irons are listed in Table 3 (values prescribed by the standard and real measured values). Nickel-manganese nodular cast iron has higher tensile strength, elongation and absorbed energy but lower hardness than nickel-chromium nodular cast iron. Both nodular cast irons have the same fatigue limit.

Table 3. Mechanical properties of selected austenitic nodular cast irons. NCI R p0.2 ( MPa ) R m ( MPa ) A ( % )

K0 ( J )

HBW 5/250/10

σ c ( MPa )

σ c /R m

NiMn

required

210–260

390–470

15–18

–

120–150

–

–

real

237.7

475.3

29.0 7–20 12.0

197.3

138.7

150

0.32

NiCr

required

210–250

370–480

–

140–255

–

–

real

251.0

374.7

42.3

150.3

150

0.40

For comparison, the mechanical properties of chosen non-austenitic nodular cast irons are listed in Table 4. Silicon-molybdenum and silicon-copper nodular cast irons have a higher yield strength, tensile strength, hardness and fatigue limit, but significantly lower elongation and absorbed energy than austenitic nodular cast irons. Different mechanical properties of individual types of nodular cast iron are caused by their different chemical compositions and consequently, different microstructures.

Table 4. Mechanical properties of selected non-austenitic nodular cast irons. NCI R p0.2 ( MPa ) R m ( MPa ) A ( % ) K0 ( J )

HBW 5/250/10

σ c ( MPa )

σ c /R m

SiMo SiCu

515.3 631.1

573.9 652.7

1.4 0.7

11.3

213.7 247.3

210 270

0.37 0.41

8.0

The results of the exposure immersion test of chosen austenitic and non-austenitic nodular cast irons are shown in Fig. 2. In all four types of nodular cast irons, the average corrosion rate (recalculated per day) gradually decreases with increasing exposure time. Nickel-chromium nodular cast iron has a lower average corrosion rate (and therefore