PSI - Issue 51

Alan Vaško et al. / Procedia Structural Integrity 51 (2023) 129–134 A. Vaško et al. / Structural Integrity Procedia 00 (2022) 000–000

131

3

Nickel ensures a homogeneous austenitic matrix, increases strength and elongation, but has little effect on yield strength and hardness. Chromium is a strongly carbide-forming element and therefore promotes the precipitation of carbon in the form of carbides. The solubility of chromium in the austenitic matrix is approximately 0.5%; above this concentration, ferromagnetic carbides of the types (FeCr) 3 C and (FeCr) 7 C 3 precipitate, increasing corrosion resistance, wear resistance, strength, and improving properties at high temperature. However, the presence of more carbides increases hardness and significantly reduces the machinability of the castings. The addition of manganese is used to stabilize the austenitic matrix and reduce production costs. Manganese does not cause any problems in the production of austenitic cast iron if its content is below approximately 2% (Kaňa 2017, Otáhal 2009, Sýkora 2000). 2. Experimental material and methods The study of fatigue behaviour was carried out on austenitic nodular cast iron alloyed with 20% nickel and 2% chromium. In accordance with STN EN 13835, this grade of nodular cast iron is designated EN-GJSA-XNiCr20-2 by symbol and 5.3500 by number. To compare the fatigue properties, alloyed nodular cast irons with a ferrite-pearlitic matrix (EN-GJS-X300SiMo4-1) and a pearlite-ferritic matrix (EN-GJS-X300SiCu4-1.5) were used. Melting was done in an electric induction furnace. The sandwich method was used for modification and inoculation in a casting ladle. The melt was cast in the form of Y-shaped blocks into sand molds. Table 1 shows the charge composition of the melt EN-GJSA-XNiCr20-2. The charge was made up of steel, pig iron, carburizer, ferrosilicon, nickel, chromium, and ferromanganese. FeSiMg7 modifier and FeSi75 inoculant were used for modification and inoculation. The composition of charging raw materials was chosen in order to achieve the required chemical composition and austenitic matrix. Table 2 provides information on the resulting chemical composition of the melt.

Table 1. Charge composition of the melt EN-GJSA-XNiCr20-2. Charging raw materials ( kg )

Modifier and inoculant ( kg )

Steel

Pig iron

C

FeSi75

Ni

Cr

FeMn80

Modifier FeSiMg7

Inoculant FeSi75

Cover plates

23.5

17.5

1.0

1.4

12.2

1.7

0.6

0.7

0.4

3.0

Table 2. Chemical composition of the melt EN-GJSA-XNiCr20-2. Content of chemical elements ( weight % )

Eut. degree

Elements

C

Si

Mn

P

S

Ni

Cr

Cu

Mo

Al

Mg

Sc

norm

max 3.00

1.50– 3.00

0.50– 1.50

max 0.08

18.0– 22.0

1.00– 3.50

max 0.50

–

–

–

–

–

real

< 0.015

2.284

2.305

1.079

0.025

19.77

1.859

0.033

0.012

0.036

0.078

0.73

Test specimens for microstructural analysis, mechanical tests, and fatigue tests were made from the Y-blocks. Subsequently, the following experiments were performed on these specimens:  metallographic analysis according to STN EN ISO 945, including automatic image analysis (using the NIS Elements software) on the specimens prepared by standard metallographic procedure;  tensile test according to STN EN ISO 6892-1 on three test specimens of circular cross-section with diameter d 0 = 10 mm and measured length l 0 = 50 mm;  impact bending test according to STN EN ISO 148-1 on three test specimens of square cross-section with a width a 0 = 10 mm and length l 0 = 55 mm without a notch;  Brinell hardness test according to STN EN ISO 6506-1 using a hardmetal ball with a diameter of D = 5 mm forced into the specimen under a load F = 2452 N;