PSI - Issue 18

Angelo Mazzù et al. / Procedia Structural Integrity 18 (2019) 170–182 A. Mazzù et al./ Structural Integrity Procedia 00 (2019) 000–000

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specimens, then in dry contact with rail steel specimens, finally in wet contact again with rail specimens. The damage in the tested wheel steel was evaluated in terms of wear, crack nucleation and propagation. 2. Materials and methods The tests were carried out on a bi-disc bench whose schematic is shown in Figure 1 (for details see Donzella et al (2011)). The discs were mounted on two shafts driven by independent engines, one of which can be displaced orthogonally to the shaft axis by means of a hydraulic piston, which also applies the contact load.

Figure 1. Schematic of the bi-disc testing machine.

The wheel discs were made of ER7 steel, which is one of the two steels permitted by the UIC 812.3 Standard for tread braked wheels for freight cars or passenger transportation in Europe. They were machined out of wheel rims, as close as possible to the running surface, with their axis perpendicular to the wheel tread. The wheel steels were tested in coupling with a brake block cast iron and subsequently with the rail steel R350HT EN 13674-1. The rail discs were made of 350 HT steel and were machined out of a rail head, with their axis orthogonal to the long axis of the rail. The chemical composition and mechanical properties of wheel and rail steels are shown in Table 1. The tensile properties were obtained using standard specimens extracted from the components, according to EN 6892-1 Standard. The Brinell hardness was measured on the radial section of the wheel rims in accordance with EN ISO 6506-1 Standard, in the same position as that of the disc extraction. The brake discs were extracted from cast iron brake blocks having a Brinell hardness of 230 HB and the chemical composition shown in Table 2.

Table 1. Main chemical elements and mechanical properties of the wheel and rail steels. Chemical composition (wt%) Ultimate tensile strength [MPa]

Yield strength [MPa]

Elongation [%]

Hardness HB

C

Mn

Si

S

P

ER7

0.49 0.75

0.34

0.002 0.008 910

584

15

280

350 HT

0.63 1.095

0.296 0.018 0.01

≥1175

-

≥9

355

Table 2. Chemical composition of the brake block cast iron. C S P Mn Cr

Ni Ti 3.03 0.18 1.70 0.61 0.10 0.05 0.01 0.15 1.66 0.006 0.04 0.05 Mo Cu Si V Al