PSI - Issue 4

Zoran Odanovic / Procedia Structural Integrity 4 (2017) 56–63 Author name / Structural Integrity Procedia 00 (2017) 000 – 000

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100 μm i n diameter and from 25 to 40 μm in depth. Corrosion pits were observed to connect with non-metallic inclusions displayed in Fig. 8. Qualitative EDX analysis was performed on non - metallic inclusions, and presented in Fig. 8 as spectrum 1 and compared to that of the matrix material presented as spectrum 2 . Results of the quantitative analysis of the non-metallic inclusion and the matrix material near the axle surface are presented in Table 5. Based on the chemical composition presented as Spectrum 1, presence of non-metallic inclusions of different types, such as (Fe,Mn)S, FeO, Al 2 O 3 , MnO, could be assumed. Analyzed inclusion is located at the crack initiation in axle surface continuing on corrosion pit and spreading through the soft ferrite. For comparison, results of the quantitative EDX analysis of the base material are also presented in Table 6. Fig. 8 could be used as an illustration for the primary mechanism of crack initiation and crack formation at corrosion pits. Formed cracks propagate through the soft ferrite in ferrite - perlite microstructure, supported with presence of the non-metallic inclusions in structure. These initial cracks, under the complex stress state and exploitation conditions, lead to formation of the tooth-like cracks in zone labeled as A in Fig. 4. Mechanism of the crack propagation until the final fracture was suggested previously.

a) wide, shallow shape b) elliptical shape Fig. 7. Corrosion pits in the axle material cross section at the transition radius zone AR from Fig. 4.

Specrum 1

Specrum 2

Fig. 8. Axle surface in a cross section (SEM) and EDX analyzed points (Spectrum 1 and Spectrum 2)

Table 6. Chemical composition of the analyzed points in Fig. 8. by EDX

Analysis of the inclusion located in the crack – Spectrum 1

Analysis of the base material – Spectrum 2

Element

Weight, %

Atomic, %

Element

Weight, %

Atomic, %

C K O K Al K S K Mn K Fe K Totals

37.69 15.41 0.22 1.81 2.27 42.60 100.00

63.14 19.38 0.16 1.14 0.83 15.35

C K O K

23.17 4.23 0.50 72.09 100.00

55.22 7.57 0.26 36.95

Mn K Fe K Totals