13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- industry, its production technology adopted the axle standard of AAR M-101[6]. Present research is based on the fatigue tests by a replication technique of this material. Different surface treatment times are chosen for five groups of specimens. The influence of surface rolling time on short crack propagation, crack density, and fatigue life is revealed. 2. Materials, Rolling Simulation, and Replication Tests 2.1. Test Materials and Specimens Test material of present work is LZ50 axle steel. Its chemical composition and mechanical properties are shown in Tables 1 and 2, respectively. The heat treatment is double normalizing and then tempering in accordance with the Chinese railway standard, TB 2945-1999. After heat treatment, the microstructure of material is coarse ferrite particles and layered pearlite particles. The banded structure is quite obvious (Figure 1a), the mean value of intervals between two rich pearlite bands, d2, is about 109 μm with high dispersion. Gathering effects exist in both ferrite structure and pearlite structure (Figure 1b). Average equivalent diameters for ferrite grains, d1, is 14.6 μm[7]. Totally 33 smooth axial hourglass shaped specimens with 10 mm diameter were machined (Figure 2). Table 1. Chemical composition of LZ50 axle steel (wt. %) C Si Mn Al Cr Ni Cu P S 0.47 0.26 0.78 0.021 0.02 0.028 0.15 <0.014 <0.01 Table 2. Mechanical properties of LZ50 axle steel σb / MPa σs / MPa δ / % Ψ / % E / MPa 656.43 383.57 54.7126.57209750 Figure1. Low (a) and high (b) magnified OM images of LZ50 axle steel after heat treatment Figure 2. Schematic of shape and dimension of the specimen for fatigue test (Unit: mm) 2.2. Surface Rolling Simulation ×500 Ferrite Pearlite (b) ×100 (a) Banded
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