Issue 37

D. Angelova et alii, Frattura ed Integrità Strutturale, 37 (2016) 249-257; DOI: 10.3221/IGF-ESIS.37.33 250 E XPERIMENTAL WORK Material and specimens or this study two spring steels were used: Steel EN10270-1SH/ DIN 17223C (Steel A) for conducting own fatigue experiments, [3] and BS250A53/DIN 55Si7 (Steel B), for using some already published results, [4, 5] and making comparative analysis with Steel A. Both, their microstructure and chemical compositions, are shown in Fig. 1 and Tab. 1. (a) (b) Figure 1 : Microstructures of: (a) Steel A; (b) Steel B with schematic presentation (A-Prior austenite grain boundaries, B-Martensite laths). Chemical composition. wt % C Mn P S Si Al Cr Ni Cu Mo N 2 EN 10270-1 SH (DIN 17223C) 0.819 0.760 0.010 0 .001 0.257 0.034 0. 251 0.016 0.011 0.003 0.005 BS 250A53 (DIN 55Si7) 0.52-0.57 0.8-1.0  0.05  0.05 1.8-2.1 - 0.2-0.3  0.3 - 0.01-0.06 - Mechanical properties Ultimate tensile strength, MPa Yield stress, MPa Elongation, % EN 10270-1 SH (DIN 17223C) 1522 1217 BS 250A53 (DIN 55Si7) 1610 1440 9.3 Table 1 : Chemical composition and mechanical properties of examined steels. F