J Fail. Anal and Preven.(2012)12: 427-437 ring, its carbon content does not meet the requirement, while of the matrix materials of the outer ring and the roller are its chromium content exceeds the requirement In terms of displayed in Fig. 3. As the heat treatment conditions of the the former one, it is common sense that steel hardness is GCr15 steel used in the bearing are quenching and temper proportional to the carbon content in it; as to the latter one, ing, it can be observed that both the materials are composed higher chromium content will bring about more retained of acicular martensites and evenly distributed carbides. austenites, which are apt to deform under stresses in the However, more grain boundaries of the retained austenites microstructure after heat treatment. Consequently, owing to were present in the outer ring, Fig. 3a. This phenomenon is these two factors, it can be concluded that hardness of the consistent with the results of the chemical compositional outer ring of the failed bearing is intrinsically unqualified. analysis. Besides, the cage consisted of both acicular a phase As for the cage, its chemical compositions are Zn 40% (white)and B phase(black), Fig 3c, showing the typical (wt %), Cu 59%0, and Pb 1%, in accordance with the AstM microstructure of casting brass alloy C37800 lead brass requiremen Hardness Survey Metallographic Structures Table 2 lists the hardness results of the outer ring and the Etched in agent of picric acid (2, 4, 6-trinitrophenol)1.0 g, roller. It clearly reveals that the outer ring possesses lower HCI5.0 mL, and ethanol 100 mL, metallographic structures hardness than GCr15 specification, which further testifies the results of its composition. Table 2 Hardness of the failed roller bearing(hrc) Test position Outer ring Roller Specification SEM and EDS Analyses 65.3 Fracture Surface 60.2 65.5 First, fracture surface of the outer ring was observed Average using SEM. As shown in Fig 4a, dissociation steps along so w spot Moon Set woo fiae Fig 4 SEM morphologies of the fracture surface:(a)total morphology, (b) trace of friction, (c) trace of squeeze, and(d) actinomorphouring, its carbon content does not meet the requirement, while its chromium content exceeds the requirement. In terms of the former one, it is common sense that steel hardness is proportional to the carbon content in it; as to the latter one, higher chromium content will bring about more retained austenites, which are apt to deform under stresses in the microstructure after heat treatment. Consequently, owing to these two factors, it can be concluded that hardness of the outer ring of the failed bearing is intrinsically unqualified. As for the cage, its chemical compositions are Zn 40% (wt.%), Cu 59%, and Pb 1%, in accordance with the ASTM C37800 lead brass requirement. Metallographic Structures Etched in agent of picric acid (2,4,6-trinitrophenol) 1.0 g, HCl 5.0 mL, and ethanol 100 mL, metallographic structures of the matrix materials of the outer ring and the roller are displayed in Fig. 3. As the heat treatment conditions of the GCr15 steel used in the bearing are quenching and temper￾ing, it can be observed that both the materials are composed of acicular martensites and evenly distributed carbides. However, more grain boundaries of the retained austenites were present in the outer ring, Fig. 3a. This phenomenon is consistent with the results of the chemical compositional analysis. Besides, the cage consisted of both acicular a phase (white) and b phase (black), Fig. 3c, showing the typical microstructure of casting brass alloy. Hardness Survey Table 2 lists the hardness results of the outer ring and the roller. It clearly reveals that the outer ring possesses lower hardness than GCr15 specification, which further testifies the results of its composition. SEM and EDS Analyses Fracture Surface First, fracture surface of the outer ring was observed using SEM. As shown in Fig. 4a, dissociation steps along Table 2 Hardness of the failed roller bearing (HRC) Test position Outer ring Roller Specification 1 60.2 65.3 65–66 2 60.3 65.8 3 60.2 65.5 Average 60.2 65.5 Fig. 4 SEM morphologies of the fracture surface: (a) total morphology, (b) trace of friction, (c) trace of squeeze, and (d) actinomorphous fracture origin 430 J Fail. Anal. and Preven. (2012) 12:427–437 123