PSI - Issue 71

Ninad Vasant Pawar et al. / Procedia Structural Integrity 71 (2025) 134–141

135

The tapered roller bearing of a pinion gear experienced failure as shown in Fig. 1, after approximately 14000 km of running. The guide flange of the bearing cone was observed to be fractured and was completely separated from the cone. No flaking, contact fatigue, or wear-related damage was reported on the bearing except the cone fracture. Consequential damage occurred on other bearing elements, such as rollers and the outer cup. The existing case occurred during the field test of the commercial vehicle. The vehicle was left inoperable after the failure. Along with the damaged, broken cone, the pinion gear shaft was also received for analysis. 2. Experimental Procedure Detailed surface analysis of the fractured area of the cone was carried out with the help of stereoscopy, photography, and scanning electron microscopy. The fractography with help of SEM was carried out on multiple flange pieces and representative images were included in following analysis. Cone material was confirmed with the help of optical emission spectroscopy, and observations are included in Table 1. The microstructure analysis was done on the mounted sample at the groove surface as well as in the material core with the help of scanning electron microscopy. Nital etchant (2%) was used for revealing the microstructure. Micro-Vickers hardness measurement was done from groove surface and flange surface to analyze hardness variation from groove area and flange area at 0.5kg test load. Rockwell hardness measurement was done on the cone surface for conformance with the hardness specification at 150kg test load. Charpy impact test was carried out on 10×10×55mm samples made as per ASTM E370. The test was carried out as per ASTM E23. One type of sample was surface treated with a patented heat treatment process and further quench-tempered to impart a hardness of 59 HRC minimum (Gupta et al., 2018). The tempering of SAE 52100 was done between 200 °C to 230 °C. The second type of samples were case-carburized, hardened, and tempered between 190 °C to 210 °C. The impact energy of 6 samples of each was recorded. The static load-carrying capacity of cones was compared with the help of the UTM machine and sample fixture. The load is applied to the flange through a fixture punch with three equally pitched projections contacting the flange surface. The flange is supported on the die, which fits into the cone bore and provides overhang to simulate actual flange overhang conditions.

3. Results and discussion 3.1. Material composition

The material observed confirms the specifications for the SAE 52100 alloy as per ASTM A295. The details are included in Table 1.

Table 1. Chemical composition specification and observation of failed cone.

Element

C

Mn

Si

S

P

Cr

Ni

Mo

Cu

V Al

Ti

Min.

0.93 0.25 0.15 -

-

1.35 -

-

-

-

0.010 -

SAE 52100 Specification

Max. 1.05 0.45 0.35 0.015 0.025 1.60 0.25 0.10 0.25 0.050 0.050 0.0030

Observation

0.99 0.35 0.28 0.001 0.012 1.40 0.047 0.020 0.072 0.004 0.012 0.0013

3.2. Microstructural analysis The microstructure of the groove surface and core of the failed was analyzed with the help of SEM, and it is shown in Fig. 2. Fig. 2(a) shows the surface microstructure taken at the groove surface, whereas Fig. 2(b) shows the core microstructure. Surface microstructure shows carbides and carbonitrides with visible polygonal retained austenite in a tempered martensitic matrix. The core microstructure showed dispersed fine carbides in a tempered martensitic matrix. The presence of a visible level of retained austenite on the surface is due to the surface treatment, which induced carbon and nitrogen on the surface. The difference between surface and core microstructure is due to the surface treatment done to enhance contact fatigue performance of the bearing cone.