PSI - Issue 14

S Usha Rani et al. / Procedia Structural Integrity 14 (2019) 142–149 Author name / Structural Integrity Procedia 00 (2018) 000–000

143

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wheel. It resists the swaying of vehicle during cornering or due to road irregularities as shown in the Fig. 1. During cornering, the ASB is designed such a way that, a force acts on either side of the vehicle to rise or drop, that resist the swaying of the vehicle. This force twists the stabilizer bar. The bar’s resistance to twist, limits the body lean during cornering. Thus, the main function of the stabilizer bar is to control the body from rolling during cornering, which is also influenced by the wheel load shift and the change of chamber angle (Khartode et al. (2016)). These anti roll bars undergo a combination of bending and torsional fatigue during its service. The fatigue occurs under the combined action of bending and torsional stresses, which is reversible in nature. The crack initiates at the highly stressed region of the bar (Bayrakceken et al. (2006)), which is around the bend region of the tube. Boron (B) steels are usually used in automotive parts that undergo heat treatment due to its hardenability. The 26MnB5 martensitic steel is used in this study, is a manganese-boron steel which exhibits a higher hardenability owing to the presence of B. A small addition of B significantly increases the hardenability of steel. The hardenability is enhanced by segregation of B along the grain boundary which tends to suppress the ferrite nucleation by reducing the grain boundary energy and without affecting the growth rates (Mejia et al. (2011)). The 26MnB5 provides high strength properties after quenching because of the presence of hardenability enhancer like B and Mn. It was concluded by Jennarong et al. (2009) that chemical composition, austenization temperature and cooling rate are the significant factors that affect the mechanical properties and microstructure development. In the hot rolled state, the 26MnB5 typically exhibits ferrite-pearlite microstructure. The steel is welded using high frequency electrical resistance welding (ERW), which is one of the most extensively used method for production of longitudinal seam welded steel tubes (Kim et. al (2007), Wright (1999)). The tubes were hardened above Ac3 temperature and followed by quenching in a sealed quench furnace. The fatigue properties are usually correlated with mechanical properties. The fatigue is also sensitive to microstructure and thus microstructure also decides fatigue life of the component. The fatigue strength will be generally higher in the material with higher ultimate tensile strength i.e., a steel with martensite microstructure. In the present work, the tempering was done at varied temperature and time using design of experiments (DoE) method and the tempering parameters were optimized.

Fig. 1: A schematic of Axle stabilizer bar (Mason (2014))

2. Materials and Method 2.1. Material investigated

The material analyzed in this study is SAE 26MnB5 steel. The chemical composition is listed in the Table 1. This composition is selected based on the required strength after heat treatment. The 26MnB5 steel tube of dimension 25x3.6 mm was taken for the study.

Table 1. Composition of SAE 26MnB5. C Si Mn P

S

Cr

Ti

B

Mo

Nb

0.267

0.278

1.22

0.0158

0.0037

0.135

0.0021

0.034

0.112

<0.001