Characterization of TiN Precipitates and It’s Morphology in Spring Steel for Commercial Vehicle Leaf Spring Suspension

Leaf springs are used for vehicle suspension to support the load. These springs are made of flat sections of spring steel in single or in stack of multiple layers, held together in bracketed assembly. The key characteristics of leaf spring are defined as ability to distribute stresses along its length and transmit a load over the width of the chassis structures. The most common leaf spring steels are carbon steels alloyed with Cr and micro-alloyed with Ti, V and Nb. The specific thermomechanical process and alloying elements result in specific strength and fatigue properties for spring steels. The unique properties which facilitate use of spring steel in leaf spring suspensions are ability to withstand considerable twisting or bending forces without any distortion. The microstructure of these steel determines the performance and reflects the process of steel manufacturing. The performance is mainly determined by evaluating fatigue life durability. The microstructural phases mainly precipitate of carbides play a vital role in fatigue life. At one side, controlled size and morphology helps in performance whereas coarse size of the precipitates is detrimental to fatigue life. In this work, attempt was made to characterize the microstructure which includes TiN precipitates and various steel phases. Detailed analysis on TiN particle size and morphology was carried out. Optical microscopy and Electron microscopy along with EDX analysis were utilized for characterization. The microstructural details were also correlated with fatigue failure of leaf spring.