Effect of Boron Addition on Microstructure and Corrosion Behaviour of Leaf Spring Steel in Automotive Suspension Systems

This study investigates the impact of adding boron as a microalloying element to low silicon spring steel grades commonly used in automobile suspension systems. Boron enhances grain refinement, hardenability, strength, toughness, heat treatment response, and potentially corrosion resistance. Corrosion significantly affects suspension system lifespan in automotive applications due to environmental factors like dust and mud. A new spring steel grade with boron microalloying was developed at Visakhapatnam Steel Plant to improve mechanical and corrosion properties. The study examined conventionally produced spring steel grades subjected to quenching and tempering at different temperatures. Microstructural analysis was conducted using optical microscopy and SEM, while corrosion behavior was assessed in a 3.5 wt% NaCl environment through open-circuit potential and potentio-dynamic polarization tests. The study established that trace amounts of boron as a micro-alloying element in spring steel significantly influence both microstructural morphology and corrosion rate. The addition of boron increases the quantity of tempered martensite while reducing retained austenite and bainite, resulting in superior corrosion resistance in a 3.5 wt% NaCl environment. Oil quenching was found to be preferable over water quenching to prevent surface microcracks in both boron-added and non-boron spring steels.