Master’s Thesis Defense - Kishlay Mishra
Prof. Arun M Gokhale, Advisor, MSE
Prof. Naresh Thadhani, MSE
Dr. Shrikant Bhat, ArcelorMittal Global R&D, East Chicago
"Effects of Microstructure and Strain Rate on Deformation Behavior in Advanced High Strength Steels"
Advanced high strength sheet (AHSS) steels have been extensively used in manufacturing of structural automotive body parts. They were developed to address two main issues, better crash worthiness and lower body weight to improve fuel efficiency. In these contexts, efforts have been made to develop thinner gage sheet steels, that have high strength and high ductility. HSLA steels were amongst the first types of Advanced High Strength Sheet (AHSS) Steels with relatively high ductility. Hot-stamped steels are amongst the newer generations of AHSS, increasingly finding new applications in manufacturing of structural automotive parts, due to their exceptionally high strength (around 1500MPa) and reasonably good ductility (around 5%). During conventional forming processes, these auto body sheet steels undergo deformation at a strain rate of 10-100/sec, while in a crash condition, they can experience strain rates on the order of 102 - 103/sec. Therefore, it is of interest to understand the deformation behavior of these steels over a range of strain rates.
To understand the effects of microstructure and strain rates on the deformation behavior these steel grades, uni-axial tensile tests were conducted at various strain rates for commercially produced HSLA 590, Ductibor 500® and Usibor 1500®. Microstructure of these steel grades were quantified. Fracture micro-mechanisms in the fracture surfaces were studied using quantitative fractography, profilometry, and digital image analysis.