Developing High Strength-High Toughness Low Carbon Steel Using Combined V-Ti-Micro-Alloying and Different Thermo-Mechanical Treatments

Abstract

This work aims at designing and developing low carbon steel alloys to meet the high tensile strength, high ductility and high impact toughness properties. The effect of solid solution mechanism, precipitation hardening, as well as grain refinement were developed with different Manganese content (0.78-2.36wt%) combined with Vanadium(0.008-0.1wt%) and Titanium (0.002-0.072wt%) microalloying additions. The controlled thermo-mechanical treatments and chemical compositions play a big role in developing the microstructure and the corresponding mechanical properties. Therefore, the studied chemical compositions were treated thermo-mechanically by two different ways of changing start and finish forging temperatures with subsequent air cooling. The first way by start forging from 1050 to 830oC and the second from 950 to730oC. The second way of forging process developed finer grain sizes and higher ultimate tensile strengths for all the studied steel alloys. In spite of finer grain sizes, the impact toughness value was lower in the second regime due to detrimental influence of precipitation strengthening in the ferrite. A combination of 544 MPa yield strength, 615 MPa ultimate tensile strength, 20% elongation and 138 Joule impact toughness has been attained.