PITA Fiscal Year 2013 Projects

The Development of New, Inexpensive Ultra-high Strength Steels of High Fracture Toughness

Lead University: Carnegie Mellon University
PI: Warren Garrison, Materials Science and Engineering
Co-PI: Sridhar Seetharaman, Materials Science and Engineering
PA Industry: Carpenter Technology Corp

This work is directed towards the development of a new class of ultra-high strength steels combining low cost with exceptionally high fracture toughness. At the present time there are only two types of ultra-high strength steel, which combine both very high strength and high fracture toughness and steels of both types contain large amounts of cobalt and nickel. Cobalt and nickel are relatively expensive alloying additions. The first family of such steels are the secondary hardening steels such as AerMetTM100. For example, the composition of AerMetTM100 in wt. % is 0.23C-13.5Co-11Ni-3.2Cr-1.2Mo. The second family of such steels are the maraging steels which also contain large amounts of nickel and cobalt. For example, the composition of the C250 maraging steel is, in wt. %, 0.03C-18Ni-9Co-4.8Mo-0.4Ti-0.1Al. Professor Garrison has recently shown that a new medium carbon secondary hardening steel having a composition in wt. % of 0.4C-4.5Cr-2Mo-0.5W-0.5V-3Ni has a strength comparable to those of AerMetTM100 and C250 maraging steel and a fracture toughness which is even higher than those of these two steels. This new steel contains no cobalt and a relatively small amount of nickel.

The proposed work has three primary objectives. The first is to examine the effects of nickel content on the strength and fracture toughness of this steel. The second is to examine the effect of nickel content on the ductile-to-brittle transition temperature of this steel. The third is to examine the effects of the amounts of the carbide forming elements molybdenum and tungsten on the strength and fracture toughness of this steel. It is believed that by understanding the effects of these alloying elements on strength, fracture toughness and the ductile-to-brittle transition temperature the development of a new family of low cost steels having high fracture toughness over a range of strength levels is possible.