Reducing Microsegregation in Next-Generation High-Strength Low-Alloy Cast Steels

The next generation of high-strength low-alloy (HSLA) cast steels is characterized by high levels of strength, as well as increased levels of ductility and impact toughness. The steels discussed in this paper are 4330, Eglin steel, and AF 9628 steel. Microsegregation of alloying elements within these materials, which is the tendency for a higher concentration of alloys to accumulate between dendrite arms, is commonly realized during the cooling stages of casting and can result in substandard mechanical properties. Since this next generation of HSLA cast steels is being utilized for critical commercial and military applications requiring both high levels of strength and ductility, methods of reducing microsegregation through proper heat treatment must be examined. Current methods of reducing microsegregation after casting primarily rely on vacancy diffusion. This effect is typically accelerated through heat treatments of the cast material. Herein, diffusion models are utilized to create a model capable of predicting microsegregation reduction in these high-strength low-alloy cast steels. This model was used to simulate high-temperature heat treatments in order to determine appropriate process parameters for microsegregation reduction of carbide-forming alloying elements in the next generation of high-strength low-alloy cast steels.