Effect of aging temperature on the precipitation behavior and mechanical properties of Fe–Cr–Ni maraging stainless steel

Abstract

Aging is an important heat treatment process for maraging stainless steel. During aging, the interaction between intermetallic compounds and dislocations has a significant impact on the mechanical properties of the material. In this article, the effect of aging temperature on the precipitation behavior and mechanical properties of Fe–Cr–Ni maraging stainless steel was studied by means of a three-dimensional atom probe (3DAP) and high-resolution transmission electron microscopy (HRTEM). The results show that coherent Ni3(Ti, Al) precipitates by heterogeneous nucleation from Ni/Ti/Al coclusters formed at defects (mainly dislocations) in the range of 350–450 °C, which leads to a rapid increase in strength and a sharp decrease in toughness. At 450–500 °C, the interface between Ni3(Ti, Al) and the matrix gradually changes from coherent to semicoherent, and an increase in the equivalent precipitate radius is accompanied by a decrease in their density. The tensile strength of the material reaches its peak value, and the toughness is improved. Within the range of 500–600 °C, Ni3(Ti, Al) continues to grow, aggregate and coarsen, and the amount of reverted austenite increases significantly. Both effects lead to a prominent decrease in the tensile strength and a substantial increase in toughness. The Ni3(Ti, Al) grows axially along the <111> dislocations through tube diffusion. The radial growth is parallel to [110]α and [11‾2]α, and the process is affected by the climbing and slipping of misfit edge dislocations. The strength increment of precipitates with different sizes formed at the peak aging temperature is calculated according to the critical transition radius, and the superposed results of the cutting and bypassing mechanisms during the yielding stage are found to be consistent with the experimental data, indicating that the two mechanisms work simultaneously. The findings provide a more accurate method for predicting the yield strength of materials.