Microstructure and mechanical properties of austenitic stainless steels manipulated by trace TiC–TiB2 nanoparticles

It is difficult to simultaneously increase strength and toughness of austenitic stainless steels through traditional heat treatment and alloying. However, adding nano-sized ceramic particles is a potential method to manipulate the microstructure and mechanical properties of austenitic stainless steels. In this study, TiC–TiB2 nanoparticles were introduced into austenitic stainless steel using an aluminum master alloy. Adding 0.02 wt% nanoparticles effectively refined the substrates including the dendritic ferrite and austenite and reduced the grain size from 23.7 μm to 18.4 μm. The edge-to-edge model indicated that the nanoparticles act as heterogeneous cores to facilitate the nucleation rates. For mechanical properties, the addition of nanoparticles simultaneously enhanced the hardness, yield strength, tensile strength and impact toughness of the austenitic stainless steels without sacrificing the ductility. The yield strength and tensile strength of as-cast austenitic stainless steels were enhanced by 4.8% and 2.1%, 7.2% and 3.9%, 10.0% and 5.7% at the temperatures of 20 °C, 200 °C, and 400 °C, respectively. The impact toughness was improved by 4.2%, 5.9%, and 4.3% at the temperatures of −20 °C, 0 °C, and 20 °C. Also, the presence of nanoparticles increased the yield strength and tensile strength of forged austenitic stainless steels by 16.6% and 5.9%, 17.7% and 7.7%, 18.5% and 12.2% at the temperatures of 20 °C, 200 °C, and 400 °C, respectively. The impact toughness was increased by 11.6%, 8.6% and 11.3% at the temperatures of −20 °C, 0 °C, and 20 °C. The nanoparticles refined the grains, inhibited dislocation movement, scattered large cracks and distributed the external loads more uniformly to strengthen and toughen the austenitic stainless steels. In wear tests, the nanoparticle reinforced austenitic stainless steels showed higher wear resistance against adhesive wear and abrasive wear by impeding the nucleation and growth of cracks, retarding the dislocation migration and plastic deformation and bearing the external loads. The wear volumes of as-cast and forged austenitic stainless steels were reduce by 15.7% and 21.5%. This innovative approach provided a promising strategy to produce high-performance austenitic stainless steels and serve as a reference in the development of other nanoparticle reinforced ferrous materials.