Series of nanocrystalline and TiC, TiB2, and B4C powders as dopants (3%-20%) embedded in an AISI 316L austenitic steel have been prepared and investigated by ferromagnetic resonance and magnetic measurements. The homogeneous composites with the dopants up to x = 7 vol. % exhibit superparamagnetic properties, characterized by bifurcation between the field-cooled MFC(T) and zero-field cooled MZFC(T) magnetization below Tir and a maximum at Tmax in low-field MZFC(T) curves. We found that the Tir and Tmax values depend proportionally on the dopant concentrations x. The magnetization measurements in fields above 1000 Oe suggested an induced phase transition from superparamagnetic state to ferromagnetic one but presumably without long-range magnetic correlation. An analysis of magnetic anisotropic energy barrier distributions implied that different sizes and compositional types of dopants may contribute to the superparamagnetic relaxation process. The results demonstrate the possibility of obtaining new steel-based materials with desired properties and potential applications as combining magnetic and mechanical advantages.