Formation of a Multilevel Hierarchical Mesosubstructure by Cross Rolling and Its Influence on the Mechanical Behavior of Austenitic Steel

Resumo

A multilevel hierarchical mesosubstructure is experimentally shown to form in metastable austenitic steel subjected to multipass cross rolling in the temperature range 950-75№C. A multilayer mesosubstructure with highly refined grains, changed grain geometry and microhardness builds up between the macro- and microlevels. Its outer layer has a finely dispersed structure and the highest microhardness H_μ = 3400 MPa. The two underlying layers are composed of globular grains 0.9 μm in diameter and exhibit the respective close microhardnesses 3100 and 3000 MPa. The near-axial layer has elongated grains of a fiber-band structure with nanosized width. Between the micro- and nanolevels, a nanosized hierarchical mesosubstructure is formed in all band structures, with the mesosubstructure of nanosized carbides and cardonitrides precipitated at low-angle boundaries. Despite a certain decrease in the steel plasticity in uniaxial tension, such a multilevel mesosubstructure causes a multiple increase in its fatigue life. The formation of hierarchical mesosubstructures is associated with the mechanism of plastic distortion under the conditions of the crystal lattice curvature, when bifurcational structural states arise in its interstices. Multilevel hierarchical mesosubstructures have a strong positive effect on the mechanical behavior of solids, by increasing their strength, wear resistance, and fatigue life.