Effect of Nanoadditives on the Structure and Properties of Austempered Ductile Irons

Abstract

In the present study austempered ductile irons (ADI) with an upper and lower bainitic structure with nanosized particles of cubic boron nitride cBN (50nm) are studied. The austempering modes include austenization at 900оС during an hour and isothermal retention at 280оС from 0.5 to 6 hours and at 380oС from 0.5 to 6 hours. The samples microstructure is investigated by means of an optical metallography, scanning electron microscopy and X-ray analysis. Tests for hardness, impact toughness and wear are performed. The influence of nanosized additives on the kinetic of the bainitic transformation and on the morphology of the obtained bainitic structure is studied. It is established that the changes of the bainitic cast irons microstructure under influence of the nanoparticles of cBN lead to the cast irons impact toughness and wear resistance increase. The research is aimed at expanding the scope for new ADI applications in the industry.

Effect of Nanoadditives on the Wear Behavior of Spheroidal Graphite Cast Irons

“…Bainite is an oriented structure consisting of needles α -phase (bainitic ferrite), carbides and unconverted austenite. α-phase is formed by martensitic mechanism in austenitic areas with low carbon content [1,2,8]. Upon cooling on the temperature of isotherm to ambient temperature, the part of the unconverted austenite undergoes martensitic transformation, and another part thereof remains in the structure as a retained austenite A.…”

“…In friction the retained austenite partially transforms to a strain induced martensite with the same quantity carbon as well a high carbon austenite and It appears untempered martensite with high hardness and capacity for intensive strengthening in a wear processing [8,12].…”

“…The experimental study of the wear is carried out using method and device for accelerated testing in kinematic scheme "thumb-disc" under friction over a fixed abrasive [6,8] …”

“…The role of added nanoparticles in the melt is in the changing of the graphite morphology for lamellar to vermicularis one [5], in the quantity graphite increase [6] and in the changing the substrate structure, which reflect in the increase irons' wear resistance [5][6][7][8][9].…”

Electron Microscopy Investigations of А356 Alloy Modified with Nanoparticles

“…The average nanoparticle size of SiC is 50 ± 5 nm (calculated from Singular Spectrum Analysis (SSA)-taken from nanopowder certificate). Nanoparticles were activated via currentless cladding with Cu [48], and SiC:Cu ratio was 1:0.1.…”