STRUCTURIZAGTION OF STEEL PRODUCED FROM IRON  DOPED WITH NANOSIZED SILICON CARBIDE COMPOSITE POWDER 

Abstract

The features peculiar to the production of iron-based metallic composites with additions of synthesized superfine composite powders as master alloys were studied. The composite powders resulted from the interaction of nanosized silicon carbide with iron oxide and sintered iron ore concentrate (SIOC). The synthesized superfine powder composites of master alloys in the SiC–Fe₂O₃ and SiC–SIOC systems have a polyphase composition containing silicon carbide, iron silicides, and silicon oxide and oxynitride (β-SiC, SiO₂, β-Si₃N₄, Si₂N₂O, Fe₂Si, Fe₅Si₃, FeO). The average particle size of the composite master alloy powders is 130 and 150 nm. The production of iron-based metal composites with 3, 5, and 7% master alloy additions by melting in an induction furnace at 1700 °C for 40 min without a protective atmosphere proceeds through the complete dissolution of doping components and the formation of a homogeneous ferrite structure. Spectral analysis shows that the total content of admixtures in the iron-based metal composites varied from 2.0 wt.% with a 3% master alloy addition to 4.1 wt.% with a 7% master alloy addition. The resultant alloys have a nanosized pearlite structure. The iron carbide lamellas reach 20–25 nm in size and the distance between them is no greater than 150 nm. Microdiffraction patterns show α-Fe phase and nanocrystalline Fe₃C and FeC carbides The mechanical properties of the metal composites were examined. The addition of the synthesized superfine powder composites to the iron melt promoted excellent mechanical characteristics: in particular, the yield strength in uniaxial compression up to 1251 MPa, hardness (HV 10) up to 3.1 GPa, and plastic deformation up to 31.1%. The influence of different heat treatment stages on the mechanical characteristics of the alloy was analyzed. Cold rolling of pre-forged metal composites increases the yield stress to 1660 MPa and hardness to 4.4 GPa. Annealing of the metal composites at 700 °C for 2 h resulted in 750 MPa yield strength, 34.5% plastic deformation, and 2.5 GPa hardness.