SHS Introduction of Nitrogen in the Composition of Alloy Steel under Gas Pressure

Abstract

The possibility of producing cast alloyed nitrided steel (up to 1.3 wt % N) by SHS metallurgy is shown. The initial mixture for making alloy cast steel includes iron, chromium, manganese, nickel, molybdenum, vanadium, silicon, and aluminum oxides. Chromium nitride is used as the main nitrogen source. Initial mixtures are shown to be capable of burning over a wide range of reagent ratios, and the combustion temperature exceeds the melting temperature of the condensed combustion products (steel, reducing-metal oxide), which makes it possible to perform their gravitational separation and to make steel in an as-cast form. Experimental studies are carried out in a reactor under nitrogen pressure and in a centrifugal installation under the combined action of overload and pressure to exclude the spread of a mixture during combustion. When the pressure in the reactor is increased from 0.1 to 5.5 MPa, the nitrogen content in steel alloyed with chromium, manganese, nickel, molybdenum, vanadium and silicon is found to increase from 0.4 to 1.3 wt %. Under overload (150g) and an increase in the pressure from 0.1 to 1 MPa, the nitrogen content increases from 0.4 to 0.55 wt %. According to X-ray diffraction and electron-probe microanalysis data, the base of the steel has the γ-Fe lattice and is a solution of alloying elements in iron. The shift of the diffraction peaks and their broadening indicate the dissolution of alloying elements in iron. α-Fe precipitates and point inclusions of vanadium, chromium, and impurity-aluminum nitrides are also detected.