High-nitrogen 23Cr9Мn1N steel manufactured by aluminothermy under nitrogen pressure: structure and mechanical properties

摘要

High-nitrogen steels are promising materials possessing a combination of high properties of strength, ductility and corrosion resistance. However, powerful and complex equipment is required for manufacture of high-nitrogen steels by metallurgy under high nitrogen pressure. From energy-saving viewpoint, aluminothermy or reduction of metal oxides by metallic aluminum is alternative and one of the most attractive techniques. High temperature synthesis process in this case occurs due to the chemical energy of exothermic oxidation-reduction reaction. In the present work, the microstructure and mechanical properties of high-nitrogen steel 23Cr9Мn1N (wt.%) manufactured by aluminothermic SHS-metallurgy under nitrogen pressure using thermodynamic modeling are investigated. The melt was saturated with nitrogen simultaneously from the gas phase and chromium nitrides in the charge. As-cast steel has ferrite-austenitic structure with attributes of austenite discontinuous decomposition with Cr2N precipitations. Forging at T = 1150-1170°C of the cast steel leads to a refinement of the structure and increase the austenite fraction in the steel. After heat treatment of the forged sample (quenching in water from 1200°C), there is a single austenite phase. The analysis of change of austenite FCC lattice parameter in the process of structure evolution under hot plastic deformation and heat treatment is carried out. Investigation of mechanical properties showed a combination of high values of strength and plasticity of steel after quenching. The conclusion is drawn that high-nitrogen steel which is not worse in mechanical properties of steel obtained by electroslag remelting under a nitrogen pressure, can be obtained by aluminothermy.