MELTING METHOD OF CARBON-FREE HEAT-RESISTANT STEEL Russian patent published in 2012 - IPC C22C1/02 C22C38/18 

FIELD: metallurgy.

SUBSTANCE: method involves loading to vacuum induction furnace of charge materials, melting, metal exposure under vacuum during 20-30 minutes at the temperature exceeding the metal liquidus temperature by 150-170°C at pressure of 5×10^-3-1×10^-2 mm Hg, bleeding of inert gas; at that, deoxidisers and high-reactivity alloying additives are introduced after the temperature is decreased to the values exceeding the liquidus temperature by 100-110°C in the atmosphere of inert gas at pressure of 70-250 mm Hg, and metal deoxidation is performed at three stages, first, with aluminium; then with alkaline-earth metals and finally with rare-earth metals and boron-containing alloy combinations, and nitrogen alloying is performed after introduction of all alloying additives, further pumping-out of inert gas, exposure of metal in vacuum during 7-10 minutes by introducing the nitrogen-containing alloy combination, at partial nitrogen pressure in furnace atmosphere of 600-700 mm Hg, metal exposure during 5-7 minutes till nitrogen is fully fixed and poured. Method allows melting the steel with carbon content a the level of 0.001-0.009%, nitrogen 0.05-0.1%, boron 0.003-0.01%, with high deoxidation properties with oxygen content of 0.0015-0.0010%, with the required level of heat resistance.

EFFECT: improvement of steel properties.

6 cl, 2 tbl