ION-PLASMA NITRATION OF LONG-SIZED STEEL PART Russian patent published in 2014 - IPC C23C8/36 

FIELD: metallurgy.

SUBSTANCE: proposed method comprises part heating, isothermal curing, pre-nitration, final nitration and cooling down. Cooling is imitated from 530°C to 370-390°C for 100-140 minutes in glow discharge plasma. Then, cooling is conducted to 240-260°C for 100-140 minutes. Final cooling to 140-160°C for 100-140 minutes is executed in furnace without plasma effects. Ionising gas feed is effected in cycles. At heating to 200-220°C gas mix of hydrogen, nitrogen and methane is fed for 15-20 minutes. Hydrogen is fed at heating to 400-440°C for 100-140 minutes at isothermal holding for 20-40 minutes. Hydrogen is fed for 20-20 minutes at further heating to 480°C. Pre-nitration is performed with hydrogen and nitrogen involved for 100-140 minutes. Final nitration is performed with involvement if nitrogen, hydrogen and methane for 14-16 houses. Cooling from 530°C - 370-390°C is [performed in atmosphere of nitrogen and hydrogen for 120 minutes while final cooling to 150-170°C for 240 minutes is conducted with participation of nitrogen only.

EFFECT: preserved geometrical sizes, metal surface resisting oxide film formation.