METHOD FOR SURFACE TREATMENT OF HEAT-RESISTANT STAINLESS STEEL Russian patent published in 2023 - IPC C23C8/26 C23C8/02 C21D1/18 C23G1/08 

FIELD: steel processing.

SUBSTANCE: methods for chemical-thermal treatment of steel, namely, methods for depassivation of steel surface with a chromium content of 16% or more, to be used when hardening steel in vacuum furnaces. The method includes preparation for depassivation and depassivation of the surface of the part, whereas the preparation the surface of the part includes cleaning from contamination, and depassivation is carried out in stages: 1) heat treatment of the part in a vacuum hardening furnace with heating to a temperature of 1000-1050°C, the residual pressure in the furnace chamber is not more than 2 mbar; 2) exposure of the part until it is completely warmed up, the residual pressure in the furnace chamber is not more than 2 mbar; 3) cooling of the part in nitrogen or argon with a purity of at least 99.99%, the residual pressure in the furnace chamber during heating and exposure is not more than 2 mbar; 4) moving the part for 30 minutes into a vacuum chemical-thermal treatment oven; 5) treatment of the part with a saturated solution of ferric chloride FeCl₃; 6) additional oxidation, which includes heating the part in a nitrogen atmosphere to a temperature of 500°C, the residual pressure in the furnace chamber is 0.3 bar; 7) after equalizing the temperature of the part, replacing nitrogen in the furnace chamber with nitrous oxide, exposure for 2 hours; 8) replacement of nitrous oxide with ammonia in the furnace chamber; 9) repeating steps 6-8; 10) nitriding without removing the part from the furnace.

EFFECT: more adapted steel surface for further nitriding.

2 cl, 1 dwg, 11 tbl