METHOD FOR REDUCING FABRICATION LEAD TIME AND COST BY LOCALIZING GAS NITRIDED TURBINE VALVES

摘要

PURPOSE: To provide a gas nitriding method of turbine valves, the method for improving quality and life of products by performing gas nitriding on the turbine valves more effectively. CONSTITUTION: The gas nitriding method of turbine valves comprises a step of charging ammonia gas into a furnace in which the turbine valves are contained; a step of heating the turbine valves to 480 deg.C at a maximum heating rate of 75 deg.C/hr; a step of maintaining temperature of products to 480 deg.C for 2 hours; a step of controlling an inflow amount of ammonia gas such that a decomposition ratio of ammonia gas becomes 36% while rapidly heating the products to 565 deg.C; a step of maintaining the decomposition ratio of ammonia gas to 25 to 35% at a product temperature of 565 deg.C for 24 hours; a step of heating temperature of the products to 595 deg.C, and maintaining the decomposition ratio of ammonia gas to 40 to 45%; a step of maintaining temperature of the products to 595 deg.C for 36 hours; a step of stopping supply of ammonia gas, and supplying nitrogen gas into the furnace; a step of cooling the products at a maximum cooling rate of 75 deg.C/hr while maintaining supply of nitrogen gas; and a step of stopping supply of nitrogen gas and completing cooling of products when temperature of the products reaches 500 deg.C.