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Ammonia gas is introduced into a stainless-steel vacuum-sealed chamber within the nitriding furnace; the temperature is then raised to 520°C and maintained for an appropriate period of time—ranging from 3 to 90 hours depending on the workpiece material and the desired properties of the nitrided layer. This process results in the formation of a nitrogen-rich strengthened layer on the surface of the workpiece, thereby imparting high hardness, excellent wear resistance, a high fatigue limit, and good durability. Operating method: 1. The mold prior to nitriding must be a workpiece that has undergone normalizing or quenching and tempering treatment. 2. First, wipe the surface of the workpiece with gasoline and alcohol; there should be no rust spots, oil stains, or dirt present. 3. After placing it in the furnace, tighten the furnace lid compression bolts symmetrically. 4. Connect cooling water to the water inlets of the furnace crucible and lid to perform circulating water cooling. At the lower end of the external water jacket on the furnace lid, water enters; at the upper end, it exits. The furnace tank has its own inlet and outlet for water. All the water pipes on the furnace lid can be connected in series following the principle of water entering from the lower side and exiting from the higher side, with water entering through one port and exiting through another. 5. Before raising the temperature, nitrogen should be introduced for exhaust; the flow rate during exhaust should be more than twice that used during operation. 10 minutes after exhaust, set the temperature control device to 150°C and turn on the automatic heating switch; heat while continuing to exhaust, maintaining this temperature for 2 hours. Then set the temperature control device to 530°C, reduce the ammonia flow rate, and maintain a positive pressure inside the furnace, so that there is a slight upward airflow at the exhaust port. Once the furnace temperature reaches 530°C, carry out nitriding at a constant temperature and flow rate for 3–20 hours. Next, increase the ammonia pressure slightly to keep the exhaust pressure at an appropriate level, and continue nitriding for 4–70 hours. After that, reduce the ammonia pressure again and carry out denitriding for 1–2 hours. Turn off the power supply and stop heating; introduce a small amount of ammonia to maintain a positive pressure inside the furnace. Nitrogen supply can be stopped only once the furnace temperature drops below 150°C. Gas carburizing process. Purpose of gas carburizing: Gas carburizing is performed to increase the carbon content on the surface of steel parts and to establish a certain carbon concentration gradient. It is a thermochemical treatment process in which steel parts are heated and held in a carburizing medium, allowing carbon atoms to penetrate into their surfaces. The steels used for carburizing are generally ordinary carbon steel, high-quality carbon structural steel, and low-carbon alloy structural steel; Q235 steel can also be utilized. Preparations before heating: (1) The surface of the carburized workpiece must be free from defects such as rust, dirt, cracks, and scratches. (2) For portions of the workpiece surface that do not require carburizing, copper plating or application of anti-carburizing coatings can be used to prevent carburization. Alternatively, after carburizing, the carburized layer on those areas can be removed by machining. The thickness of the copper plating should generally be greater than 0.03 mm ； The thickness of the anti-carburization coating should generally be greater than 0.3 mm, with a dense coating being required. (3) When using drip carburizing, the carburizing agent is generally methanol (to form the carrier gas) ； Kerosene or propane, ethyl acetate (to form a rich gas); under appropriate conditions, other forms of controlled-atmosphere carburizing can also be used. To achieve high-quality carburizing and reduce carbon black, it is best to use aviation kerosene for dripping. (4) Prepare the test sample and intermediate sample. The test specimens should be taken from parts of the same batch; there must be no rust or oil contamination on their surfaces. The intermediate sample is generally a Φ10mm×10 steel rod. Carburizing operation: ① Inspect the equipment before starting the furnace (refer to the operating procedures for vertical gas carburizing furnaces). ② Carry out carburizing of the furnace vessel in accordance with the process specifications, based on the duration of shutdown and the condition of the furnace vessel. The carburizing time for furnaces and tanks is generally 6–12 hours for new ones, and around 2–4 hours for old ones. ③Furnace charging: a. Workpieces with the same material, identical requirements for the carburized layer, and the same heat treatment method after carburizing are processed in the same furnace. Place the sample in a representative position within the basket. The load per furnace and the loading height should be less than the maximum values specified by the equipment. b. To ensure smooth circulation of the carburizing atmosphere inside the furnace and achieve a uniform carburized layer, gaps of more than 5 mm in both length and width should be left between the workpieces. c. When loading the baskets into the furnace, they should be placed vertically; all layers of baskets must be aligned properly without any gaps, and the intermediate sample rod should be inserted while hanging. d. After the workpiece is placed in the furnace, seal the furnace lid tightly to prevent any air leakage; after adding the carburizing agent, maintain the pressure inside the furnace at 196–490 Pa. Ignite the exhaust gas; the flame height should be 200–300 mm. ④ Carburizing a. Carburizing process curve: Based on the requirements of the material and the microstructure of the carburized layer, the carburizing process curve is specified in the relevant process documents