1. Quenching
(1) Carbon and alloy structural steel pipes
① For carbon steel parts and some alloy steel parts with complex shapes, water, and oil are used for cooling.
② This section is used for carbon steel parts and some alloy steel parts with complex shapes.
(2)Chromium stainless steel pipes and austenitic steel pipes
(3) Preheating of tool steel pipes and low alloy steel pipes depends on the shape and size of the workpiece.
2. Normalized steel pipe and annealed steel pipe
(1) Normalizing
(2) Annealing
3. Tempering, aging, and stress-relief steel pipes
(1) Tempering Note: Calculate the tempering time according to this coefficient below 530℃.
(2) Aging (austenitic steel)
(3) Stress relief
① Use air cooling to straighten stress on parts with simple shapes.
② When the actual heating rate of the furnace exceeds ≤80℃/hour and cannot meet the process requirements, the parts should be loaded into the furnace and heated to 300℃ for 1 to 2 hours, and then heated to 100℃ for 1 hour with the furnace, and then kept for 1 hour for each 100℃ temperature rise. until kept warm. For parts with complex shapes and easy deformation such as valve stems, it must be guaranteed to be ≤50℃/hour, and manual control can be used when necessary.
A few notes on process specifications:
(1) “Transparency” refers to the time from when the workpiece is loaded into the furnace until the furnace is warmed up until the fire color of the workpiece and the furnace are consistent.
(2) “Unlimited” in the furnace charging temperature column generally refers to temperatures that do not exceed the holding temperature in the curve. (If there are two insulation temperatures in the curve, it should not exceed the insulation temperature of the first section)
(3) The quenching and holding time of 38CrMoAlA steel should be extended by an additional 30% as specified.
(4) The tempering and heat preservation time of hardened parts is required to be at least 1 hour.
(5) The time for stress removal: the stress removal for machining and straightening shall not be less than 3 hours; the stress removal for welding and casting shall not be less than 4 hours.
(6) When the alignment stress is removed after nitriding the nitrided parts, nitrogen must be passed through the entire stress removal process.
(7) According to Z75.22-86 GH2136 aging heat treatment, it is put into the furnace at ≤300℃, then the furnace temperature is raised to 10±10℃, kept warm, and burned through +12~16h, and then air-cooled out of the furnace to reach HRC32~42.
4. Chemical heat treatment process specifications
(1) Nitriding
① For specific regulations on furnace cooling, see Notes ④.
② The heat preservation time of the nozzle group is 6 to 8 hours.
③ Add pills to remove the passivation film on the surface of the parts. The dosage is 100 to 120 pills per furnace.
Precautions:
① Before parts are nitrided, surface rust spots must be removed and surface oil stains must be cleaned with gasoline.
② When loading parts into the furnace, all surfaces to be nitrided must not be in contact with each other. Pay special attention to large workpieces not being placed near the thermocouple, and workpieces are strictly prohibited from leaning on the thermocouple. For partially nitrided parts, check whether the tinned parts are correct. For screw holes below M16 and blind holes and through holes below ￠16, as well as the threaded parts and undercuts of nitrided parts with threads protected by tin plating, all are protected by paint before nitriding.
③ After the nitrided parts are put into the furnace, nitrogen should be passed through for 30 minutes to eliminate the air in the box. The ammonia pressure should be controlled at 100~150mm oil column. After the air is eliminated, the pressure should be adjusted according to the process requirements to control the decomposition rate. Ammonia gas must not be interrupted from beginning to end during the nitriding process.
④ During nitriding cooling, first cut off the power and then stop the ammonia when the furnace cools to ≤150℃ and take out the parts.
⑤ The ammonia pressure in the furnace is for reference only, and the decomposition rate should be controlled during operation.
(2)Carburizing
1) The holding time of solid carburizing depends on the number of boxes packed in the carburizing furnace and the size of the boxes.
2) Several notes on gas carburizing:
① Solid carburizing agent formula: 7% BaCO3 + 2.5% Na2CO3 and the remaining 90.5% wood carbon. The ratio of new and old carburizing agents is 1:2.
②Gas carburizing agent:
(a) Benzene drop rate: control at 30-35 drops/min during temperature rise and 60-70 drops/min during heat preservation. (b)* Kerosene + alcohol 50% each, the dripping rate is the same as that of benzene. When using for the first time, conduct a test to determine the appropriate dripping rate.
③Check the pre-test sample 1 to 1.5 hours before the carburizing and holding time is reached, and determine the release time based on the measured results.
④ When loading the furnace for gas carburizing, a certain distance should be kept between parts, at least 5 to 10 mm. The distance between solid carburizing boxing parts or box walls shall not be less than 15~20mm.
⑤ If it is found that there are network carbides in the carburizing layer after carburizing, normalizing treatment should be carried out to eliminate them.
5. Forging die heat treatment process specifications
Forging molds and tire molds are quenched and put into the prepared tempering furnace immediately after the oil is discharged. Tempering 5CrNiMo tempering oil cooling. illustrate:
(1) The dovetail adopts self-tempering. Quenching process: Fill all small molds (H≤250mm) with 5′~8′ of oil (8′~12′ for medium and large ones), then lift the dovetail out of the oil surface, and then immerse it in the oil when the oil surface burns, repeat for 2~ 3 times to make the dovetail temper on its own. Medium mold H=250~400mm, large mold H>400mm.
(2) The oil outlet temperature is 250~300℃, and shall not be lower than 250℃. Prepare a tempering furnace with a temperature of 350~400℃, and enter the tempering furnace immediately after the oil is discharged.
Precautions for heat treatment of forging dies:
(1) Mold repair or renovation must be annealed first to prevent cracking.
(2) The forging mold must be protected during the quenching and heating of the mold. See the schematic diagram for protection. The working surface of other molds should be protected with pig iron filings and dry charcoal to prevent decarburization, and the mold should be padded by 50 to 100 mm.
(3) Tempering must be carried out in time after quenching.
(4) The holding time in the curve = mold height × heating coefficient (minutes/mm). “Transparency” refers to the duration from the time when the furnace temperature rises until the color of all parts of the workpiece is consistent with the color of the furnace.
Post time: May-28-2024