These regulations guide the heat treatment of carbon structural steel, alloy structural steel, carbon tool steel, and general alloy tool steel in the heat treatment workshop.

　　1. Furnace Preparation for Heat Treatment

　　Furnace preparation for heat treatment is a crucial step in ensuring quality. Improper furnace preparation significantly impacts heat treatment quality and requires careful attention. Several factors should be considered:

　　1) The type of heat treatment is the primary consideration. Select annealing, normalizing, quenching, or tempering based on the workpiece's chemical composition, and prepare the furnace accordingly. When preparing furnaces for different types of heat treatment, analyze the entire heat treatment process for all materials, organize the operational sequence rationally, and determine if combined furnace use is feasible.

　　2) When preparing the furnace, consider the materials undergoing heat treatment in the same furnace. The difference in the upper limit of the maximum heating temperature for quenching and normalizing should be less than 20℃. The tempering temperature should fall within a unified range, and the heating rate should be the slowest. Batch unloading can also be used to coordinate.

　　3) Furnace preparation should also consider the size of the heat-treated workpieces; the ratio of the largest to smallest cross-section should generally be controlled within 2-2.5. Batch unloading of large and small pieces can also be used to coordinate. If there is a significant size difference within the same workpiece, consider using an insulating cover for protection.

　　4) The same batch of products of the same type and furnace number should be heat-treated in the same furnace as much as possible. Separated samples should also be heat-treated in the same furnace. When loading the furnace, samples should be placed in appropriate positions within the furnace.

　　2. Preparation Work Before Loading for Heat Treatment

　　1) Before loading, check the equipment for damage or defects in the furnace body. Ensure all moving parts (furnace door, trolley, etc.) function normally and that electrical circuits are in good working order. Clean the trolley surface.

　　2) Check the cooling medium for sufficiency and ensure the circulation system is functioning properly.

　　3) Check the thermocouple, temperature recording instruments, and control system for proper functioning.

　　4) Check the completeness of tools and equipment. In particular, check that lifting equipment, steel wire ropes, slings, and fixtures are suitable, undamaged, and safe.

　　5) Inspect the quality of the heat-treated workpieces: verify the steel grade and workpiece dimensions. Check the workpiece surface for defects, cracks, and potential defects that could cause cracking during heat treatment. For workpieces with cavities, check for residual oil, water, or debris inside the cavity and consider cleaning and filling with heat-resistant material. Clean and straighten any defects or bends.

　　3. Loading for Heat Treatment

　　1) The amount loaded per furnace should not exceed the maximum load specified for the electric furnace. The dimensions of all workpieces should be compatible with the dimensions of the electric furnace working chamber.

　　2) The workpieces should be placed within the heating zone of the electric furnace. Maintain a certain distance from the top, walls, and resistance wires. Place iron pads underneath, and separate pieces by 30mm to ensure airflow.

　　3) The placement of workpieces should be based on the analysis during furnace preparation, ensuring that the loading sequence for different grades and sizes of workpieces is suitable for unloading.

　　4) When loading, ensure the bottom pads are level, the workpieces are evenly distributed on the trolley, and stacked rationally from bottom to top. Ensure even loading to prevent uneven temperature distribution in the furnace and to prevent tilting, collapse, or impact against the furnace walls during trolley movement.

　　5) For ultra-thin and ultra-long workpieces, consider their placement in the furnace and use process measures to prevent deformation during heating and lifting.

　　6) For workpieces that have undergone precision machining, protect the surface and edges during loading to prevent oxidation, decarburization, and damage. Protect areas prone to cracking (recesses, sharp corners, threads, grooves, etc.) with insulating material.

　　7) After the trolley enters the furnace, seal any large gaps caused by furnace damage to minimize heat loss.

　　4. Control of Normalizing, Quenching, Tempering, and Annealing Temperatures and Holding Times

　　1) Heating and holding during heat treatment are primarily based on instrument temperature readings. Throughout the heat treatment process, regularly check if the furnace and workpiece temperatures match the instrument readings. If there are discrepancies, promptly notify the electrician to check and repair the instrument.

　　2) Heat treatment operators should be diligent: frequently monitor furnace temperature, workpiece temperature, and adjust controls to ensure uniform temperature throughout the furnace and maintain positive pressure.

　　3) Comprehensive selection of normalizing, quenching, tempering, and annealing temperatures and strict adherence to the guidelines during operation are paramount to ensuring heat treatment quality. If the heating temperature is too low, phase transformation will not occur; if it is too high, the austenite grains will grow excessively, making phase transformation during cooling difficult. Therefore, strictly follow the operating instructions; do not arbitrarily adjust the temperature.

　　4) The holding time for normalizing, quenching, tempering, and annealing must also be strictly controlled. Insufficient time will result in incomplete phase transformation, while excessive time will cause grain growth and deterioration of properties.

　　5) Generally, before the holding stage of heat treatment, there should be an equalization stage. Equalization begins when the instrument temperature reaches the holding temperature; equalization ends and holding begins when the surface temperature of all workpieces in the furnace reaches the holding temperature.

　　5. Control of the Heat Treatment Cooling Process

　　1) To ensure effective cooling for normalizing, workpieces should be removed from the furnace and allowed to air cool. Raise the workpieces using pads, and ensure adequate ventilation space around them. The workpiece temperature should be controlled at 300℃ before loading for tempering after cooling.

　　2) When quenching workpieces, start the cooling medium (water or oil) circulation system first. Move the workpiece back and forth in the medium to enhance cooling. Replenish the medium if the level is low.

　　3) Pay attention to fire safety when immersing workpieces in oil.

　　4) For small-item quenching, if the cooling tank is too far from the heating furnace, affecting the cooling effect, a temporary small water (oil) tank should be used to ensure that the workpiece can be put into the cooling medium immediately after leaving the furnace to achieve the desired cooling effect.

　　5) For high-alloy steel (such as 3Cr2w8v), which is prone to cracking during high-temperature quenching, it should be pre-cooled after leaving the furnace before being put into the quenching medium to prevent thermal stress from causing quenching cracks.

　　6) Immerse together in the medium on a large flat plate to reduce deformation.

　　7) For workpieces undergoing double-liquid quenching, if there are concave grooves or cavities, the accumulated water should be drained after removal from the water before putting them into the oil tank for cooling. The oil temperature in the oil tank should generally be 150～200℃ (the workpiece slightly smokes).

　　8) Quenched workpieces must be tempered promptly, generally no more than 2 hours before returning to the furnace.

　　6. Heat Treatment Inspection

　　1) Inspection must be carried out after the heat treatment process is completed. First, check for any deformation, bending, or cracking. If bending occurs, straightening is required. Then, check the hardness, generally checking 20%～50%. When checking the hardness, select the points carefully and control the depth of grinding wheel polishing. When grinding with a grinding wheel, pay attention to safety to prevent the grinding wheel from shattering and injuring people. The results of each inspection should be recorded in the "Production Daily Report".

　　2) If the heat-treated workpiece requires physical and chemical testing, the physical and chemical laboratory should be notified promptly to take samples for testing.

　　7. Heat Treatment Records

　　Shift handover records must be filled out every shift. The date, furnace number, and material of the heat-treated workpiece should be filled in on the heat treatment instrument record paper. Fill in the "Production Daily Report" as required every day. All heat treatment records should be properly kept for reference.

　　8. Heat-treated workpieces should be stacked separately by user to prevent mixing and reduce unnecessary losses.