Heat treatment workshop work instructions

1. Furnace for heat treatment

A heat treatment matching furnace is an important link to ensure the quality of heat treatment. Improper furnace allocation will have a great impact on the quality of heat treatment and must be paid special attention to. The following factors should generally be considered:

The first thing to consider is the type of heat treatment. According to the chemical composition of the workpiece, annealing, normalizing, quenching, and tempering are selected, and the furnace is matched with the same heat treatment. When different types of heat treatment are matched with furnaces, the whole process of heat treatment of all materials must be analyzed, and the operation sequence must be reasonably organized to see if they can be combined.

When matching the furnace, the materials that are heat treated in the same furnace should also be considered. The difference between the upper limit of the maximum heating temperature of quenching and normalizing should be less than 20 °C, the tempering temperature should be within a uniform range, and the heating rate should be the slowest. A sort of. It can also be coordinated in batches.

When matching the furnace, it should also be considered that the size of the heat-treated workpiece should not be too different. Generally, the ratio of the maximum section to the minimum section should be controlled by 2 to 2.5. Large and small pieces can also be released in batches for coordination. When the size of the same workpiece is too different, it should be considered to be covered with a thermal insulation layer for protection.

The same batch of products of the same type and the same furnace number should be matched with the same furnace heat treatment as much as possible. The divided samples are also heat treated in the same furnace. When loading the furnace, the sample should be placed in the appropriate position in the furnace.

2. Preparations before heat treatment

Before installing the furnace, check whether the equipment is in good condition and whether the furnace body is damaged. Whether all moving parts (furnace door, trolley, etc.) move properly. Whether the electrical circuit is in good working condition. Whether the trolley surface is clean.

Check whether the cooling medium is sufficient and whether the circulation system works normally.

Check whether the thermocouple, temperature measuring and recording instrument, and control system are in good condition.

Check whether the tools and accessories are complete. In particular, whether lifting equipment, wire ropes, spreaders, and fixtures are suitable, damaged, and safe.

Check the quality of the heat-treated workpiece: check the steel number and workpiece size. Inspect the workpiece surface for defects, cracks, and potential defects that would cause heat treatment cracking. For workpieces with a cavity, whether there is any residue such as oil, water, or garbage in the cavity, consider whether it should be filled with heat-resistant materials after cleaning. If there are defects or bends, they should be cleaned and straightened first.

3. Heat treatment furnace

The loading capacity of each furnace should not exceed the maximum loading capacity specified by the electric furnace. The size of all workpieces should be compatible with the size of the electric furnace studio.

The position where the workpiece is loaded into the furnace should be within the heating zone of the electric furnace. Keep a certain distance from the furnace roof, furnace wall, and resistance wire up, down, front, back, left, and right. A pad iron should be added underneath, and the pieces should be separated by 30mm to ensure the circulation of hot air.

The position of the workpiece to be installed in the furnace should be based on the analysis of the furnace configuration, and the workpieces of various grades and sizes should be adapted to the considered sequence of operations and can be released from the furnace.

When loading the furnace, the bottom pads should be leveled, the workpieces should be evenly distributed on the trolley, and should be stacked reasonably from bottom to top, and the pads should be flat and firm to avoid uneven charging in the furnace and cause temperature differences in various regions. And prevent the trolley from tipping, stacking, and hitting the furnace wall when the trolley moves.

For ultra-thin and ultra-long workpieces, when assembling the furnace, the stacking position in the furnace should be considered, and technological measures should be adopted to prevent deformation during heating and hoisting.

For the workpiece that has been finished, the surface and edges of the workpiece should be protected when charging to prevent oxidation, decarburization, and bumps. The parts of the workpiece that are prone to cracking (cavities, sharp corners, threads, slots, etc.) should be protected by thermal insulation materials.

After the trolley enters the furnace, if there is a large heat dissipation gap caused by damage to the furnace body, it should be blocked.

4. Control of heat treatment normalizing, quenching, tempering, annealing temperature, and holding time

The temperature rise and heat preservation of heat treatment are based on the instrument temperature. During the entire heat treatment process, it is necessary to frequently check whether the temperature of the furnace and the workpiece is consistent with the temperature displayed by the instrument. If there is a problem, promptly notify the electrician to check and repair the meter.

The heat treatment workers must do three diligent work: diligently watching the furnace temperature, watching the material temperature, and diligently adjusting and controlling, to ensure that the temperature of each part in the furnace is uniform, and the furnace maintains a positive pressure.

The comprehensive selection of normalizing, quenching, tempering, and annealing temperature and furnace matching and control in strict accordance with the requirements of the instruction book in actual operation are the primary conditions to ensure the quality of heat treatment. Because the heating temperature is too low, the phase structure transformation will not occur; however, if the heating temperature is too high, the austenite grains will grow excessively, resulting in the difficulty of the phase structure transformation during cooling. Therefore, it is necessary to strictly follow the requirements of the homework instruction, and not arbitrarily set high and low.

The holding time of normalizing, quenching, tempering, and annealing should also be strictly controlled. Because the time is not enough, the phase structure will not be completely transformed, and if the time is too long, the phase structure will grow up and the performance will deteriorate.

Before the heat preservation stage of general heat treatment starts, there should be a temperature equalization stage. The start of temperature averaging starts when the instrument temperature reaches the holding temperature; when the surface temperature of all workpieces in the furnace reaches the holding temperature, the temperature averaging ends and the holding starts.

5. Control of heat treatment cooling process

To ensure the cooling effect of the heat treatment, the normalized workpiece should be hoisted from the furnace to disperse air cooling during cooling, the underside of the workpiece should be cushioned, and a certain space should be reserved around for ventilation. After cooling, the temperature of the workpiece should be controlled at 300 ℃ when tempering and charging.

When the workpiece is quenched, the circulation system of the cooling medium (water or oil) should be started first. After the workpiece is immersed in the medium, it should swing back and forth to increase the cooling effect. If the medium liquid is found to be insufficient, it should be replenished in time.

Pay attention to fire safety when the workpiece is immersed in an oil medium.

For quenching of small pieces if the cooling tank is too far from the heating furnace to affect the cooling effect, small water (oil) tank should be temporarily used to ensure that the workpiece can be put into the cooling medium in time to obtain the proper cooling effect after it is released from the furnace.

For high-alloy steel (such as 3Cr2w8v) when high-temperature quenching is easy to crack, it should be pre-cooled and then put into the quenching medium to prevent thermal stress from causing quenching cracks.

Immerse the medium together on a large plate to reduce deformation.

For the two-liquid quenched workpiece, if there are grooves or mold cavities, after coming out of the water, the accumulated water should be poured out and then put into the oil tank for cooling. Generally, the oil outlet temperature of the oil tank is 150～200℃ (the workpiece emits a little blue smoke).

The quenched workpiece must be tempered in time, generally not more than 2 hours.

6. Heat treatment inspection

Inspection must be carried out after the heat treatment process is completed. The first check for deformation, bending and cracking. Straighten it if it is bent. Then check the hardness, generally 20% to 50%. When checking the hardness, make a good selection and control the grinding depth of the grinding wheel. When grinding the grinding wheel, pay attention to safety to prevent the grinding wheel from breaking and flying out and hurting people. The results of each inspection shall be recorded in the “Production Daily Report”.

When the heat-treated workpiece has physical and chemical inspection requirements, the physical and chemical laboratory should be notified for sampling inspection in time.

7. Heat treatment records

A shift record must be filled out for each shift. The date, heat, and material of the heat-treated workpiece should be filled on the recording paper of the heat treatment instrument. Fill in the “Production Daily Report” every day as required. All heat treatment records are to be kept for future reference.

8. The workpieces after heat treatment should be stacked by users to prevent mixing and reduce unnecessary losses.

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