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Heat treatment wi a hand, heat treatment workshop
These provisions shall apply to guide the heat treatment workshop on carbon structural steel, alloy steel, carbon tool steel and alloy tool steel heat treatment commonly.
1. Heat treatment furnace
Heat treatment furnace is a key link to ensure the quality of heat treatment. With improper furnace will make a big difference to the quality of heat treatment, must pay special attention to. Usually should consider the following factors:
1) first of all to consider the category of the heat treatment. According to the chemical composition of workpiece choose annealing, normalizing, quenching, tempering, match with the same heat treatment furnace. Not similar with heat treatment furnace, then we must analysis the whole process of the whole heat treatment of all materials, reasonable organization its sequence of operation, to see if it can and furnace.
2) with the furnace, but also with the furnace heat treatment of materials, quenching, normalizing the highest maximum heating temperature difference should be less than 20 ℃, the tempering temperature shall be within the scope of the unified, the heating rate should choose the slowest one. Also can use the method of partial out coordination.
3) with the furnace, also want to consider heat treatment of workpiece size difference is not too large, the average maximum cross section and the ratio of the minimum cross section should be controlled within 2 ~ 2.5. Can also take the size of a batch out coordination. The same workpiece size is too big, should consider package cover insulating layer to protect it.
4) and the type, and the furnace size and strive for a batch of products together with the furnace heat treatment. The separated sample should also be in the same furnace heat treatment. Furnace charging, the sample should be placed in the right place in the furnace.
2. The preparing work before heat treatment furnace charging
1) to check whether the equipment is in good condition before loading furnace, furnace body is damaged. All activities of the components (oven door, car, etc.) if the movement is normal. Electric circuit working condition are in good condition. Car surface is clean.
2) check whether the cooling medium is spare, circulatory system work is normal.
3) check the thermocouple temperature measurement recording instrument, control systems are in good condition.
4) check the auxiliary equipment is complete. Especially lifting equipment, steel wire rope, sling, fixture whether adaptation, is damaged, is safe.
5) check the heat treatment of workpiece quality: check the steel grade, size of workpiece. Check whether there is any defect on the surface, cracking, and will cause heat cracking potential defects. Artifacts, with mold cavity with and without oil, water and waste residue, consider after clean, whether to fill with heat-resistant material. If there are any defects, bending, should be cleaning and straightening.
3. Heat treatment furnace
1) each furnace furnace charging amount shall not exceed the maximum number of furnace charging electric regulation. All the size of the workpiece should be adapted to the size of the electric furnace studio.
2) the position of the workpiece loading furnace should be within the furnace heating zone. Before and after the up and down or so, and keep a certain distance with resistance wire. Should be padded under iron, should be separated with a 30 mm, to ensure the circulation of the heat flow.
3) the position of the workpiece loading furnace should be according to the distribution of furnace analysis, for a variety of brand and the size of the workpiece to adapt to consider operation order can be released.
4) furnace charging, the underlying block should be flat, artifacts in the car to be uniform, from bottom to top to arrange, paperback stable MATS, in order to avoid furnace charging, cause the regional temperature difference, and prevent the car moves side, pour the crib, impact furnace wall.
5) for ultra-thin long workpiece, when assembling furnace, all want to consider its stack location in the furnace, adopting technology measures, to prevent against deformation heating and lifting.
6) for artifacts have been finishing, furnace charging protection response to the workpiece surface and the edges and corners, to prevent oxidation decarburization and bruised. The parts of the workpiece is prone to cracking (concave cavity, the sharp corners, thread, slots, etc.) application of the insulation to protect it.
7) after the car into the furnace, if there is heat furnace damage to cause major gaps to be sealed.
4. Normalizing heat treatment, quenching, tempering, annealing temperature and holding time control
1) the temperature of heat treatment, heat preservation are important basis for instrument temperature. In the heat treatment process, must check the temperature of the furnace and the temperature of the workpiece and the instrument shows. If there is a problem to inform electrician to check repair instrumentation.
2) heat treatment industry to do three frequently: regular temperature, frequently look at material temperature, regular adjustment control, ensure that each part of the furnace temperature uniformity, maintain positive pressure in the furnace.
3) normalizing, quenching, tempering, annealing temperature and furnace integrated and selected in practice strict control, according to the requirement of the instruction is to ensure that the first condition of heat treatment quality. Organizations because of low heating temperature, phase shift will happen; And the heating temperature is too high, can make the austenitic grain size grew up too much, cause problems for cooling phase the organization change. So must be strictly in accordance with the requirements of the work instruction, do not arbitrarily set high set lower.
4) normalizing, quenching, tempering, annealing, heat preservation time should also be strictly controlled. Because enough time will make the organization transformation is not completely, and the time too, and can make the organization grow up, make bad performance.
5) general heat treatment of heat preservation phase started in the past, should have a mean temperature stage. Mean temperature began to begins with instrument temperature of heat preservation temperature calculation; When all the surface of the workpiece temperature in furnace to heat preservation temperature, mean temperature is over, start heat preservation.
5. Heat treatment of cooling process control
1) in order to ensure that the cooling effect of heat treatment, normalizing the workpiece during cooling should be hung from the furnace under air cooling, block pad high artifacts, ventilation around to retain a certain space. The temperature of the cooling after tempering furnace charging when the workpiece should be controlled at 300 ℃.
2) the workpiece quenching, should start the cooling medium (water or oil) system. Artifacts to and fro to increase the cooling effect after immersion medium, medium fluid amount found enough should fill in a timely manner.
3) when the workpiece immersion oil medium should pay attention to fire safety.
4) small quenching, if the cooling groove are too far away from furnace effect, cooling effect should be temporary using low water (oil) tank, to ensure the workpiece into the cooling medium in time after can get proper cooling effect.
5) for high alloy steel (e.g., 3 cr2w8v), high temperature quenching is cracked, then the introduction should precooling once again into the quenching medium, quenching cracks in order to prevent the thermal stress.
6) on the large flat together into medium, in order to reduce deformation.
7) for double liquid quenching workpiece, if there is a groove or cavity, is coming out from the water, net should pour water into the tank after cooling. General tank oil temperature at 150 ~ 150 ℃ (artifacts slightly emit smoke) is advisable.
8) artifacts must promptly tempering after quenching, re-blows are generally not more than 2 hours.
6. Heat treatment, inspection
1) heat treatment process after the completion of the inspection must be conducted. First check with or without deformation, bending, cracking. If you have to bend straightening. Then check the hardness, should check commonly 20% ~ 50%. Do you choose when check the hardness, control of grinding wheel grinding depth. When grinding wheel grinding, should pay attention to safety, prevent fly out of grinding wheel rupture cuts. Every inspection results recorded in the "production daily report".
2) heat treatment of workpiece with the physical and chemical inspection requirements, shall promptly notify the physics and chemical office sampling inspection.
7. Heat treatment records
Each class must fill out the hand-over records. Heat treatment instrument record sheet to fill in the date, the time of blast furnace and heat treatment of workpiece material. Every day to fill in the "daily production report" as required. All heat treatment records properly to keep for future reference.
8. After heat treatment of workpiece will divide the user stack, prevent mixing, reduce undue losses.