1. How can H13 die steel be heat treated to achieve a hardness of 58℃?
Heating and quenching at 1050~1100°C and oil quenching can meet the requirements, but generally hot work dies do not require such high hardness, such high hardness performance will be very poor, not easy to use, generally good performance in HRC46~50, durable.
2. What is used to wash the surface of the mold after heat treatment?
Supplementary question: I run a mold polishing shop. Generally, the molds are first hit with a whetstone and then taken off for nitriding. After nitriding, the black layer should be whitened with a whetstone. It is very troublesome to polish again. Without the mirror surface, the materials are H13, and there are many imported ones. If there is a potion that can whiten it, it can be polished directly.
(1) It can be cleaned with stainless steel pickling solution or hydrochloric acid. Sandblasting is also possible. The cost of grinding by a grinder is high, and the processing volume is large, which may make the size substandard. If the hydrochloric acid cannot be washed off, it is estimated that you are using high-chromium die steel? Is it D2 or H13? The oxide layer of high chromium die steel is more difficult to wash off. It should be possible to use stainless steel pickling solution, which is available in mold stores or stainless steel stores.
(2) Do you have no stainless steel pickling paste? That can. Die steel with high chromium content such as H13, the oxide layer is difficult to wash off with hydrochloric acid. There is another way that I use myself. Since your mold has been ground with oil stone, the surface is relatively smooth. In fact, it can be ground with only a coarse whetstone, or with an abrasive belt, and then heat treated. When it comes back, sand it with a fine oil stone. The method I use is to use a fiber wheel to grind first, which can effectively remove the black skin, and then grind and polish. Or sandblasting, try sandblasting with 800-mesh boron carbide, you should be able to remove the black skin, and you don't need too much effort to regrind.
3. How does the heat treatment plant heat the metal?
There are a lot of equipment in the heat treatment plant. The furnaces probably include box furnaces, pit furnaces, and box furnaces. Many heat treatments can be processed here, such as the heating process of annealing, normalizing and quenching, and tempering. These common heat treatment.
In fact, it is a furnace heated by electricity. First, the furnace is heated to a predetermined temperature, and then the workpiece is thrown into it, waited for a period of time to reach the predetermined temperature, then kept for a period of time, and then taken out, or cooled together in the furnace. The pit furnace is generally As a carburizing treatment equipment, it is a furnace buried underground. After the workpiece is put in, it is sealed, and then some carbon-rich liquid, such as kerosene or methanol, is dropped into the furnace, and then these liquids are decomposed into carbon atoms and penetrate into the workpiece at high temperature. surface.
The quenching pool is a place for quenching, which is a pool with an aqueous solution or oil in it. It is the place where the workpieces from the box furnace are quenched and cooled. Generally, they are directly thrown in, and then fished out after a period of time. There are other devices, such as a high-frequency machine, which is a device that can convert 50 Hz power frequency electricity into a super-power of 200 kHz current, such as the common maximum power of 200 kW, and then use an internal cooling The coil made of water copper tube is placed outside the workpiece. Generally, the workpiece is several tens of millimeters. When it takes a few seconds to ten seconds, you will see that the surface of the workpiece turns red, and when the surface temperature reaches a predetermined value, there will be a water The sleeve rises to spray quenching liquid to the surface of the workpiece to complete the quenching process. These are the common ones.
4. Our recent Cr12 or Cr12MoV material has been heat treated and cracked several times, why?
On the metal mold, it is best to tell the size, shape and heat treatment requirements of the parts, and the heat treatment process curve you have adopted, otherwise it is difficult to tell. These two steels are one type of high-carbon and high-chromium ledeburite steel, which has a tendency to cold crack. The heat treatment process is also more complicated.
Let me talk about my experience without the above information: 950-1000 ℃ quenching, oil cooling, HRC>58. In order to obtain hot hardness and high wear resistance, the quenching temperature is increased to 1115-1130 ℃, oil cooling. Thin can be air-cooled, in order to reduce deformation, it is also cooled in salt solution at 400-450℃. Do not temper at 300-375 °C, it will reduce the toughness of the tool and cause temper brittleness. In addition, temper immediately after quenching. Quenched above 1100℃, tempered at 520℃ for 2-3 times. Please note that if the quenching temperature is too high, there will be a tendency for decarburization. For this reason, pre-heat treatment - spheroidizing annealing can be performed before quenching.
5. How to distinguish between heat-treated workpieces and workpieces without heat treatment?
Supplementary question: The worker accidentally mixed an unheated raw part with a batch of debugged and heat-treated workpieces. How to distinguish them now Shipping? Heat treatment process 30Cr is normalized, re-quenched, and then tempered, and the green part is a casting without heat treatment. Both of them have been shot blasted, and the discoloration cannot be distinguished, and the hardness is between 35-45HRC, which cannot be distinguished by hardness.
If it can't be judged by hardness and heat treatment oxidation color. I suggest that you identify by tapping the sound. Castings and quenched + tempered workpieces have different metallographic structures and internal friction, which may be distinguished by light tapping.
6. What does over-burning in heat treatment mean?
Exceeding the specified heating temperature will cause the grains to grow, and the mechanical properties will deteriorate, such as increased brittleness, decreased toughness, easy deformation and cracking, etc. Controlling the heating temperature can avoid over-burning. When the steel is heated above a certain temperature in the temperature range of the solid liquidus, the chemical composition of the austenite grain boundary changes, and the local or whole grain boundary appears sintered. At this time, S, P and other compounds will be enriched on the grain boundary, resulting in a decrease in the bonding force of the grain boundary and a serious deterioration in mechanical properties. After overburning, the steel cannot be remedied by heat treatment or processing.
7. Reasons and preventive measures for mold quenching cracks?
cause:
1) There is serious segregation of network carbide in the mold material.
2) There is mechanical processing or cold plastic deformation stress in the mold.
3) Improper operation of mold heat treatment (too fast heating or cooling, improper selection of quenching cooling medium, too low cooling temperature, too long cooling time, etc.).
4) The mold has complex shape, uneven thickness, sharp corners and threaded holes, etc., which makes the thermal stress and tissue stress too large.
5) The mold quenching heating temperature is too high to cause overheating or overburning.
6) After the mold is quenched, the tempering is not timely or the tempering holding time is insufficient.
7) When the mold is repaired and quenched, it is reheated and quenched without intermediate annealing.
8) If the mold is heat treated, the grinding process is improper.
9) During the EDM process after heat treatment of the mold, there are high tensile stress and microcracks in the hardened layer.
Precaution:
1) Strictly control the inherent quality of mold raw materials.
2) Improve the forging and spheroidizing annealing process, eliminate reticulated, banded and chain carbides, and improve the uniformity of the spheroidized structure.
3) After machining or cold plastic deformation, the mold should be subjected to stress relief annealing (>600℃) before heating and quenching.
4) For molds with complex shapes, asbestos should be used to block threaded holes, dangerous sections and thin walls should be wrapped, and graded quenching or isothermal quenching should be used.
5) Annealing or high temperature tempering is required when repairing or refurbishing the mold.
6) The mold should be preheated during quenching and heating, and pre-cooling measures should be taken during cooling, and an appropriate quenching medium should be selected.
7) The quenching heating temperature and time should be strictly controlled to prevent overheating and overburning of the mold.
8) After the mold is quenched, it should be tempered in time, and the holding time should be sufficient. The high-alloy complex mold should be tempered 2-3 times.
9) Select the correct grinding process and suitable grinding wheel.
10) Improve the mold EDM process and perform stress relief tempering.
8. How to heat treatment of large stamping dies? In particular, molds such as trimming are often produced with burrs and cannot operate normally.
(1) Vacuum heat treatment should be selected as far as possible for mold heat treatment to obtain the smallest amount of deformation.
(2) The mold can adopt a splicing structure, and it can be divided into small pieces for heat treatment. It is best to use slow wire cutting, with high precision, high finish and small deformation. The gap is guaranteed, and the burr will be small. See if your device has poor accuracy.
(3) Large burr on the trimming edge In addition to the above mentioned, I think that the punch is subjected to unilateral force and the strength is not enough. Is the punch too thin? Is it designed to rely on knives? There is also residual stress after heat treatment of the sheet metal, and deformation will occur after wire cutting. It can be considered that larger wire cutting holes are milled out in advance and then heat treated, leaving 3~4mm wire cutting.
9. I use H13 steel as a hot extrusion die. The forging workpiece is brass heat treatment at 45~48°. The die diameter is 120mm and the height is 70mm. The die cracks after working for several hours?
(1) The forging temperature is about 900~1000℃? Is the temperature too high? The mold may also be prone to cracking if it is not sufficiently preheated before use. Unreasonable mold design may also be prone to cracking. Increase the tempering temperature of the mold to narrow the gap with the actual forging temperature, and the tempering is actually longer.
(2) This should be considered comprehensively. When necessary, a metallographic examination should be done to basically judge the cause.
10. What are the causes and prevention of soft spots on the mold surface?
cause:
1) There are oxide scale, rust spots and local decarburization on the surface of the mold before heat treatment.
2) After the mold is quenched and heated, the cooling and quenching medium is improperly selected, and the impurities in the quenching medium are too much or aging.
Precaution:
1) The oxide scale and rust spots should be removed before heat treatment of the mold, and the surface of the mold should be properly protected during quenching and heating.
2) When the mold is cooled after quenching and heating, an appropriate cooling medium should be selected, and the cooling medium used for a long time should be filtered frequently or replaced regularly.
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