Heating and quenching at 1050-1100 ℃ and oil quenching can meet the requirements, but generally hot work molds do not require such high hardness. Such high hardness performance will be poor and difficult to use. Generally, HRC46-50 has good performance and durability.

2. What is used to whiten the surface of the mold after heat treatment?

Question supplement: I run a mold polishing shop, and usually the molds are first polished with an oilstone before being nitrided. After nitriding, the black layer needs to be wiped white with an oilstone, which is very troublesome to polish. Without wiping white, the mirror surface cannot be achieved. There are various materials available, including H13 and imported ones. If there is a medicine that can wash white, it can be directly polished.

(1) Stainless steel pickling solution or hydrochloric acid can be used for cleaning. Sandblasting treatment is also acceptable. The cost of grinding with a grinder is high, and the processing volume is large, which may result in substandard dimensions. If hydrochloric acid cannot wash it off, it is estimated that you are using high chromium mold steel? Is it D2 or H13? The oxide layer of high chromium mold steel is difficult to wash off. It should be possible to use stainless steel pickling solution, which can be sold in both grinding tool stores and stainless steel stores.

(2) Do you not have stainless steel pickling paste? That kind of thing is possible. Mold steels with high chromium content, such as H13, have an oxide layer that is difficult to remove with hydrochloric acid. There is another way, I am also using it myself. Since your mold has been polished with oilstone, the surface is relatively smooth. In fact, you can first use a coarse oilstone to polish, or use a sandbelt to polish, and then proceed with heat treatment. After returning, use a fine oilstone to polish it. And the method I use is to use a fiber wheel to polish first, which can effectively remove the black skin, and then grind and polish. Or sandblasting, try sandblasting with 800 mesh boron carbide once, it should be able to remove the black skin without requiring too much effort to regrind.

3. How does a heat treatment plant heat treat metals?

There are a lot of equipment in heat treatment plants, and there are probably box furnaces, well furnaces, and box furnaces that are most commonly used. Many heat treatments can be carried out here, such as annealing, normalizing, quenching heating processes, tempering, and other common heat treatments.

It is actually a furnace heated by electricity. First, the furnace is heated to the predetermined temperature, then the workpiece is thrown in, waited for a period of time to reach the predetermined temperature, kept warm for a period of time, and then taken out, or cooled together in the furnace. A well type furnace is usually used as a carburizing treatment device, which is a buried underground furnace. After the workpiece is placed in the furnace, it is sealed, and then some carbon rich liquids, such as kerosene or methanol, are dropped into the furnace. At high temperature, these liquids decompose into carbon atoms and infiltrate the surface of the workpiece.

A quenching pool is a place for quenching, which is a pool containing aqueous solution or oil. It is the cooling place for quenching workpieces from a box furnace. Generally, it is directly thrown in and then taken out after a period of time. There are also some other devices, such as high-frequency machines, which are devices that can convert 50 Hz power frequency electricity into a high-power current of 200 kHz. For example, a common maximum power of 200 kW is achieved, and a coil made of copper tube with internal cooling water is placed on the outside of the workpiece. Generally, for workpieces of several tens of millimeters, you can see the surface of the workpiece turn red after a few seconds to more than ten seconds. When the surface temperature reaches the predetermined value, a water jacket rises up and sprays quenching liquid onto the surface of the workpiece to complete the quenching process. That's all for the common ones.

4. How many times have our recent Cr12 or Cr12MoV materials undergone heat treatment and cracking? Why?

It is best to inform the size, shape, and heat treatment requirements of the parts on the hardware mold, as well as the heat treatment process curve you have adopted, otherwise it is difficult to explain. These two types of steel belong to the same category, belonging to high carbon and high chromium martensitic steel, which itself has a tendency towards cold cracking. The heat treatment process is also relatively complex.

Below is my experience without the above information: quenching at 950-1000C, oil cooling, HRC>58 To achieve thermal hardening and high wear resistance, the quenching temperature is increased to 1115-1130C and oil cooled. Thin and air cooled, also cooled in salt solution at 400-450C to reduce deformation. Do not temper at 300-375C, as it will reduce the toughness of the tool and cause tempering brittleness. In addition, temper immediately after quenching. Temper 2-3 times at 520C for quenching above 1100C. Please note that excessively high quenching temperatures may have a tendency for decarburization. Therefore, pre heat treatment - spheroidizing annealing can be performed before quenching.

5. How to distinguish between heat-treated parts and workpieces without heat treatment?

Question supplement: The worker accidentally mixed an untreated workpiece with a batch of pre adjusted heat-treated workpieces. How can they be distinguished now? Do not cut the workpiece to see the metallographic structure, as it will damage the product. Urgent shipment is necessary? The heat treatment process for 30Cr involves normalizing, re quenching, and then tempering. The raw material is a casting that has not undergone heat treatment. Both have undergone shot blasting treatment and the color change cannot be distinguished, and the hardness is between 35-45, which cannot be distinguished by hardness. If it cannot be distinguished by hardness and heat treatment oxidation color. I suggest you identify it by tapping the sound. The metallographic structure of castings and quenched and tempered workpieces is different, and there are differences in internal friction, which can be distinguished by gentle tapping.

6. What does overburning in heat treatment mean?

Exceeding the specified heating temperature can lead to grain growth, deterioration of various mechanical properties such as increased brittleness, decreased toughness, and susceptibility to deformation and cracking. Controlling the heating temperature can avoid overburning. When steel is heated above a certain temperature range in the solid-liquid phase, there is a chemical composition change in the austenite grain boundaries, and local or entire grain boundaries undergo melting. At this point, compounds such as S and P will accumulate on the grain boundaries, leading to a decrease in the bonding strength of the grain boundaries and a serious deterioration of mechanical properties. Overburned steel cannot be remedied through heat treatment or processing methods.

7. The causes and preventive measures of quenching cracks in molds?

Cause of occurrence:

preventive measure

(1) Vacuum heat treatment should be chosen as much as possible for mold heat treatment to achieve the minimum deformation.

(2) The mold can adopt a splicing structure and be divided into small pieces for heat treatment. It is best to use slow wire cutting, which has high accuracy, high smoothness, and small deformation. The gap is guaranteed, and the burrs will be small. Check if your device's accuracy is very poor.

(3) Apart from the ones mentioned above, I believe that if the convex mold is subjected to force on one side, the possibility of insufficient strength is high. Is the convex mold too thin? Is it designed to rely on a knife? After heat treatment, there is residual stress in the sheet metal, and deformation may occur after wire cutting. It is possible to consider pre milling larger wire cutting holes for reheat treatment, leaving 3-4 mm wire cutting.

9. I used H13 steel to make hot extrusion molds for forging workpieces, which were made of brass with a heat treatment of 45-48 °. The mold diameter was 120mm and the height was 70mm. After working for several hours, the mold cracked?

(1) The forging temperature is approximately 900~1000 ℃? Is the temperature too high? Without sufficient preheating before use, the mold may also be prone to cracking. Unreasonable mold design may also lead to cracking. Raise the tempering temperature of the mold to narrow the gap with the actual forging temperature and achieve a longer tempering time.

(2) This needs to be comprehensively considered, and if necessary, a metallographic examination should be conducted to determine the underlying cause.

10. What are the causes and prevention measures for soft spots on the surface of the mold?

Cause of occurrence:

Preventive measures:

Cause of occurrence: