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Shearing Tool Heat Treatment Process

Shearing tools are generally made of T10, 9CrSl, 6CrW2Si, H13 alloy steel and other materials.

Processing before heat treatment: After forging, carbide unevenness is less than or equal to grade 6

Technical requirements: hardness HRC63~66

Heat treatment process:

The first preheating: 500~550℃, 120 minutes.

The second preheating: 800~820℃, 2 times for 12 minutes.

Heating: 1200~1265℃, 12 minutes→air cooling for about 20 seconds.

The first classification: 580~620℃, 10 minutes→air cooling for about 1 minute

The second classification: 350~400℃, 10 points.

Isothermal: 240~280℃, 120~180 minutes slow cooling to about 150℃ and tempering in time

The first tempering: 560℃, 60 minutes→260~280℃, 120 minutes. slow cooling;

The second, third and fourth tempering: 560 ℃, 3 times for 60 minutes.

Shearing Tool Heat Treatment Process Operation essentials:

(1) The preheating time must be sufficient;

(2) The high temperature furnace must be deoxidized and then quenched to prevent decarburization;

(3) After entering the high-temperature furnace for 1 minute, the temperature should be increased slowly, and the heating temperature should be strictly controlled;

(4) The temperature of the workpiece before the first tempering should be around 150℃;

(5) For the first tempering, it is best to put it into the furnace at 400°C, keep the temperature for 30 minutes, and then slowly heat up. For other tempering, the temperature of entering the furnace should be controlled below 500 ℃, and then slowly heat up;

(6) The tempering cooling should be slow, and it is best to place it in an iron cylinder for air cooling;

(7) After the tempering is completed, it can be cleaned after it has cooled thoroughly.

The above process adopts secondary bainite quenching, so that the large-scale combined shearing machine tool can meet the technical requirements. Generally, large-scale tools only use bainite quenching once, which can prevent cracking (such as razors).

The shearing machine tool produces deformation and cracking, which is mainly affected by tissue stress and thermal stress.

1. The influence of microstructure stress, the tool undergoes various microstructure transformations during the heating and cooling process. Since the specific volume of each microstructure in the steel is different, the volume changes during the phase transformation. Especially for high-speed steel, quenching and cooling can obtain martensitic structure with high alloy degree, and the specific volume of martensite is large, which makes the tool expand in volume after quenching. On the other hand, due to the complex geometry of the tool, the tissue transformation of heating and cooling is not simultaneous, and some sharp corners are prone to cause stress concentration, resulting in tool deformation and cracking.

There are many factors that affect the size of tissue stress, such as heating temperature, cooling method and so on. To reduce the structural stress, it is mainly to try to adjust the martensite in the heat treatment. The relative amount of austenite and bainite, which is directly related to the quenching method (oil quenching classification and isothermal quenching).

2. The influence of thermal stress, thermal stress is caused by the temperature difference between the inside and outside of the tool during heating and cooling. Due to the temperature difference between the inside and outside of the workpiece, the thermal expansion and contraction are inconsistent. The thermal conductivity of high-speed steel is poor, and the effect of thermal stress is more severe. Therefore, multiple preheating, multiple grading, and even isothermal processes should be used for commonly cracked and volatile tools.

3. Segregation of carbides in raw materials leads to deformation and cracking. In production practice, due to the inhomogeneity of carbides, tools are cracked along the concentration of carbides. For example, the inner holes of shearing cutters, shaving knives and other tools are cracked, most of which are caused by the above reasons.

4. There is a large stress inside the tool before quenching, which is easy to cause deformation and cracking during the processing. For example, the cutting tool of the thin saw blade shearing machine is stress-relieved before processing, and the deformation can be reduced after processing.

5. Too high quenching temperature will greatly reduce the strength of steel, so deformation and cracking are prone to occur during heating and cooling. Practical experience has proved that if the knife has the phenomenon of overheating and overburning, the deformation of the tool will be large (such as turning tools, drill bits, etc.), which is easy to cause cracking (such as shearing machine tools, hob, etc.).

6. If the cooling is too fast, it is easy to cause deformation and cracking under the complex action of thermal stress and tissue stress. Similarly, heating too fast can easily cause deformation and cracking. High-speed steel has excellent hardenability, and only slow cooling after 600 ° C does not hinder the hardness and other cutting properties of the tool. For example: when our factory is dealing with the cutting tool of the combined shearing machine (larger and needs to be heated for 10~15 minutes), due to the excessive isothermal nitrate content and the rapid cooling, all the cutting tools of the combined shearing machine are cracked.

7. Deformation and cracking caused by improper tempering. Although large-scale tools do not crack during the quenching process, they are easy to crack during the tempering process (refer to the tempering of high-speed steel). For example: once, when our factory was dealing with a large finger shear cutter, the cracking occurred in the tempering furnace, so later we stipulated that the tempering of the large cutter should be carried out at a low temperature and slowly heated up. For slender knives (such as broaches), it is best to temper them vertically.

8. Water-cooling treatment will cause cracking of large and complex knives. Our factory has performed ice-cold treatment (-70°C) on quenching of shaving knives, and cracking occurs as a result; Therefore, for razors, the cold treatment can only be carried out after the secondary tempering.

9. Premature cleaning is easy to cause cracking. When our factory handles some forming shearing tools and thick diameter (above φ40) broaches, the workpiece is cleaned too early because the workpiece is not cooled to room temperature. Cracks occur at the forming shearing tool) and the center hole (such as the broach). For larger tools, timely tempering should be used (tempered immediately after quenching to about 100 °C).

10. When the tool is heated, it is easy to cause deformation. According to the practical experience of our factory, the vertical heating of the iron wire is better than the heating of the rack, and it is not easy to cause deformation.

11. If the design is unreasonable (multi-pointed corners, large thickness disparity), it will cause stress concentration; indicate decarburization; insufficient tempering; repeated quenching without intermediate annealing; loose materials, etc., are easy to cause cracking.