What is the quenching heat treatment of automobile connecting rod forging dies?

(1) Working conditions and technical requirements. The size of the automobile engine connecting rod forging die is 340mm Function, coupled with the use of water-based graphite liquid as cooling and lubricating medium, the surface of the mold cavity receives alternating hot and cold effects. Therefore, the mold should have high hardness, good thermal conductivity, good impact toughness and high temperature strength. According to the working characteristics of the connecting rod forging die, the material used to make the die should have the following properties:

1.Higher high temperature strength and hardness

2. Good wear resistance and high corrosion resistance

3. Strong impact toughness

4. Anti-corrosion and anti-oxidation

5. Has good thermal conductivity

Taking into account the need to meet the specific characteristics mentioned above

Automobile connecting rod forging die heat treatment process:

1. Technical requirements: a. Hardness 39-44HRC; b. Straightness and flatness not greater than 0.02mm, parallelism and verticality 0.05mm. If heat treatment is performed after carbonitriding, the penetration layer is 0.5-0.8mm, the cavity hardness is 48-52HRC, and the core hardness is 43-46HRC.

Heat treatment process and implementation key points of automobile connecting rod forging die

2. For die forging, parts with large thickness differences and sharp corners should be protected to prevent local overheating. It is recommended to use methods such as wrapping asbestos ropes and wrapping iron sheets to prevent the parts from cooling rapidly during the quenching of the forging die. Cracking, and in order to prevent the stress generated after high-temperature tempering, stress tempering is finally supplemented, the specification is 200℃X4h.

3. To prevent oxidation and decarburization of the mold surface during heating, it is generally heated in a vacuum furnace or a controlled atmosphere furnace. For those who do not meet the conditions, a box furnace can be used, but the premise is that it must be buried in a charcoal-sealed furnace. It should be protected and heated during the phase to ensure that the original state of the surface exists. It should be quickly removed at the end of heating and quenched in the selected cooling medium. When heating the box furnace, attention should be paid to keeping a certain distance between the two molds and between the mold and the fireplace to facilitate uniform heating.

4. In order to reduce large quenching deformation and prevent cracking of large molds, it is important to note that the key to cooling is to control the cooling time in the air and the cooling time in oil. Precooling can effectively reduce the internal stress during quenching to reduce Deformation. For 5CRNIMO, it is about to be pre-cooled to about 780℃ and quenched with oil. Generally, the cooling time in the air is controlled within the range of 3-8mm. The oil is discharged at about 200℃. At this time, it smokes but does not catch fire. Then it can be air-cooled. After quenching The hardness should be above 45HRC, otherwise it may cause cracking due to the huge internal stress inside the mold.

5. Some information recommends that the quenching temperature of the material 5crnimo steel be increased from 800-86 degrees Celsius to 900 degrees Celsius for heating and quenching, followed by tempering at 500 degrees Celsius, to obtain a single lath martensite, which can effectively prevent mold damage. Early brittleness can also lead to increased hardness. The structure of the rail process is flake martensite + lath martensite. If reviewed, the impact toughness and service life can be improved, that is, 160-180℃ The heat treatment process of graded cooling + 280-300℃ isothermal tempering for 2-3H is very effective.