H13 steel mold vacuum heat treatment

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In recent years, the development of my country’s mold industry is very rapid, especially the continuous development and wide application of CAD/CAM technology, so that the production capacity of molds has increased rapidly, and the annual rate of increase is about 15%. In industries such as automobiles, electrical appliances, electronics, instrumentation and construction, 70% to 90% of the parts and components are formed by molds, and the market demand for molds has huge potential. However, there is still a big gap between the production level of large, complex, precise and long-life molds compared with developed countries, and many products rely on imports. Therefore, improving the quality of mold heat treatment and giving full play to the potential of steel is an effective way to occupy the mold heat treatment market.

Properties of H13 Die Steel and Requirements for Heat Treatment

H13 is an American grade, which is equivalent to my country’s 4Cr5MoSiV1 steel. The composition determines that this steel has high hardenability and tempering resistance stability. After quenching and high temperature tempering, it has high toughness and strength. If a scientific and reasonable heat treatment process is adopted, its potential can be fully exerted, and relatively high high temperature strength, thermal fatigue resistance, wear resistance and high thermal stability can be obtained, which greatly meets the performance requirements of the mold and improves the service life.

Technical requirements for molds

Generally, the hardness requirements for small complex parts are 46~48HRC, and the hardness requirements for simple parts are 48~52HRC; the hardness requirements for medium mold complex parts are 42~44HRC, and the simple parts are 44~46HRC. For complex parts of large molds, the hardness requirement is 40-42HRC, and the simple parts are 42-46HRC.

Advantages of vacuum heat treatment

The advantages of vacuum heat treatment are radiation heating, slow heating speed and uniform temperature, which can greatly reduce thermal stress, reduce heat treatment deformation, and effectively solve the problem of easy cracking of large and complex molds during heat treatment. At the same time, it can effectively prevent heat treatment defects such as oxidation, decarburization and corrosion of the mold surface, and improve the surface roughness. Practice has proved that compared with box furnace and salt bath heat treatment, the service life of the mold and the processing effect have been greatly improved.

heat treatment process

Quenching process route: cleaning (surface cleaning) → furnace loading → vacuuming → preheating → final heating → pressurized gas quenching → first tempering → hardness testing → second tempering → final tempering.

(1) Cleaning (surface cleaning) For small molds, clean them in a cleaning machine and dry their surfaces before loading them into the furnace; for large molds, use a clean rag to clean the dirt and oil stains on their surfaces before loading them into the furnace.

(2) Furnace installation

When loading the furnace, there should be a gap between the molds, and the amount of the furnace should not be more than 400kg at a time to ensure that the molds can be fully and uniformly heated and cooled.

(3) Preheating

After closing the furnace door, vacuumize and input the process parameters into the microcomputer. When the pressure in the furnace drops to 0.133Pa, the power transmission starts to heat up. For medium and large molds, use a lower rate of heating, generally about 500 °C/h, to reduce the temperature difference between the furnace and the mold and prevent deformation and cracking. For H13 steel mold, we use segmental preheating, the first time is 560 ℃, the second time is 850 ℃ preheating holding time is 1.5min/mm × effective thickness The calculation method of effective thickness is the minimum thickness × (1.2 ~ 1.3 ).

(4) Final heating and pressurized gas quenching

The final heating temperature is 1030°C, and the holding time is 30min + 0.4min/nm × effective thickness.

(5) The first tempering

The mold is cooled to about 80°C, and tempered for the first time. The temperature is 560°C, and the holding time is 2h+1min/mm×effective thickness (calculated when the instrument indicates that the tempering temperature is reached). The gas pressure in the furnace during tempering and cooling is: 1×105~2×10PPa. After H13 steel is quenched at normal temperature, the peak hardness can be reached by tempering at 560°C due to the effect of secondary hardening. After the first tempering, it is cooled to room temperature to test the hardness. The second tempering is the tempering that determines the hardness. The temperature is mainly determined according to the hardness after the first tempering.

(6) The last tempering

The temperature is generally 560 ℃, if the hardness after the second tempering fails to meet the technological requirements, it can be adjusted appropriately.

Application range:

According to the experience of vacuum heat treatment of H13 steel in recent years, the following typical process examples can fully demonstrate that the vacuum heat treatment process has fully met the needs of production.

(1) Manufacture of rocker arm mold, material H13, hardness 44~48HRC. After normal quenching and first tempering, the second tempering temperature is 592°C, and the hardness after cooling is 46-48HRC.

(2) Die-casting mold manufacturing, material H13 hardness requires 42~46HRC. After normal quenching and first tempering, the second tempering temperature is 605℃. The hardness measured after cooling is 44-46HRC.

(3) For the manufacture of engine molds, the quenched and tempered hardness is required to be 31~35HRC. After normal quenching and first tempering, the second tempering temperature is 650℃. The hardness measured after cooling is 32-34HRC.

Equipment selection: The VOGQ series vacuum heat treatment furnace produced by SIMUWU is a high-quality product for the vacuum heat treatment of tooling and molds. The good temperature control accuracy and temperature control uniformity ensure the effective progress of the vacuum heat treatment process. SIMUWU specializes in the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum air quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.