Die tool steel used in the stamping process requires high hardness, wear resistance, and a certain toughness. Cold work die steel can meet the needs of the public very well. Therefore, a large number of steel grades have been developed to meet the needs of cold work die steel.
The organization and performance of cold work die steel under different heat treatment processes are different, so the heat treatment process has a great influence on the service life of the mould. So, what factors affect the life of cold work die steel?
Cr12, Cr12MoV, Cr12Mo1V1 and other martensitic die tool steel have a large amount of eutectic carbides. When the forging ratio is small or the casting temperature is not properly controlled, the steel is prone to segregation of banded or networked carbides, which often leads to severe cracking along the banded or networked carbides during quenching of the mould parts, or the internal cracks are further extended during use, resulting in failure.
For example, using steel with eutectic carbide unevenness exceeding level 4 and a diameter of Φ50mm to make a punch will easily cause fracture during use.
The quality of steel forging directly affects the service life of the mould. Improper heating and deformation processes of forging can cause steel to produce burning, surface cracks, internal cracks, corner cracks and other defects. These will reduce the service life of the mould, and even cause it to be scrapped directly.
For high carbon and high chromium martensitic steel, if the heating speed during forging is too fast and the insulation time is insufficient, internal cracks will occur due to the large temperature difference between the inside and outside of the steel ingot during forging.
If the surface decarburization of alloy die tool steel is serious, there will still be residual decarburization layer after machining, so the final stress caused by different internal and external structure during heat treatment of the mould will cause quenching cracks in the mould; on the other hand, the hardness of the surface layer of the mould after quenching is low, and the distribution of section hardness is uneven, which reduces the service life of the mould.
Inclusions in steel are the source of internal cracks in molds. Especially for brittle oxide and silicate inclusions, they do not undergo plastic deformation during thermal processing, causing brittle fracture and forming microcracks. In further heat treatment and use, the crack will further cause the mold to crack.
For example, the cold punching die used for punching watch parts made of Cr4W2MoV steel was found to have many small holes in the center of the head after rough machining, heat treatment and grinding. A batch of punches were scrapped due to this issue. Analysis identified that the steel contained a large amount of silicate inclusions distributed in a chain-like manner, which peeled off after machining and caused small holes.
Cold work die steel is common die tool steel used in industry. Cold work die steel has good plasticity and has a wide range of applications. The above is the relevant content of die tool steel. I hope it can help everyone.
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