1. The content of inclusions increases

钢中的夹杂物是工模具内部产生裂纹的起源。尤其是脆性氧化物和硅酸盐等夹杂物，在热加工是不发生塑性变形，从而引起脆性的碎裂而形成微裂纹，在进一步的热处理和使用中，该裂纹进一步引起模具的开裂。例如。Cr4W2MoV钢制造的冲压手表零件用的冷冲模，其冲头经粗加工、热处理并磨削加工后，发现头部中心有许多小孔洞，致使一批冲头全部报废，经分析发出钢中含有大量的呈链状分布的硅酸盐夹杂物，经机加工后剥落而造成小孔洞。

The inclusion in steel is the origin of crack in the die. In particular, brittle oxide and silicate inclusions do not produce plastic deformation during hot working, which leads to brittle fragmentation and formation of microcracks. In further heat treatment and use, the cracks further cause mold cracking. For example. After rough machining, heat treatment and grinding, many small holes were found in the center of the punch head of the cold stamping die for stamping watch parts made of Cr4W2MoV steel. As a result, a batch of punch heads were scrapped. After analysis, a large number of silicate inclusions with chain distribution were found in the steel, which peeled off after machining, resulting in small holes.

2、碳化物分布不均匀引起的失效

2. Failure caused by uneven distribution of carbides

Cr12、Cr12MoV、Cr12Mo1V1等莱氏体型模具钢，具有大量共晶碳化物，当锻造比小或浇注温度控制不适当时，在钢材中易呈带状或网状碳化物的偏析，使模具零件在淬火时常常出现沿着带状或网状碳化物严重的部位裂纹，或在使用过程中内部裂纹进一步扩展而引起失效。例如，采用Φ50mm的共晶碳化物不均匀度超过4级的钢材制造冲头在使用过程中易发生断裂。

Cr12, Cr12MoV, Cr12Mo1V1 and other ledeburite die steels have a large number of eutectic carbides. When the forging ratio is small or the pouring temperature is not suitable, the segregation of banded or reticulated carbides is easy to appear in the steel, so that the die parts often appear cracks along the serious parts of banded or reticulated carbides during quenching, or the internal cracks further expand during use, resulting in failure. For example, the punch made of steel with the nonuniformity of eutectic carbide of Φ 50mm exceeding grade 4 is prone to fracture during use. 

3、锻造质量不好引起的失效

3. Failure caused by poor forging quality

钢材的锻造质量的好坏，直接影响模具的使用寿命。锻造的加热制度与变形工艺不当，会引起钢材产生过烧、表面裂纹、内裂、角裂等缺陷。这些会降低模具的使用寿命，甚直接报废。对于高碳高铬的莱氏体钢，由于导热性较差，若锻造加热时加热速度过快，保温时间不足，造成锻造时钢坯内外温差大，产生内部裂纹。

The forging quality of steel directly affects the service life of die. Improper heating system and deformation process of forging will cause defects such as overburning, surface crack, internal crack and corner crack. These will reduce the service life of the mold, or even directly scrap. For high carbon and high chromium ledeburite steel, due to the poor thermal conductivity, if the heating speed is too fast and the holding time is not enough during forging, the temperature difference between the inside and outside of the billet will be large and internal cracks will occur.

4、表面质量差

4. Poor surface quality

合金模具钢材如果表面脱碳严重，在机加工后，仍有残留脱碳层，这样在模具的热处理时，由于内外层组织不同而造成明显的应力，从而导致模具的淬火裂纹；另一方面，淬火后模具表面层的硬度偏低，且截面硬度分布不均匀，降低了模具的使用寿命。

If the surface decarburization of alloy die steel is serious, there will still be residual decarburization layer after machining. In this way, during the heat treatment of the die, obvious stress will be caused due to different internal and external structures, which will lead to quenching cracks of the die. On the other hand, the hardness of the surface layer of the die after quenching is low, and the hardness distribution of the cross section is uneven, which reduces the service life of the die.