铜铸件的表面有一个低碳层，包括一个显示铁素体结构的完全脱碳层和一个低碳含量的半脱碳层。脱碳层的深度与铸件的质量，尺寸，厚度和加工条件密切相关。通常，在正确和错误的真空铸造条件下生产少量的非脱碳熔模铸造铸件并不容易。通常，铸件的总脱碳层厚度为0.3-0.6mm，严重时为0.7-0.9mm。

There is a low carbon layer on the surface of copper casting, including a complete decarburization layer showing ferrite structure and a semi decarburization layer with low carbon content. The depth of decarburized layer is closely related to casting quality, size, thickness and processing conditions. In general, it is not easy to produce a small amount of non decarburized investment castings under correct and wrong vacuum casting conditions. Generally, the total thickness of decarburized layer is 0.3-0.6 mm, and 0.7-0.9 mm in severe cases.

原因：在铸件冷却期间，空气中的氧气与钢水中的碳元素以及渗碳体和奥氏体中的碳发生反应，并且铸件表面发生脱碳。

Cause: during casting cooling, oxygen in air reacts with carbon in molten steel and carbon in cementite and austenite, and decarburization occurs on casting surface.

化学反应如下：2C + O2 = 2CO C + O2 = CO2

The chemical reaction is as follows: 2C + O2 = 2CO C + O2 = CO2

综上所述，高温，中温或低温区的化学反应具有很明显的自发倾向。

In conclusion, the chemical reactions at high temperature, medium temperature or low temperature have obvious spontaneous tendency.

注意事项：

matters needing attention:

1.适当调整型壳和铸件温度，以加快铸件的冷却速度。

1. Adjust the temperature of shell and casting properly to accelerate the cooling rate of casting.

2.向外壳增强层的沙子或沙子填充物中添加碳化物，例如碳砂，活性炭，无烟煤等。

2. Add carbides, such as carbon sand, activated carbon, anthracite, etc. to the sand or sand filling of the shell reinforcement layer.

3.在铸模的外围，会产生人造的修复气体，例如在铸造后用盖覆盖模具壳，将火油滴入盖中或撒上适当的废蜡，可有效减少表面的脱碳铸造层。

3. Artificial repair gas will be produced at the periphery of the mold, such as covering the mold shell with a cover after casting, dropping kerosene into the cover or sprinkling appropriate waste wax, which can effectively reduce the decarburized casting layer on the surface.

4.在铸造零件的热处理过程中，也应在恢复气氛中进行。防止铸件表面脱碳的关键方法是在铸件上铺一层焦炭颗粒，并预先准备炉口的密封。

4. In the heat treatment process of casting parts, it should also be carried out in recovery atmosphere. The key method to prevent decarburization of casting surface is to lay a layer of coke particles on the casting and prepare the sealing of furnace mouth in advance.