The heat treatment of grey cast iron is an important factor affecting the comprehensive performance of cast iron parts. Before using grey cast iron to make castings, the heat treatment process is adopted to eliminate the tissue defects inside the mortar, so as to make the performance of the alloy reach the best effect.
Grey cast iron heat treatment includes preheating, heating, holding, cooling, tempering and so on.
1 Pre-heat
The preheating process of grey cast iron is to heat the original graphite at low temperature, so as to get rid of the internal moisture in the mortar, expel the gas and facilitate mechanical processing. The preheating temperature of carbon-containing gray cast iron is 100-150℃, and the holding time is affected by the thickness of the matrix.
2. Heat up
The heating process of grey cast iron is to heat the matrix containing graphite at a certain temperature to make it reach the solid solution temperature. The heating temperature of grey cast iron is generally 800-900℃.
3. Heat preservation
The holding process of grey cast iron is to keep the mortar at a certain temperature to ensure that all parts of the mortar are evenly heated. The holding temperature of low carbon gray cast iron is 950~1000℃, while that of high-special gray cast iron is 1060~1100℃.
4. Cooling
The cooling process of grey cast iron is that after the furnace temperature is slowly reduced to 500-800℃, liquid cast iron is slowly cooled and different cooling cooling methods are adopted according to the parts performance requirements.
5. Tempering
The tempering process of grey cast iron refers to the process that the heat-treated parts are heated to a temperature below the austenitization temperature and held for a certain time, so as to make the structure stable and eliminate brittleness. The tempering temperature of grey cast iron is generally 200-400℃.
For grey cast iron heat treatment, there are many ways in China, such as annealing and isothermalizing. In China, molds are usually made of annealed grey cast iron as raw materials. The heat treatment of grey cast iron can keep the graphite in equilibrium state, and reduce the brittleness and improve its comprehensive mechanical properties.
In summary, the heat treatment of grey cast iron is an important part of improving the comprehensive performance of cast iron parts. It uses different heating and cooling methods to change the inner structure and performance of castings, so as to transfer the raw materials of grey cast iron into high-quality castings. It is important to note that the heat treatment process of grey cast iron should be carried out strictly in accordance with the process requirements of the process specifications to ensure the quality of the castings.
