Such castings are slow to cool due to the thick section, the solidification time of the metal liquid is long, and the inside of the casting is prone to shrinkage.
In the production of ferritic ductile iron, in order to obtain high tensile strength, yield strength and elongation, ferritic heat treatment has been carried out in the past. The heat treatment temperature is based on the presence of free cementite or pearlite in the as-cast microstructure. And a high temperature heat treatment of 900-950 ° C is employed. However, the high production cost, complicated process and long production cycle bring great difficulties to the production organization and delivery time, which requires that the ferrite matrix must be obtained in the as-cast state. Therefore, the difficulties in producing this material are mainly as follows:
a. The casting is to be subjected to radiographic inspection in a designated area, and how to solve the internal shrinkage of the casting;
b. How to ensure that more than 90% of the ferrite matrix is obtained in the as-cast state;
c. How to make the material have sufficient tensile strength and yield strength;
d. How to get enough elongation (>18%) in the alloy