The composition control of molten iron plays a very important role in the process design of casting anti shrinkage. Zhang Ruifen, a senior engineer of zhycasting, thinks that the main influencing factor of shrinkage defect is the chemical composition of cast iron, while Li Shuhui, a senior engineer of zhycasting, directly believes that as long as the carbon equivalent is kept between 4.5% and 4.6%, the casting without shrinkage defect can be obtained. However, based on the needs of actual production, other factors need to be taken into account in the composition control of molten iron.
As mentioned above, the shrinkage tendency of castings can be effectively reduced by controlling the carbon and silicon content in molten iron. However, considering the use demand of castings, the control of carbon and silicon content will be limited in some aspects.
In the actual production, because of the improvement of the mechanical properties of the cast iron, the requirements of the mechanical properties of the material are paid more and more attention, while the requirements of the mechanical properties focus on the tensile strength and hardness. According to the research of zhycasting senior engineer team, the tensile strength and hardness of gray cast iron are closely related to carbon equivalent.
It can be seen from the above two formulas that with the increase of CE, the tensile strength and hardness of the material decrease. The reason for the above results is that the increase of carbon equivalent and the content of graphite and ferrite in grey cast iron lead to the increase of A-type graphite and ferrite in grey cast iron, which leads to the decrease of tensile strength and hardness of grey cast iron. However, the tensile strength and hardness of gray cast iron decrease with the increase of C content. From the above two studies, it can be seen that the requirements for carbon and silicon content of gray cast iron based on material mechanical properties may be different from those based on preshrunk technology. The results show that when CE is less than 4.26%, i.e. the casting material is hypoeutectic cast iron, the shrinkage tendency of the casting decreases with the increase of carbon content. However, in the actual production, most of the iron castings are hypoeutectic iron castings, so it is very important to choose between them based on shrinkage resistance and mechanical properties.
In practical production, in order to improve the mechanical properties of castings, the method of adjusting low carbon equivalent is usually used. However, reducing carbon equivalent can improve the tensile strength and hardness of castings to some extent, but at the same time, it can improve the tendency of shrinkage and porosity of castings, on the contrary, it can reduce the service performance of castings. Therefore, the gray cast iron with excellent comprehensive properties can be obtained by increasing the ratio of carbon to carbon, and then by means of inoculation and addition of alloy elements, which will be widely used in the near future. The research shows that the gray cast iron with high carbon ratio has the following characteristics:
(1) Under the same carbon equivalent condition, the tensile strength can be increased by 30mpa-60mpa and the hardness can be increased by 20-30hb by increasing the carbon ratio.
(2) The results show that the microstructure and hardness distribution of gray cast iron with high gui-c ratio are uniform at different wall thickness.
(3) , the tendency of white speaking decreased, the tendency of looseness and crack decreased.
Although the mechanical properties of cast iron can be significantly improved by increasing the carbon ratio under the same carbon equivalent condition, the ferrite tendency of cast iron structure will also increase with the increase of the carbon ratio, so it is necessary to select the appropriate carbon ratio under the appropriate conditions.
It is not suitable to increase the ratio of cinnamon to carbon for heavy section castings (wall thickness greater than 60mm) without alloy elements. For thin-walled castings (wall thickness less than 60mm), the effect of increasing Si / C ratio is obvious.
Therefore, through the summary of the above discussion, we can get the following conclusions:
- The mechanical properties of cast iron can be significantly improved by using high carbon ratio.
- The hardness and tensile strength of cast iron can reach a high level by adjusting the carbon equivalent and carbon ratio, i.e. CE = 3.6% – 3.8%, Si / C = 0.75.
- When CE is too high, that is CE > 4.0%, it is not suitable to increase the ratio of carbon to Eva.
- The increase of Si / C ratio has some limitation. When Si / C is too high, the mechanical properties will decrease.
- For heavy section castings, it is not suitable to increase the Si / C ratio.