What is the process of increasing the spheroidization rate in the production of ductile iron? The specific scheme will be introduced in detail below.
The spheroidization level of domestic ordinary spheroidal graphite cast iron castings is required to reach level 4 or above, (that is, the spheroidization rate is 70%), the spheroidization rate reached by the general foundry is about 85%. In recent years, with the development of nodular cast iron production, especially in industries with high requirements for wind power casting production and casting quality, the spheroidization level is required to reach level 2, that is, the spheroidization rate reaches more than 90%. The author's company analyzed and improved the spheroidization and inoculation process used in QT400-15, as well as the spheroidizing agent and inoculant, so that the spheroidization rate of nodular cast iron reached more than 90%.
1. Original production process
Original production process: The inoculant used in the inoculation treatment is 0.7% to 0.9% 75SiFe-C alloy. The spheroidizing treatment adopts the two-shot iron rushing method: first tap 55% to 60% of the iron, perform spheroidizing treatment, then add the inoculant, and then add the rest of the molten iron. Due to the traditional method of spheroidization and inoculation, the spheroidization rate detected with a 25 mm thick single-cast wedge test block is generally about 80%, that is, the spheroidization level is 3rd.
2. The test plan
to increase the spheroidization rate In order to increase the spheroidization rate, the original spheroidization and inoculation treatment process has been improved. The main measures are: increasing the amount of spheroidizing agent and inoculant, purifying molten iron, desulfurization, etc. . The spheroidization rate is still tested with 25 mm single-cast wedge test blocks. The specific plan is as follows:
(1) Analyze the reason for the low spheroidization rate of the original process. It was thought that the amount of spheroidizing agent was small, so the spheroidizing agent was added The amount increased from 1.3% to 1.4% to 1.7%, but the spheroidization rate did not meet the requirements.
(2) Another guess is that the low spheroidization rate may be caused by poor gestation or fertility decline. Therefore, the experiment increased the inoculation dose from 0.7% to 0.9% to 1.1%, and the spheroidization rate did not meet the requirements.
(3) Continue to analyze and believe that more inclusions in molten iron and high spheroidization interference elements may be the cause of the low spheroidization rate. Therefore, high-temperature purification of molten iron is carried out. The high-temperature purification temperature is generally controlled at 1500±10°C, but Its spheroidization rate has not exceeded 90%.
(4) The high amount of ω(S) seriously consumes the spheroidizing dose and accelerates the decline of spheroidization. Therefore, the desulfurization treatment is increased to reduce the original iron liquid ω(S) amount from 0.035% to less than 0.020%, but the spheroidization rate is also Only reached 86%.
The test results of the above four schemes are shown in Table 1. The structure and mechanical properties of the wedge-shaped test block did not meet the requirements.
3. The final improvement plan adopted
3.1 Specific improvement measures
Raw materials are pig iron, rust-free or less rusty scrap and reclaimed materials; the original molten iron is desulfurized with soda ash (Na2CO3) in the furnace; Foseco 390 pretreatment agent is used in the package Pre-deoxidation treatment; spheroidizing treatment with Foseco nodulizer; combined inoculation with silicon carbide and ferrosilicon.