Quality and selection of rare earth spheroidizing agents (3)

6. Supporting measures for stabilizing ductile iron production

To stabilize the production of ductile iron, it is crucial to choose a suitable spheroidizing agent, but it is definitely not the only factor. In general, any spheroidizing agent can successfully produce ductile iron. However, to stably produce ductile iron parts, it is actually a systematic project. This article is called a stable production control system for ductile iron. In addition to the correct selection of spheroidizing agents, the following supporting measures are required:

(1) Correct spheroidization process. These include the selection of treatment methods, design of treatment packs, placement of spheroidizing agents, and the way in which molten iron is flushed into treatment packs. The spheroidization treatment method now has more than 10 kinds of punching method, cover method, feeding method, pressure plus magnesium method, and intra-spheroidal spheroidization, but it is commonly used as a rare earth magnesium spheroidizing agent for spheroidizing, but Hot metal cannot be directly rushed to the alloy. The height of the treatment bag is generally 1.5-2 times of its diameter. The rough bag should not be used. The bottom of the bag should be provided with a dam. The space on one side of the dam can be placed with all the spheroidizing agents and covering materials.

(2) Establish a suitable amount of spheroidizing agent and residual amount of spheroidizing elements. It is better to add more spheroidizing agent. It is better to ensure the residual spheroidized element content after the reaction, and it is often a difficult problem in the production of iron parts. Nowadays, enterprises control and evaluate the production cost of the workshop. It is always desirable that the amount of spheroidizing agent added is as small as possible. Otherwise, it is difficult to use the spheroidizing agent. In fact, the amount of spheroidizing agent to be added is controlled according to the content of the residual spheroidized elements of the intended design, and the residual spheroidizing elements are established according to the specific casting structure, spheroidization grade and performance requirements, etc. When the residual amount is Mg0.04-0.06% and Re0.02-0.03%, the carbide-free and spheroidized casting can be obtained. The medium-thickness (50-100mm) casting can increase the residual Mg by 0.01%, thicker than the thin wall. Wall castings can be increased to 0.050-0.08%. The thick-section castings have a bismuth-based light rare earth of more than 0.006%, and the core has a fragmentation. The amount of the rare earth element should be limited. The strontium-based rare earth spheroidizing agent should be replaced by a cerium-based rare earth spheroidizing agent. The residual cerium content should be less than 0.018%.

(3) Select a reasonable chemical composition of the original molten iron. The starting point for the selection of the chemical composition of ductile iron is to fully consider the matrix structure, performance requirements, wall thickness structure and whether it is casted. The recommended ingredients are as follows:

Ferritic ductile iron recommended ingredients

The above components are the components that meet the requirements of the casting after the spheroidizing treatment in the furnace. The composition of the original molten iron and these contents may vary. Specifically, C is higher. Generally, the carbon reduction after spheroidization is the original molten iron. -8%, the higher the residual magnesium, the more carbon reduction. This is because the temperature of molten iron decreases rapidly during the spheroidization process, and some of the primary graphite floats and combines with magnesium sulfide, magnesium silicate, etc. in molten iron. Slag; the content of Si in the original molten iron is generally much lower than the final silicon content of the ductile iron. This is because the spheroidizing agent and the inoculant are brought into the Si (the loss is transferred into the slag during the process, and the total content is brought into the slag. 70-80%), the actual content and expected value of Si in the original molten iron generally fluctuate by 0.10-0.15%; the reduction of Mn after treatment is about 3-8% of the content of the original molten iron; the P content does not change substantially before and after treatment. ;S is a harmful element, the lower the original molten iron should be as good as possible.

The allowable content of the anti-spherication element in the original molten iron is as follows: 锑 0.002%, 铋 0.002%, lead 0.002%, selenium 0.03%, titanium 0.07%, 碲 0.02%.
Al tends to cause pores in the casting; when producing high-toughness ductile iron, elements that promote the formation of pearlite and carbide should be as small as possible, such as copper, bismuth, nickel, tin, and the like.

(4) Maintain proper molten iron treatment temperature and pouring temperature. During the spheroidization process, the molten alloy, magnesium gasification, secondary gestation, turbid water radiation, magnesium on the surface of molten iron, desulfurization reaction and silicon oxidation reaction, etc., about 600-95 degrees of subway water temperature, so the molten iron furnace The pretreatment temperature is higher than the casting temperature by 110-130 degrees. If the treatment temperature is too high, the burning of magnesium will be aggravated, the recovery rate is unstable, and the spheroidization is poor.
The pouring temperature should be determined according to the casting wall, the complexity, the feeding requirements, the amount of sand to be poured in the same package of molten iron, the weight of the casting, whether it needs secondary gestation, etc. The thick parts should not exceed 1320 degrees, and the thin-walled parts are in 1320- At 1350 degrees, low temperature casting may cause defects such as slag inclusions, cold partitions, and keyholes in the casting.
The temperature at the exit of the fireplace can be 20-30 degrees higher. When the temperature is too high, you can stop in the bag.

(5) Desulfurization. Although the spheroidization treatment can remove the sulfur to the expected content, the high sulfur paste water treatment tends to produce more magnesium silicate slag, "black slag" defects, "sulphur recovery" phenomenon, etc., reducing the spheroidization rate of ductile iron. . Although the original molten iron containing more than 0.1% of sulfur can also produce qualified ductile iron parts, the cost is that the spheroidizing agent and the slag removing agent are added in a high amount, and the spheroidizing level is low. Therefore, the desulfurizing agent is used to hedge the high-sulfur molten iron of the furnace. Desulfurization pretreatment is one of the effective measures to stabilize the production of ductile iron. As for the use of pre-desulfurization, each plant should be comprehensively measured and compared economically and technically.

(6) Guarantee that pregnancy does not decline. When the spheroidized molten iron is solidified under a higher degree of subcooling, it tends to produce white-mouth tissue, so it is necessary to carry out the inoculation treatment.
- Inoculants, commonly used inoculants are mainly ferrosilicon, but to ensure that the Si content is above 70%, usually the national standard 75 can be, because of the low grade ferrosilicon impurities and Al and other harmful elements. At present, there are some compound inoculants containing elements such as Ca, Ba, Sr, Bi and Re. The as-cast ferrite and as-cast pearlite special inoculant produced by Shandong Huachen Co., Ltd. is a compound long-acting inoculant with strong ink, anti-white mouth, anti-recession, and strong desulfurization and deoxidation ability. (see subscript)
——Inoculation process, good inoculant, more need to accurately add amount, correct treatment process. The amount of inoculant added is related to the composition of molten iron, the temperature of boiling and pouring, the residence time after treatment, the thickness of castings, the pouring time, etc.; the usual method of inoculation is to cover the spheroidizing agent, in addition to the second gestation, floating silicon gestation, type Internal gestation and feeding and so on.
- Pregnancy of recession, which is a problem in the breeding process. In order to avoid this problem, the measures are: to ensure that the ingredients of the inoculant are not mixed, the particle size is appropriate, the long-acting inoculant is selected, and the treatment method is appropriate.
(7) Rapid analysis before the furnace. For example, the purchase of a spectrum analyzer can promptly and promptly guide the adjustment of molten iron composition, pre-furnace treatment and tracking and monitoring of tissue performance.

(8) Computer integration technology application. Casting production is a process in which a material is transformed into a solid-liquid-solid state and produced in one shot to complete the production process. Using the computer simulation of the ductile iron casting process, that is, the casting process CAD, to simulate the solidification process, the filling process and the thermal stress and microstructure of the casting, to achieve the optimal design of the casting process, improve the quality and scientific design, and shorten the design. Cycle, guarantee casting quality and improve economic efficiency. At the same time, the implementation of computer integrated manufacturing system (CMIS), the comprehensive use of modern management technology, manufacturing technology, network technology, e-commerce, system engineering technology, the procurement, equipment, technology, quality, personnel and other production operations in the production process of ductile iron The management elements are compiled into the database to integrate the logistics, people flow and information flow to achieve the overall optimization of casting production, so as to achieve high quality and low consumption operation in the foundry industry.

Reference material
1, Guan Hongye, etc., basic knowledge of ductile iron, Guangdong Science and Technology Press, 1980
2. Hao Shijian, Modern Cast Iron, Metallurgical Industry Press, 2004
3 Fu Xianqiang, medium frequency induction furnace smelting rare earth magnesium alloy, data, 1993
4 Shengda, Rare Earth-Containing Spheroidizing Agent and Evaluation of Its Quality, Tsinghua University Press, 2004

Description : Author Fu Xianqiang, senior engineer, Shandong Province, the first mechanical industry technology top talent, Shandong Huachen Co., Ltd. Chairman and General Manager. In 1986, after graduating from the Foundry University of Jiangsu University, he has been engaged in the research, development, promotion and application of rare earth alloy spheroidizing agents and creeping agents. He won the second prize and the third prize of the Science and Technology Progress Award of the former Ministry of Machinery and Shandong Science and Technology Commission. Project, the company mainly develops and produces rare earth series spheroidizing agents, creeping agents, compound inoculants, non-ferrous metal additives.

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