Casting high toughness ductile iron castings and shortening the supply cycle is the direction that enterprises strive to pursue in the manufacturing process. It is to reduce heat treatment links and save intermediate transportation costs on the basis of meeting special performance requirements. Especially in the current fierce market competition Under the environment, the production cost of the enterprise has been effectively reduced, take QT600-10 material as an example to introduce its control method, then, let's learn how to melt cast high toughness ductile iron!

Selection of Chemical Composition of High Toughness Ductile Iron

1, carbon carbon to promote the absorption of magnesium, improve the spheroidization, promote graphitization, reduce the tendency. However, too high carbon can easily cause graphite to float and improve the roundness of graphite balls; it can improve the fluidity of molten iron, reduce the loose defects and shrinkage tendency of castings, and reduce the comprehensive performance of castings. Therefore, the carbon is controlled at 3.5 to 3.7%.

2. Silicon is an element that promotes graphitization. Although Si is controlled at 2.0 to 2.5%, it is beneficial to the generation of pearlite tissue. In the production of ductile iron, the inoculation of silicon will change the ratio of pearlite to ferrite. It is necessary to appropriately improve the culture effect, but in order to make the elongation rate reach 10% on the basis of the strength of 600MP and ensure a certain proportion of ferrite tissue, the silicon is controlled at 2.5~2.8

3, manganese can stabilize the pearlite elements, easy to form compounds in the eutectic block boundary, reduce the mechanical properties of castings, thicker large castings more serious. The strength and hardness are improved, and the plasticity and toughness are reduced; however, manganese is prone to segregation, and the amount of manganese is too much, and manganese is generally not used as an element for forming cast flake pearlite.

4. Sulfur has strong affinity with magnesium and rare earth. The higher the sulfur, the more spheroidizing agent is consumed. Therefore, the high sulfur content in iron liquid is the main reason for poor spheroidization caused by less residual spheroidizing elements. Consumption of spheroidizing elements in iron liquid forms slag of MgS and RES, reducing spheroidization rate; In addition, when sulfur content is high, defects such as slag and subcutaneous pores are easy to occur.

5, phosphorus in the ball iron solubility is low, reduce the plasticity, toughness and strength of the casting, and make the casting cold crack, phosphorus exceeds a certain content, easy to segregate in the boundary of the eutectic block to form phosphorus eutectic.

6, magnesium and rare earth iron liquid has a certain amount of magnesium and rare earth elements can ensure the graphite ball. Interference elements to prevent spheroidization. The content of Mg is controlled in the range of 0.030 to 0.05 and the content of RE is controlled in the range of 0.030 to 0.05. In rare earth magnesium ductile iron, magnesium plays the main role of spheroidization, and rare earth plays the role of auxiliary spheroidization to purify molten iron.

7, copper tin copper in the eutectic transformation to promote graphite, reduce or completely restrain the formation of ferrite. Reduce or eliminate the formation of free carburizing body, and promote the formation of pearlite during the co-analysis phase change, which is an ideal alloy element in the production of cast high-strength and high-toughness ball-ink cast iron. On the other hand, according to the wall thickness conditions, the range of Cu is 0.20~0.50; when the amount of copper is less than 0.4, it has no obvious effect on the large increase of pearlite. The use of copper as an alloying element in thin-walled castings is ideal to ensure toughness.

On the other hand, high toughness ductile iron can obtain tin as a certain proportion of trace alloying elements for thick-walled parts (cast flake pearlite with ferrite removed by 0.04%; In addition, free cementite is not formed. When 0.06~0.10 is added, the 64mm thick section is completely pearlite in the billet state). Copper is mixed according to a certain proportion, and the thickness of the billet Cu Sn% is 0.2~0.5 0.02~0.05, control the proportion of matrix tissue, strengthen the microstructure.

Dissolution of High Toughness Ductile Iron Liquid

High toughness ductile iron liquid using medium frequency induction furnace melting technology, try to use pure pig iron. P, S, interfering spheroidizing elements and various alloying elements should be as low as possible; Repeated use of alloys is easy to reduce costs and is also conducive to the control of molten iron components. Return iron is generally the riser, waste product or processed iron filings of the same material. Copper and tin are the key to whether the product performance can meet the requirements. Special spheroidizing agent and inoculant are not used, scrap steel should try to choose a single type, clean, no sand, rust and other garbage scrap scrap steel; Considering that the two alloys will not burn out during the smelting process, the chemical composition control of copper and tin as alloys entering the original molten iron at the bottom of the furnace in the early stage of smelting is moderate in principle. How to ensure the uniformity of the alloy in the molten iron is the basis for the stabilization of product quality and performance.

The above is how to melt cast high toughness ductile iron, if you need to know more, please feel free to contact us!