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Measures to increase spheroidization rate during casting:
1. Xinyuanzhu obtained the influence of main elements on the spheroidization rate based on casting practice
C, Si: C can promote graphitization and reduce the tendency of white mouth, but a high amount of ω (C) will make the CE too high and easy to cause graphite to float, generally controlled at 3.7% to 3.9%. Si can strengthen the graphitization ability and eliminate cementite. When Si is added as an inoculant, it can greatly reduce the supercooling capacity of the molten iron. In order to improve the inoculation effect, the amount of ω (Si) in the original molten iron was reduced from 1.3% to 1.5% to 0.8% to 1.2%, and the amount of ω (final Si) was controlled at 2.60% to 3.00%.Mn: During the crystallization process, Mn increases the tendency of cast iron to overcool and promotes the formation of carbides (FeMn) 3C. In the eutectoid transformation process, Mn reduces the eutectoid transformation temperature, stabilizes and refines pearlite. Mn does not have much influence on the spheroidization rate. Due to the influence of raw materials, generally control ω (Mn) <0.30%.
P: When ω(P)<0.05%, it is solid soluble in Fe, it is difficult to form a phosphorus eutectic, and it has little effect on the spheroidization rate of ductile iron.
S: S is a despheroidizing element. S consumes Mg and RE in the spheroidizing agent during the spheroidizing reaction, hindering graphitization and reducing the spheroidizing rate. Sulfide slag will also return to sulfur before the molten iron solidifies, again consuming spheroidizing elements, accelerating the decline of spheroidization, and further affecting the spheroidizing rate. In order to achieve a high spheroidization rate, the amount of ω (S) in the raw iron should be reduced to less than 0.02%.
2. Xinyuanzhu recommends desulfurization treatment
After the charge is melted, take samples and analyze the chemical composition. When the amount of ω (S) is higher than 0.02%, desulfurization is required. The principle of soda ash desulfurization is: put a certain amount of soda ash in the ladle, use molten iron flow to flush and stir, soda ash decomposes at high temperature, the reaction formula is Na2CO3=Na2O+CO2↑: the generated Na2O is in the molten iron again Sulfuration and formation of Na2S, (Na2O) + [FeS] = (Na2S) + (FeO). Na2CO3 separates and resolves CO2 to cause violent agitation of molten iron, which promotes the desulfurization process. Soda ash slag is easy to flow and float quickly, and the desulfurization reaction time is very short. After desulfurization, the slag should be removed in time, otherwise it will return to sulfur.
Pre-deoxidation treatment, spheroidization treatment and inoculation treatment
The pre-treatment agent plays the role of pre-deoxidation treatment in the bag, and at the same time increases the graphite nucleation core and the number of graphite spheres per unit area. It can also increase the absorption rate of Mg, greatly improve the anti-fading ability, and increase the spheroidization rate. The inoculant contains ω(Si)=60%~70%, ω(Ca)=0.4%~2.0%, ω(Ba)=7%~11%, of which Ba can prolong the effective incubation time. Since the molten iron has undergone desulfurization and pre-deoxidation treatments, the elements that consume nodulizers in the molten iron are greatly reduced, so a nodulizer with a low amount of ω (RE) is selected to reduce the deterioration of the spheroidal graphite morphology by RE; The main element of action is Mg; Ca and Al can play a role in strengthening gestation. Using silicon carbide and ferrosilicon combined inoculation treatment, the melting point of silicon carbide is about 1600℃, and graphite crystal nucleus is increased during solidification, and large doses of ferrosilicon are used for inoculation, which can prevent spheroidization from declining.
3. When producing ferritic ductile iron, when the spheroidization rate is required to reach more than 90%, Xinyuanzhu recommends the following measures:
3.1 Choose high-quality charge to reduce the de-spheroidization elements in the charge.
3.2 Choose a spheroidizing agent with a low amount of ω (RE) to reduce the deteriorating effect of RE on the morphology of spheroidal graphite.
3.3 The ω(S) content of the original molten iron should be less than 0.020%, which can reduce the consumption of spheroidizing agent, especially the spheroidizing elements consumed by the secondary sulfurization of the sulfide slag.
3.4 Pre-deoxidize the molten iron, increase the number of graphite spheres per unit area, increase the spheroidization rate, greatly improve the resistance to decline, and extend the effective incubation time.
3.5 Reduce the amount of ω (Si) in the original molten iron, increase the amount of spheroidizing agent, inoculant and various pretreatment agents to strengthen incubation.
Xinyuanzhu Group specializes in the production of Ductile iron castings, Pig iron gray iron casting, Steel casting, Brass Casting, Malleable Iron Casting, and undertakes batch casting processing of castings. Welcome guests to cooperate with pictures or samples.
