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The core value of silicon magnesium spheroidizer lies in the efficient realization of graphite spheroidization. It is the 'standard configuration' for the production of ductile iron (QT400-18 to QT800-2 and other grades). The specific applications are as follows:
General mechanical and automotive parts (core fields)
Key parts of the engine: such as crankshafts, connecting rods, camshafts, requiring high fatigue strength (>300MPa) and impact toughness (Akv>15J). After the silicon magnesium spheroidizing agent is treated, the graphite spheroidization rate can reach 85-95% (≥80% is qualified). Spherical graphite can reduce stress concentration and increase the fatigue life of the casting by 2-3 times (compared with gray cast iron). For example, after the crankshaft of the automotive engine (QT600-3) is treated with silicon magnesium, the tensile strength is increased from 250MPa of gray cast iron to above 600MPa, and the elongation is increased from 1% to 3-5%.
Chassis components: For example, steering knuckles and wheel hubs, both strength and toughness are required. Silicon magnesium spheroidizer can stably control the graphite ball diameter (φ20-50μm) to avoid the risk of brittle breaking caused by sheet graphite. The impact toughness of low temperature (-20℃) can reach 20-30J.
Engineering pipelines and pressure vessels
Ductile iron pipes: used in urban water supply and gas pipelines (DN100-DN2000), requiring pressure bearing capacity (≥10MPa) and corrosion resistance. After the silicon magnesium spheroidizing agent is treated, the cast iron matrix is mainly ferrite (70-80%), and combined with spherical graphite, the elongation of the pipeline reaches 10-15%, and can withstand trace deformation (≤3%) caused by soil settlement without rupture, and its service life is more than 50 years.
Pressure vessel accessories: such as valve housing and pump body, silicon magnesium spheroidization can reduce the cracking of graphite on the substrate, increase the compressive strength of the casting to 400-500MPa, meeting the pressure resistance requirements (≤1.6MPa operating conditions).
Wind power and heavy machinery
Wind power hub, bearing seat: castings with large sections (wall thickness 50-200mm) need to avoid core graphite distortion. Silicon magnesium spheroidizing agent (including rare earth type) can maintain the core spheroidization rate above 80% through the 'anti-declination' effect of rare earth elements (ordinary silicon magnesium agents are prone to poor core spheroidization due to slow cooling), ensuring uniform overall mechanical properties (tensile strength fluctuations ≤50MPa).
The core reason why silicon magnesium spheroidizers have become mainstream is that they have high spheroidization efficiency, mature processes and wide application range:
Strong spheroidization ability and stable effect
Magnesium is the 'high-efficiency element' of graphite spheroidization: When the magnesium content in molten iron is controlled at 0.04-0.08%, graphite can be prevented from expanding along the base surface (sheet growth direction) by adsorption at the graphite growth interface, forcing it to grow in three-dimensional spheroidization, and the spheroidization rate can reach 85-95% (much higher than 70-80% of cerium-based spheroidizers). Moreover, the spheroidization effect of silicon magnesium spheroidizer is less affected by fluctuations in molten iron composition (such as carbon content 3.6-4.2%), and is suitable for large-scale industrial production.
The reaction with molten iron is mild, and the process is easy to control.
Silicon magnesium spheroidizer is usually treated with the 'pull in' method. Treatment: Place the spheroidizer at the bottom of the molten iron bag. After the molten iron is washed in, the magnesium gradually evaporates at 1400-1500℃ (magnesium boiling point 1107℃), and reacts evenly with molten iron to avoid violent splashing (compare the pure magnesium block directly). After treatment, the spheroidization effect is stable within the sedation time of the iron (10-15 minutes) and is suitable for assembly line production (such as the beat of automobile castings 3-5 minutes/piece).
Coordinated optimization performance of composite elements
Silicon in the formula can improve the molten fluidity (reduced the melting point by 50-80℃) and reduce the defect of insufficient water pouring; rare earths (such as cerium) can extend the effective time of spheroidization (resistance resistance is extended from 30 minutes to 60 minutes), which is suitable for scenarios where the molten iron transport distance is long; calcium can refine graphite balls (the average ball diameter is reduced from 50μm to 30μm), further improving toughness.
The cost is moderate, and the cost-effectiveness is better than the special spheroidizer.
The price of magnesium (about 20-30 yuan/kg) is much lower than that of rare earth (cerium about 100-150 yuan/kg). The unit price of silicon magnesium spheroidizer (about 8-15 yuan/kg) is only 1/3-1/2 of the pure rare earth spheroidizer. It is cost-effective in medium and high-strength ductile iron (QT400-18 to QT600-3), and is suitable for large-scale production.
