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The unique value of silicon zirconium inoculant lies in improving the high-temperature mechanical properties and tissue stability of cast iron, and also has the function of refining grains. The specific applications are as follows:
Heat-resistant cast iron production (core application field
Heat-resistant cast iron (such as RQTSi5 and RQTSi4Mo) need to maintain strength and oxidation resistance under high temperature (400-800℃) environment.
The role of silicon zirconium is reflected in:
Inhibiting high-temperature graphite coarseness: Zirconium can form stable ZrC (high melting point compound, melting point 3540℃) with the carbon in molten iron, preventing graphite from growing or spheroidizing and decaying at high temperatures, and keeping the graphite form stable in long-term high-temperature service. For example, in the boiler heat-resistant cast iron grate (operating temperature 600-700℃), after adding 0.5-0.8% silicon zirconium, the average graphite size can be controlled from φ80-100μm to φ40-60μm, and the high-temperature tensile strength (600℃) is increased from 180MPa to 220-240MPa, and the service life is extended by 30-50%.
Enhanced oxidation resistance: Zirconium can promote the formation of dense SiO₂-ZrO₂ composite oxide film (melting point >1700℃) on the surface of cast iron, reducing the high-temperature oxidation rate. Compared with ordinary heat-resistant cast iron incubated by ferrosilicon, after oxidation of castings in 800°C for 100 hours, the oxidation weight gain dropped from 0.15g/cm² to below 0.08g/cm².
The homogenization of thick and large-section ductile iron is nurtured.
Thick and large ductile iron parts (such as wind turbine hubs and turbine wheels, wall thickness > 100mm) are prone to coarse graphite in the core and low spheroidization rate due to slow cooling speed. The role of silicon zirconium is:
Refining the core graphite sphere: The 'heterogenous nucleation' of zirconium can promote the uniform nucleation of graphite spheres during the slow cooling process, so that the size of the core graphite spheres will decrease from φ60-100μm to φ30-50μm, and the number of spheres from 50-80 pieces/mm² to 100-120 pieces/mm². For example, after the wind turbine hub (QT400-18) is incubated with silicon zirconium, the hardness difference between the heart and the surface layer drops from ±40HB to ±15HB, meeting the requirements of low-temperature impact toughness (-40℃ Akv ≥ 20J).
Inhibit the pearlite dilated: The center of the thick and large section is prone to form a mesh pearlite due to segregation of solute elements. Zirconium can refine the austenite grains to make the pearlite evenly distributed and avoid brittlement.
Wear-resistant cast iron and high-strength gray cast iron
Wear-resistant cast iron: such as machine tool guide rails, roll cast iron (HT350), silicon zirconium improves the casting hardness by 15-20% (from 220HB to 250-260HB), while reducing surface peeling caused by abrasive wear.
High-strength gray cast iron: In castings with tensile strength >300MPa (such as diesel engine cylinder blocks), silicon zirconium can cooperate with silicon to strengthen the matrix, increasing the pearlite content from 80% to more than 90%, and increasing the tensile strength from 280MPa to 320-340MPa.
Compared with incubators such as strontium silicon and calcium silicon, the advantages of zirconium silicon are concentrated in high-temperature performance and tissue stability:
High-temperature performance is outstanding, suitable for high-temperature service scenarios
The high melting point characteristics of zirconium can maintain its incubation effect at 400-800℃, which is irreplaceable by strontium silicon (high-temperature easily fails) and calcium silicon (high-temperature easily oxidized). In heat-resistant cast iron, silicon zirconium can increase the high-temperature strength retention rate of castings by 20-30%, and is the first choice inoculant under high temperature conditions.
Strong grain refinement ability, improve thick and large sectional structure.
The nucleation activity of zirconium (ZrC as the graphite nucleation core) is 5-8 times that of silicon. Especially in thick and large castings with slow cooling speed, it can effectively inhibit the coarseness of graphite and the segregation of components, reducing the tissue difference between the heart and the surface by more than 50%, solving the problem of 'insufficient heart performance' of traditional inoculants.
The long anti-fertilization decline time is suitable for complex production processes.
The effective duration of silicon zirconium inoculant can reach 60-90 minutes, far exceeding that of strontium silicon (40-60 minutes) and ordinary ferrosilicon (20-30 minutes). It is suitable for the production of large castings with long iron transport distances and long casting cycles (such as heavy mechanical castings).
Low sensitivity to oxygen and sulfur, high process error tolerance.
The reactivity of zirconium and oxygen and sulfur is lower than that of strontium and calcium. Even if the oxygen content (>0.01%) or sulfur content (>0.06%) in the molten iron is relatively high, it can still maintain a stable incubation effect (and strontium silicon is prone to failure under high sulfur, and calcium silicon is prone to inclusions under high oxygen), reducing the difficulty of process control.
