Silicon-calcium alloys: Multifunctional modifiers in the metallurgical industry and key alloys in high-end manufacturing

I. Core Definition of Silicon-Calcium Alloy Silicon-calcium alloy is a binary composite alloy formed by silicon (Si) and calcium (Ca), with silicon and calcium as the main alloying elements and iron as a minor matrix component. Typical silicon content ranges from 50% to 80%, and calcium content from 10% to 30%. It is a high-performance composite deoxidizer, desulfurizer, and alloying agent in the metallurgical industry. Its core value lies in utilizing the synergistic effect of silicon and calcium to achieve deep purification and performance optimization of steel materials. Simultaneously, thanks to the strong chemical reactivity of calcium and the stability of silicon, it has expanded into diverse applications in high-end casting, new energy, and other fields, becoming an important functional material connecting traditional metallurgy and high-end manufacturing. II. Development History The industrial production of silicon-calcium alloy began in the 1930s. With the breakthrough in electric arc furnace reduction technology, Europe and the United States achieved large-scale smelting for the first time. Initially, it was mainly used for deoxidation treatment of military special steels, solving the problem that traditional single deoxidizers could not remove trace oxygen and sulfur impurities from steel. From the 1960s to the 1980s, the rise of the global machinery manufacturing and automotive industries led to increased demands for steel purity and mechanical properties. The "composite modification" advantages of silicon-calcium alloys became prominent, and production processes were upgraded from open electric furnaces to closed submerged arc furnaces, significantly improving capacity and product stability. Since the 21st century, the "dual-carbon" strategy and high-end manufacturing upgrades have driven industry transformation, accelerating the research and development of high-purity and low-carbon silicon-calcium products. Application scenarios have expanded from traditional steel to new energy, special materials, and other fields, continuously enhancing their strategic importance. III. Core Characteristics Analysis

(I) Metallurgical Core Characteristics

The core advantage of silicon-calcium alloys lies in the synergistic effect of silicon and calcium: calcium has extremely strong deoxidizing ability (superior to silicon and aluminum), capable of forming low-melting-point (1544℃) calcium silicate (CaSiO₃) with oxygen in molten steel, which easily floats and separates, achieving deep deoxidation; simultaneously, calcium can combine with sulfur to form stable calcium sulfide (CaS), with a desulfurization efficiency of over 85%, effectively avoiding the hot brittleness defects in steel caused by sulfide inclusions. In addition, calcium can refine the grain size of steel, improve the morphology of inclusions, and enhance the toughness, fatigue strength, and corrosion resistance of steel, achieving the triple effect of "deoxidation - desulfurization - grain refinement". (II) Physical and Chemical Properties The appearance of silicon-calcium alloy is a silver-gray metallic block. The surface is easily oxidized to form a light gray oxide film. The density varies with the composition, ranging from 2.5 to 2.8 g/cm³, and the melting point ranges from 1250 to 1350℃ (the higher the calcium content, the lower the melting point). It is chemically active and easily absorbs moisture and oxidizes at room temperature, requiring sealed storage. At high temperatures, it has strong reducing properties and can react with various harmful elements such as oxygen, sulfur, and nitrogen, but does not react harmfully with beneficial elements such as manganese and chromium in steel, making it highly compatible. (III) Process Adaptability Silicon-calcium alloy dissolves uniformly in molten steel and has good fluidity. It can be added through various methods such as wire feeding, blowing, and in-stream addition, making it suitable for various smelting processes such as converters, electric furnaces, and continuous casting. Products with different component ratios can be precisely matched to needs: high-calcium silicate (Ca≥28%) is suitable for deep purification of special steels; medium-calcium silicate (Ca15%~25%) is widely used in the production of ordinary steels; and low-calcium silicate (Ca10%~15%) is suitable for the incubation modification needs in the casting field. IV. Mainstream Production Processes

(I) Electric Arc Furnace Silicon Thermal Reduction Method (Mainstream Process)

This is currently the core process for global silicon-calcium alloy production. It uses silica (quartz sand) and calcium oxide (quicklime) as raw materials, and ferrosilicon and coke as reducing agents. These are mixed in a specific ratio and then loaded into a closed submerged arc furnace (commonly 25000~33000kVA). High temperatures are generated through the electrode arc (furnace temperature reaches 1900~2100℃), causing calcium oxide to be reduced to calcium by silicon, while simultaneously combining with silicon and iron to form a silicon-calcium alloy. The molten alloy is discharged through the taphole, cast into ingots, cooled, crushed, and screened to the target particle size (commonly 10~50mm). This process has the advantages of large capacity and mature technology, but the traditional process consumes about 9,500 to 10,500 kWh of electricity per ton of product, which is higher than that of ferrosilicon. (II) Process Technology Upgrade Direction With the upgrading of environmental protection and "dual carbon" requirements, the industry is accelerating process innovation: First, green electricity coupled smelting, enterprises in Inner Mongolia, Xinjiang and other places have introduced wind and solar green electricity, which can save 720 to 800 yuan in electricity costs per ton of product and reduce carbon emissions by more than 80%; Second, intelligent transformation of equipment, large closed submerged arc furnaces are equipped with intelligent batching and waste heat recovery systems, which improve energy efficiency by 15% to 20%; Third, refining process optimization, through vacuum degassing and ladle refining technology to remove impurities such as phosphorus and aluminum, producing high-purity silicon-calcium alloy (total impurities < 0.3%); Fourth, new reduction technology, the carbothermic reduction-aluminothermic assisted process is in the pilot stage, which can reduce energy consumption by 10% to 12%. (III) Product Form Optimization To improve efficiency, the industry has launched various specialized product forms: silicon-calcium wire (diameter 13~16mm) is adapted to continuous casting wire feeding processes, allowing for precise control of the addition amount; silicon-calcium powder (particle size < 1mm) is used for injection desulfurization and deoxidation; composite alloy products such as silicon-calcium-barium and silicon-calcium-manganese further expand functional scenarios. V. Core Application Areas (I) Steel Industry (Traditional Core Area) More than 80% of the world's silicon-calcium alloys are used in steel production, making them an indispensable modifier for special steels and high-quality steels. In the production of bearing steel, spring steel, and high-strength structural steel, adding 0.2%~0.5% silicon-calcium alloy can reduce the oxygen content in the steel to below 20ppm and the sulfur content to below 10ppm, significantly improving the fatigue life and impact resistance of the steel. In the production of stainless steel and heat-resistant steel, the desulfurization effect of silicon-calcium can avoid hot brittleness during high-temperature processing, ensuring product qualification rate. In the production of high-strength steel for automobiles and steel for engineering machinery, its grain refinement effect can achieve a balance between "strength and toughness" in steel. (II) Casting Field (Important Application Scenarios) Silicon-calcium alloy is a high-quality inoculant and modifier in cast iron production. After addition, it can refine the graphite structure, reduce the tendency of white cast iron, and improve the mechanical strength, wear resistance, and machinability of castings. It is widely used in the production of automobile engine blocks, crankshafts, machine tool beds, and engineering machinery castings, especially suitable for high-strength gray cast iron and ductile iron castings, which can reduce the scrap rate of castings by 15%~20%. (III) Emerging High-End Fields (Growth Engines) In the new energy field, high-purity silicon-calcium alloys can be used to adjust the purity of electrolytes in vanadium redox flow batteries, improving battery cycle stability; in the special materials field, they are used as raw materials for the production of high-temperature alloys and hard alloys, enhancing the high-temperature strength and corrosion resistance of materials; in the chemical field, they serve as catalyst carriers for organic synthesis reactions, utilizing their high specific surface area and chemical stability to improve catalytic efficiency; in the aerospace field, they meet the smelting needs of ultra-high-strength steel, used to manufacture key components such as aircraft landing gear and engine parts. VI. Market Development Trends (I) Steady Demand Growth and a Shift Towards High-End Industries In 2024, China's silicon-calcium alloy production capacity was approximately 1.8 million tons, with a market size exceeding 15 billion yuan. The average annual compound growth rate is expected to remain at 5.8%~7.2% over the next five years. Among them, the demand for high-purity silicon-calcium alloy (Si≥75%, Ca≥25%, total impurities <0.3%) is growing the fastest, with its share increasing from 12.3% in 2024 to over 25% in 2029. Currently, the domestic supply-demand gap is 18,000 tons, with an import dependency of about 28%, mainly relying on imports from Russia and Kazakhstan. High-end steel and new energy storage are becoming the core driving forces for demand. (II) Optimization of production capacity structure, and intensified regional and enterprise differentiation. Global silicon-calcium alloy production capacity is mainly concentrated in China (accounting for over 65%), Russia, Ukraine and other countries, while domestic production capacity is mainly distributed in the Northwest (Inner Mongolia, Ningxia) and North China (Hebei, Shanxi) regions. Affected by the dual control policies of ecological red lines and energy consumption, the production capacity share of the traditional production areas in the Northwest will decrease from 70% to 55% in 2029. Xinjiang, Qinghai and other regions will take over the incremental production capacity by virtue of their green electricity advantages, forming a layout of "smelting moving westward and deep processing moving eastward". Industry concentration continues to increase, with the top ten companies accounting for 52.6% of the total capacity. Leading companies such as Baogang Group, Ningxia Shengyan, and Inner Mongolia Junzheng have built competitive barriers through resource integration and technological upgrades, while small and medium-sized enterprises are focusing on niche markets or transforming into composite alloy production. (III) Green and Low-Carbon Driven, Technological Innovation Becomes Key The "dual-carbon" strategy is driving the industry's low-carbon transformation, with green electricity smelting and energy efficiency improvement becoming core directions. Policies require that all production capacity failing to meet energy efficiency benchmarks (electricity consumption per ton of product ≤ 9200 kWh) be phased out by 2025, forcing companies to increase investment in technological upgrades. The adoption rate of intelligent batching and waste heat recovery technologies is expected to increase from 38% in 2024 to 60% in 2027. In the medium to long term, the research and industrial application of carbon-free reduction technologies (such as hydrogen-based reduction) will reshape the industry landscape, and the development of high-purity, composite products will become a core competitive advantage for enterprises. (IV) Price Fluctuations and Strategic Layout The price of silicon-calcium alloys is affected by multiple factors: fluctuations in the prices of upstream raw materials such as silica (average price of RMB 390/ton in 2024, an increase of 11.4%), quicklime (average price of RMB 420/ton, an increase of 18.6%), and coke directly affect production costs; downstream factors such as the operating rate of the steel industry, demand for high-end casting, and new energy policy guidance influence the demand side; while green electricity policies and environmental standards affect supply elasticity. Due to its key role in the high-end steel and new energy industry chains, silicon-calcium alloys have been included in the key mineral supply chain management of many countries. Enterprises are strengthening their reserves of resources such as silica and quicklime and aligning with green electricity to ensure the security of the industry chain.