Currently, Toray Industries of Japan is the world’s largest producer of carbon fiber and firmly controls the market share for high-end carbon fiber applications. Due to Toray’s leadership in the carbon fiber field, its carbon fiber product grades have become universally recognized benchmarks worldwide.
The first important specification related to carbon fiber is the number of fibers in a tow
Carbon fiber is a fine, elongated filament with a diameter of 5-7 μm. A single carbon fiber filament has limited mechanical properties and is difficult to handle, so in most applications, multiple carbon fiber filaments are bundled into a tow for use. The number of carbon fiber filaments in a tow is measured in K, with 1K representing 1,000 carbon fiber filaments in a single tow. Common tow specifications include 1K, 2K, 3K, 6K, 12K, 24K, 48K, 60K, 80K, and 120K. Carbon fibers with fewer than 24K fibers are referred to as small-tow, while those with more than 48K fibers are referred to as large-tow. Small-tow carbon fibers have higher tensile elastic modulus and tensile strength compared to large-tow carbon fibers. When woven into composite materials, small-towel carbon fiber exhibits superior mechanical properties and is commonly used in the aerospace industry, hence it is also referred to as aerospace-grade carbon fiber. Although it offers superior performance, the production cost of small-towel carbon fiber is significantly higher than that of large-towel carbon fiber.
The fundamental reason for the cost difference between carbon fibers of the same model but different specifications lies in the differences in their manufacturing processes. Small-towel carbon fibers require finer precursor fiber dimensions, longer oxidation times, and higher carbonization temperatures to achieve higher carbon content, resulting in significantly higher production costs for small-towel carbon fibers. Under the same quality conditions, small-tow carbon fiber has higher strength compared to large-tow carbon fiber, making it widely used in the manufacture of load-bearing components for aerospace vehicles, such as wings, propellers, and hulls. Large-tow carbon fiber has lower tensile strength but offers better cost-effectiveness, and is primarily used in fields such as medical equipment, civil engineering, and transportation.
Another important specification related to carbon fiber is the carbon fiber grade
Toray Industries categorizes its carbon fiber products into the “T” series and the “M” series. The T series consists of high-strength carbon fibers, with grades selected based on tensile strength, divided into standard modulus-based and high-strength medium modulus grades. The M series is graded based on tensile modulus, divided into medium modulus and high modulus types. Later, the MJ series of carbon fibers was developed, which achieves both high strength and high modulus. The higher the number in the designation, the higher the performance grade of the carbon fiber. Those with letters at the end have better performance than those without letters.
Standard modulus carbon fibers generally have a tensile modulus of around 230 GPa, covering various specifications from 1K to 24K. Common standard modulus carbon fibers include T300, T400H, T700S, T700SC, and T700G.
T300 has been in commercial production for over 30 years and is the most widely used carbon fiber product, recognized as the industry standard. It is extensively used in the aerospace sector, with 1K, 3K, 6K, and 12K tow being the most common specifications. T400H features high tensile strength and is commonly available in 3K and 6K tow specifications. T700S is the highest modulus model among standard modulus carbon fibers, offering excellent processability and suitability for manufacturing pressure vessels via fiber winding or weaving methods. The most commonly used specifications are 6K, 12K, and 24K.
Medium-modulus carbon fibers have tensile strengths around 290 GPa and can be further classified into high-strength medium-modulus carbon fibers (T800H, T800S, T1000G) and ultra-high-strength medium-modulus carbon fibers (T1100G, T1100S) based on tensile strength. T800H was developed to meet the lightweight requirements of aircraft and is primarily used in secondary load-bearing structures such as vertical wings and horizontal stabilizers, with main filament specifications of 6K and 12K. T1000G has the highest elongation and is widely used in the manufacturing of pressure vessels, with only the 12K specification available. T1100G and T1100S have the highest tensile strength and are particularly suitable for processing methods such as weaving and winding, with only the 12K specification available.