Carbon cold rolled and hot rolled wire rods are widely used in the production of fasteners. The low-carbon SWRCH6–16A series are non-heat-treated steels suitable for cold heading and cold extrusion. These materials are ideal for manufacturing various types of fasteners with lower strength requirements. Due to the high deformation involved in cold heading, especially when the deformation exceeds one-third, annealing is often necessary. It is recommended that customers choose low-carbon grades such as SWRCH6A, particularly for large deformation applications. When selecting wire material specifications, it's best to match them as closely as possible to the required product dimensions, which helps reduce drawing deformation and minimize work hardening effects. Free return cold rolled steel and hot rolled wire rods have been developed with advanced technologies to improve efficiency and quality. In 2004, Maanshan Iron & Steel Co., Ltd. initiated the National 863 Program titled "Research on High Performance and Low Cost Cold Rolled Steel" (2003AA331030), aiming to develop an independent, cost-effective cold heading steel production technology in China. High-strength fasteners rated at 8.8 and above are typically made from medium carbon or medium carbon alloy steels. The standard process involves hot rolling, spheroidizing annealing, cold drawing, forming, and quenching and tempering. Spheroidizing annealing ensures sufficient plasticity for cold heading, which can involve up to 70–80% total deformation. Therefore, raw materials must have low hardness, usually not exceeding HRB82. This step is time-consuming and energy-intensive, prompting the industry to seek ways to simplify or eliminate it. Ma Steel’s high-line technology has introduced unique hot-rolling processes with independent intellectual property rights. They have developed annealed SWRCH35K-M and CH35A-M hot-rolled wire rods, as well as SWRCH35K-MT and CH35A-MT for the U.S. market. These products offer a range of sizes and are suitable for manufacturing hex bolts and similar fasteners. For large deformation applications, spheroidizing annealing is still required. However, for nuts, MFM-1 and MFM-3 wire rods have been developed without annealing, while MFM-2 eliminates both annealing and quenching + tempering, directly producing grade 8 nuts. Non-tempered cold heading steel is primarily used for high-strength bolts like 8.8, 9.8, and 10.9. Using this type of steel simplifies the production process by eliminating pre-drawing annealing and post-bolting quenching and tempering. This reduces energy consumption, shortens the production cycle, and avoids issues like surface oxidation and decarburization. Japan has already implemented mass production of such materials. In 2005, Maanshan Iron & Steel Co., Ltd. participated in the National 863 Program Guided Project “Research and Development of Non-Quenched and Tempered Steel Wire for Low Temperature Controlled Rolling and Controlled Cooling Fasteners†(2005AA001110). In 2008, they further contributed to the National Support Program Project “Development of Low-Cost, High-Strength Non-Quenched and Tempered Cold-Rolled Steel Products for Steel Structure Joints†(2007BAE30B04). The non-tempered steel series developed by Maanshan Iron & Steel uses micro-alloying, controlled rolling, and cooling techniques to achieve ultra-fine grain structures. This allows for the omission of annealing and preparation steps in fastener manufacturing, ensuring performance meets current mechanical standards (GB/T 3098.22-2009). This green production method significantly reduces energy use, costs, and environmental impact, while also minimizing defects like quenching cracks and surface decarburization. Alloy cold heading steels such as 10B21, ML40Cr, and SCM435 are used for high-grade fasteners ranging from 8.8 to 12.9. Through strict process control, these materials deliver excellent performance and cost-effectiveness, making them ideal for demanding applications. Siemens
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