Cold Heading Steel

Cold-heading steel, also known as cold-forging steel or rivet-and-screw steel, refers to a specialized steel grade used to produce standard and non-standard fasteners—such as screws, pins, and nuts—through cold heading at room temperature, utilizing metal plastic forming processes and applying one or more impact loads. The cold heading process conserves raw materials (reducing metal consumption by 10% to 30%), lowers costs, and improves the tensile strength of workpieces through cold work hardening, thereby enhancing their performance. Steel for cold heading must possess good cold heading properties; generally, a yield-to-tensile strength ratio of 0.5 to 0.65 and a cross-sectional reduction of more than 50% are required. At the same time, the content of impurities such as sulfur and phosphorus in the steel must be reduced, with sulfur and phosphorus levels typically controlled at ≤0.035%. Strict requirements are placed on the surface quality of the steel, and surface decarburization must be minimized as much as possible; high-quality carbon structural steel or alloy structural steel is typically selected. If the carbon content of the steel exceeds 0.25%, spheroidizing annealing heat treatment is required to transform lamellar pearlite into granular pearlite, thereby improving the steel’s cold heading performance.

In China, the prefix “ML” is used to designate this type of steel; the main grades include ML08Al, ML10, ML15Mn, ML20Cr, ML30CrMo, ML35, ML40Cr, and ML45. To facilitate international communication, these grades generally correspond to commonly used international standards: ML08Al corresponds to SWRCH8A (JIS) and 1010 (ASTM); ML15 corresponds to SWRCH15K (JIS) and 1015 (ASTM); ML35 corresponds to SWRCH35K (JIS) and 1034 (ASTM); ML20Cr corresponds to 5120 (ASTM), and ML40Cr corresponds to 5140 (ASTM) and 41Cr4 (EN). Major international standards for steels used in cold heading and cold extrusion include ISO 4954, EN 10263, ASTM A493, and JIS G3507, which specify requirements for chemical composition, mechanical properties, hardenability, grain size, carbide spheroidization grade, non-metallic inclusions, and surface quality.

Production Process of Cold-Heading Steel

The production process for cold-heading steel typically consists of the following steps:
Molten iron pretreatment → Converter smelting → Refining furnace (LF refining; high-end products require RH vacuum treatment) → Continuous casting (protected casting) → Ingot inspection and grinding → Heating → Rolling (rough rolling, intermediate rolling, pre-finishing, finishing, and sizing) → Controlled cooling (Steelmore cooling line) → finished product inspection → warehousing.
The key to smelting cold-heading steel lies in improving the purity of the molten steel and reducing contamination from non-metallic inclusions. Stabilizing the carbon content at the end of the smelting process within the specified range is the primary measure for reducing the degree of oxidation in the molten steel and minimizing contamination from non-metallic inclusions. High-quality cold-heading steel, achieved by integrating key technologies from refining, continuous casting, and rolling, can control the total oxygen content in the cast billet to within 12 ppm, maintain an inclusion rating below Grade 1.5, and achieve a cast billet yield rate of over 98%.

Advantages of Cold-Heading Steel
High Strength: Cold-heading steel possesses high strength and hardness, enabling it to withstand heavy loads and impact forces, thereby ensuring that parts made from cold-heading steel have high durability and a long service life.
Good Machinability: Cold-heading steel has good plasticity and machinability, making it easy to cold-head and form into parts of various shapes to meet the needs of different industrial sectors.
Excellent Corrosion Resistance: After undergoing special treatment, cold heading steel exhibits excellent corrosion resistance, enabling long-term use in harsh operating environments and extending the service life of parts.
Cost-Effective: Cold heading steel parts, with their high strength and hardness, reduce material consumption and lower production costs. The cold heading process is characterized by high efficiency and low energy consumption; it produces parts with high dimensional accuracy and good surface finish, thereby improving production efficiency.
Environmentally Friendly and Energy-Efficient: Cold heading is a near-net-shape forming process that produces virtually no scrap and requires no cutting fluid, thereby reducing environmental pollution. Cold-headed steel parts have a long service life, which reduces resource consumption.

Applications of Cold-Headed Steel
Bolts and Nuts: Cold-headed steel possesses excellent mechanical properties and high strength, making it commonly used in the manufacture of bolts and nuts. Bolts and nuts are standard fasteners in mechanical connections and are widely used in the automotive, machinery, and construction industries.
Studs and Pins: Studs and pins made from cold-headed steel offer high strength and good wear resistance, making them suitable for the drive systems of various types of machinery. Studs and pins are commonly used transmission components in mechanical equipment, serving to transmit force and rotational motion.
Wire Ropes: Wire ropes made from cold-headed steel possess excellent tensile strength and corrosion resistance, and are widely used in fields such as lifting and transportation. Wire ropes are important industrial ropes used for lifting, towing, and securing operations.
Coil Springs: Coil springs made from cold-headed steel feature high elasticity and good resilience, and are widely used in the automotive and home appliance industries. Coil springs are common elastic components used for vibration damping, cushioning, and support in various mechanical equipment.
Cold-Headed Parts: Cold-headed steel can be processed through cold heading to produce parts of various shapes, such as screws, pins, and blind rivets. These cold-headed parts are widely used in the automotive industry (covering the five major systems: steering, body, chassis, drivetrain, and powertrain), mechanical equipment, electronic products, and other fields, and are indispensable components in mechanical manufacturing.

Thanks to its wide range of applications and numerous advantages, cold-headed steel has become one of the indispensable base materials in industrial production. With the continuous advancement of technology, the application areas of cold-headed steel will expand further, offering more possibilities for the development of various industries.

Overview of Major Standards
The international standard system for cold-headed steel is centered on the ISO 4954 and EN 10263 series, and major industrialized nations have developed their own national standards based on these.
Chinese Standards

Among these, GB/T 6478-2015 is China’s most fundamental standard for cold-headed steel, specifying comprehensive requirements for non-alloy steels and alloy structural steels, including classification, grades, dimensions, shapes, weights and allowable tolerances, technical requirements, test methods, and inspection rules. The upper limit for the nominal diameter of wire rod has been expanded from 40 mm in the previous edition to 60 mm.
International Standards
ISO 4954: Consists of two parts—Part 1 covers non-alloy and alloy steels, applicable to products with diameters ranging from 2 to 100 mm; Part 2 covers stainless steels, with austenitic stainless steels ranging from 0.8 to 50 mm in diameter, ferritic stainless steels up to 25 mm, and martensitic stainless steels up to 100 mm.
EN 10263: European standard for steels for cold heading and cold extrusion; Parts 2–4 cover products with diameters ≤100 mm; Part 5 covers stainless steels, with ferritic/austenitic-ferritic stainless steels up to ≤25 mm, austenitic stainless steels up to ≤50 mm, and martensitic stainless steels up to ≤100 mm.

Japanese Standards
JIS G3507: Carbon steel wire rod for cold heading; commonly supplied in diameters ranging from 5.5 to 42 mm (hot-rolled wire rod); spheroidized-annealed cold-heading wire is available in diameters ranging from φ2.0 to 42.0 mm.
U.S. Standards
ASTM A29/A29M: General Requirements for Hot-Forged Carbon and Alloy Steel Bars, covering bars with diameters ranging from 3 to 300 mm. Wire for cold heading typically has diameters ranging from 5 to 25.4 mm.

Common Size Ranges
Cold-heading steel is classified into three categories based on product form: hot-rolled wire rod, hot-rolled round bar, and cold-heading wire, each with its own size range.
Hot-rolled wire rod (the most commonly supplied form)

In actual production, the φ5.5–20 mm range is the most in-demand size range, covering the material requirements for the vast majority of standard fasteners (bolts, nuts, and screws). Zhongtian Steel supplies cold-heading steel wire rod in sizes ranging from φ5.5 to 42.0 mm, compliant with various standards including GB, JIS, ASTM, and DIN/EN. Baosteel’s cold-heading steel wire rod is available in diameters ranging from φ5.5 to 28.0 mm. The typical specifications for -10B21 cold-heading steel wire rod are φ6.5 to 20 mm, primarily used for manufacturing high-strength self-tapping screws and Grade 8.8 standard fasteners.
Hot-Rolled Round Bars
GB/T 6478-2015 specifies that the nominal diameter of hot-rolled round bars ranges from φ12 to 100 mm; they are suitable for larger-sized fasteners or parts requiring subsequent machining. -
Cold-Heading Steel Wire
Cold-heading steel wire is produced from wire rod through further processing such as drawing and annealing, resulting in higher precision. GB/T 5953.1/.2-2009 expanded the wire diameter range from the previous version’s φ1.00–16.00 mm to φ1.00–45.0 mm and tightened the requirements for dimensional accuracy and straightness. Among these, wires with diameters not exceeding 16 mm are controlled to Grade 10 accuracy as specified in Table 3 of GB/T 342-1997.

Notes
The selection of cold-heading steel dimensions should be based on the downstream processing methods: wire rod is suitable for direct cold heading or for use after drawing; steel wire is suitable for precision fasteners that require higher dimensional accuracy and surface quality; and round bar is typically used for larger-sized parts or applications requiring turning. The material is usually supplied in coils, with each coil typically weighing between 1,800 and 2,500 kg.