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Help CenterSteel Round Bar & Round Steel Bar，Q235B、Q355B、45#、35#、20#、40Cr、35CrMo、42CrMo
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1. Product Definition
Round Steel Bar is a long solid steel product with a circular cross-section, a basic and general-purpose steel profile. According to production processes, it is divided into Hot Rolled Round Bar, Cold Drawn Round Bar and Precision Ground Round Bar. It covers carbon structural steel, high-quality carbon steel, alloy steel and other grades. Featuring complete specifications and stable performance, it is widely used in mechanical processing, steel structures, fasteners, molds, construction machinery and hardware accessories.
2. Core Product Advantages
Pure and stable material: Refined molten steel with few internal inclusions and uniform structure, ensuring consistent mechanical properties to meet various machining and load-bearing requirements.
Excellent workability: Moderate plasticity and toughness, suitable for cutting, bending, forging, stamping, turning, milling, tapping and other secondary processing.
Diversified dimensional accuracy: Hot rolled bars are cost-effective for rough machining; cold drawn and precision ground bars feature high dimensional accuracy and smooth surface for precision parts.
Wide range of strength grades: Covers low-carbon to high-strength alloy materials, adapting to light structures, heavy-duty equipment, high-temperature and wear-resistant working conditions.
Reliable & flexible supply: Manufactured in accordance with national standards with material certificates and test reports. Large stocks are available, and custom services including fixed length cutting, heat treatment and galvanizing are supported.
3. Common Material Grades & Applications
Carbon Structural Steel Bar (General Use)
Q195/Q215: Low carbon grade with good plasticity and easy processing. For general hardware, light supports, simple connectors and stamping parts.
Q235B/A3/SS400: Excellent overall performance and good weldability with low cost. Widely used for steel structure frames, embedded parts, general mechanical components, scaffolding and pipe supports.
Q355B/C/D: High-strength low-alloy steel with high strength, good low-temperature resistance and impact resistance. For construction machinery, equipment bases, load-bearing components and structural parts in low-temperature environments.
High-Quality Carbon Structural Steel Bar (Machining & Fasteners)
20#: High-quality low-carbon steel with good toughness and carburizing performance. For bolts, nuts, sleeves, welded parts and carburized gears.
35#: Moderate strength and available for quenching and tempering. For shafts, connecting rods and ordinary mechanical parts.
45#: The most commonly used medium-carbon quenched and tempered steel with balanced strength, hardness and toughness. For main shafts, gears, crankshafts, pin shafts and various machined standard parts.
Alloy Structural Steel Bar (High Strength / Wear Resistance / High Temperature Resistance)
40Cr: Chromium alloy steel with good hardenability, high strength, wear resistance and fatigue resistance. For transmission shafts, gears, hydraulic parts and heavy-duty fasteners.
42CrMo: High-grade alloy steel with outstanding high temperature resistance and impact resistance. For large gears, main shafts of construction machinery, high-pressure valves and mold accessories.
35CrMo: Excellent toughness, fatigue resistance and pressure resistance. For petroleum machinery, high-pressure pipe fittings and engine components.
4. Specification Parameters
Diameter Range
Hot rolled round bar: Φ10mm – Φ300mm (common sizes: Φ12/16/20/25/30/40/50/60/80/100mm)
Cold drawn / Precision ground round bar: Φ3mm – Φ120mm, mainly small diameter with high precision.
Standard Length
Regular length: 6m, 9m, 12m. Custom length from 2m to 12m is available, length tolerance ±50mm.
Theoretical Weight
Calculation formula: W(kg/m) = 0.00617 × Diameter²
Dimensional Tolerance & Surface Condition
Hot rolled round bar: Diameter tolerance ±0.5mm~±1.2mm, hot rolled black surface with oxide scale.
Cold drawn round bar: Diameter tolerance ±0.03mm~±0.1mm, smooth surface without oxide scale.
Precision ground round bar: Tolerance up to ±0.01mm with mirror finish, for precision equipment.
5. Production Process
Hot Rolled Round Bar (Mainstream)
Steel billet heating (1100–1250℃) → Multi-pass rolling into circular section → Cooling → Straightening → Fixed-length cutting → Inspection → Packaging.
Cold Drawn Round Bar
Hot rolled bar billet → Pickling to remove oxide scale → Cold drawing forming → Straightening → Polishing → Inspection → Packaging (improves dimensional accuracy and surface quality).
Precision Ground Round Bar
Cold drawn round bar → Centerless grinding → Straightening → Cleaning → Inspection → Packaging (for precision machinery).
Subsequent Heat Treatment
Normalizing, annealing, quenching and tempering, quenching and carburizing are available to adjust hardness and strength as required.
6. Execution Standards
Carbon structural steel: GB/T 700
High-strength low-alloy steel: GB/T 1591
High-quality carbon structural steel: GB/T 699
Alloy structural steel: GB/T 3077
General standard for hot rolled round steel: GB/T 702
Export standards: ASTM A108, JIS G4051, DIN 1013
7. Main Applications
Steel Structure Engineering: Factory frames, building embedded parts, supports, tie rods and guardrails. Main grades: Q235B, Q355B.
General Mechanical Processing: Ordinary shafts, gears, connecting rods and shell parts. Main grades: 45#, 35#, 20#.
Fastener Industry: Bolts, nuts, studs, rivets and standard parts. Main grades: 20#, 35#, 45#, 40Cr.
Construction & Heavy Machinery: Load-bearing parts and travelling mechanisms for excavators, loaders and cranes. Main grades: Q355B, 40Cr, 42CrMo.
Petroleum & Chemical Equipment: Mechanical parts, valve shafts and pipe pile connectors. Main grades: 35CrMo, 42CrMo.
Hardware Products: Stamping parts, handles, small fittings and daily hardware. Main grades: Q195, Q215, Q235B.
8. Delivery Cycle
Regular stock (Q235B, 45# hot rolled round bar): 3–5 working days
Alloy round bar (40Cr, 42CrMo, 35CrMo): 3–5 working days
Cold drawn / precision ground bar & custom cutting: 4–7 working days
Custom orders with heat treatment, galvanizing and finish machining: 7–10 working days
Export orders with inspection documents, English certificates and export packaging: 8–12 working days
9. Quality Inspection
Full inspection items: chemical composition, tensile strength, yield strength, elongation, impact toughness, hardness, dimensional tolerance, surface defects and metallographic structure. Defects such as cracks, folds, slag inclusion, eccentricity and excessive bending are strictly prohibited. Original material certificates and mechanical test reports are provided for each batch with full quality traceability.
10. Packaging Method
Domestic packaging: Bundled with steel straps, marked with specification, material grade, heat number and batch number, suitable for land transportation.
Export packaging: Wrapped with inner waterproof film and protected by outer woven bag or steel sheet, fixed on wooden pallets. Moisture-proof, rust-proof and collision-proof, complying with marine transportation and inspection standards.
Custom packaging: Small-diameter precision ground bars are individually or layered packed with anti-rust oil paper to avoid scratches.
11. Storage & Usage Precautions
Storage: Store in dry and ventilated warehouse, keep the stack over 15cm above the ground to avoid moisture and rain. Stack by material grade, diameter and specification separately, and keep away from acid and alkali corrosive substances.
Processing: Low-carbon steel features good weldability and stamping performance. Preheating is recommended before welding medium-carbon steel and alloy steel. Avoid improper high-temperature reheating for quenched and tempered bars.
Selection: Choose Q235B for general structures; 45# is preferred for machined standard parts; 40Cr, 42CrMo for heavy-duty and wear-resistant parts; Q355C/D for low-temperature working conditions.
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