B550L Hot Rolled Steel Coil
B550L Hot Rolled Steel Coil – Q/BQB 310-2009 Automotive Structural HSLA Steel
Comprehensive data on B550L hot rolled steel coil according to Baosteel Q/BQB 310-2009: chemical composition, mechanical properties, thermal and electrical physical performance, equivalent grades, and typical automotive applications.
Bending, cutting, welding, cold forming, hot forming
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B550L Hot Rolled Steel Coil Introduction
B550L is a micro-alloyed high-strength low-alloy (HSLA) steel grade specified in Q/BQB 310-2009, an enterprise standard of Baosteel. It utilizes small additions of niobium and titanium to achieve grain refinement and precipitation strengthening, delivering a minimum yield strength of 550 MPa while retaining good formability and excellent weldability. This grade is engineered for cold- and hot-forming operations typical in the manufacture of chassis and structural components for commercial vehicles. The low carbon equivalent and low sulfur/phosphorus contents ensure reliable toughness even at low temperatures, making it suitable for safety-critical dynamic load applications. Supplied in the as-hot-rolled condition, the product is available in coil or sheet form and can be processed by bending, cutting, and moderate drawing operations.
B550L Hot Rolled Steel Coil Chemical Composition
The chemical composition of B550L is designed to balance strength and formability. Niobium and titanium are the key precipitation strengthening and grain-refining elements. Carbon is kept low to ensure weldability, and sulfur and phosphorus are tightly controlled to enhance toughness and surface quality.
| Element | Standard Value | Remark |
|---|---|---|
| Carbon (C) | ≤ 0.12 | |
| Silicon (Si) | ≤ 0.50 | |
| Manganese (Mn) | ≤ 1.80 | |
| Phosphorus (P) | ≤ 0.025 | |
| Sulfur (S) | ≤ 0.015 | |
| Aluminum (Alt) | ≥ 0.015 | Total aluminum |
| Niobium (Nb) | ≤ 0.09 | |
| Titanium (Ti) | ≤ 0.15 |
B550L Hot Rolled Steel Coil Thermal and Electrical Physical Properties
The physical properties listed below are typical for micro-alloyed structural steels and are provided as engineering reference data. Variations may occur depending on the exact composition, processing, and service environment. The values are valid at room temperature unless otherwise specified.
| Property | Standard Requirement Value | Unit | Test Condition |
|---|---|---|---|
| Density (ρ) | 7.85 | g/cm³ | At 20 °C |
| Elastic modulus (E) | 210 | GPa | At room temperature |
| Shear modulus (G) | 81 | GPa | At room temperature |
| Poisson's ratio (ν) | 0.30 | – | |
| Thermal expansion coefficient (α) | 12.0 × 10⁻⁶ | /K | Between 20 °C and 200 °C |
| Thermal conductivity (λ) | 50 | W/(m·K) | At 20 °C |
| Specific heat capacity (c) | 460 | J/(kg·K) | At 20 °C |
| Electrical resistivity (ρ_e) | 0.18 | μΩ·m | At 20 °C |
B550L Hot Rolled Steel Coil Mechanical Properties
The data below represent the minimum requirements as per Q/BQB 310-2009 for the as-hot-rolled condition. Tensile testing is conducted at room temperature following ISO 6892-1 or equivalent GB/T 228.1. Impact toughness is determined on Charpy V-notch specimens at the agreed-upon temperature, typically -20°C for structural applications.
| Property | Standard Requirement Value | Unit | Test Condition |
|---|---|---|---|
| Lower yield strength (ReL) | ≥ 550 | MPa | Thickness ≤ 16 mm, room temperature |
| Tensile strength (Rm) | 600 – 750 | MPa | Thickness ≤ 16 mm, room temperature |
| Elongation after fracture (A) | ≥ 11 | % | Thickness < 3 mm, gauge length L₀ = 50 mm |
| Elongation after fracture (A) | ≥ 13 | % | Thickness 3 mm to 6 mm, gauge length L₀ = 50 mm |
| Elongation after fracture (A) | ≥ 14 | % | Thickness > 6 mm, gauge length L₀ = 50 mm |
| Bend test (mandrel diameter) | d = 2a | – | Thickness ≤ 6 mm, 180° bend |
| Bend test (mandrel diameter) | d = 3a | – | Thickness > 6 mm, 180° bend |
| Charpy V-notch impact energy (KV₂) | ≥ 27 | J | At -20 °C, transverse specimen |
B550L Hot Rolled Steel Coil Equivalent Standards and Replaceable Grades Recommendation
| Country/Region | Standard | Grade | Remark |
|---|---|---|---|
| China | GB/T 3273 | 550L | Hot rolled steel plate for automobile frame; same yield strength class |
| Europe | EN 10149-2 | S550MC | Thermomechanically rolled high strength steel for cold forming; closely matches chemistry and mechanicals |
| International | ISO 6930-1 | HR550LA | High-strength low-alloy steel sheet and strip; direct correspondence |
B550L Hot Rolled Steel Coil Application Introduction
B550L is specially tailored for load-bearing automotive structures that require high strength, good fatigue resistance, and reliable cold-forming behaviour. Its micro-alloyed design permits thickness reduction compared to conventional mild steels, contributing to vehicle light-weighting. Typical delivery conditions (hot rolled, optionally pickled) enable direct press-forming, welding, and assembly without additional heat treatment.
Product Applications: Truck chassis frame rails, Cross members and reinforcement beams, Bumper reinforcement bars, Lifting arm segments, Dump truck bodies and tipper bodies, Container underframes
Processed into products: Longitudinal frame members (side rails), Cross member brackets, Suspension arm brackets, Spring hangers and mounts, Reinforcement plates for chassis joints, Tie-down anchor points
Application industries: Automotive, Commercial vehicle and truck manufacturing, Construction machinery, Railway wagons, Lifting and handling equipment
B550L Hot Rolled Steel Coil Similar/Compatible Alternative Materials Recommendation
| Country/Region | Standard | Grade | Remark |
|---|---|---|---|
| China | Q/BQB 310 | B510L | Lower yield strength (510 MPa) variant; suitable where strength requirements allow slight relaxation |
| Europe | EN 10149-2 | S500MC | Slightly lower yield strength; widely available alternative with comparable forming characteristics |
| Sweden | SSAB Domex | Domex 550 MC | Commercial brand equivalent to S550MC; very similar chemistry and mechanical properties |
| Japan | JIS G 3134 | SPFH 590 | High strength hot-rolled steel for automobile structural uses; tensile strength 590 MPa class, slightly different yield profile but process-compatible |
Notes:
Note: The values provided are based on the Baosteel Enterprise Standard Q/BQB 310-2009 and typical product data. Actual supply conditions, including specific inspection items, supplementary requirements, and agreement on impact test temperatures, shall be confirmed at the time of order. Suitable welding consumables should be selected according to the carbon equivalent and joint design. For severe forming, it is recommended to consult with the steel manufacturer for optimum process windows.
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