B440QK Hot Rolled Steel Coil
B440QK Hot Rolled Steel Coil: Q/BQB 310-2009 High-Strength Low-Alloy Grade
Comprehensive material data for Baosteel B440QK high-strength hot rolled steel coil according to Q/BQB 310-2009, including chemical, mechanical and physical properties.
Cold forming, bending, roll forming, stamping, welding, cutting, punching
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B440QK Hot Rolled Steel Coil Introduction
B440QK is a hot rolled, high-strength low-alloy (HSLA) steel grade specified in Baosteel corporate standard Q/BQB 310-2009 for cold-forming applications. It offers a minimum yield strength of 440 MPa combined with good formability and weldability. The improved mechanical properties are achieved through a fine grain structure and microalloying with elements such as niobium and titanium.
- Material category: High-strength low-alloy steel for cold forming
- Typical delivery condition: Hot rolled, as-rolled or controlled rolled
- Key features: High yield strength, excellent cold formability, good weldability, and uniform mechanical properties throughout the coil
B440QK Hot Rolled Steel Coil Chemical Composition
The chemical composition of B440QK is designed to ensure the specified high yield strength while maintaining good weldability and formability. The steel is microalloyed with niobium and/or titanium for grain refinement and precipitation strengthening. Maximum values apply unless a range is given; values are based on the standard's requirements.
| Element | Standard Requirement (max, %) | Remarks |
|---|---|---|
| C | ≤0.12 | Carbon |
| Si | ≤0.50 | Silicon |
| Mn | ≤1.50 | Manganese |
| P | ≤0.025 | Phosphorus |
| S | ≤0.020 | Sulfur |
| Alt | ≥0.015 | Total aluminum |
| Nb | ≤0.09 | Niobium |
| Ti | ≤0.22 | Titanium |
| V | ≤0.20 | Vanadium (optional; can be added individually or in combination) |
| Nb+V+Ti | ≤0.22 | Sum of microalloying elements |
B440QK Hot Rolled Steel Coil Thermal and Electrical Physical Properties
The following physical properties are typical for low-carbon, microalloyed hot rolled steel at room temperature unless otherwise indicated. Exact values may vary slightly with actual composition and processing. These are provided as reference data for design and simulation.
| Property | Standard Requirement Value | Unit | Test Condition |
|---|---|---|---|
| Density (ρ) | 7.85 | g/cm³ | 20 °C |
| Modulus of elasticity (E) | 210 | GPa | 20 °C, static |
| Shear modulus (G) | 81 | GPa | 20 °C, calculated |
| Poisson's ratio (ν) | 0.3 | — | elastic range |
| Thermal expansion coefficient (α) | 11.5 × 10-6 | 1/K | 20–100 °C |
| Thermal expansion coefficient (α) | 12.5 × 10-6 | 1/K | 20–200 °C |
| Thermal conductivity (λ) | 48 – 52 | W/(m·K) | 20 °C |
| Specific heat capacity (cp) | 450 – 480 | J/(kg·K) | 20 °C |
| Electrical resistivity (ρe) | 0.22 – 0.28 | μΩ·m | 20 °C |
B440QK Hot Rolled Steel Coil Mechanical Properties
Mechanical properties are specified for transverse test specimens at room temperature. The values apply to thicknesses ≤8.0 mm for hot rolled coil; for greater thicknesses a slight reduction in yield strength may be allowed. All tests are performed in accordance with the relevant ISO or ASTM standards. Minimum values are guaranteed unless noted as typical.
| Property | Standard Requirement | Unit | Test Condition |
|---|---|---|---|
| Yield strength (ReH) | ≥440 | MPa | transverse, room temperature, thickness ≤8 mm |
| Tensile strength (Rm) | 490 – 620 | MPa | transverse, room temperature |
| Elongation (A80) | ≥19 | % | gauge length 80 mm, transverse, t ≤3 mm |
| Elongation (A5) | ≥22 | % | proportional gauge length, transverse, t >3 mm |
| Bend test (180°) | d=0.5a | — | bend radius at least 0.5× thickness, no cracking |
B440QK Hot Rolled Steel Coil Exact Equivalent Material Standards & Replaceable Grades
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| China | Q/BQB 310-2009 | B440QK | Original proprietary grade; no internationally identical equivalent exists |
B440QK Hot Rolled Steel Coil Application Introduction
B440QK is specifically designed for cold-formed structural parts requiring high strength and good fatigue resistance. Its combination of mechanical properties and weldability makes it suitable for lightweight automotive design.
- Best suited for: Roll forming, press braking, stamping of components with moderate deformation.
- Processing considerations: The grade exhibits some spring-back due to its high yield strength; tooling design should compensate accordingly. It can be welded using all common methods (MIG/MAG, spot welding) with appropriate parameters.
Product Applications: Automobile body-in-white structural parts, Chassis longitudinal members and cross members, Suspension control arms and subframes, Wheel rims and discs, Truck frames and trailers, Seat structures and safety components, Cold-formed sections for construction
Processed into products: Front and rear longitudinal beams, B-pillar reinforcements, Engine cradles (subframes), Suspension spring brackets, Transmission tunnel reinforcements, Door impact beams, Axle housings
Application industries: Automotive, Commercial vehicle, Railway rolling stock, General engineering, Agricultural machinery
B440QK Hot Rolled Steel Coil Similar or Alternative Material Recommendations
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| Europe | EN 10149-2:2013 | S420MC | Yield strength min. 420 MPa; similar formability, lower strength, may be upgraded to meet 440 MPa min. |
| Europe | EN 10149-2:2013 | S460MC | Yield strength min. 460 MPa; slightly higher strength, equivalent formability, suitable substitution when 440 MPa min. is not mandatory |
| Japan | JIS G 3134:2018 | SPFH590 | Minimum tensile strength 590 MPa; yield strength typically 420–500 MPa; comparable forming class |
| International | ISO 6930-1:2010 | HSLA420 | Similar microalloyed concept, nominal yield 420 MPa, but may be processed to reach 440 MPa |
Notes:
Welding: B440QK is readily weldable by conventional processes. Carbon equivalent (CEV) is typically ≤0.22%, so preheating is not required for thicknesses under 20 mm. Surface condition: Supplied with mill scale or pickled and oiled; special surface quality must be agreed upon. Tolerances: Thickness and flatness tolerances comply with Q/BQB 310 or as negotiated. Test certificates: Typically provided according to EN 10204 type 2.2 or 3.1 upon request.
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