B440QK Automotive High-Strength Steel
B440QK Automotive High-Strength Steel: Cold Forming Structural Grade per Q-BQB 310-2009
Technical data and properties of B440QK automobile structure steel plate defined by Baosteel standard Q-BQB 310-2009. Includes chemical composition, mechanical properties, physical characteristics, and global equivalents.
Cold bending, stamping, drawing, welding, shearing, punching
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B440QK Automotive High-Strength Steel Introduction
B440QK is a high-strength low-alloy (HSLA) hot-rolled steel plate specifically designed for cold forming applications in automotive structures. It conforms to Baosteel enterprise standard Q-BQB 310-2009. This steel offers a minimum yield strength of 305 MPa and tensile strength in the range of 440–590 MPa, combined with good ductility and excellent weldability. The alloying design typically includes microalloying elements (e.g., niobium or titanium) to achieve grain refinement and precipitation strengthening, ensuring reliable performance in critical safety and load-bearing components. It is widely used for longitudinal beams, cross members, and reinforcements where enhanced strength enables weight reduction without compromising formability.
B440QK Automotive High-Strength Steel Chemical Composition
The ladle analysis limits for B440QK according to Q-BQB 310-2009. Values are maximum unless a range is indicated. Microalloying elements may be added singly or in combination to achieve required mechanical properties. Aluminum is typically present as a deoxidizer and grain refiner.
| Element | Standard Value (max %) | Remarks |
|---|---|---|
| Carbon (C) | 0.10 | Controls weldability and formability |
| Silicon (Si) | 0.50 | Deoxidation and strength |
| Manganese (Mn) | 1.60 | Key strengthening element |
| Phosphorus (P) | 0.025 | Lower limit for toughness |
| Sulfur (S) | 0.025 | Lower limit to avoid hot shortness |
| Aluminum (Alsol) | ≥0.015 | Soluble aluminum for grain refinement |
| Niobium (Nb) / Titanium (Ti) / Vanadium (V) | Added as necessary | Microalloying elements for grain refinement and precipitation; exact content by mill practice |
B440QK Automotive High-Strength Steel Thermal and Electrical Physical Properties
The following physical constants are typical for HSLA steels of this grade and are provided for engineering calculations. These values are not part of the delivery specification but are representative of B440QK at room temperature.
| Property | Typical Value | Unit | Test Condition |
|---|---|---|---|
| Density (ρ) | 7.85 | g/cm³ | At 20 °C |
| Modulus of elasticity (E) | 210 | GPa | At 20 °C, dynamic method |
| Shear modulus (G) | 80.8 | GPa | Calculated from E and ν |
| Poisson's ratio (ν) | 0.3 | – | Room temperature |
| Thermal expansion coefficient (α) | 12.0 × 10⁻⁶ | K⁻¹ | Average 20 – 200 °C |
| Thermal conductivity (λ) | 42 | W/(m·K) | At 20 °C |
| Specific heat capacity (cp) | 460 | J/(kg·K) | At 20 – 100 °C |
| Electrical resistivity (ρe) | 0.20 – 0.25 | µΩ·m | At 20 °C |
B440QK Automotive High-Strength Steel Mechanical Properties
Mechanical properties are from tensile tests performed on transverse specimens according to Q-BQB 310-2009. The values are guaranteed for thicknesses up to 6.0 mm unless otherwise stated. The minimum elongation may vary depending on gauge length and sheet thickness. Bend test requirement: 180° bend over a mandrel diameter equal to 0.5 times the sheet thickness (d=0.5a) without cracking.
| Property | Standard Requirement | Unit | Test Condition |
|---|---|---|---|
| Yield strength (ReH/Rp0.2) | ≥305 | MPa | Transverse specimen, room temperature |
| Tensile strength (Rm) | 440 – 590 | MPa | Transverse specimen, room temperature |
| Elongation after fracture (A) | ≥24 | % | Gauge length A80 mm (t ≤ 3.0 mm); for t > 3.0 mm, A5.65√So ≥ 26 |
| Bend test | Mandrel diameter d = 0.5a (no cracks) | – | 180° bend, sample width ≥ 50 mm, at room temperature |
| Impact toughness (KV) | Not specified | – | Not mandatory for Q-BQB 310; may be agreed upon if needed |
B440QK Automotive High-Strength Steel Fully Equivalent Material Standards and Replaceable Grades
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| China | Q-BQB 310-2009 | B440QK | Original standard and designation |
| Japan | JIS G3113:2018 | SAPH440 | Comparable in strength but different production process; properties close, often interchangeable |
| Europe | EN 10149-2:2013 | S420MC | Slightly lower tensile range (420–520 MPa vs 440–590 MPa); replace after checking forming requirements |
| International | ISO 6930-1:2017 | HR Fe420 | General HSLA grade; mechanical property overlap, but requires verification of chemical composition limits |
B440QK Automotive High-Strength Steel Application Introduction
B440QK is engineered for applications where high static and dynamic loads are combined with a need for weight reduction. It is readily weldable by common methods (resistance spot, MIG/MAG, laser) and can be cold formed with moderate springback compensation. Typical thickness ranges from 1.5 to 6.0 mm.
Product Applications: Longitudinal beams and cross members of commercial vehicle frames, Passenger car chassis sub-frames, Wheel rim components and disc wheel parts, Bumper beams and reinforcement tubes, Seat structures and safety cage parts, Suspension arms and spring brackets
Processed into products: Pressed and bent brackets with load-bearing functions, Welded assemblies of engine cradles, Formed U-channels and L-profiles for structural members, Stamped reinforcement plates for door impact beams, Flanged joints and connectors in body-in-white structures
Application industries: Automotive (passenger cars, commercial vehicles, buses), Agricultural and construction machinery (light structural parts), Railway wagons (non-pressure components), General engineering (brackets, supports, profiled sections)
B440QK Automotive High-Strength Steel Similar / Alternative Materials for Comparable Performance
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| China | GB/T 3273-2015 | 440L | Similar strength level for automobile frame, may require adjusted forming parameters |
| Europe | EN 10149-2 | S460MC | Higher strength (Re ≥ 460 MPa), lower elongation, suitable for downgauging but less formable |
| Europe | EN 10149-2 | S355MC | Lower strength alternative, more ductile; use when higher formability is needed at expense of strength |
| USA | SAE J2340 | 440XF | Cold-formed or hot-rolled HSLA, similar tensile grade but property ranges differ; source-specific qualification advised |
| VDA | VDA 239-100 | CR440Y380T-DH | Dual phase or high-ductility cold-rolled grade; higher formability but different manufacturing process and cost |
Notes:
Surface condition: Typically supplied pickled and oiled (PO) or as dry (non-oiled). Special mill finishes can be requested.
Weldability: Excellent under standard procedures; pre-heating is not required for thicknesses below 8 mm.
Tolerances: Thickness, width, and flatness tolerances according to Q-BQB 301 or agreed upon at order.
Test certificates: Inspection certificate EN 10204 3.1 is normally supplied, type 3.2 upon agreement.
For applications involving dynamic bending fatigue, fine blanking, or extreme forming degrees, it is recommended to consult the steel manufacturer for specific processing guidelines.
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