Q345 hot-rolled steel plate is a high-strength low-alloy (HSLA) structural steel widely used in China and recognized internationally. Its designation follows the Chinese GB/T 1591 standard (now superseded by GB/T 1591-2018, where it is largely equivalent to grades such as Q355B, but the Q345 designation remains widely used and understood).

This steel is renowned for its excellent combination of strength, toughness, weldability, and formability, making it a versatile and cost-effective choice for a multitude of heavy-duty applications.

Key Characteristics & Properties

High Strength and Good Toughness: Q345 offers significantly higher strength than ordinary carbon steels like Q235. Its alloying elements (like Mn, V, Nb, Ti) provide fine grain strengthening and precipitation hardening, which also enhances impact toughness, especially at lower temperatures.

Excellent Weldability: Due to its controlled carbon equivalent (CEV), Q345 plate can be easily welded using all standard methods (SMAW, GMAW, SAW, etc.) without preheating in most cases, though preheating is recommended for thicker sections or stringent applications to prevent cracking.

Good Formability and Machinability: It possesses satisfactory ductility, allowing it to be bent, rolled, and formed into various shapes. It also responds well to cutting, drilling, and other machining operations.

Hot-Rolled Process: The hot-rolling process involves shaping the steel at temperatures above its recrystallization point. This results in a scaled surface and a product with improved toughness and ductility compared to cold-rolled steel.

ommon Applications

Q345 Hot-rolled steel plate is a fundamental material for construction and manufacturing, including:

Building and Bridge Construction: Structural frames, beams, columns, and trusses.

Heavy Machinery: Manufacturing of mining equipment, bulldozers, cranes, and excavators.

Pressure Vessels and Storage Tanks: For industries like oil, gas, and chemical processing.

Shipbuilding: Hull structures, decks, and bulkheads.

Automotive Chassis: Parts for trucks, buses, and special vehicles.

Transmission Towers and other infrastructure projects.

Advantages over Carbon Steel (e.g., Q235)

Higher Strength-to-Weight Ratio: Allows for the design of lighter structures without compromising load-bearing capacity.

Better Fatigue Resistance: More suitable for dynamic and cyclic loading applications.

Superior Low-Temperature Performance: Grades C, D, and E offer good impact toughness at sub-zero temperatures.

International Equivalents (Similar Grades)

European: S355JR, S355J0, S355J2 (EN 10025-2)

American: ASTM A572 Gr. 50 (Yield 345 MPa / 50 ksi), ASTM A36 (often used interchangeably for many applications, though A36 has a lower minimum yield)

Japanese: SM490YA, SM490YB (JIS G3106)

In summary, Q345 hot-rolled steel plate is a versatile, economical, and high-performance material that forms the backbone of modern heavy industry and construction due to its superior mechanical properties and excellent weldability.