Q345r steel

Types

Q345D

Q345D steel is a type of structural-grade alloy steel that is used extensively in engineering and construction applications. The Q345D steel material's chief attributes are its toughness, strength, and elasticity, which allow it to be practically used in extreme weather and load-carrying frames and structures. According to the Chinese National Standard, the letter "Q" denotes a certain yield point, and the number "345" refers to the material's yield strength measured in megapascals (MPa). The additional letter "D" explains that, unlike some coarse-grained steel varieties, Q345D is charpy impact test (CT) rated for -40°C.

Hence, this makes Q345D a preferred choice in frozen environments for shipbuilding, oil and gas rigs, and bridges. Nonetheless, though the material is resistant to hardening and can be welded without preheating, bending Q345D steel sheet requires moderate force; otherwise, it may crack. Optimal cutting results on this steel grade are also obtained when using blades specially designed for cutting alloys due to its toughness.

Q345E

Like Q345D, Q345E is another structural steel alloy with high tensile strength and excellent workability. Its yield strength stands at 345 MPa, making it suitable for heavy-duty applications. It also has better low-temperature toughness than Q345B, which makes it suitable for construction purposes in even extremely cold-weather conditions. Q345E also features good weldability and can be easily shaped and formed, allowing its usage in various complex structural designs.

Specifications

Typical chemical compositions of the two common varieties of the Q345 steel grade - Q345D and Q345E - as per the Chinese standard include these alloying elements in approximate proportions:

• Carbon: Up to 0.20% for strength and reduced wear and deformation.
• Silicon: 0.50-0.70% for increased corrosion resistance.
• Manganese: 1.20-1.40% for improved hardness and toughness.
• Sulphur: Up to 0.045% for improved machinability, but as low as possible to avoid brittleness.
• Phosphorus: Up to 0.045% for improved formability and after welding.

Q345 steel contains other trace elements, such as copper, chromium, and nickel, to improve corrosion resistance and enhance the material's overall properties. Some steel sheets classified under this grade feature different thicknesses ranging from 1.5 mm to 25 mm and widths from 600 mm to 1,500 mm. The length is usually custom-made depending on the order. Common sizes and forms include these:

• Q345 steel plate: Standard sizes include 2,000 × 1,000 mm, 3,000 × 1,500 mm, and 6,000 × 2,000 mm
• Q345 steel beam: Common I-beam sizes are 200 mm × 102 mm to 300 mm × 300 mm
• Q345 steel channel: C-channels usually come in lengths of 6 m or 12 m
• Q345 steel pipe: Pipes are typically manufactured in diameter sizes ranging from 20 mm to 325 mm

Industrial Use Cases

Due to its impressive strength, weldability, and low-temperature toughness, Q345 steel is a structural steel alloy used in many industries for construction purposes. Key uses include:

• Q345D steel: Mostly used in making pressure vessels, boilers, and pipelines due to low-temperature toughness. Also, used in construction for welding structures subjected to heavy loads and stress.
• Q345E steel: Typically utilized in shipbuilding and offshore structures due to excellent toughness down to -40 °C. Other common uses include making steel frames for high-rise buildings, bridges, and heavy machinery in mining and construction.

Besides these, Q345 steel is also popular in the automotive industry. The steel imbues parts like chassis with the strength required to bear weight while allowing for flexibility to absorb shocks from uneven terrains or extreme weather elements. Also, the alloy steel is used to build jibs and booms of cranes and the main frame and superstructure of heavy trailers and flatbed trucks to enable delicate transportation of extremely heavy loads across any distance.

How To Choose

Some important criteria to consider when buying Q345 steel plate or structural steel alloy integrating Q345D and Q345E include:

• Material properties: The Q345 steel grade is available in two common varieties - Q345D and Q345E. While both are tough and easy to weld, the latter is better suited for extreme cold than the former. So, depending on the project location and structure, choose either.
• Plate thickness: The steel grade is often available in multiple plate thicknesses ranging from 1.5 to 25 mm. Select the appropriate one based on the project's structural requirements. The thicker the plate, the more load it can carry and, thus, the stronger the structure.
• Fabrication methods: While Q345 steel is easy to weld, some precautions must be taken to ensure optimal results. For instance, preheating might be required for thicker plates and offshore or mining projects. Less toughness often requires more elaborate welding techniques to prevent cracking or warpage.
• Q345D vs Q345E: The two only differ in the grade's toughness. While D can withstand temperatures as low as -40 °C, E can endure far lower temperatures. Only one must be chosen based on the project location, among other factors.

Maintenance and Repair

Some general maintenance tips for welding Q345 steel to ensure optimal results and increased longevity include:

• Corrosion protection: Although Q345 steel is an alloy, which means it is more resilient than other common steel grades. Nonetheless, like any steel, it is prone to rust. A basic yet effective protection measure is periodic painting with anti-corrosive paint or galvanizing the structure.
• Regular inspection: Structural steel maybe even more resilient than many materials. However, it is still susceptible to environmental wear and tear, particularly cracks, fatigue, or deformation. Periodic inspection of the structure helps in the early detection of such issues.
• Preventive measures: Environmental factors like strong winds, temperature, humidity, and heavy rains could warp or even crack the toughest of structure metals. Furthermore, due to its weight, heavy rains on steel frame rooftops may cause puddles on the roof, endangering the frame as these stress the structure. Thus, install weep holes for effective water drainage and reinforcement for wind pressure.

As for reparability, because Q345 steel is welded, repairs can be easily effected by a welder skillful in working with alloy metals. Basic but effective tools for quick fixes include a wire brush, grinder, and basic welding equipment. However, note that the amount of work required and techniques used will vary depending on the level of damage. Small cracks, for instance, only require the grinding of the area around the crack and rewelding, while large cracks may require the cutting out of entire sections and the welding of new plates.

Q&A

What is Q345 steel used for?

Q345 steel is popular in construction, particularly for making structures like bridges and frames for razed buildings, ship jibs and booms, oil and gas rig components, heavy trailers, and mining equipment, as well as in the automotive industry.

What is the difference between Q235 and Q345 steel?

Q345 contains more carbon and mangane and is thus significantly stronger than Q235. The latter is also less resistant to extreme cold temperatures.

Can Q345 steel be welded?

Yes, one of the benefits of Q345 steel is its weldability. It can even be easily welded using basic welding methods. However, preheating may be required for thick plates or extreme environmental conditions.

What is the difference between Q345B and Q345C?

There is no difference between Q345B and C in the chemical composition. The two only differ in the test conditions. Q345B is often tested at room temperature, while Q345C is tested at -40 °C to ensure it is not brittle at that temperature.