What is the difference between Q550D steel plate and Q345B steel plate

What is the difference between Q550D steel plate and Q345B steel plate?
Q550D steel plate and Q345B steel plate are two kinds of low alloy high strength steel with improved properties by adding a small amount of alloy elements.

1. The difference of chemical composition between Q550D steel plate and Q345B steel plate is as follows:
The chemical composition of Q550D steel plate: C ≤ 0.18, Si ≤ 0.60, Mn ≤ 2.0, P ≤ 0.030, S ≤ 0.025, Nb ≤ 0.11, V ≤ 0.12, Ti ≤ 0.20, Cr ≤ 0.80, Ni ≤ 0.80, Cu ≤ 0.80, N ≤ 0.015, Mo ≤ 0.30, B ≤ 0.004, Al ≤ 0.015.

The chemical composition of Q345B steel plate: C ≤ 0.20, Si ≤ 0.50, Mn ≤ 1.70, P ≤ 0.035, S ≤ 0.035, Nb ≤ 0.07, V ≤ 0.15, Ti ≤ 0.20, Cr ≤ 0.30, Ni ≤ 0.50, Cu ≤ 0.30, N ≤ 0.012, Mo ≤ 0.10.

2. Mechanical properties of Q550D steel plate and Q345B steel plate are different:
Mechanical properties of Q550D steel plate: yield strength ≥ 550 Mpa, tensile strength 600-780 Mpa, elongation after fracture ≥ 16%, impact energy ≥ 47J.
The mechanical properties of Q345B steel plate yield strength ≥ 345 Mpa, tensile strength 450-630 Mpa, elongation after fracture ≥ 17%, impact energy ≥ 27J.

3. The application difference between Q550D steel plate and Q345B steel plate:
Q550D steel plate is mainly used for manufacturing various large-scale engineering structural components and construction machinery. Due to its high strength, it can meet the requirements of large-scale and lightweight construction machinery.

Q345B steel plate is widely used in various welding structures, such as bridges, vehicles, ships, pipelines, boilers, large vessels, storage tanks, heavy machinery and equipment, mining machinery, power station, workshop structure, low-temperature pressure vessels, textile machinery parts, etc.