Q245R and Q345R are two commonly used pressure vessel steel plate materials. The "R" in the designation stands for "vessel," and the number indicates the yield strength grade.

Yield Strength:
Q235R has a yield strength of approximately 235 MPa, while Q345R has a yield strength of up to 345 MPa. This means that under the same external force, Q345R is more resistant to deformation and offers greater structural safety.

Chemical Composition:
Q235R has a relatively high carbon content, while its manganese content is within a certain range. Q345R, on the other hand, has a lower carbon content and stricter control over impurities such as phosphorus and sulfur. This allows Q345R to maintain good strength while also exhibiting superior ductility, toughness, and weldability.

Q235R typically has a temperature limit of around 400°C, making it suitable for low- to medium-temperature and pressure environments. Q345R, on the other hand, boasts increased strength and thermal stability due to the addition of trace alloying elements, allowing for safe long-term use below 450°C. Both steels are widely used in petrochemical, boiler, and storage tank equipment, and the selection process should consider both operating temperature and pressure requirements.

Both Q235D and Q235B are carbon structural steels. Ordinary carbon structural steel plate is a type of steel.
The "Q" represents the yield strength of the material, and the "235" at the end refers to the yield value of the material, which is approximately 235 MPa.

Chemical Composition
Q235B: C ≤ 0.20; Mn ≤ 1.40; Si ≤ 0.35; S ≤ 0.045; P ≤ 0.045.
Q235D: C ≤ 0.17; Mn ≤ 1.40; Si ≤ 0.35; S ≤ 0.035; P ≤ 0.035.

Low-Temperature Impact Toughness
Q235D: -20°C impact toughness test performed.
Q235B: Room-Temperature (20°C) impact toughness test performed.

Q235B is suitable for applications where performance requirements are guaranteed at room temperature (20°C), while Q235D requires performance to be maintained at -20°C.

Strength and Plasticity:
Both have similar yield strength (≥235 MPa) and tensile strength (375–500 MPa);
However, due to its pure composition and rigorous manufacturing process, Q235D exhibits superior plasticity and low-temperature stability.

Hot-dip pure zinc (Z)
In the hot-dip pure zinc process, the zinc content in the molten pool must be no less than 99%. Pure zinc coatings can produce spangles of varying sizes. While these spangles affect the surface appearance, they do not affect corrosion resistance.

Hot-dip galvanized aluminum (ZA)
The molten metal in the molten pool contains approximately 5% aluminum (Al) and a small amount of rare earth elements, with the remainder being zinc. Zn-Al coatings have a brighter surface and offer greater corrosion resistance than pure zinc coatings, but are less commonly used in China.

Hot-dip aluminum silicon (AS)
The molten metal in the molten pool contains approximately 8% to 11% silicon (Si), with the remainder being aluminum. Al-Si coatings form a distinct aluminum-iron-silicon alloy layer on the steel surface. They offer excellent high-temperature resistance, making them suitable for high-temperature processing and operating environments. Hot-dip Al-Si coated steel sheets and strip are a type of "aluminum-coated sheet" referred to in the trade.

Hot-dip galvanized magnesium (ZM) coatings, also known as zinc-aluminum-magnesium (ZAM), consist of a molten metal pool composed of aluminum and magnesium, typically 1.5-8% combined (at least 0.2% magnesium is required), with the remainder being zinc. This coating offers exceptionally good overall corrosion resistance, particularly for shear fracture protection.