Q345R is a grade of pressure vessel steel plate specified in the Chinese national standard GB 713, widely used in the fabrication of boilers, pressure vessels, and other pressure-bearing equipment that require good strength, toughness, and weldability; in English technical documents, it is commonly referred to as "Q345R pressure vessel steel plate" or "Q345R grade pressure vessel steel plate (GB standard)", and since it is a China-specific designation, there is no direct equivalent grade in international standards such as ASTM or EN, though it is often compared to grades like ASTM A516 Grade 70 or EN 10028-2 P355GH in engineering practice.
Q345R material chemical composition:
| Grade | C % | Si % | Mn % | Cu % | Ni % | Cr% | Mo % | V % | Ti % | Alt % | P % | S % | Nb |
| Q345R | 0.20 | 0.55 | 1.2-1.7 | 0.30 | 0.30 | 0.30 | 0.08 | 0.050 | 0.030 | 0.020 | 0.025 | 0.010 | 0.050 |
Q345R material mechnical property:
| Thickness (mm) | > 3 ≤ 16 | > 16 ≤ 36 | > 36 ≤ 60 | >60 ≤ 100 | >100 ≤ 150 | >150 |
| Yield strength (≥Mpa) | 345 | 325 | 315 | 305 | 285 | 265 |
| Tensile strength (Mpa) | 510-640 | 500-630 | 490-620 | 480-610 | 470-600 | |
advantages
Q345R steel offers several key advantages that make it widely used in pressure vessel and boiler applications. First, it provides excellent strength and toughness balance, with a minimum yield strength of 345 MPa and good low-temperature impact performance, ensuring reliable operation under various loading conditions. Second, it exhibits outstanding weldability, allowing for easy fabrication using common welding methods such as SMAW, GMAW, and SAW, which helps reduce production costs and improve construction efficiency. Third, Q345R has good corrosion resistance in many industrial environments, particularly in moderate corrosive conditions, which enhances the service life of pressure-bearing equipment. Fourth, it demonstrates stable mechanical properties across different thicknesses, from thin plates to heavy sections, making it suitable for a wide range of structural designs. Finally, as a domestically standardized grade in China, Q345R is readily available, cost-effective, and supported by mature manufacturing and inspection processes, ensuring consistent quality and supply for large-scale engineering projects.
Main Applications
Boiler Manufacturing: Core components like boiler drums, water walls, superheater headers, and economizers. It adapts to high-temperature and high-pressure working environments of industrial boilers and power plant boilers (below 400℃, medium and low pressure levels).
Pressure Vessel Fabrication: Widely used in petroleum, chemical, pharmaceutical, and food industries for vessels such as storage tanks (for oil, gas, chemicals), reaction vessels (for chemical synthesis reactions), heat exchangers (for fluid heat transfer), and separators (for material separation).
Petrochemical and Pipeline Equipment: Low-pressure and medium-pressure pipelines, pipe fittings, and pressure-bearing supports in oil refining, chemical processing, and natural gas transmission systems, especially for medium-temperature and medium-pressure fluid transportation.
Other Industrial Fields: Pressure-bearing structures in thermal power plants, nuclear power auxiliary equipment (non-core pressure parts), marine pressure vessels, and heavy machinery hydraulic tanks, meeting the strength and toughness requirements of pressure-bearing operations.
Application Conditions
Temperature Range: Suitable for normal temperature to medium-high temperature environments, generally -20℃ to 400℃. It maintains stable mechanical properties within this range; above 400℃, its strength decreases significantly, and below -20℃, it may lose toughness (brittleness risk), so low-temperature modification is needed for cryogenic applications.
Pressure Requirement: Designed for low-pressure to medium-pressure working conditions (usually ≤10 MPa). For high-pressure equipment (above 10 MPa), it needs to be matched with thicker plates or combined with other high-strength steels, and strict flaw detection and quality control are required.
Medium Compatibility: Applicable to non-strongly corrosive media, such as water, steam, oil, natural gas, and weak acid/alkali solutions. In strong corrosive environments (e.g., concentrated acid, strong alkali, chloride-containing media), anti-corrosion treatment (coating, lining) or matching with corrosion-resistant alloys is necessary.
Fabrication and Inspection Conditions: Must be processed by qualified welding methods (SMAW, GMAW, SAW, etc.) with strict welding procedure qualification; post-weld heat treatment (PWHT) is required for thick plates (above 12mm) to eliminate welding stress. Before use, non-destructive testing (UT, RT, MT) must be carried out to ensure no internal defects affecting pressure-bearing safety.
Standard Compliance: Must meet GB 713 national standard requirements for chemical composition, mechanical properties, and flaw detection. It is not applicable to special working conditions such as ultra-high temperature, ultra-high pressure, strong corrosion, or radiation without special modification and certification.
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What is Q345R and what is its main application field?
Q345R is a low-alloy high-strength boiler and pressure vessel steel. It is mainly used to manufacture pressure-bearing equipment such as boilers, storage tanks, and pressure vessels, suitable for high-temperature and high-pressure working environments.
What are the chemical composition characteristics of Q345R steel?
Q345R mainly contains C, Si, Mn as basic elements, with strict control of P and S impurities. It may also contain trace alloying elements like V, Nb, Ti to improve its strength and toughness, meeting pressure vessel safety standards.
What is the minimum yield strength of Q345R steel?
The minimum yield strength of Q345R steel is 345 MPa, which is the core index that defines its grade. This strength ensures it can withstand certain pressure and load without permanent deformation in pressure-bearing applications.
Can Q345R steel be used in low-temperature environments? If yes, what is the applicable temperature range?
Yes, Q345R can be used in low-temperature environments. Its general applicable low-temperature range is -20℃ to room temperature. For lower temperatures, it needs to pass additional low-temperature impact tests to ensure toughness.
What heat treatment processes is Q345R steel usually subjected to?
Q345R is often treated with normalizing, annealing or tempering. Normalizing improves its structure uniformity and toughness; annealing reduces hardness for easy processing; tempering eliminates internal stress after welding or forming.
What are the requirements for welding Q345R steel?
Welding Q345R requires matching low-alloy steel electrodes, controlling preheating temperature (usually 80-150℃) and interpass temperature. Post-weld heat treatment is necessary to eliminate residual stress and prevent cold cracks.
What is the tensile strength range of Q345R steel?
The tensile strength of Q345R steel ranges from 470 MPa to 630 MPa. This range ensures the steel has sufficient strength to resist tensile loads in pressure-bearing equipment operation, ensuring structural safety.
Is Q345R steel corrosion-resistant? What corrosion protection measures are usually taken?
Q345R has general corrosion resistance. Common protection measures include anti-corrosion coating (such as epoxy resin coating), galvanizing, adding corrosion inhibitors in the medium, or using it with corrosion-resistant liners.
What standards does Q345R steel comply with?
Q345R complies with the Chinese national standard GB/T 713-2014 "Boiler and Pressure Vessel Steel Plates". This standard specifies its chemical composition, mechanical properties, inspection methods and delivery requirements.
What is the difference between Q345R and Q235B steel?
Q345R is low-alloy high-strength steel with higher yield and tensile strength than Q235B (carbon structural steel). Q345R is for pressure vessels, while Q235B is for general structural use, with stricter quality requirements for Q345R.