Q345R is a GB 713-standard pressure vessel steel plate, widely used for boilers, pressure vessels and other pressure-bearing equipment requiring good strength, toughness and weldability. In English technical documents, it is usually called "Q345R pressure vessel steel plate" (GB standard). As a China-specific grade, it has no direct equivalent in ASTM, EN and other international standards, but is often compared to ASTM A516 Grade 70 or EN 10028-2 P355GH in engineering.
Processes Adopted for Q345R Steel
Smelting Process:
Adopts converter or electric arc furnace smelting combined with LF (Ladle Furnace) refining and VD (Vacuum Degassing) treatment. This process effectively reduces harmful impurities (P, S ≤ 0.025%) and gas content (H, O, N), ensures uniform chemical composition, and improves the purity and internal quality of the steel.
Rolling Process:
Applies controlled rolling and controlled cooling (TMCP) technology. The steel is rolled at a specific temperature range, followed by rapid cooling, which refines the grain structure, enhances mechanical properties (strength and toughness), and ensures stable performance across the plate thickness.
Welding Process:
Commonly uses shielded metal arc welding (SMAW), gas metal arc welding (GMAW), and submerged arc welding (SAW). Pre-welding preheating (60-150℃) and post-weld heat treatment (PWHT) are required for thick plates to eliminate welding stress, prevent cold cracks, and ensure weld joint quality matching the base metal.
Inspection and Testing Process:
Includes chemical composition analysis, mechanical property testing (tensile, impact, bending), and non-destructive testing (ultrasonic UT, radiography RT, magnetic particle MT). These processes fully verify the steel's quality and ensure it meets GB 713 standards and application requirements.
Main chemical elements composition
| C | Si | Mn | P | S | Alt(min.) |
| ≤0.20 | ≤0.55 | 1.20-1.60 | ≤0.025 | ≤0.015 | ≥0.020 |
Main mechanical properties
| Thickness (mm) | Tensile strength (MPa) | Yield strength (MPa) | Elongation (%) |
| >16-36 | 510-640 | ≥345 | ≥21 |
| >36-60 | 500-630 | ≥325 | ≥21 |
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.
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What is the maximum thickness of Q345R steel plates that can be supplied?
The maximum supply thickness of Q345R steel plates is usually 200mm, but it can be customized according to user needs. Thicker plates may require special rolling and heat treatment processes to ensure uniform performance.
What impact toughness requirements does Q345R steel have?
Q345R requires a transverse impact energy Akv ≥ 34 J at 20℃ (standard temperature). For low-temperature use, the impact test temperature is lowered, and the Akv value still needs to meet the standard to avoid brittle fracture.
Can Q345R steel be used to manufacture steam boilers?
Yes, Q345R is widely used in manufacturing steam boilers. It can withstand high temperature and pressure of steam, but it must meet the design requirements and pass strict quality inspection, including non-destructive testing of welds.
What is the hardness range of Q345R steel after normalizing?
After normalizing, the hardness of Q345R steel is usually between 137 HB and 179 HB. This hardness range balances strength and toughness, making it easy to process and weld, and suitable for pressure vessel manufacturing.
What non-destructive testing methods are commonly used for Q345R pressure vessels?
Common non-destructive testing methods for Q345R pressure vessels include ultrasonic testing (UT) for internal defects, radiographic testing (RT) for weld quality, and magnetic particle testing (MT) for surface cracks.
What is the thermal conductivity of Q345R steel? How does it affect equipment design?
The thermal conductivity of Q345R is about 45 W/(m·K) at room temperature. Good thermal conductivity helps heat transfer in boilers and heat exchangers, affecting the design of heat transfer area and wall thickness.
Can Q345R steel be cold-formed? What precautions should be taken?
Q345R can be cold-formed, but it is necessary to control the forming speed and deformation amount to avoid excessive stress. After cold forming, stress relief annealing should be performed to restore toughness and eliminate residual stress.
What is the melting point range of Q345R steel?
The melting point range of Q345R steel is approximately 1450℃ to 1500℃. This range is an important parameter for welding and heat treatment processes, ensuring that the steel is processed within a reasonable temperature range.
What is the difference between Q345R and Q345B steel in terms of application?
Q345R is specially designed for pressure vessels, with stricter requirements on impact toughness and purity. Q345B is for general structures like bridges and frames. Q345R cannot be replaced by Q345B in pressure-bearing scenarios.
What are the requirements for the surface quality of Q345R steel plates?
Q345R steel plate surface should be free of cracks, folds, delaminations, bubbles and other defects. Minor surface defects can be ground, but the grinding depth shall not exceed the allowable deviation of the plate thickness, ensuring structural integrity.