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Q345R Steel: A Comprehensive Guide to Quality Steel

What is Q345R Steel?

Q345R steel is a low alloy steel for pressure vessels with yield strength of 345MPa grade, which has good comprehensive mechanical properties and process performance. Phosphorus and sulfur content is slightly lower than low alloy high strength steel plate Q345 (16Mn) steel, in addition to tensile strength, elongation requirements than Q345 (16Mn) steel has increased, but also to ensure impact toughness.

Q is the first letter of Chinese Pinyin, 345 represents yield strength, r is the first letter of Chinese Pinyin, and its brand naming method is low alloy high-strength structural steel brand, represented by the first letter of Chinese Pinyin for yield strength value and pressure vessel capacity.

Chemical Composition of Q345R Steel

Q345R (16MnR) steel combines various elements, including carbon, manganese, silicon, phosphorus, sulfur, and several other alloying elements. The precise percentages of these elements determine the steel’s unique characteristics, such as its strength, ductility, and weldability.

Grade C % Si % Mn % Cu % Ni % Cr% Mo % V % Ti % Alt % P % S % Nb
Q345R 0.2 0.55 1.2-1.7 0.3 0.3 0.3 0.08 0.05 0.03 0.02 0.025 0.01 0.05

Mechanical Properties of Q345R steel

Some of the key mechanical properties of Q345R steel include high tensile strength, good elongation, and excellent impact resistance. These properties make it suitable for applications that require a material capable of withstanding extreme conditions, such as high pressure and temperature.

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

Applications of Q345R Steel

Pressure Vessels
Q345R steel is widely used in manufacturing pressure vessels, containers designed to hold gases or liquids at a pressure significantly different from the ambient pressure. Its excellent strength and durability make it an ideal choice for this application.
Boilers, used to generate steam or hot water for various industrial processes, are another common application for Q345R steel. Its ability to withstand high temperatures and pressures make it a popular choice for boiler construction.
Heat Exchangers
Heat exchangers, which transfer heat between two or more fluids, also rely on Q345R steel for construction. The steel’s excellent thermal conductivity and corrosion resistance make it ideal for this application.

Advantages of Q345R Steel

Strength and Durability
One of the primary benefits of Q345R steel is its high strength and durability. Its excellent mechanical properties enable it to withstand extreme conditions, making it an ideal choice for applications that require a strong, reliable material.
Q345R steel is also a cost-effective option compared to other high-pressure steel grades. Its relatively low cost and wide availability make it an attractive choice for many industries that require pressure and temperature-resistant materials.
Another advantage of Q345R steel is its excellent weldability. It can be easily welded using various methods, making it convenient for manufacturers to work with and assemble components. This feature also contributes to its cost-effectiveness.

Comparison with Other Steel Grades

Q345R vs. Q245R

Q345R and Q245R are popular steel grades used for pressure vessels and boilers. However, Q345R offers higher tensile strength and better impact resistance than Q245R, making it more suitable for applications requiring higher pressure and temperature resistance.

Q345R vs. Q370R

Q370R is another steel grade that shares similarities with Q345R. Both are designed for pressure vessel applications, but Q370R offers slightly higher strength and toughness. However, Q345R remains popular due to its cost-effectiveness and widespread availability.

Precautions for the use of Q345R

1. Must consider the operating conditions of the equipment (such as design pressure, design temperature, characteristics of the medium), welding properties of the material, hot and cold processing properties, heat treatment and the structure of the vessel.
2. Under the premise of meeting the first article, consider the economic rationality of:

  • ① When the required thickness of steel plate is less than 8mm, between carbon steel and low-alloy high-strength steel, carbon steel plate should be used as far as possible (except for multi-layer containers).
  • ② In the stiffness or structural design-oriented occasions, should try to use ordinary carbon steel. In the strength design-oriented occasions, should be used according to the pressure, temperature, medium and other restrictions, in order to choose Q235B, 20R (20g), Q345R (16MnR) and other steel plates.
  • ③ Required stainless steel thickness greater than 12mm, should try to use lining, composite, overlay welding and other structural forms.
  • ④ Stainless steel should be used as far as possible not as a design temperature less than or equal to 500 degrees Celsius heat-resistant steel.
  • ⑤ Pearlite heat-resistant steel should be used as far as possible not as the design temperature is less than or equal to 350 degrees Celsius heat-resistant steel. In the must use pearl body heat-resistant steel for heat-resistant steel or hydrogen-resistant purposes, should try to reduce, merge the variety of steel, specifications.

3. Thickness greater than 60mm Q345R steel plate, the upper limit of carbon content can be increased to 0.22%.

4. Q345R steel plate can add niobium, vanadium, titanium elements, the content should be filled in the quality certificate, the sum of the above three elements content should not be greater than 0.050%, 0.10%, 0.12%.

What is Q345R steel plate?

  • Q345R(R-HIC) steel plate is hydrogen resistant container plate, with low P and S content in the steel plate and good welding performance.
  • Q345R(R-HIC) steel plate execution standard: Execution of GB713-2014 standard.

Technical standards of Q345R(R-HIC) steel plate:

  • The size, weight, shape and permissible deviation of Q345R(R-HIC) shall conform to the provisions of GB/T709.
  • The thickness deviation of Q345R(R-HIC) shall be executed according to the deviation of class B in GB/T709.
  • Delivery condition of Q345R(R-HIC) steel plate: Normalized, or the delivery condition can be specified according to technical requirements.
  • Q345R(R-HIC) steel plate thickness direction performance requirements: Z15, Z25, Z35.
  • Q345R(R-HIC) steel plate flaw detection requirements: one probe, two probe, three probe.
  • Q345R(R-HIC) steel plate size: thickness 8mm-160mm, width 1600mm-2500mm, length 6000-12000mm.
  • Q345R grade hydrogen resistant plates are Q345R(HIC) and Q345R(R-HIC), other material hydrogen resistant plates: Q245R(R-HIC)/SA516Gr70(HIC)/14Cr1MoR(H)/12Cr2Mo1R(H).

Q345R(R-HIC) steel plate production and cutting process

Smelted by electric furnace + extra-furnace refining, the smelting process is Ca-treated, and because of the nature of fine-grain steel, its actual grain size is grade 5 or above.

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Production process:

Primary refining → LF refining → VD treatment → continuous casting (die casting) → cleaning, heating → rolling → (stacking) → surface inspection → batching → flaw detection → heat treatment → cutting and sampling → performance inspection

Cutting process: Q345R (R-HIC) steel plate factory inspection of the performance indicators meet the requirements by the cutting and processing process; you can cut processing and drawings under the material, the general steel plate thickness is not greater than 20mm priority to choose CNC plasma cutting or CNC laser cutting method, if the thickness of the steel plate is greater than 30mm or more, usually will choose CNC flame cutting, can control the cutting Accuracy and time.

The Effect of Cold Deformation on the Recrystallization Temperature of Hot Rolled Q345R Steel Plate

A hot-rolled Q345R steel plate may exhibit recrystallization behavior in engineering applications, affecting product performance. To study the effect of cold deformation on its recrystallization temperature, a hot-rolled Q345R steel plate was subjected to cold deformation with 0,5%, 10%, 15%, 31%, and 53%. Afterward, samples were cut and kept at different temperatures of 450-700 ℃ for 1 hour, followed by hardness testing and metallographic observation. The results show that when the deformation is 15% or less, recrystallization will not occur at 450-700 ℃; When the deformation is 31% and 53%, the recrystallization temperature range of the sample is 615-650 ℃ and 565-600 ℃, respectively.
At the end of steel plate production, recrystallization temperature is important for the reasonable development of the steel plate rolling process. For cold-rolled steel plates, the deformation produced by cold rolling is large. It is necessary to eliminate the internal stress and improve the microstructure through recrystallization annealing to ensure the strength and toughness of the steel plate. Therefore, the recrystallization temperature is more studied. For hot-rolled steel plates, in the rolling process through dynamic recovery, dynamic recrystallization, and grain growth, accurate estimation of steel recrystallization temperature is also critical.
At the application end of the steel plate, GB/T150.4-2011 “Pressure Vessel Part 4: Manufacturing, Acceptance and Inspection” and GB/T16507.5-2013 “Water Tube Boiler Part 5: Manufacturing” both use “recrystallization temperature” as the cold (including warm forming), hot forming temperature limit, but the standard does not give the material recrystallization temperature but also does not specify the recrystallization temperature acquisition method. When a hot-rolled Q345R steel plate is used to manufacture head, cylinder, and other pressure-bearing parts, especially under cold and warm forming conditions, the deformation generated by forming is superimposed on the deformation of the steel plate itself. The austenite transformation organization and deformed ferrite substructure organization may have an important impact on the recrystallization behavior of the material and even trigger static recrystallization and affect the product performance.
To study the recrystallization behavior of hot-rolled Q345R steel plate in engineering applications, this paper refers to the forming deformation rate of common steelhead and the forming heating temperature or final stress relief heat treatment temperature of the product and selects a steel mill hot-rolled Q345R steel plate for cold deformation with less than 15% deformation and 31% and 53% large deformation, and then conducts hardness test after heat treatment at different temperatures to determine the recrystallization temperature at different The recrystallization temperature under the cold deformation is determined.

Test materials and methods

Test material

The test material is a steel mill hot-rolled Q345R steel plate; its thickness is 16mm, the chemical composition is shown in Table 1, its mechanical properties are shown in Table 2, and its metallurgical organization is shown in Figure 1.
Table.1 Chemical composition of Q345R steel plate

Project C Si Mn P S Al V Ti Nb Cr Ni Cu
Measured value 0.18 0.29 1.36 0.015 0.003 0.041 0.003 0.003 0.0007 0.02 0.009 0.022
GB/T 713 standard value ≤0.20 ≤0.55 1.201.60 ≤0.025 ≤0.015 ≥0.020 Sum ≤ 0.10 ≤0.30 ≤0.30 ≤0.30

Table.2 Mechanical properties of Q345R steel plate

Project Yield strength/MPa Tensile strength/MPa Elongation after fracture (%) Reduction of Area (%) Impact absorption energy at 0/J Brinell hardness (HBW2.5/187.5)
Measured value 377 537 31 69 131 165,166,167
GB/T 713 standard value ≥345 510640 ≥21 ≥34

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Figure.1 Q345R steel plate microstructure

Specimen processing

Steel plate deformation
The deformation of the original steel plate is counted as 0; 5%, 10%, and 15% uniformly deformed steel plate is obtained by stretching method; to obtain a larger deformation, the steel plate is compressed by a press method at room temperature, and the deformation is 31% and 53% respectively.
Specimen preparation
The specimens were processed into 15mm×10mm by wire-cutting method and tested in a KSL-1100 chamber resistance furnace from 450-700℃ with an interval of 50℃ and holding time of 1h, and air-cooled; the specimens after heat treatment at different temperatures were inlaid, ground and polished, and after corrosion by 2% nitric acid alcohol solution, their metallographic organization was observed, followed by hardness testing.

Test Equipment and Methods

Metallographic testing
Use Nikon EPIPHOT 300 optical microscope (OM) to observe the microstructure of the specimen section.
Hardness testing
The hardness of the ferrite region on the specimen cross-section was measured using a 401MVD micro-Vickers hardness tester with 10 points per specimen uniformly tested at a test load of 4.903N (500gf).

Test results and discussion

Vickers hardness

The relationship between the hardness of each deformation specimen and the heat treatment temperature is shown in Figure 2.
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Figure.2 Relationship curve between hardness and heat treatment temperature of each deformation amount specimen
From Figure 2, it can be seen that the hardness of 0,5%,10%, and 15% deformation specimens in the range of 450-700℃, after heat treatment at the same temperature, increases significantly with the increase of deformation; 31%,53% deformation specimens below 550℃, after heat treatment at the same temperature, the hardness increases with the increase of deformation. It was also found that the increase in hardness of the 31% and 53% deformation specimens was smaller than that of the 15% or fewer deformation specimens. Among them, the hardness of 0,5%,10%, and 15% deformation specimens after heat treatment at 450-700℃, the trend of hardness change is the same, i.e., it remains the same or slightly decreases; the hardness of 31% of deformation specimens below 600℃ does not change much, and the hardness of 600-650℃ decreases sharply, and the hardness of unheated treated specimens (HV0.5) decreases from 258 to 153, a decrease of 41%. Similarly, the hardness of the deformed 53% specimens decreased significantly at 550-600°C.
With the increase in deformation, the hardness increases as a result of deformation strengthening, the plastic deformation increases, the dislocation density increases, and the dislocation movement of mutual cross-cutting phenomenon intensifies, resulting in fixed dislocation entanglement and other barriers, thus increasing the resistance to dislocation movement to enhance the deformation resistance of the material, the deformation continues to increase will appear a large number of cross-slip shift, so that the dislocation bypass the barrier forward, which is the deformation of 31%, 53% specimens This is the intrinsic reason why the strengthening effect is not as obvious as that of the specimens below 15%. As the temperature rises, the deformed grains first revert. When the energy is sufficient, the original elongated, finely divided grains are equiaxed, defects such as dislocations are greatly reduced, and the hardness changes significantly, called recrystallization. After heat treatment of 0,5%,10%, and 15% specimens, the hardness is basically unchanged or slightly decreased, which should result from the reversion effect. Deformation amount to 31% and 53% of specimens at 600-650 ℃ and 550-600 ℃, respectively, the hardness drops sharply; according to the significant change in hardness, it can be determined that the test material in this temperature range occurred recrystallization.
To accurately determine the recrystallization temperature range of the material, the heat treatment was supplemented with 615,630°C for the 31% deformation specimen and 565,580°C for the 53% deformation specimen, and the holding time remained 1 h. Figure 3 shows the hardness versus heat treatment temperature curves for the 31% and 53% deformation specimens. It can be seen that the recrystallization temperature range of the deformation is 31%, and 53% of specimens are 615-650℃ and 565-600℃ respectively; it can also be seen that the larger the deformation, the lower the insulation temperature of the hardness drop, the lower the recrystallization temperature of the material, which is due to the increase in deformation, the increase in deformation energy storage, the greater the tendency to transform to a low energy state, the lower the heating temperature required.
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Figure.3 Supplementary test results of 31% and 53% deformation specimens


The microstructure of a typical deformation specimen at partial heat treatment temperature is shown in Figure 4. It can be seen that: without heat treatment, compared with the deformation amount of 15% specimen (a), the deformation amount of 31% specimen (d) grain deformation is obvious, along the deformation direction grain is flattened, while the deformation amount 53% specimen (g) grain deformation degree is more serious, deformation grain is more slender; deformation amount 15% specimen after heat treatment at 650 ℃ (b) and 700 ℃ (c), there is no obvious grain nucleation, combined with After heat treatment at 615℃ (e), a small amount of recrystallized grains appeared in the microstructure (arrowed in the figure), and the original flattened grains tended to irregular shape, which can be judged to have recrystallized; by 650℃ (f), the deformed grains were close to equiaxed crystals, indicating that at this temperature, the grains were heavily nucleated and grew, and the recrystallization process was completed. The recrystallization process is completed; similarly, the deformation of 53% specimen at 565 ℃ recrystallizations to 600 ℃ recrystallization is completed.
It can also be seen from the microstructure that the starting temperature of pearlite aging of the microstructure of 15%, 31%, and 53% deformation specimens decreases from 700, 650, and 565℃ respectively, which is caused by the energy storage of deformation and further confirms the conclusion that the recrystallization temperature decreases with the increase of deformation judged from the hardness method.
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Figure.4 Microstructure of deformation 15%, 31%, and 53% specimens at partial heat treatment temperature

Recrystallization temperature

The recrystallization temperatures of different materials are different. The recrystallization temperature of the same material is not a definite value; it is not only related to the state of the raw material but also to the cold deformation, deformation speed, deformation temperature, grain size, solid solution strengthening effect, the second phase, etc. In engineering, there are more definitions of recrystallization temperature, such as the temperature of 50% softening of material as recrystallization temperature or the minimum temperature of recrystallization volume fraction greater than 95% under large deformation, etc.
For this test of hot-rolled Q345R steel plate, 31% deformation specimen at 615 ℃ that recrystallization, 53% deformation specimen at 565 ℃ recrystallizations, the reason why the definition is different from the previous because this test is to provide a basis for the development of temperature forming process, in order not to recrystallization, and therefore the recrystallization volume fraction or hardness (strength) softening degree of the two is different.


For hot-rolled Q345R steel plate, no recrystallization occurs when the cold deformation is controlled at 15% and below; the recrystallization temperature range is 615-650°C at 31% deformation; the recrystallization temperature range is 565-600°C at 53% deformation.

Author: He Xiaoming



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