A Comprehensive Guide To Q345 steel

What is Q345 steel?

Q345 steel is a low-alloy, high-strength structural steel that originated in China. The designation “Q” represents the yield point of the material, while “345” refers to its minimum yield strength of 345 MPa. This type of steel is designed to withstand harsh conditions and provide excellent mechanical properties.

Q345 Steel Grades

There are five different Q345 steel grades, each with slightly different properties. These grades include Q345A, Q345B, Q345C, Q345D, and Q345E. The difference between the grades lies mainly in their impact temperature, with Q345A having the highest impact temperature and Q345E having the lowest.

Low Alloy Structural Steel Q345 Equivalent
China		US	Germany		Japanese		ISO
Standard	Grade	Standard	Standard	Grade (steel number)	Standard	Grade	Standard	Grade
GB/T 1591 – 2008 (Year)	Q345A	ASTM A529 Grade 50;			JIS G3135	SPFC590	ISO 630-2	S355C, S355D (S355)
		ASTM A572 Grade 50;
GB/T 1591 – 2008	Q345B	ASTM A588 Grade 50;	DIN EN 10025-2;	S355, S355JR (1.0045),	JIS G3135	SPFC 590	ISO 630-2	S355C, S355D (S355)
		ASTM A678 Grade 50	DIN 17100	E355 (1.0060);
				St52-3
GB1591 – 2008	Q345C		DIN EN 10025-2;	S355J0 (1.0553),	JIS G 3135	SPFC590	ISO 630-2	S355D (S355)
			DIN 17100	E335 (1.0060);
				St52-3
GB 1591 – 2008	Q345D	ASTM A656 Grade 50;	DIN EN 10025-2;	S355J0 (1.0553),	JIS G 3135	SPFC590	ISO 630-2	S355D (S355)
		ASTM A529 Grade 50	DIN EN 10025: 1993;	E335 (1.0060);
			DIN 17100	S355J2G3 (1.0570);
				St52-3
GB/T 1591 – 2008	Q345E	ASTM A656/A656M Grade 50;	DIN EN 10025-2;	S355J2 (1.0553),	JIS G3135	SPFC 590
		ASTM A529/A529M Grade 50;	DIN EN 10025: 1993	S355K2 (1.0596),
		ASTM A808 Grade 50		E335 (1.0060);
				S355J2G4 (1.0577),
				S355K2G3 (1.0595),
				S355K2G4 (1.0596)

Q345A，Q345B，Q345C，Q345D，Q345E. This is a distinction between grades, mainly because the impact temperature is different!

Q345A grade, without impact; Q345B grade, impact at 20 °C ambient temperature; Q345C level, 0-degree impact; Q345D level, impact at -20 degrees; Q345E grade, with an impact of -40 degrees. At different impact temperatures, the impact values also vary. In sheet metal, it belongs to the low alloy series. Among low alloy materials, this material is the most common. Q345 used to be called 16Mn.

The external execution standard of Q345 is GB709, and the internal execution standard is GB/T1591-2008.

Due to the implementation of standards, this type of steel plate allows for negative tolerance delivery.

Characteristics of Q345

Q345 will decrease in yield value as the thickness of the material increases, and domestic ones may be less than 345MPa. Therefore, in mechanical design, the strength must be less than 345MPa, otherwise there will be problems.
Reference standard: GB/T1591-2018 “Low alloy high-strength structural steel”
Note: The most significant change in Q345’s latest standard GB/T1591-2018 compared to the old standard is the change in Mn element content, which has been corrected from 1.0 to 1.60 to ≤ 1.70, eliminating the minimum value limit.
With the development of modern industry and the continuous progress of technology, the application of various trace elements in steel plates has become more widespread. Mn content is no longer the only factor affecting the strength and mechanical properties of steel. So the Low Alloy High Strength Structural Steel Standard jointly issued and implemented by the General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China and the National Standardization Administration of China cancels the limit of Mn content range and only specifies the maximum value.
For the testing of Q345 steel, on the one hand, it is whether the element content of the steel meets the requirements of the national standard, and the most important aspect is whether the mechanical properties (yield strength, tensile test) of the steel meet the standards through professional institutions.

Uses of Q345

The Q345 material boasts outstanding mechanical characteristics, superior low-temperature performance, and exceptional welding and formability qualities. It is predominantly utilized in the construction of buildings, low-pressure containers, cranes, mechanical components, bridges, marine vessels, oil storage tanks, hoisting equipment, power plants, mining machinery, general metal parts, and other structures subjected to temperatures of -40°C or lower, or those that endure high-load conditions.

Chemical Composition of Q345 Steel

The chemical composition of Q345 steel consists primarily of iron, with small amounts of carbon, manganese, silicon, phosphorus, sulfur, chromium, nickel, copper, and niobium. These elements provide Q345 steel with its desired mechanical properties, such as high strength and resistance to corrosion.

Chemical Composition Content (≤%)
Steel Grade	Quality Grade	C	Si	Mn	P	S	Cr	Ni	Mo	Cu	Ti	N	Nb	V	B	Als, ≥
Q345	Q345A	0.2	0.5	1.7	0.035	0.035	0.3	0.5	0.1	0.3	0.2	0.012	0.07	0.15	–	–
	Q345B				0.035	0.035
	Q345C				0.03	0.03										0.015
	Q345D	0.18			0.03	0.025
	Q345E				0.025	0.02

Notes: The P and S contents of profiles and bars can be increased by 0.005%, and the upper limit of Grade A steel can be 0.0045%.

Properties of Q345 Steel

Physical Properties	Metric	US/Imperial
Density	7.80 g/cc	0.282 lb/in³

Q345 Mechanical Properties

Q345 steel is known for its high strength, ductility, and toughness. It has a minimum yield strength of 345 MPa and a minimum tensile strength of 470-630 MPa. Its elongation, a measure of ductility, can range between 21-26%, depending on the specific grade used. The steel’s toughness enables it to withstand high stress and resist fracture or failure.

Mechanical Properties: Yield Strength (≥ MPa)
Steel Grade	Quality Grade	d ≤16	16< d ≤ 40	40<d ≤ 63	63<d≤ 80	80 < d ≤ 100	100 < d ≤ 150	150 < d ≤ 200	200 < d ≤ 250	250 < d ≤ 400
Q345	Q345A	345	335	325	315	305	285	275	265	–
	Q345B
	Q345C
	Q345D									265
	Q345E

Notes:

• d= Thickness or wire diameter in mm;
• 1 MPa = 1 N/mm².

Mechanical Properties: Tensile Strength (MPa)
Grade	Quality Level	d≤ 40	40<d ≤ 63	63<d ≤ 80	80<d≤ 100	100 < d≤ 150	150 < d ≤ 250	250 < d ≤ 400
Q345	Q345A	470-630	470-630	470-630	470-630	450-600	450-600	–
	Q345B
	Q345C
	Q345D							450 – 600
	Q345E

d mm, Elongation (≥%)
Grade	Quality Level	d≤40	40<d ≤ 63	63 < d≤ 100	100<d≤ 150	150 < d ≤ 250	250<d ≤ 400
Q345	Q345A	20	19	19	18	17	–
	Q345B
	Q345C	21	20	20	19	18
	Q345D						17
	Q345E

Charpy Impact of Q345 Steel

Charpy (V-notch) impact test temperature and impact absorption energy (KV₂/J), thickness (t).

Quality	Temperature, °C (°F)	12-150 (mm)	150<t≤250 (mm)	250<t≤400 (mm)
Q345B	20 (68)	≥34J	≥27J	–
Q345C	0 (32)
Q345D	-20 (-4)			27J
Q345E	-40 (-40)

Welding of Q345 Steel

Q345 Steel can be easily welded using common welding techniques, such as shielded metal arc welding (SMAW), gas metal arc welding (GMAW), and submerged arc welding (SAW). It’s crucial to follow proper welding procedures to ensure a strong, long-lasting joint. Preheating the steel is often recommended to prevent cracking and ensure a quality weld.

Q345 Steel vs. Other Steel Grades

Q345 Steel vs. Q235 Steel

Q235 steel is another popular Chinese steel grade, often used in construction projects. However, Q345 steel has a higher yield strength, making it more suitable for applications requiring high strength and durability. Q235 steel has a lower carbon content, which makes it more ductile but less strong than Q345 steel.

Q345 Steel vs. A36 Steel

A36 steel is a common structural steel grade used in the United States. It has a similar yield strength to Q345 steel, but its tensile strength is lower. Q345 steel is also more ductile than A36 steel, making it a better choice for applications that require forming and shaping.

Study on the microstructure and properties of Q345 steel after heat treatment

We try to develop a Q345 steel plate with high comprehensive performance for construction by combining hot rolling and tempering heat treatment and optimizing the heat treatment process of Q345 steel; the results can provide technical support for developing and applying low-cost, low-cost, non-polluting, and high-performance construction steel.

Test materials and methods

The test metal material is the hot rolled Q345 steel plate with a thickness of 8mm obtained by air cooling after casting and rolling compound forming. The specific chemical composition is listed in Table 1.

Table.1 Chemical composition of Q345 steel for test w (%)

C	Si	Mn	P	S	Nb	Ti	Fe
0.13	0.3	1	0	0.003	0.03	0.1	allowance

Using the thermal expansion meter to measure the Q345 steel plate Ac3 = 823 ℃, according to the quenching temperature higher than the Ac3 temperature 30-50 ℃ experience, selected 860 ℃ and 900 ℃ as the quenching temperature of Q345 steel plate, quenching holding time set to 60min, followed by cooling in 10% NaCl solution; tempering temperature between 200-680 ℃, holding time set to The tempering temperature is between 200-680℃, the holding time is set to 120min, and then air-cooled to room temperature. Figure 1 shows the schematic diagram of the heat treatment process of the Q345 steel plate.

Figure.1 Heat treatment process of Q345 steel plate

The specimens of 15mm×20mm were processed by wire-cutting method for mechanical grinding and polishing with diamond grinding paste, etched with 4% nitric acid alcohol solution and hot dipped with a saturated picric acid solution, respectively, and observed by metallographic microscope for metallographic organization and grain size; the microscopic morphology and fracture morphology was observed by field emission scanning electron microscope; the tensile mechanical properties were tested according to GB/T228.2-2015 method, and the heat treatment process was carried out in the hydraulic universal testing room. 2015 method, in the hydraulic universal tensile tester, tensile speed set to 1.5mm/min; impact specimens processed into 10mm × 10mm × 55mm V-notch specimens, in the impact tester for room temperature impact power test; hardness test using Brinell hardness tester, loading load of 29421N, the average value of three points as the results.

Test results and analysis

Figure 2 shows the metallographic organization of the hot-rolled Q345 steel plate. Due to the difference in plastic deformation in different parts of the steel plate during the casting and rolling compound forming process and the different cooling rates in the subsequent air cooling process, the metallographic organization of the Q345 steel plate is ferrite and pearlite. The grain size and shape of the matrix organization are different and irregular, and there is also a small amount of mixed crystal organization.

Figure 3 shows the microstructure of Q345 steel quenched at different quenching temperatures. It can be seen that, whether at 860 ℃ or 900 ℃, the quenched Q345 steel organization is quenched martensite, but there are obvious differences between the two martensite organizations. Among them, the quenching temperature is 860 ℃; due to the lower quenching temperature, austenitization is not sufficient, resulting in the cooling of the martensite lath bundle shape is fuzzy; and when the quenching temperature increases to 900 ℃, the original ferrite and pearlite organization is fully austenitic homogenization, the matrix organization can be seen in a clear slender lath martensite parallel to each other and the formation of martensite bundle. Therefore, 900 ℃ was selected as the suitable quenching temperature for the Q345 steel plate. Figure 4 shows the microstructure of the tempered Q345 steel plate at different tempering temperatures. It can be seen that, at a lower tempering temperature (200 ℃), quenching martensite has a small amount of decomposition and the formation of ε– carbide but still maintain the quenching martensite form; when the tempering temperature increases to 400 ℃, ε– carbide melted back into the ferrite, and accompanied by a small amount of Fe3C precipitation, the organization at this time for the tempered austenite; at a higher tempering temperature (600 ℃), the matrix organization At a higher tempering temperature (600°C), Fe3C precipitated continuously in the matrix organization, and the needle-like ferrite had been transformed into an irregular form; by continuing to increase the tempering temperature to 680°C, the carbide precipitation in the matrix organization became more obvious, and the carbide spheroidization was seen locally.

Figure 5 shows the effect of tempering temperature on the room temperature mechanical properties of the Q345 steel plate. It can be seen that, with the increase of tempering temperature, the yield strength and tensile strength of Q345 steel show the characteristics of increasing first and then decreasing, and the maximum strength is obtained at the tempering temperature of 400℃; the elongation after the break and section shrinkage increase first and then decrease with the increase of tempering temperature, and the maximum value is obtained at the tempering temperature of 600℃. When the tempering temperature continues to increase to 680℃, both have different degrees of decrease. This is mainly related to the return of dislocations during the high-temperature tempering process and the transformation of pin-like ferrite into irregular polygonal ferrite; from the results of room temperature impact work test, the impact work at tempering temperatures of 200℃ and 400℃ is not much different, and both remain below 60J, which may be related to the low temperature tempering brittleness. In contrast, when the tempering temperature increases to 600℃ and 680℃, the impact work at room temperature reaches 145J and 200J. The impact work reached 145J and 200J when the tempering temperature increased to 600℃ and 680℃, which showed good impact toughness.

Figure.2 Metallographic organization and grain size of hot rolled Q345 steel plate

Figure.3 SEM morphology of Q345 steel at different quenching temperatures

Figure.4 SEM morphology of Q345 steel at different tempering temperatures (quenching temperature 900℃)

Figure.5 Effect of tempering temperature on mechanical properties of Q345 steel (quenching temperature 900℃)

Figure 6 shows the tensile fracture morphology of Q345 steel at different tempering temperatures. It can be seen that the tensile fractures of Q345 steel plates at different tempering temperatures show tough nests and tearing ribs of different sizes, which are characterized by ductile fractures. The average diameter and depth of the tough nests tend to increase and deepen with the increase in tempering temperature, and the size and depth of the tough nests are proportional to the plasticity of the material. Thus, the increase in tempering temperature will improve the toughness of Q345 steel, i.e., the resistance to deformation and damage is enhanced, which is consistent with the test results in Figure 5. This is mainly related to the periodization of carbide.

Figure 7 shows the impact fracture morphology of the Q345 steel plate at different tempering temperatures. It can be seen that, at a lower tempering temperature (200℃), the impact fracture can be seen as a river-like deconstruction pattern, showing the characteristics of brittle fracture; when the tempering temperature is increased to 400℃, the impact fracture can be seen as a river-like pattern, tearing ribs and small local toughness nests, showing the characteristics of quasi-deconstruction fracture; when the tempering temperature is 600℃, the fracture can be seen as toughness nests of different sizes, and some of the toughness nests are relatively larger and deeper When the tempering temperature was increased to 680℃, parabolic fracture fractures were seen, which were produced under the action of shear stress, indicating that the impact specimen had a stronger ability to resist impact deformation. The impact absorbed work would be increased as a result. The results of the impact fracture morphology are in good agreement with the results of the room temperature impact work test in Fig. 5, i.e., at low tempering temperatures (200°C and 400°C), the impact fractures exhibit destructive and quasi-destructive fracture characteristics with lower impact work. In comparison, at higher tempering temperatures (600°C and 680°C), the impact fractures exhibit ductile fracture characteristics with higher impact work.

Figure.6 Tensile fracture profile of Q345 steel plate at different tempering temperatures

Figure.7 Impact fracture of Q345 steel plate at different tempering temperatures

• (1) The metallographic organization of the hot rolled Q345 steel plate is ferrite and pearlite. The grain size and shape of the matrix organization are different and irregular, and it also contains a small amount of mixed crystal organization.

• (2) With the increase of tempering temperature, the yield strength and tensile strength of Q345 steel show the characteristics of increasing first and then decreasing, and the maximum strength is obtained at the tempering temperature of 400℃; the elongation after fracture and the shrinkage at section increase first and then decrease with the increase of tempering temperature, and the maximum value is obtained at the tempering temperature of 600℃; the impact work is low at the tempering temperature of 200℃ and 400℃, and when the tempering temperature increases to 600℃ and 400℃, the impact work is low at the tempering temperature of 400℃. When the tempering temperature increased to 600℃ and 680℃, the impact work at room temperature reached 145J and 200J, respectively, which showed good impact toughness.

• (3) The tensile fracture of Q345 steel exhibited ductile fracture characteristics when tempered at 200-680℃; the impact fracture exhibited destructive and quasi-destructive fracture characteristics when tempered at low temperatures (200℃ and 400℃), while the impact fracture exhibited ductile fracture characteristics at higher tempering temperatures (600℃ and 680℃).

Purchasing Tips for Q345 Steel

When purchasing Q345 steel, it is essential to consider the following factors to ensure you make the right choice for your project:

• Manufacturer Reputation: Research and select a reputable manufacturer with a proven record of producing high-quality Q345 steel. This will ensure that the material meets industry standards and is of the highest quality.

• Material Certification: Verify that the manufacturer provides material certifications, which outline the chemical composition, mechanical properties, and other relevant information about the steel. These certifications ensure that the material meets the required specifications for your project.

• Size and Shape: Determine the size and shape of the Q345 steel you need for your project, whether in the form of plates, sheets, bars, or other configurations. Ensure the manufacturer can provide the required dimensions and form to avoid delays or additional costs.

• Pricing: Compare prices among various suppliers to ensure you get the best value for your investment. However, do not sacrifice quality for cost savings, as this could compromise the integrity of your project.

• Delivery and Lead Time: Consider the lead time and delivery options when purchasing Q345 steel. Choose a supplier with a reliable shipping process and reasonable lead times to ensure your project stays on schedule.

Ensuring Quality and Compliance in Q345 Steel

To ensure the Q345 steel you purchase meets industry standards and regulations, it is important to:

• Request Material Test Reports (MTRs): MTRs provide detailed information about the chemical composition, mechanical properties, and other relevant data for the steel. Review these reports to confirm that the material meets the required specifications.

• Perform Third-Party Inspections: Consider hiring a third-party inspector to verify the quality of the Q345 steel before it is shipped to your facility. This can help identify potential issues or non-conformities before they become problematic.

• Stay Informed About Industry Standards and Regulations: Stay up-to-date on the latest industry standards and regulations to ensure your Q345 steel meets all requirements. This can help avoid any potential compliance issues or project delays.

Maintenance and Care for Q345 Steel Structures

Regular maintenance and care are essential to maximizing the lifespan and performance of structures built with Q345 steel. Here are some best practices to follow:

• Regular Inspections: Conduct routine visual inspections of the Q345 steel structures to identify any signs of corrosion, wear, or damage. Address any issues promptly to prevent further deterioration and maintain structural integrity.

• Cleaning: Keep the surfaces of the Q345 steel clean and free of dirt, debris, and other contaminants that may contribute to corrosion. Use appropriate cleaning solutions and techniques to prevent steel protective coatings damage.

• Protective Coatings: Apply and maintain protective coatings, such as paint or galvanizing, to the steel surfaces to enhance corrosion resistance and prolong the life of the structures.

• Monitor Environmental Conditions: Be aware of the environmental conditions surrounding your Q345 steel structures, such as humidity, temperature, and exposure to corrosive chemicals. Take necessary precautions to protect the steel from these elements and ensure its longevity.

Working with Q345 Steel: Safety and Precautions

When working with Q345 steel, it is crucial to follow safety guidelines and precautions to prevent accidents and ensure the well-being of workers. Some important safety measures include:

• Personal Protective Equipment (PPE): Provide appropriate PPE for workers handling Q345 steel, including safety goggles, gloves, and steel-toed boots to protect against potential hazards.

• Proper Training: Ensure that all workers handling Q345 steel receive adequate training in material handling, welding, cutting, and other relevant processes. This will help minimize the risk of accidents and injuries.

• Ventilation: Proper ventilation is essential when welding or cutting Q345 steel to reduce exposure to potentially harmful fumes and gases. Ensure adequate ventilation systems are in place and workers are trained.

• Fire Safety: Implement fire safety measures, such as having readily available fire extinguishers and training workers when working with Q345 steel, as welding and cutting processes can pose a fire risk.

By following these safety and precautionary measures, you can create a safe working environment for your team and ensure the successful completion of your projects involving Q345 steel.

Conclusion

Q345 steel is a versatile, high-strength, and affordable steel grade that has found widespread use in various industries. Its excellent mechanical properties, corrosion resistance, and cost-effectiveness make it an ideal choice for construction, automotive, shipbuilding, and heavy machinery applications. By understanding the characteristics and advantages of Q345 steel, you can make informed decisions about the best material for your project.
Source: China Q345 Steel Plate Manufacturer – Yaang Pipe Industry (www.epowermetals.com)