Q345 is a low alloy steel material commonly used in motor vehicles, bridges, ships, and construction. Also known as GB/T 1591, the Q signifies the yield point, and the 345 references the strength of yield. As such, it is essential to note that the yield value decreases as the material thickness increases.

These two types both belong to 16Mn steel grade and are usually produced in several hot rolled processes such as in steel plate and in steel coil/sheet. They are actually a Chinese standardized type of steel, and are becoming some of the most useful steels in the market today due to their mild temper, formability, and easy welding capability. This type of steel has robust mechanical and welding properties, thus providing good performance in structural applications. They are widely used as structural parts in producing ships, railways, bridges, automotives, steel tanks, and vessel containers among, other uses.

Q235 steel pipe

Q235 and Q345 both have the same chemical composition, both have the chemicals Carbon, Silicon, Manganese, Phosphorus and Sulfur. The main difference in their composition is the percentage of each chemical, outlined in the following charts:

Steel Grade	Chemical Composition of Q235
Steel Grade	C(≤)	Mn(≤)	Si(≤)	S(≤)	P(≤)	Cu(≤)
A36	0.26		0.4	0.05	0.04	0.2min
Q235A	0.14~0.22	0.3~0.65	0.3	0.05	0.045
Q235B	0.12~0.20	0.30~0.70	0.3	0.045	0.045
SS400	–	–		0.05	0.05

Steel Grade	Chemical Composition of Q345
Steel Grade	C≤	Mn	Si≤	P≤	S≤	V	Nb	Ti	Al≥
A	0.02	1.00~1.60	0.55	0.045	0.045	0.02~0.15	0.015~0.060	0.2	–
B	0.02	1.00~1.60	0.55	0.04	0.04	0.02~0.15	0.015~0.060	0.2	–
C	0.02	1.00~1.60	0.55	0.035	0.035	0.02~0.15	0.015~0.060	0.2	0.015
D	0.02	1.00~1.60	0.55	0.03	0.03	0.02~0.15	0.015~0.060	0.2	0.015
E	0.02	1.00~1.60	0.55	0.025	0.025	0.02~0.15	0.015~0.060	0.2	0.015

In this regard, these two types of steel also have different recommended applications due to their differing alloy contents:
• One should go for Q235 if the actual application is a type of metal construction that does not require much of steel strength, ie. tie rods, bolts and nuts, hooks/couplers, sleeves or welding parts.
• Opt for Q345 if you are building oil tanks, automotives, low-pressure vessels, cranes, mining machineries, power stations, building structures and other general parts. This is due to the fact that it has good mechanical properties, can perform in lower temperatures, has excellent plasticity as well as good welding properties. They are normally delivered in hot rolled or in normalizing state, and they can be used on areas with low temperatures that can go down to -40C.

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Other properties

• Strengths
Q345 has a tensile strength range of 490-675 Mpa, while the Q235 has a 375-500 Mpa range.
Q345 has a yield strength of ≥ 345 Mpa, while the Q235 has a ≥ 235 Mpa.
Q345 has an elongation rate after fracture of ≥ 21%, while the Q235 has ≥ 26%.

There may be some end users who question the quality and the reliability of these steel types. Quite possibly this is due to the fact that each steel type has different chemical contents thus some properties such as welding properties may be compromised. We hope that the above information will be helpful and serve as a guide on which steel type would be perfect for each application.

Characteristics of Q345
The yield strength of Q345 is where the material begins to deform plastically. Before hitting deformation, it will return to its original shape when stress is removed. For Q345, the yield strength is 345 MPa.

Like many in its grade, it will endure elongation before pulling apart, which typically occurs at 20 percent of its initial length. Q345 has a tensile strength rating of 470 to 660 MPa, which means that it can handle heavy-duty stress and use before ever failing.

The welding property of Q345 may be questioned by end-users, even though the welding properties are primarily affected by the chemical content. However, the production technology has rapidly and significantly improved after many years of research, which means that it is an excellent steel standard for structural purposes.

Q345 steel is from the 16 Mn steel grade, typically manufactured in a hot rolled steel coil or sheet or a hot rolled steel plate. It is an excellent choice when you need high-pressure durability.