Q355 seamless steel pipe material analysis and introduction

Q355 is a high-quality low-alloy high-strength structural steel. It is the new name of the old standards 16Mn and q345. Since the q345 specified in the original GB/T 1591-2008 standard cannot be synchronized with the EU S355, the National Standards Committee issued a new regulation GB/T 1591-2018, which stipulates that q345 be changed to q355, which will be implemented from February 1, 2019.

Q355 seamless steel pipe has excellent comprehensive properties, including low-temperature resistance, easy welding, excellent cutting performance, high strength, excellent toughness, good wear resistance, fatigue resistance, and corrosion resistance. Widely used in bridges, vehicles, ships, buildings, pressure vessels, special equipment, etc. Among them, "Q" means yield strength and 355 means that the yield strength of this steel is 355MPa, and its yield value will decrease as the thickness of the material increases.

Q355 seamless steel pipe is divided into five grades: A, B, C, D, and E, which represent the difference in impact temperature:
- Grade Q355a: No impact test is performed.
- Q355b level: impact test at 20 degrees normal temperature.
- Q355c level: 0 degree impact test.
- Q355d level: -20 degree impact test.
- Q355e level: -40 degree impact test.

Under different impact temperatures, the impact values are also different. The chemical composition of Q355 includes C, Si, Mn, P, S, Cr, Ni, and Cu. The contents of C, Si, and Mn are strictly controlled to ensure their mechanical properties and process performance.

The mechanical properties of Q355 include yield strength, tensile strength, and elongation. Yield strength is the material's ability to resist deformation at the yield point. For Q355, its yield strength gradually decreases as the pipe wall thickness increases. Tensile strength is the maximum stress that a material can withstand before tensile rupture, while elongation is the degree of plastic deformation that a material can withstand before tensile rupture. Q355 shows good mechanical properties in terms of tensile strength and elongation.

Seamless steel pipes produced using Q355 steel are called Q355 seamless steel pipes. Commonly used standards include GB8162 (seamless steel pipe for structural use), GB8163 (seamless steel pipe for transporting fluids), GB6479 (seamless steel pipe for fertilizer equipment) GB9948 (seamless steel pipe for petroleum cracking), etc.