A brief introduction to Chinese GB standard Q345 series of seamless steel pipes

A brief introduction to Chinese GB standard Q345 series seamless steel pipes

 

Defination of Q345

Q345 steel, with charicteristics of 7.85 g/cm3 material density, and 470-630 Mpa tensile strength, is a Chinese GB standard low alloy high strength structural steel. “Q” is the first letter of Chinese Pinyin: “qu fu dian”, which means Yield Point, “345” is the minimum value of yield strength for steel thickness less than 16mm. It is commonly used material among low alloy materials, and it was called 16Mn in the past.

 

Quality Grades

It has 5 quality grades: Q345A, Q345B, Q345C, Q345D and Q345E. These five grades are mainly different in whether steel pipe need to be impact tested and impact test temperture. Q345A don’t need to be tested; Q345B need to be test at 20℃(also called room temperature), Q345C need to be test at 0℃, Q345D need to be test at -20℃ and Q345E need to be test at- 40℃.

 

Application

Q345 steel has good weldability, cold & hot workability and corrosion resistance. Widely used in bridges, ships, boilers, pressure vessels, petroleum storage tanks, lifting transport machinery and other high-load welded structural parts.

 

Chemical Composition

Chemical Composition Content (≤%) ≥%
Steel Grade Quality Grade C Si Mn P S Nb V Ti Cr Ni Cu N Mo B Als
Q345 Q345A 0.20 0.50 1.70 0.035 0.035 0.07 0.15 0.20 0.30 0.50 0.30 0.012 0.10
Q345B 0.035 0.035
Q345C 0.030 0.030 0.015
Q345D 0.18 0.030 0.025
Q345E 0.025 0.020

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%.

 

Mechanical Properties

Mechanical Properties: Yield Strength (≥ N/mm2)
Steel Grade Quality Grade Ø ≤16 16 < Ø ≤ 40 40 < Ø ≤ 63 63 < Ø ≤ 80 80 < Ø ≤ 100 100 < Ø ≤ 150 150 < Ø ≤ 200 200 < Ø ≤ 250 250 < Ø ≤ 400
Q345 Q345A ≥345 ≥335 ≥325 ≥315 ≥305 ≥285 ≥275 ≥265
Q345B
Q345C
Q345D ≥265
Q345E

Notes: Ø = Thickness or wire diameter in mm;

1 MPa = 1 N/mm2

Mechanical Properties: Tensile Strength (N/mm2)
Grade Quality Level Ø ≤ 40 40 < Ø ≤ 63 63 < Ø ≤ 80 80 < Ø ≤ 100 100 < Ø ≤ 150 150 < Ø ≤ 250 250 < Ø ≤ 400
Q345 Q345A 470 – 630 470 – 630 470 – 630 470 – 630 450 – 600 450 – 600
Q345B
Q345C
Q345D 450 – 600
Q345E

 

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

Charpy Impact

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

Quality Temperature, ℃ 12-150 (mm) 150<t≤250 (mm) 250<t≤400 (mm)
Q345B 20 ≥34J ≥27J
Q345C 0
Q345D -20 27J
Q345E -40

 

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