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