Q620E and Q690E are high-strength low-alloy structural steel plates specified by Chinese national standard GB/T 1591. The designation denotes their minimum yield strength (620 MPa and 690 MPa, respectively) and the "E" suffix guarantees impact toughness at a test temperature of -40°C. These grades represent the high-end tier of domestic structural steel, engineered for critical and heavily loaded welded structures such as large-span bridges, offshore platforms, heavy-duty mining equipment, and high-performance construction machinery, where an optimal combination of ultra-high strength and reliable low-temperature toughness is paramount.
Key Differences:
The primary distinction is their strength level. Q620E offers a minimum yield strength of 620 MPa, while Q690E provides a higher yield strength of 690 MPa. This increment allows for greater load-bearing capacity or further weight optimization in advanced structural design.
Achieving the higher strength of Q690E while maintaining the demanding -40°C toughness requires a more advanced alloy design and precise thermomechanical controlled processing (TMCP). Compared to Q620E, Q690E typically involves a more refined chemical composition with carefully balanced additions of micro-alloying elements (such as Niobium, Vanadium, Titanium) and stricter control of carbon and manganese content. Consequently, Q690E possesses a significantly higher carbon equivalent (Ceq). This results in notably more stringent fabrication challenges. Welding Q690E demands extremely strict procedures: the use of specially qualified, ultra-high-strength and high-toughness welding consumables, meticulous control of preheating (often requiring temperatures above 100°C) and interpass temperatures, strict limits on heat input, and in many cases mandatory post-weld heat treatment (PWHT) to prevent hydrogen-induced cracking and preserve the toughness in the weld heat-affected zone.
Q620E Chemical requirement
|
Grade |
Chemical requirement or element Max % |
|||||||||||||
|
|
C |
Si |
Mn |
P |
S |
Cu |
Cr |
Ni |
Mo |
B |
V |
Nb |
Ti |
|
|
Q620E |
0.2 |
0.8 |
1.7 |
0.020 |
0.010 |
0.5 |
1.5 |
2 |
0.7 |
0.005 |
0.12 |
0.06 |
0.05 |
|
Q690E Chemical requirement
|
Grade |
Chemical requirement or element Max % |
|||||||||||||
|
|
C |
Si |
Mn |
P |
S |
Cu |
Cr |
Ni |
Mo |
B |
V |
Nb |
Ti |
|
|
Q690E |
0.2 |
0.8 |
1.7 |
0.020 |
0.010 |
0.5 |
1.5 |
2 |
0.7 |
0.005 |
0.12 |
0.06 |
0.05 |
|
Q620E Property in tensile and yield strength, and impact test requirement
|
Grade |
Property |
Impact test |
|||||||||
|
Q620E |
Yield Mpa Min |
Tensile Mpa |
Elongation |
Min J |
|||||||
|
Thickness mm |
Thickness mm |
Degree |
|||||||||
|
50 |
50-100 |
100-150 |
50 |
50-100 |
100-150 |
% |
0 |
-20 |
-40 |
-60 |
|
|
620 |
580 |
560 |
700-890 |
650-830 |
15 |
|
|
37 |
|
||
Q690E Property in tensile and yield strength, and impact test requirement
|
Grade |
Property |
Impact test |
|||||||||
|
Q690E |
Yield Mpa Min |
Tensile Mpa |
Elongation |
Min J |
|||||||
|
Thickness mm |
Thickness mm |
Degree |
|||||||||
|
50 |
50-100 |
100-150 |
50 |
50-100 |
100-150 |
% |
0 |
-20 |
-40 |
-60 |
|
|
690 |
650 |
630 |
770-940 |
710-900 |
14 |
|
|
37 |
|
||
