How to Select Steel Grades for Transmission Towers: Q235, Q355 and Q420
Sep 15, 2026
Leave a message
Choosing the right steel grade for a transmission tower is not just a technical detail-it directly affects the tower's strength, weight, cost, and service life. In China, three grades are most commonly used: Q235, Q355, and Q420. Here's a simple guide to help you understand the differences and make the right choice.
Quick Comparison of the Three Grades
|
Aspect |
Q235 |
Q355 |
Q420 |
|
Yield Strength |
235 MPa |
355 MPa |
420 MPa |
|
Tensile Strength |
375–500 MPa |
510–650 MPa |
550–720 MPa |
|
Carbon Content |
~0.12% |
~0.20% |
~0.25% |
|
Weldability |
Easiest |
Moderate |
More difficult |
|
Cost |
Lowest |
Middle |
Highest |
|
Corrosion Resistance |
Standard |
Good |
Best |
|
Availability |
Most common |
Common |
Longer lead times |
Source: Comparison of key differences between Q235, Q355, and Q420 in transmission projects
What Do These Numbers Actually Mean?
The "Q" stands for the Chinese word for yield , and the number is the minimum yield strength in MPa. Simply put:
Q235 – the standard structural steel. It bends under 235 MPa of stress.
Q355 – a high-strength low-alloy steel. It can handle 355 MPa before bending.
Q420 – a higher-strength steel, handling 420 MPa.
The higher the yield strength, the less steel you need to carry the same load. Research shows that replacing Q235 with Q420 can save about 18.8% in steel weight on a tower.
When to Use Each Grade
Q235 is best for:
Bracing members and secondary components
Areas with low wind and ice loads
Projects where cost is the primary concern
Situations where welding simplicity matters
Q355 is best for:
Main legs and primary load-bearing members
Medium-to-high voltage towers (220kV and above)
Areas with moderate wind and ice conditions
A balanced choice between cost and performance
Q420 is best for:
Heavily loaded main members on tall or high-voltage towers
Large-angle or heavy-duty sections (limb width ≥ L125×10)
Critical connection plates and nodes
Projects where reducing tower weight is a priority
A Practical Rule of Thumb
Industry practice suggests a mixed-grade approach works best:
Main compression members (legs, main diagonals): use Q420 or Q355 to take advantage of high strength.
Secondary bracing: use Q235 for cost savings.
Connection plates: generally Q235 or Q355; important nodes may use Q420.
Cold regions: For temperatures below -30°C, Q420C or Q235B is recommended for better low-temperature toughness.
This "high strength where it counts, standard steel where it doesn't" approach optimizes both cost and performance.
Standards to Follow
Transmission tower steel selection in China follows these key standards:
GB/T 700 – Carbon Structural Steel (covers Q235)
GB/T 1591 – High Strength Low Alloy Structural Steel (covers Q355, Q420)
GB 50017 – Standard for Design of Steel Structures
GB 50545 – Code for Design of 110kV–750kV Overhead Transmission Lines
GB/T 2694 – Technical Conditions for Manufacturing of Transmission Line Towers
All tower steel must meet at least Grade B quality requirements.
International Equivalents
If you're working on an international project, these grades have direct equivalents:
Q235B ≈ ASTM A36
Q355B ≈ ASTM A572 Gr50 / S355JR
Q420B ≈ ASTM A572 Gr60
Source: Material specifications for 220kV transmission towers
Why Partner with Qingdao Jiudingli?
At Qingdao Jiudingli Steel Structure Engineering Co., Ltd. , we have over 20 years of experience manufacturing transmission towers in Q235, Q355, and Q420. We hold a 500kV transmission tower production license and a 1000kV tower test report, with ISO 9001/14001/45001 and CE certifications.
We can help you select the right steel grade for your project conditions, optimize tower weight, and deliver with full documentation-including material test certificates, galvanizing reports, and structural analysis.
Planning a transmission line project? Contact us for a free consultation.
Mia Lee
Overseas Sales Representative
Qingdao Jiudingli Steel Structure Engineering Co., Ltd.
Tel/WhatsApp: +86 151 9256 2309
Email: support@jiudinglichina.com
Website: www.jiudinglichina.com
Send Inquiry