In industrial ,especially for our pipe fittings manufacture , that we provide Custom made pipe fitting service , that we often get the drawing , the first thing is study the oversea material and china material grade . Then figure out which material equivalent to the drawing material . One typical material is EN10025 S355 , it is equivalent to Q345 steel ,but it is one old material and not produce any more in China.
This is not a market rumor — it is the result of an official national standard upgrade.
Under GB/T 1591-2018, China formally replaced Q345 with Q355, a higher-performance low-alloy structural steel. Today, most Chinese steel mills no longer produce Q345. Instead, Q355 has become the new standard material for structural components, CNC turning parts, and pipe fittings.
As a professional pipe fittings manufacturer with years of CNC machining experience, we encounter this situation frequently in export projects. In this article, we explain:
- The relationship between Q345 and Q355
- Chemical composition differences
- Why Q345 is no longer supplied in China
- A real pipe fitting case from Israel
- Whether Q355 can directly replace Q345
What Are Q345 and Q355?
Both Q345 and Q355 belong to low-alloy high-strength structural steel (HSLA steel).
The main difference lies in China’s updated national standard:
| Steel Grade | Standard |
|---|---|
| Q345 | GB/T 1591-2008 |
| Q355 | GB/T 1591-2018 |
Since February 2019, GB/T 1591-2018 officially came into force, and Q355 replaced Q345 nationwide.
In practical terms, Q355 is not a completely new steel — it is the upgraded version of Q345, offering improved strength consistency, cleaner chemistry, and better mechanical performance.
Yield Strength Comparison for Q345 and Q355
The “355” designation comes directly from its minimum yield strength:
| Material | Minimum Yield Strength |
|---|---|
| Q345 | ≥345 MPa |
| Q355 | ≥355 MPa |
Although the increase is only 10 MPa, the real improvement lies in chemical control and toughness, not just strength.
Chemical Composition: Q345 vs Q355
Typical composition limits:
| Element | Q345 (%) | Q355 (%) |
|---|---|---|
| Carbon (C) | ≤0.20 | ≤0.20 (tighter control) |
| Manganese (Mn) | ≤1.70 | ≤1.70 (optimized balance) |
| Phosphorus (P) | ≤0.035 | ≤0.025 |
| Sulfur (S) | ≤0.035 | ≤0.025 |
Key improvements in Q355:
- Lower phosphorus and sulfur
- Cleaner steel with fewer impurities
- Better micro-alloy element matching
- Improved batch consistency
These changes result in:
- Higher toughness
- More stable welding performance
- Lower risk of cold cracking
- Better reliability for CNC machining
For pipe fittings, hydraulic adapters, and threaded connectors, these advantages are critical.
Why Q345 Is No Longer Available in China
Many overseas customers still specify Q345 on drawings, but in reality:
Q345 has been phased out by Chinese steel mills.
Major manufacturers such as Baosteel, Ansteel, Shagang, and HBIS have fully switched to Q355 production.
Today, if a supplier claims to offer Q345, it usually means:
- They are actually supplying Q355 under the old name
- Old inventory with unclear origin
- Non-standard material from small mills
For export pipe fittings, this creates unnecessary quality risk.
Real Case: Israeli Pipe Fittings Inquiry
Recently, we received a pipe fitting RFQ from Israel.
The drawing specified:
EN 10025 S355
Based on material equivalence:
| European Standard | China Standard |
|---|---|
| S355 | Q345 / Q355 |
Initially, we referenced Q345. However, after confirming with our steel suppliers, we were informed:
Q345 is no longer produced. All supply has been upgraded to Q355.
We explained to the customer:
- China’s national standard has officially shifted to Q355
- Q355 offers cleaner chemistry and slightly higher strength
- Q355 fully satisfies S355 mechanical requirements
- No design changes are required
The customer approved Q355, and the project proceeded smoothly.
This scenario is now very common in international pipe fitting orders.
Can Q355 Directly Replace Q345 in cnc turning parts?
Yes — absolutely.
✔ Direct replacement
✔ No redesign required
✔ Better mechanical consistency
In engineering practice, Q355 can be used wherever Q345 was originally specified.
In our CNC turning production, Q355 is widely applied to:
- Hydraulic pipe fittings
- Threaded adapters
- CNC turned connectors
- Structural coupling parts
- Elbow fitting
- Hose fitting
Machinability is nearly identical to Q345, while material uniformity is noticeably improved.
S355 Steel Grades vs Chinese Q355 Grades
| EN10025 Grade | China Equivalent | Former Grade | Impact Test Requirement | Typical Applications |
|---|---|---|---|---|
| S355JR | Q355B | Q345B | No mandatory low-temperature impact | General structural parts, standard pipe fittings |
| S355J0 | Q355C | Q345C | 0 °C Charpy impact test | Moderate low-temperature structures |
| S355J2 / S355K2 | Q355D | Q345D | −20 °C Charpy impact test | Outdoor structures, pressure components, export pipe fittings |
| S355NL | Q355E | — | −50 °C Charpy impact test | Severe cold environments, high-safety applications |
FAQ
Is Q355 more expensive than Q345?
Slightly, typically 2–5%, depending on market conditions.
Is Q355 suitable for CNC turning?
Yes. Q355 offers stable cutting behavior, fewer hard spots, and good tool life. If you have some pipe fittings need produce , welcome to contact yuhuan hongqian .
Can Q355 meet EN10025 S355 requirements?
Yes. Q355 is China’s standard equivalent to S355. it is suitable to produce various pipe fittings .
Can I still specify Q345?
Technically yes, but practically no. Q345 is no longer produced by mainstream Chinese mills.
Conclusion
Q355 has officially replaced Q345 in China.
From national standards to real supply chains, this transition is complete. For overseas buyers sourcing pipe fittings or CNC turning parts, Q355 is now the default material.
If your drawings still specify Q345, upgrading to Q355 is not only acceptable — it is recommended.
As a professional pipe fittings manufacturer, we support Q355 machining for global projects and provide full material traceability for export orders.
Looking for a reliable pipe fittings manufacturer? Contact Yuhuan Hongqian for high-precision CNC turning parts and custom pipe fitting services in Q355 steel.
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