The meaning of naming:
P355GH:
- The letter 'G' denotes other properties, which are not specific to heat treatment.
- The letter 'H' indicates that this material is suitable for use in medium and high temperature environments, with a maximum temperature of 600 ℃.
P355NH:
- The letter 'N' denotes that the material has been normalised or normalised rolled, resulting in grain refinement.
- The letter 'H' also indicates high temperature suitability, but with a greater emphasis on the strengthening effect of the normalising process.
Differences in chemical composition
| Element | P355GH | P355NH | Tips |
|---|---|---|---|
| C | 0.10%~0.22% | ≤0.18% |
P355NH has a lower carbon content to enhance welding performance. |
| Si | ≤0.60% | ≤0.50% | The silicon content limit for P355NH is more stringent. |
| Mn | 1.10%~1.70% | 1.10%~1.70% |
Manganese content is consistent between the two. |
| Cr+Cu+Mo | ≤0.70% | ≤0.45% |
P355NH has lower total alloying element limits. |
Delivery state and microstructure:
- P355GH is usually delivered in a normalised rolled condition, with a relatively large grain size, making it suitable for use in medium and high temperature scenarios.
- P355NH, on the other hand, requires normalised treatment, resulting in a finer grain size that enhances low temperature impact toughness and welding performance.
Comparison of Mechanical Properties
| Terms | P355GH | P355NH |
|---|---|---|
| Yield strength(ReH) | ≥355MPa | ≥355MPa |
| Tensile strength(Rm) | 510~650MPa | 490~630MPa |
| Elongation(A5) | ≥20%(thickness ≤16mm) | ≥22%(thickness ≤16mm) |
| Impact toughness(-20℃) | ≥27J(KV) | ≥30J(KV) |
| High Temperature Strength(300℃) | ≥260MPa(Rp0.2) | ≥240MPa(Rp0.2) |
Core Application Scenarios
P355GH:
High-temperature and high-pressure equipment: petroleum refining reactor, high-temperature steam pipeline, metallurgical blast furnace gas pipeline.
Corrosive media: acid and alkali solution conveying system.
P355NH:
Low temperature and welding sensitive scenes: nuclear power plant pressure vessels, low temperature storage tanks, welding intensive chemical equipment.
High toughness requirements: earthquake-prone areas or dynamic load environment.
Domestic benchmark materials
P355GH: close to Q345R (GB 713), but with better high temperature performance.
P355NH: similar to 16MnDR (low-temperature container steel), but the composition needs to be adjusted to meet the normalising requirements.
