25CrMoV5-8 vs 21CrMoV5-7: Both Cr-Mo-V bolt steels — slightly different Cr/Mo balance
25CrMoV5-8 vs 21CrMoV5-7
Side-by-side chemical composition and mechanical property comparison.
Overview
25CrMoV5-8
1.7755
Cr-Mo-V high-temperature bolt steel for service up to ~540°C. Used alongside 21CrMoV5-7 in power plant bolting — slightly higher Cr+Mo for improved creep resistance at the cost of toughness. Used for turbine casing bolts, high-pressure steam valve studs, and boiler fasteners.
21CrMoV5-7
1.7709
Cr-Mo-V high-temperature alloy steel for bolting at elevated temperatures up to ~550°C. Higher Cr and Mo than 15CrMoV5-9 for improved creep resistance. Used for turbine casing bolts, main flange bolts in steam power plants, and high-pressure/high-temperature petrochemical fasteners.
| 25CrMoV5-8 | 21CrMoV5-7 | |
|---|---|---|
| Material Number | 1.7755 | 1.7709 |
| Category | Alloy Steel | Alloy Steel |
| Standard | EN 10269 | EN 10269 |
Chemical composition (wt%)
| Element | 25CrMoV5-8 | 21CrMoV5-7 | Overlap |
|---|---|---|---|
| C | 0.22–0.29% | 0.17–0.25% | Partial |
| Si | 0–0.3% | 0–0.35% | OK |
| Mn | 0.3–0.7% | 0.3–0.8% | OK |
| P | 0–0.02% | 0–0.02% | OK |
Mechanical properties
| Property | 25CrMoV5-8 | 21CrMoV5-7 | Unit |
|---|---|---|---|
| tensile_strength | 780–930 | 800–950 | MPa |
| yield_strength | ≥ 590 | ≥ 600 | MPa |
| elongation | ≥ 14 | ≥ 14 | % |
Compatibility Assessment
25CrMoV5-8 has higher Cr (1.2-1.7 vs 1.2-1.5) and Mo (0.7-1.0 vs 0.55-0.80) for marginally better creep resistance. 21CrMoV5-7 has slightly higher strength. Both suitable to ~540-550°C. Practically interchangeable for most power plant bolting.
Frequently Asked Questions
Is 25CrMoV5-8 the same as 21CrMoV5-7?
25CrMoV5-8 and 21CrMoV5-7 have a 85% composition overlap. Both Cr-Mo-V bolt steels — slightly different Cr/Mo balance
Can I replace 25CrMoV5-8 with 21CrMoV5-7?
In many cases, yes. The compositions overlap significantly (85%). However, always verify mechanical property requirements and heat treatment compatibility for your specific application.
What is the difference between 25CrMoV5-8 and 21CrMoV5-7?
The main differences are in the following elements: C, Mo. 25CrMoV5-8 is a Alloy Steel grade, while 21CrMoV5-7 is a Alloy Steel grade.
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Data provided for reference only. Always verify against the applicable specification for critical applications.
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