The valve is a core component of the engine and operates under extremely harsh conditions:
High temperature: The exhaust valve temperature can reach 650-850℃
High pressure: Suffering from the impact of explosive pressure
Corrosion: Oxidation and corrosion by the high-temperature gas (containing sulfur and lead)
Abrasion: Frequent impact and friction with the valve seat
Fatigue: Mechanical fatigue and thermal fatigue caused by repeated opening and closing
Therefore, the valve steel must possess:
High thermal strength and hardness: Not softening at high temperatures and maintaining high strength
Excellent oxidation resistance: Resisting oxidation by high-temperature gas
High wear resistance: Resistant to impact and friction
Good thermal fatigue resistance: Not cracking under cold and hot cycles
Toughness: Performance not deteriorating under long-term high-temperature use
II. Main classifications and typical grades
Valve steel is mainly divided into two categories: Martensitic and Austenitic:
1. Martensitic valve steel (medium-low load, medium temperature)
Characteristics: Higher carbon content (0.4-0.6%), mainly containing Cr and Si. It can be strengthened through quenching + tempering, with high hardness, good wear resistance, and lower cost.
Usage temperature: ≤ 700℃, mostly used for intake valves or light-load exhaust valves.
Typical grades:
4Cr9Si2 (1.4718): The most commonly used, general-purpose valve steel
4Cr10Si2Mo (1.4731): Contains Mo, with better high-temperature strength and toughness
2. Austenitic valve steel (high load, high temperature)
Characteristics: High Cr, Ni, and adding N, W, Mo, etc. The high-temperature strength, creep resistance, and thermal fatigue resistance are far superior to martensitic type, but the price is high and the processing is difficult.
Usage temperature: 700-850℃, mainly used for heavy-load exhaust valves.
Typical grades:
5Cr21Mn9Ni4N (21-4N): The most classic austenitic valve steel, nitrogen strengthening, high cost-performance ratio
23-8N (5Cr23Ni8Mn3N): High Cr, excellent oxidation resistance
GH4751 (Nimonic 80A): Nickel-based high-temperature alloy, used in ultra-high temperature and ultra-high strength scenarios
| C | Cr | Si | Mn | Ni | Mo | N | ||
|---|---|---|---|---|---|---|---|---|
| 4Cr9Si2 | 0.35~0.50 | 8.0~10.0 | 2.0~3.0 | - | - | - | - | |
| 4Cr10Si2Mo | 0.35~0.45 | 9.0~11.0 | 1.9~2.6 | - | - | 0.7~1.0 | - | |
| 21-4N | 0.45~0.60 | 20.0~22.0 | ≤1.0 | 8.0~10.0 | 3.2~4.3 | - | 0.3-0.5 |
4Cr9Si2 Martensitic Heat Resistant Steel X45CrSi9-3 (1.4718) ≤700℃ Ordinary gasoline engine, light diesel engine intake valve / low-load exhaust valve
4Cr10Si2Mo Martensitic Heat Resistant Steel X40CrSiMo10-2 (1.4731) ≤750℃ Medium-load diesel engine, vehicle exhaust valve
5Cr21Mn9Ni4N (21-4N) Austenitic Valve Steel 21-4N 750~800℃ Heavy trucks, ships, high-power engines exhaust valve