10705MBU, 12CrMoWVNb
10705MBU is a high-performance alloy steel specifically developed for use in turbine blades, compressor components, and other critical applications in the aerospace and power generation industries. It is designed to offer a balanced combination of strength, toughness, and corrosion resistance under high-temperature and high-stress environments.
Table of Contents
What is 10705MBU, 12CrMoWVNb?
10705MBU steel is a high-strength, high-temperature performance excellent martensitic heat-resistant steel, commonly used in key parts of large gas turbines (especially heavy industrial gas turbines), such as static blades and moving blades. This steel grade has good high-temperature strength, creep resistance, and oxidation resistance, suitable for long-term high-temperature and high-pressure conditions.
Referenced Standards
The following documents, effective on the date of investigation for bids, form part of this specification:
- JIS G 0404: Steel and Steel Products - General Technical Delivery Requirements
- JIS G 0551: Steel - Macroscopic Examination by Etching
- JIS G 0555: Steel - Microscopic Examination for Non-Metallic Inclusions
Key Characteristics:
- High Strength at Elevated Temperatures: Maintains structural integrity and mechanical properties in high-heat environments.
- Excellent Fatigue Resistance: Withstands cyclic loading conditions common in turbine and engine operations.
- Good Corrosion and Oxidation Resistance: Suitable for operation in aggressive atmospheric and combustion environments.
- Stable Microstructure: Engineered for long-term reliability under thermal and mechanical stress.
Applications
- Steam and gas turbine blades
- Compressor discs and rotors
- Jet engine components
- High-temperature structural parts in aerospace systems
Chemical Composition (%)
| Element | Heat Analysis | Product Analysis |
|---|---|---|
| C | 0.12 ~ 0.16 | 0.11 ~ 0.17 |
| Mn | 0.30 ~ 0.70 | 0.27 ~ 0.73 |
| P | 0.020 Max | 0.025 Max |
| S | 0.015 Max | 0.020 Max |
| Si | 0.06 Max | 0.08 Max |
| Cr | 10.00 ~ 11.00 | 9.90 ~ 11.10 |
| Mo | 0.30 ~ 0.50 | 0.30 ~ 0.50 |
| Ni | 0.35 ~ 0.65 | 0.32 ~ 0.68 |
| W | 1.50 ~ 1.90 | 1.42 ~ 1.98 |
| V | 0.14 ~ 0.20 | 0.12 ~ 0.22 |
| Nb | 0.05 ~ 0.11 | 0.05 ~ 0.11 |
| N | 0.040 ~ 0.080 | 0.040 ~ 0.080 |
| Cu | 0.50 Max | 0.55 Max |
Material Properties
Full cross-section coupons shall conform to the properties specified below when heat treated as shown in Section 6.2.2:
| Property | Value | Alternative Units |
|---|---|---|
| Tensile Strength | 930N/mm² Min | (94.9 kgf/mm² Min) [135,000 p.s.i. Min] |
| 0.2% Yield Strength | 760N/mm² Min | (77.3 kgf/mm² Min) [110,000 p.s.i. Min] |
| Elongation (GL=4D) | 14% Min | |
| Reduction of Area | 32% Min | |
| V-notch Impact Absorbed Energy | 20 J Min | (2.0 kgf-m Min) |
Tensile Strength (Ultimate Strength)
- Room Temperature (20°C):
≥ 950 MPa - At Elevated Temperatures (e.g., 500–600°C):
Decreases with temperature but maintains high strength:- At 500°C: ~750–800 MPa
- At 600°C: ~600–650 MPa
Creep Resistance
- Excellent long-term creep resistance under continuous stress at elevated temperatures.
- Typical Creep Rupture Strength:
- At 600°C for 100,000 hours: ≥ 100 MPa
- This makes it suitable for components in turbines where dimensional stability over time is critical.
Fatigue Strength
- High fatigue resistance, especially in cyclic high-stress applications such as rotating blades.
- Fatigue Limit (Endurance Limit) at Room Temperature:
~450–550 MPa (depending on surface finish and geometry) - High-Temperature Fatigue:
Performance declines with increasing temperature, but 10705MBU retains useful fatigue strength up to ~550°C.
Summary Table
| Property | Value (Typical) |
|---|---|
| Tensile Strength (RT) | ≥ 950 MPa |
| Yield Strength (RT) | ≥ 800 MPa |
| Creep Rupture Strength (600°C) | ≥ 100 MPa (100,000 h) |
| Fatigue Strength (RT) | ~450–550 MPa |
| Service Temperature Range | Up to 600°C |
Physical Properties
10705MBU is a high-performance martensitic stainless steel developed for use in turbine blades and high-temperature structural components. It exhibits excellent mechanical and thermal stability under demanding operational conditions.
1. Density:
- ~7.75 g/cm³ (7750 kg/m³)
2. Thermal Conductivity:
- ~20–25 W/m·K at room temperature
(Varies slightly depending on tempering condition and exact alloy composition)
3. Specific Heat Capacity:
- ~460–500 J/kg·K
4. Coefficient of Thermal Expansion:
- ~11.5–12.5 × 10⁻⁶ /K (from 20°C to 600°C)
(This is important for dimensional stability under thermal cycling.)
5. Electrical Resistivity:
- ~0.65–0.75 μΩ·m at room temperature
6. Magnetic Properties:
- Magnetic in quenched and tempered condition
(Due to its martensitic microstructure)
7. Oxidation Resistance:
- Good up to 600–650°C in air
(Exact performance depends on surface finish and operating environment)
These physical properties make 10705MBU suitable for high-temperature and high-stress environments, such as turbine engines and compressor stages.
Heat Treatment
The heat treatment of 10705MBU blade steel is critical to achieving its optimal mechanical properties, particularly for applications requiring high strength, toughness, and thermal stability. The typical heat treatment process includes annealing (if needed), quenching, and tempering.
Typical Heat Treatment Regimen:
Forging (if applicable)
- Forging Temperature: 1000–1150°C
- Final Forging Temperature: Not below 850°C
- After forging, slow cooling in furnace or insulating material is recommended to avoid cracking.
Normalizing / Pre-heat Treatment (optional):
- Temperature: 880–920°C
- Holding Time: 1 hour per 25 mm thickness
- Cooling: Air cool
(Used to refine grain structure before hardening.)
Quenching (Austenitizing):
- Temperature: 950–980°C
- Holding Time: 30–60 minutes depending on thickness
- Cooling Medium: Oil or air (depending on part size and required hardness)
- Purpose: Achieves martensitic structure for high strength.
Tempering:
- Temperature: 620–700°C
- Holding Time: 1–2 hours depending on section size
- Cooling: Air cool
- Purpose: Improves toughness, reduces brittleness, and relieves internal stress.
Optional Secondary Tempering (for stress relief or dimensional stability):
- Often conducted at 650–680°C
Resulting Mechanical Properties (Typical After Heat Treatment):
- Tensile Strength: ≥ 950 MPa
- Yield Strength: ≥ 800 MPa
- Impact Toughness: ≥ 50 J (at room temperature)
- Hardness: ~260–320 HB (Brinell Hardness)
Note: The actual heat treatment parameters may vary depending on component geometry, service conditions, and manufacturer-specific specifications. Always refer to technical datasheets or consult metallurgical engineers for final treatment standards.
Processing Performance
Processing Properties of 10705MBU Blade Steel
1. Hot Workability (Hot Forming Performance)
- Excellent hot workability within the temperature range of 1000–1150°C.
- Should be forged or hot rolled within this range; avoid working below 850°C to prevent cracking or damage to the microstructure.
- Good resistance to thermal fatigue and low risk of hot cracking if proper forging practices are followed.
- After hot working, slow cooling in the furnace or dry ash is recommended to prevent internal stresses or unwanted phase transformations.
2. Cold Workability (Cold Forming Performance)
- Moderate cold formability. Due to its strength and alloy content, it has higher deformation resistance compared to low-alloy steels.
- Cold forming operations such as bending or drawing should be done with caution, and preheating may be recommended for complex shapes to reduce risk of cracking.
- Intermediate annealing may be required for large deformations.
- Generally used in the heat-treated condition, not widely used for extensive cold forming.
3. Weldability
- Fair weldability, but not classified as an easy-to-weld steel due to its alloying elements and hardened microstructure.
- Preheating before welding (typically 200–350°C) is recommended to reduce the risk of cold cracking.
- Post-weld heat treatment (PWHT) such as tempering at 600–680°C is often necessary to restore toughness and relieve residual stresses.
- Recommended welding methods: TIG, MIG, or submerged arc welding, using filler materials with compatible composition.
- Cleanliness and proper joint preparation are critical to avoid porosity and weld defects.
Additional Machinability Notes:
- Machinability is considered moderate to difficult due to its hardness and strength after heat treatment.
- Use high-speed steel or carbide tools with controlled cutting parameters.
- Optimal to machine in the annealed condition before final heat treatment when tight tolerances are required.