PROPERTY CLASS 14.9 ULTRA-HIGH-STRENGTH FASTENERS — TECHNICAL DATASHEET AND ENGINEERING GUIDE
Property Class 14.9 represents the developmental peak of high-strength structural fasteners, engineered for extreme mechanical configurations where standard fasteners fail. Governed by standards such as JIS B 1051-1976, GOST 1759.4-87, and proprietary manufacturer specifications, this ultra-high-strength classification exceeds the limits of standard ISO 898-1 specifications.
The "14.9" designation indicates a nominal ultimate tensile strength of 1400 MPa and a yield ratio of 0.9, equating to a nominal yield threshold of 1260 MPa. Achieving these limits requires micro-alloyed steel formulations designed to limit grain boundary impurities and facilitate precipitation hardening via ultra-fine alloy carbides.
■ Chemical Composition and Core Material Designations
Traditional carbon and low-alloy steels are susceptible to sudden brittle failure above 1200 MPa. Class 14.9 utilizes micro-alloyed formulations with precise additions of Vanadium (V), Titanium (Ti), and Molybdenum (Mo) to ensure deep hardenability and microstructural stability.
| Element | KNDS4 (Kobelco) | 40CrMoV | Bainitic Wire Rod |
|---|---|---|---|
| Carbon (C) | 0.39 – 0.40% | 0.36 – 0.44% | 0.38 – 0.45% |
| Chromium (Cr) | 0.95 – 1.07% | 0.90 – 1.10% | 0.85 – 1.35% |
| Molybdenum (Mo) | 0.95 – 1.09% | 0.57 – 0.80% | 0.45 – 0.65% |
| Vanadium (V) | 0.085% | 0.15 – 0.28% | 0.20 – 0.50% |
| Titanium (Ti) | 0.042% | — | — |
| Manganese (Mn) | 0.45 – 0.50% | 0.25 – 0.51% | 0.30 – 0.60% |
| Phosphorus (P) max | ≤ 0.015% | ≤ 0.015% | ≤ 0.015% |
| Sulfur (S) max | ≤ 0.015% | ≤ 0.008 – 0.012% | ≤ 0.015% |
■ Proprietary Datasheet Download
Property Class 14.9 — Complete Technical Yield & Tolerance Datasheet
Contains empirical data for stress simulations, high-temperature reduction factors, and advanced clamp load charts. Corporate/engineering credentials required.
⬇ DOWNLOAD DATASHEET■ Mechanical Properties and Physical Limits
Class 14.9 fasteners are engineered to combine extreme load-bearing capacity with physical toughness, maintaining elongation percentages similar to conventional Class 10.9 fasteners.
| Mechanical Property | Property Class 14.9 Limit |
|---|---|
| Minimum Tensile Strength (Rm, min) | 1373 – 1400 MPa |
| Minimum Yield Strength (ReL / Rp0.2) | 1236 – 1280 MPa |
| Guaranteed Proof Stress (Sp) | 1120 MPa |
| Elongation after Fracture (A5, min) | 7 – 9% |
| Reduction of Area (Z, min) | 30 – 40% |
| Core Hardness Range (HRC) | 40 – 50 HRC |
| Minimum Vickers Hardness (HV) | 395 – 485 HV |
| Minimum Impact Energy (KV) | 15 – 20 Joules |
■ Elevated Temperature Performance
Unlike standard carbon steels which soften above 150°C, Class 14.9 micro-alloyed steels exhibit superior thermal stability, retaining high strength up to 400°C due to precipitation strengthening.
| Temperature (°C) | Yield Strength (MPa) | Tensile Strength (MPa) | Yield Reduction Factor |
|---|---|---|---|
| 20°C (Ambient) | 1348.8 | 1497.9 | 1.000 |
| 200°C | 1363.3 | 1514.8 | 1.011 |
| 400°C | 1130.6 | 1256.2 | 0.838 |
| 500°C | 1007.4 | 1118.9 | 0.747 |
| 600°C | 672.2 | 746.8 | 0.498 |
■ Preload and Tightening Torque (Coarse Threads)
Due to the extreme forces, verifying preload is critical. The torque-to-tension relationship is highly dependent on thread friction. Tightening a dry joint to lubricated torque specifications will result in severe under-tensioning.
| Thread Size | Oil Lube (μ=0.15) Torque (Nm) | Oil Lube (μ=0.15) Clamp (kN) | Dry (μ=0.18-0.20) Torque (Nm) | Dry (μ=0.18-0.20) Clamp (kN) |
|---|---|---|---|---|
| M10 | 62.0 | 28.0 | 56.0 | 23.0 |
| M12 | 107.0 | 40.0 | 97.0 | 33.0 |
| M16 | 260.0 | 75.0 | 237.0 | 62.0 |
| M20 | 510.0 | 118.0 | 464.0 | 97.0 |
| M24 | 878.0 | 169.0 | 800.0 | 140.0 |
| M30 | 1750.0 | 269.0 | 1596.0 | 222.0 |
■ Engineering Considerations and Embrittlement Risk
- Hydrogen Embrittlement (HE) Susceptibility: Due to extreme core hardness (40–50 HRC), Class 14.9 is highly susceptible to HE. Electroplating (e.g., standard zinc plating) is strictly prohibited.
- Corrosion Protection: To prevent hydrogen infiltration from acid pickling and electroplating, non-electrolytic Zinc Flake Coatings (e.g., Geomet, Delta Protect) should be specified. These provide high barrier protection without cathodic charging risks.
- Preload Verification: Given the low ductility margin of ultra-high-strength steel, ultrasonic transit-time measurement is highly recommended over standard torque wrenches for critical joints, improving assembly accuracy to ±3%.
- Post-Fire Replacement: Exposing Class 14.9 bolts to temperatures above 750°C causes phase transition and severe structural softening. Pre-exposure up to 800°C induces auto-quenching upon cooling, forming a hard, highly brittle matrix. Fasteners exposed to >700°C must be replaced.
- Thread Geometry: For dynamic and high-fatigue joints, Metric MJ threads (ISO 5855-1) are strongly recommended due to their enlarged root radius, mitigating local stress concentration factors.