ISO 10269
EN ISO 10269 is a European standard that defines the technical characteristics and requirements of metallic materials used for screws, bolts and fastening systems intended to work in high temperature or low temperature conditions. This standard is essential to ensure that the materials chosen can operate in extreme environments while maintaining their mechanical performance and required strength.
The standard covers steel and nickel-based alloy products intended for the manufacture of screws, tie rods, bolts and nuts. These materials must be able to withstand high loads and harsh environmental conditions, such as high temperatures (up to 500°C and above) and low temperatures (down to -200°C).
High Temperature Steels
Steels designed for high-temperature applications must maintain mechanical strength and ductility even under thermal and mechanical stress conditions. EN ISO 10269 divides these steels into several classes based on chemical composition and performance at elevated temperatures:
- Chromium-molybdenum (Cr-Mo) steels: These steels, with the addition of chromium and molybdenum, are commonly used because of their excellent resistance to creep deformation and oxidation at elevated temperatures. Chromium improves corrosion and oxidation resistance, while molybdenum increases mechanical strength at elevated temperatures. Typically used in environments between 400°C and 600°C, they find wide use in turbine, boiler and piping components.
- Austenitic stainless steels: Austenitic stainless steels (such as AISI 304 and 316) are characterized by high corrosion resistance due to their high chromium and nickel content. These steels can withstand temperatures up to about 800°C, making them ideal for applications in oxidizing and corrosive environments, such as those in chemical and petrochemical plants.
Nickel Alloys
Nickel alloys find wide use in extreme environments where temperatures exceed the limits of steels. EN ISO 10269 specifies high-performance nickel alloys that provide performance stability and reliability up to over 800°C.
- Nickel-chromium alloys (Inconel): Nickel alloys containing chromium are among the most widely used due to their excellent resistance to oxidation and corrosion in high-temperature environments. Fasteners such as screws, tie rods and nuts made of alloys 2.4668 INCONEL®718 and 2.4952 NIMONIC® 80, for example, maintain stable mechanical properties up to about 700°C. These alloys are used in critical applications, such as in jet engines and gas turbines, where the combination of fatigue and corrosion resistance is critical.
Mechanical Requirements and Testing
The mechanical requirements specified by EN ISO 10269 mainly concern tensile strength, creep behavior, resilience, hardness, fatigue strength and dimensional stability. Below is a table summarizing the main mechanical requirements for various materials:
| Material designation | Type | Rp 0.2% (MPa) min. | Rm (MPa) | Elongation after fracture A% min. | Reduction area Z% min. | Ompact energy (ISO-V) 20°C KV2 J min. |
|---|---|---|---|---|---|---|
| 1.4913 (+QT) | High temperature resistant steel | 750 | 900 – 1050 | 11 | 35 | 20 |
| 1.4923 (+QT1) | High temperature resistant steel | 600 | 800 – 950 | 14 | 40 | 47 |
| 1.4923 (+QT2) | High temperature resistant steel | 700 | 900 – 1050 | 12 | 40 | 20 |
| 1.4301 (+AT) | Austenitic stainless steel | 190 | 500 – 850(*) | 12 | 80 | |
| 1.4307 (+AT) | Austenitic stainless steel | 175 | 450 – 850(*) | 12 | 80 | |
| 1.4404 (+AT) | Austenitic stainless steel | 200 | 500 – 850(*) | 12 | 80 | |
| 1.4401 (+AT) | Austenitic stainless steel | 200 | 500 – 850(*) | 12 | 80 | |
| 1.4910 (+AT) | Austenitic stainless steel | 260 | 550 – 750 | 35 | 100 | |
| 1.4980 (+AT+P) | High-temperature resistant steel | 600 | 900 – 1150 | 15 | 50 | |
| 1.4986 (+WW+P) | High temperature resistant steel | 500 | 650 – 850 | 16 | 50 | |
| 2.4952 (+AT+P) | Nickel alloy | 600 | 1000 – 1300 | 12 | 12 | 22 |
| 2.4668 (+P) | Nickel alloy | 1030 | min. 1230 | 12 | 12 | |
| 2.4669 (+AT+P) | Nickel alloy | 650 | 1000 – 1200 | 20 | 28 | 22 |
The mechanical properties of steels suitable for making screws, nuts, bolts, and fastening systems intended for high-temperature applications vary with operating temperature. Therefore, the judicious choice of a suitable material to meet the design conditions must anticipate the loss of performance during system operation; in detail, the tables below show the values of Rp0.2 and Rm for the most commonly used materials for making screws, nuts and tie rods for high-temperature applications such as, gas turbines, exhaust systems, brake systems, etc.
Graph variation of Rp value 0.2% as temperature increases
Graph variation of Rm value as temperature increases
Proof of Creep
Creep is the tendency of a material to gradually deform under constant loads over time, especially at elevated temperatures. Creep resistance is a crucial parameter for fasteners and bolts operating under prolonged stress conditions. EN ISO 10269 establishes creep tests to determine material deformation as a function of:
- Applied load
- Temperature
- Time (typically long duration tests, such as 1000 or 10,000 hours)
During the creep test, the progressive plastic deformation that the material undergoes under a given load at elevated temperatures is measured. It is essential that materials can withstand such deformation within acceptable limits to prevent critical components, such as bolts and screws, from losing their structural functionality.
Resistance to Thermal Fatigue
Fatigue strength is the ability of the material to withstand cyclic or repeated loads without suffering premature failure. At elevated temperatures, the fatigue behavior of materials can be affected by heating and cooling cycles that induce repeated thermal stresses.
High-temperature steels must show good resistance to thermal cycling to prevent cracks or crazing that can propagate rapidly and cause component failure.
Nickel alloys, by virtue of their thermal stability, offer better fatigue resistance than steels, especially under extreme cyclic conditions, such as in aircraft engines or gas turbines.
EN ISO 10269 covers materials critical to the design of fasteners and bolts intended to operate in high temperature environments and extreme stress conditions. Nickel alloys and high-temperature steels are the main families of materials, each with specific characteristics in terms of mechanical strength and thermal stability. These materials ensure safety and reliability in the most demanding industrial applications.