What Is 15Mo3 Material?
15Mo3 is a low-alloy molybdenum steel defined by the former German standard DIN 17175, with the Werkstoff number 1.5415. It is supplied as a seamless tube for boiler and pressure-vessel service at temperatures up to about 450 degrees Celsius. The molybdenum addition improves creep strength and resistance to hydrogen attack at elevated temperature, which makes the grade a standard choice for heating surfaces, water walls, economizers and superheaters in low- and medium-pressure boilers.
Chemical Composition
The composition of 15Mo3 is tightly controlled to balance weldability and high-temperature strength.
| Element | Content, % |
|---|---|
| Carbon | 0.12-0.20 |
| Silicon | 0.10-0.35 |
| Manganese | 0.40-0.80 |
| Phosphorus, maximum | 0.035 |
| Sulfur, maximum | 0.035 |
| Molybdenum | 0.25-0.35 |
Mechanical Properties and Heat Treatment
The minimum room-temperature mechanical properties of 15Mo3 tubes are a yield strength of 270 MPa, a tensile strength of 450-600 MPa and a minimum elongation of 22% on a 5.65-square-root gauge length. The standard delivery condition is normalized or normalized and tempered, which produces a fine ferrite-pearlite microstructure suitable for boiler service. Heat treatment for the tube itself is performed at the mill; field fabrication requires controlled welding and, where the code demands it, post-weld heat treatment.
| Property | Value |
|---|---|
| Yield strength, minimum | 270 MPa |
| Tensile strength | 450-600 MPa |
| Elongation A5, minimum | 22% |
| Delivery condition | Normalized or normalized and tempered |
Equivalents and Successor Standards
DIN 17175 was withdrawn and its scope is now covered by the European standard EN 10216-2, where 15Mo3 is replaced by 16Mo3. Comparable specifications include EN 10028-2 grade 16Mo3 for plates, UNI 5869 grade 15Mo3 in Italy, and the molybdenum-alloyed boiler steels of ASTM A204. For higher temperatures and pressures, chromium-molybdenum grades such as those of ASTM A213 T11 provide additional creep strength.
| Comparison Item | 15Mo3, DIN 17175 | 16Mo3, EN 10216-2 | A213 T11, ASME |
|---|---|---|---|
| Standard system | German standard, withdrawn | European standard | American standard |
| Material type | Molybdenum steel | Molybdenum steel | Chromium-molybdenum steel |
| Chromium | Not specified | Not specified | 1.00-1.50% |
| Molybdenum | 0.25-0.35% | 0.25-0.35% | 0.44-0.65% |
| Tensile strength | 450-600 MPa | 450-600 MPa | 415-585 MPa |
| Typical service | Up to about 450 degrees Celsius | Up to about 450 degrees Celsius | 450-650 degrees Celsius |
Typical Applications
15Mo3 and its successor 16Mo3 are used for boiler heating-surface tubes, water-wall tubes, economizers and superheaters where the working pressure does not exceed about 5.88 MPa and the temperature stays below 450 degrees Celsius, as well as in high-pressure boiler economizers. Outside boiler work the grade appears in heat exchangers, feed-water lines and general elevated-temperature piping where molybdenum-bearing steel is specified.
Welding and Fabrication Points
15Mo3 is weldable by all conventional processes. Use consumables matched to the molybdenum content, keep the heat input moderate, and follow the project code for preheat and post-weld heat treatment. Because the steel relies on molybdenum for creep strength, filler metals must not introduce uncontrolled alloying, and the welding procedure qualification should include the actual tube thickness. Verify the delivery condition on the mill certificate, because normalized tubes must not be re-hardened by local heating during fabrication.
Common Misconceptions
15Mo3 is not a tool steel and is never oil-quenched to high hardness in service; its correct treatment is normalization. The grade is not suitable for steam service above about 450 degrees Celsius, where chromium-molybdenum steels are required. DIN 17175 certificates should be converted to EN 10216-2 16Mo3 for new European projects. The mechanical table must always be read together with the delivery condition, because the values are guaranteed only in the specified heat-treated state.
FAQ
What does 15Mo3 mean?
15 is the nominal carbon content in hundredths of a percent, Mo marks molybdenum as the main alloying element, and 3 is a series number. The material number is 1.5415.
What is the equivalent of 15Mo3?
The direct successor is EN 10216-2 grade 16Mo3. Similar molybdenum steels include EN 10028-2 16Mo3 plates and ASTM A204 boiler steels.
What are the mechanical properties of 15Mo3?
Minimum yield strength 270 MPa, tensile strength 450-600 MPa, minimum elongation 22%.
Can 15Mo3 be used above 450 degrees Celsius?
For long-term pressure service the practical limit is about 450 degrees Celsius; higher temperatures need chromium-molybdenum grades such as A213 T11.
Is 15Mo3 weldable?
Yes, with matching molybdenum consumables, controlled heat input, and preheat and post-weld heat treatment per the project code.
Is DIN 17175 still valid?
The standard has been withdrawn in Europe; specify EN 10216-2 16Mo3 for new projects or ASME-compatible equivalents for American-code work.