What DIN 17175 10CrMo9-10 Is
10CrMo9-10 is a seamless tube grade of chromium-molybdenum heat resistant steel, standardised originally in DIN 17175, the German standard for seamless tubes of heat resistant steels, under material number 1.7380. DIN 17175 has been withdrawn and replaced by DIN EN 10216-2, and the grade designation has been carried over into the European standard, where it is written as 10CrMo9-10 with the same material number. The designation follows the older German composition notation, indicating approximately 0.10 percent carbon together with chromium and molybdenum additions in the nominal 2.25 to 1 percent ratio, and it is the actual analysis in the standard that governs the supply.
In practice the steel is the classic 2.25 percent chromium and 1 percent molybdenum (2.25Cr-1Mo) alloy used throughout the power and process industries. It is described as a pearlitic or bainitic heat resistant steel, ferritic in structure, and it is chosen because its creep rupture strength remains useful when carbon steel and 1.25Cr-0.5Mo steel have run out of allowable stress.
Chemical Composition
| Element | Typical specification range | Function |
|---|---|---|
| Carbon | 0.08 - 0.14 percent | Strength and hardenability |
| Silicon | 0.50 percent maximum | Deoxidation |
| Manganese | 0.40 - 0.70 percent | Strength, deoxidation |
| Phosphorus | 0.025 percent maximum | Restricted for toughness and creep ductility |
| Sulphur | 0.020 percent maximum | Restricted for hot ductility |
| Chromium | 2.00 - 2.50 percent | Oxidation resistance and creep strength |
| Molybdenum | 0.90 - 1.10 percent | Solid solution strengthening, creep resistance |
Chromium provides oxidation and scaling resistance at temperature, and molybdenum raises the creep rupture strength by solid solution strengthening and by stabilising carbides. The carbon content is deliberately low to keep weldability and creep ductility acceptable while still allowing the carbide forming elements to do their work.
Heat Treatment and Mechanical Behaviour
The grade is supplied in the normalised and tempered condition, occasionally in the quenched and tempered condition for specific engineering agreements. Normalising heat treatment is carried out in the range typical for this alloy, followed by tempering at a temperature above the intended service temperature so that the microstructure and, with it, the creep properties remain stable in service. The tube is generally supplied hot finished, with cold finished product available for smaller diameters where dimensional control is tighter.
At room temperature the alloy behaves as a medium strength steel; at service temperature its advantage is the retained proof strength and creep rupture strength, which is what the design calculation uses. For orientation against the American system, ASME A335 grade P22, UNS K21590, specifies a minimum tensile strength of 415 MPa and a minimum yield strength of 205 MPa at room temperature, and the EN grade sits in the same property band. Where a project mixes codes, an equivalence statement should be supported by the actual material certificate rather than by the designation alone.
Service Applications
Typical applications are superheater and reheater tube banks, steam headers, main steam piping and hot reheat line pipe in fossil fired boilers, together with high pressure steam and hydrogen service piping in petrochemical plants. The grade is also used in heat exchanger tubing where the process side temperature exceeds the range of low alloy carbon steel. Service temperature limits are set by the applicable design code and by the creep data in the material data sheet rather than by the product standard alone, and in German practice the VdTUEV material data sheets have traditionally supplied the creep values used in design.
Because the tubes operate in the creep range, procurement attention falls on the heat treatment record, the grain size and the creep test data rather than on room-temperature tensile values alone. Buyers normally require the normalising and tempering temperatures on the certificate, a reference to the creep data set used, and for header applications an ultrasonic or eddy current examination of the full length.
Frequently Asked Questions
Q: Is 10CrMo9-10 the same as A335 P22?
A: They are close counterparts of the same 2.25Cr-1Mo composition family, but they are separate standards with separate property tables, so the actual certificate is needed before they are treated as interchangeable.
Q: What is the material number of 10CrMo9-10?
A: 1.7380, which is the Werkstoff number that appears on European mill certificates alongside the grade designation.
Q: In what condition is the tube supplied?
A: Normally in the normalised and tempered condition, with the heat treatment temperature recorded on the inspection certificate because the creep properties depend on it.
Q: Why is molybdenum added at about 1 percent?
A: Molybdenum raises creep rupture strength through solid solution strengthening and carbide formation, which is what allows the grade to serve above the temperature limit of carbon steel.
Q: Which applications most often specify this grade?
A: Superheater and reheater tubes, steam headers and main steam piping in power boilers, and high temperature piping in process plants.
Q: Is the standard still DIN 17175?
A: No. DIN 17175 has been withdrawn and replaced by the EN 10216-2 designation, and new orders should reference the current European standard while retaining the grade and material number.