What Is EN 10297-1 Seamless Alloy Mechanical Tube?
EN 10297-1 specifies seamless steel tubes for mechanical and general engineering purposes, covering both non-alloy and alloy quality steels. The alloy grades in the standard are heat treatable medium carbon, chromium-molybdenum and chromium-nickel-molybdenum steels. Heat treatment gives them a wide range of toughness and strength combinations, so a single tube size can be delivered either softened for machining or quenched and tempered for high strength service.
The alloy family is characterised by good hardenability together with a useful balance of strength, wear resistance, toughness and ductility. Typical parts include axle journals, gears, high strength compressor and turbine components, working elements of heavy ground and underground equipment, and components of agricultural machinery.
Size Range and Supply Condition
| Parameter | Range |
|---|---|
| Outside diameter | 26.9 - 610 mm |
| Wall thickness | 2.3 - 100 mm |
| Length | 3000 - 12000 mm |
| Alloy grades | 41Cr4, 25CrMo4, 30CrMo4, 34CrMo4, 42CrMo4, 36CrNiMo4, 30CrNiMo4, 41NiCrMo7-3-2 |
| Delivery condition | Normalized for the E quality grades, quenched and tempered for the Cr-Mo and Cr-Ni-Mo grades |
Tubes are ordered by outside diameter, wall thickness and length, with tolerances taken from the tables of EN 10297-1. Because the standard addresses mechanical tubing rather than line pipe, concentricity, internal cleanliness and surface finish are usually agreed in addition to the dimensional requirements of the standard.
Chemical Composition of the Alloy Grades
The table below gives the ladle analysis limits that control hardenability and response to heat treatment.
| Grade | C (%) | Si max (%) | Mn (%) | Cr (%) | Mo (%) | Ni (%) |
|---|---|---|---|---|---|---|
| 41Cr4 | 0.38 - 0.45 | 0.40 | 0.60 - 0.90 | 0.90 - 1.20 | - | - |
| 25CrMo4 | 0.22 - 0.29 | 0.40 | 0.60 - 0.90 | 0.90 - 1.20 | 0.15 - 0.30 | - |
| 30CrMo4 | 0.27 - 0.34 | 0.35 | 0.35 - 0.60 | 0.80 - 1.15 | 0.15 - 0.30 | - |
| 34CrMo4 | 0.30 - 0.37 | 0.40 | 0.60 - 0.90 | 0.90 - 1.20 | 0.15 - 0.30 | - |
| 42CrMo4 | 0.38 - 0.45 | 0.40 | 0.60 - 0.90 | 0.90 - 1.20 | 0.15 - 0.30 | - |
| 36CrNiMo4 | 0.32 - 0.40 | 0.40 | 0.50 - 0.80 | 0.90 - 1.20 | 0.15 - 0.30 | 0.90 - 1.20 |
| 30CrNiMo4 | 0.26 - 0.34 | 0.40 | 0.30 min | 1.80 - 2.20 | 0.30 - 0.50 | 1.80 - 2.20 |
| 41NiCrMo7-3-2 | 0.38 - 0.44 | 0.30 | 0.60 - 0.90 | 0.70 - 0.90 | 0.15 - 0.30 | 1.65 - 2.00 |
Phosphorus and sulphur are held to a maximum of 0.035% in most grades, and to 0.025% for 41NiCrMo7-3-2, which reduces the risk of hot shortness during hot working and improves impact toughness. Where the nitrogen content is already fixed by other elements, the minimum aluminium requirement for fine grain treatment does not apply. The maximum combined niobium and vanadium content is limited to 0.20% in the micro-alloyed grades.
Mechanical Properties of the Fine Grain Quality Grades
The E grades combine normalizing with a fine grain microstructure and are ordered with a guaranteed minimum impact energy at minus 20 degrees Celsius. Yield strength values below are quoted for wall thickness up to 16 mm; the standard reduces the minimum as wall thickness increases.
| Grade | ReH min (MPa) | Rm (MPa) | Elongation min (%) | Charpy KV min at -20 C |
|---|---|---|---|---|
| E275K2 | 275 | 410 | 22 | 40 J longitudinal, 27 J transverse |
| E355K2 | 355 | 490 | 20 | 40 J longitudinal, 27 J transverse |
| E420K2 | 420 | 600 | 19 | 27 J longitudinal, 20 J transverse |
| E460K2 | 460 | 550 | 19 | 40 J longitudinal, 27 J transverse |
| E590K2 | 590 | 700 | 16 | 40 J longitudinal, 27 J transverse |
| E730K2 | 730 | 790 | 15 | 40 J longitudinal, 27 J transverse |
Carbon is limited to a maximum of 0.20% in the E275K2, E355K2, E460K2 and E730K2 grades and held between 0.16% and 0.22% in E420K2 and E590K2. Manganese ranges from 0.50 - 1.40% in E275K2 up to 1.40 - 1.70% in E730K2, and the finer the grain refining addition, the higher the strength that can be reached at a given carbon level.
Mechanical Properties of the Heat Treated Alloy Grades
| Grade | ReH min (MPa) | Rm (MPa) | Elongation min (%) |
|---|---|---|---|
| 41Cr4 | 800 | 1000 | 11 |
| 25CrMo4 | 700 | 900 | 12 |
| 30CrMo4 | 750 | 950 | 12 |
| 34CrMo4 | 800 | 1000 | 11 |
| 42CrMo4 | 900 | 1100 | 10 |
| 36CrNiMo4 | 900 | 1100 | 10 |
| 30CrNiMo4 | 1050 | 1250 | 9 |
| 41NiCrMo7-3-2 | 950 | 1150 | 9 |
The values above apply to the quenched and tempered condition for wall thickness up to 8 mm, with longitudinal test pieces. Minimum yield strength and elongation fall as wall thickness increases, and the standard gives separate columns for each thickness band. Transverse test values are lower than longitudinal values and are quoted separately.
Heat Treatment and Fabrication
Normalizing refines the grain structure of the E grades and produces a uniform ferrite-pearlite microstructure.
Quenching and tempering develops the high strength and toughness combination of the Cr-Mo and Cr-Ni-Mo grades.
Stress relieving after machining reduces residual stress and dimensional movement in precision components.
Machinability is improved by ordering a softened or annealed condition for parts that require extensive turning.
Welding of alloy grades requires preheat and post weld heat treatment matched to the carbon equivalent of the grade.
Inspection and Marking
Tubes are supplied with a test certificate that records heat number, grade, size, delivery condition and the results of the tests required by the order. Hydrostatic testing, eddy current or ultrasonic examination, and magnetic particle inspection of the surface can be specified for safety related parts. Dimensional verification of diameter, wall thickness, length and straightness is performed before the tubes are marked, protected and packed for transport.
Frequently Asked Questions
Q: What does EN 10297-1 cover?
It covers seamless steel tubes for mechanical and general engineering purposes, including non-alloy quality steels and the heat treatable alloy grades listed in its tables.
Q: Which alloy grades belong to this standard?
The alloy range runs from 41Cr4 through 25CrMo4, 30CrMo4, 34CrMo4, 42CrMo4, 36CrNiMo4 and 30CrNiMo4 to 41NiCrMo7-3-2, all supplied with controlled chemistry and heat treatment.
Q: What sizes are available?
Outside diameter from 26.9 mm to 610 mm, wall thickness from 2.3 mm to 100 mm and length from 3000 mm to 12000 mm, subject to the tolerances of the standard.
Q: What is the difference between the E grades and the Cr-Mo grades?
The E grades are fine grain normalized steels intended for structural and general mechanical duty, while the Cr-Mo and Cr-Ni-Mo grades are quenched and tempered to reach much higher yield strength for gears, axles and shafts.
Q: At what temperature is the impact test performed?
The K2 designation requires a minimum average absorbed energy of 40 J longitudinal or 27 J transverse at minus 20 degrees Celsius for most grades, with lower values for the higher strength qualities.
Q: How should alloy mechanical tube be ordered?
Quote the standard, grade, delivery condition, outside diameter, wall thickness, length, test requirements and certificate type so that the mill can confirm chemistry and properties before rolling.
