EN25 High Tensile Steel

EN25 is a 2.5% nickel - chromium - molybdenum high hardenability, high tensile steel, generally supplied hardened and tempered in the tensile range 930 - 1080 Mpa (Condition U) Rc 28 - 36.

Characterised by high strength and toughness in very large sections - similar to EN26 but with lower carbon content.
Pre hardened and tempered EN25 can be further surface hardened by flame or induction hardening, and by nitriding.
EN25 is used extensively in most industry sectors for applications requiring higher tensile and yield strength than 4140 can provide
Typical uses are: Adapters, Axles, Connecting Rods, Die Holders, Drill Shanks, Ejector Rods, Hydraulic Clamps, Jack Shafts, Line Shafts, Motor Shafts, Nuts, Pins, Piston Rods, Pump Shafts, Rams, Spindles, Torsion Bars Winch Gears etc.
Colour Code Stocked Sizes
Dark Green (Bar End)

Available subject to enquiry
Related Specifications

Australia AS 1444-1996-X9931
Germany W.Nr 1.6743 32 NiCrMo10 4
Great Britain BS970: Part 3: 1991 826M31
BS970: 1955 - EN25
Chemical Composition (Base Material)
Min. % Max %
Carbon 0.27 0.35
Silicon 0.10 0.40
Manganese 0.45 0.70
Nickel 2.30 2.80
Chromium 0.50 0.80
Molybdenum 0.45 0.65
Phosphorous 0 0.04
Sulphur 0 0.04
Mechanical Property Requirements for Steels in the Heat-Treated Condition for Black, Peeled, Turned or Ground Finish to AS1444-1996 X9931 and BS970 Part 3-1991 826M31
Mechanical Property Designation T T U U V W X Y Z
Limited Ruling Section mm 250 150 250 150 150 100 63 63 63
Tensile Strength Mpa Min 850 850 930 930 1000 1080 1150 1230 1550
Max 1000 1000 1080 1080 1150 1230 1300 1380
0.2% Proof Stress Mpa Min 635 665 725 740 835 925 1005 1080 1125
Elongation on

5.65√S0 %
Min 13 13 12 12 12 11 10 10 5
Izod Impact J Min 40 54 34 47 47 40 34 34 10
Charpy Impact J Min 35 50 28 42 42 35 28 28 9
Hardness Brinell HB Min 248 248 269 269 293 311 341 363 444
Max 302 302 331 331 352 375 401 429
Heat to 1150 oC - 1200 oC maximum, hold until temperature is uniform throughout the section.

Do not forge below 850 oC.
Following forging operation the work piece should be cooled as slowly as possible in sand or dry lime etc..
Heat Treatment
Heat to 800 oC - 850 oC, hold until temperature is uniform throughout the section and cool in furnace.
Flame or Induction Hardening
EN25 hardened and tempered bar can be further surface hardened by either the flame or induction hardening methods resulting in a case hardness of Rc 50 approx. Parts should be heated as quickly as possible to the austenitic temperature range (830 oC - 850 oC) and required case depth followed by an immediate oil or water quench, depending upon hardness required, workpiece size/shape and quenching arrangements.

Following quenching to hand warm, most components should be tempered between 150 oC - 200 oC to remove quenching stresses in the case. This will have little effect on case hardness.
Heat to 830 oC - 850 oC, hold until temperature is uniform throughout the section, soak for 10 - 15 minutes per 25 mm of section, and quench in oil, water, or polymer as required.

*Temper immediately while still hand warm.
EN25 hardened and tempered bar can also be successfully nitrided, giving a surface hardness of up to Rc 60. Nitriding is carried out at 490 oC - 530 oC, followed by slow cooling (no quench) reducing the problem of distortion. Parts can therefore be machined to near final size, leaving a grinding allowance only. The tensile strength of the core is usually not affected since the nitriding temperature range is generally below the original tempering temperature employed.

N.B. Nickel is inert to the action of nitrogen and in general resists its diffusion into steel, and this can result in a lower case hardness or longer nitriding cycle times for steels containing nickel such as EN25.
Stress Relieving
Heat to 640 oC - 660 oC, hold until temperature is uniform throughout the section, soak for 1 hour per 25 mm of section, and cool in still air.
Re-heat to 450 oC - 660 oC as required, hold until temperature is uniform throughout the section, soak for 1 hour per 25 mm of section, and cool in still air.

N.B.Tempering should be avoided if possible within the range 250 oC - 450 oC due to temper brittleness.
Notes on Heat Treatment
Heating temperatures, rate of heating, cooling and soaking times will vary due to factors such as work piece size/shape also furnace type employed, quenching medium and work piece transfer facilities etc..

Please consult your heat treater for best results.
EN25 in the hardened and tempered as supplied condition is still regarded as being readily machinable and operations such as turning and drilling etc. can be carried out satisfactorily using machine manufacturers, recommendations for suitable tool type - feeds and speeds.
Welding of EN25 in the hardened and tempered condition (as normally supplied), is not recommended and should be avoided if at all possible, as the mechanical properties will be altered within the weld heat affected zone. It is preferred that welding be carried out on EN25 while in the annealed condition, and that the work piece, immediately on cooling to hand warm, is then stress relieved at 640 oC - 660 oC prior to hardening and tempering.

If welding in the hardened and tempered condition is really necessary, then the work piece, immediately on cooling to hand warm, should be stress relieved at 15 C below the original tempering temperature.
Welding Procedure
Welding of EN25 in whatever condition should always be carried out using low hydrogen electrodes - please consult your welding consumables supplier.
Suggested pre-heat temperature
Section 25 mm 40 mm 50 mm 75 mm 150 mm 200  mm +
oC 370 400 425 455 510 550
Post Welding
Maximum cooling rate 95 oC per hour down to 95 oC, follow by cooling in still air. N.B. No draught.
It is recommended that the work piece if possible is wrapped in an heat resistant blanket or buried in sand etc..
Interlloy believes the information provided is accurate and reliable. However no warranty of accuracy, completeness or reliability is given, nor will any responsibility be taken for errors or omissions.