EN25/826M31/X9931 Alloy nickel chromium forged steel rings
Description: 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
X9931 is suitable for the most severe duties where freedom from
temper brittleness is necessary. It has high strength and toughness
in large sections. Applications include heavy drive shafts, axles,
gears, excavator pins, automotive, and general, engineering
applications, such as Shafts, connecting rods, pump and gear
shafts, Die Holder Blocks, and long wall coal mining roof support
Australia AS 1444-2007 X9931
Germany W.Nr 1.6743 32NiCrMo10 4
Great Britain BS970: Part 3: 1991 826M31
BS970: 1955 EN25
Chemical Composition %:
Phosphorus 0.04 max
Sulphur 0.04 max
Process: EAF+LF+VOD+Forged+Heat Treatment(optional)
OD up to 8,000mm; ID up to 7,800mm; Thickness up to 500mm
Black, Peeled K12, Cold Drawn, Turned & Polished H10, H11,
Precision Ground H9, H8
Ultrasonic test :ASTM A 388 or according to customers' requirement
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 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
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
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.
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
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
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 if possible stress relieved at 15 C below the
original tempering temperature (if known).
Welding of EN25 in whatever condition should always be carried out
using low hydrogen electrodes
Certificate of Quality: issued in English, in addition the normal terms, production
process, the mechanical property yield strength, tensile strength,
elongation and hardness, forged ratio, UT test result, Grain size,
heat treatment methods and the sample of is shown on the
Certificate of Quality.
Marking: Heat No. will be cold stamped and Steel grade, diameter mm, length
mm, and the manufacturer LOGO and weight kg is painted