4340 High Tensile Steel | Interlloy | Engineering Steels + Alloys

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4340 High Tensile Steel

4340 is a 1.8% nickel - chromium - molybdenum high hardenability high tensile steel - generally supplied hardened and tempered in the tensile range of 930 - 1080 Mpa (condition U) - (Rc 28 - 36).. Characterised by high strength and toughness in relatively large sections. Pre hardened and tempered 4340 can be further surface hardened by flame or induction hardening and by nitriding. 4340 is used in most industry sectors for applications requiring higher tensile/yield strength than 4140 can provide. Typical applications are: Heavy Duty Shafts, Gears, Axles, Spindles, Couplings, Pins etc

4340 is a 1.8% nickel - chromium - molybdenum high hardenability high tensile steel - generally supplied hardened and tempered in the tensile range of 930 - 1080 Mpa (condition U) - (Rc 28 - 36)..

Characterised by high strength and toughness in relatively large sections.

Pre hardened and tempered 4340 can be further surface hardened by flame or induction hardening and by nitriding.

4340 is used in most industry sectors for applications requiring higher tensile/yield strength than 4140 can provide.

Typical applications are: Heavy Duty Shafts, Gears, Axles, Spindles, Couplings, Pins etc

Colour Code	Stocked Sizes
Green & Yellow (Bar End)	Rounds	36 mm to 500 mm Diameter
	Bar Finish
	Peeled, Turned and Polished, or Hot Rolled.

Related Specifications
Australia	AS 1444-1996-4340
Germany	W.Nr 1.6565 40NiCrMo6
Great Britain	BS970-1955 EN24 BS970 Part 3:1991 - 817M40
Japan	JISG 4103 SNCM439 JISG 4103 SNCM8
USA	AISI 4340 ASTM A29/A29M-1991 4340 ASTM A322 4340 ASTM A331 4340 Cold Finished SAE 4340 UNS G43400

Chemical Composition (Base Material)
	Min. %	Max. %
Carbon	0.37	0.44
Silicon	0.10	0.35
Manganese	0.55	0.90
Nickel	1.55	2.00
Chromium	0.65	0.95
Molybdenum	0.20	0.35
Phosphorous	0	0.04
Sulphur	0	0.04
Mechanical Property Requirements for Steels in the Heat-Treated Condition for Black,Turned, Peeled or Ground Finish to AS1444-1996 4340
Mechanical Property Designation	T	*U	V	W	X	Y	Z
Limited Ruling Section (mm)	150	100	63	30	30	30	30
Tensile Strength (Min.)	850	930	1000	1080	1150	1230	1550
Tensile Strength (Max.)	1000	1080	1150	1230	1300	1380
0.2% Proof Stress Mpa (Min.)	665	740	835	925	1005	1080	1125
Elongation on 5.65√S₀ %	13	12	12	11	10	10	5
Izod Impact J (Min.)	54	47	47	41	34	24	10
Charpy Impact J (min.)	50	42	42	35	28	20	9
Brinell Hardness HB (Min.)	248	269	293	311	341	363	444
Brinell Hardness HB (Max.)	302	331	352	375	401	429
*Material stocked generally in condition U. Check test certificate if critical for end use.
Forging
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
Annealing
Heat to 800 ^oC - 850 ^oC, hold until temperature is uniform throughout the section and cool in furnace.
Flame or Induction Hardening
4340 hardened and tempered bar can be further surface hardened by either the flame or induction hardening methods resulting in a case hardness in excess of Rc 50. Parts should be heated as quickly as possible to the austenitic temperature range (830 ^oC - 860 ^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..
Hardening
Heat to 830 ^oC - 860 ^oC, hold until temperature is uniform throughout the section, soak for 10 - 15 minutes per 25 mm section, and quench in oil, water, or polymer as required.*Temper immediately while still hand warm.
Nitriding
4340 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. This can result in lower case hardness or longer nitriding cycle times for steels containing nickel such as 4340.
Stress Relieving
Heat to 600 ^oC - 650 ^oC, hold until temperature is uniform throughout the section, soak for 1 hour per 25 mm section, and cool in still air.
Tempering
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 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.
Machining
4340 in the hardened and tempered as supplied condition is still regarded as being readily machinable and operations such as sawing, turning, drilling, etc. can be carried out satisfactorily using machine manufacturers recommendations for suitable tool type - feeds and speeds.
Welding
Welding of 4340 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 4340 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 ^oC below the original tempering temperature (if known).
Welding Procedure
Welding of 4340 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.