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4340

AISI 4340 Nickel – Chrome - Moly High Tensile Steel, generally supplied hardened and tempered to condition “U” in sections up to 100mm, with a tensile strength of 930 – 1080 MPa and aiming for this strength range in larger sections. It offers a very good balance of strength, toughness and wear-resistance.

TYPICAL APPLICATIONS

Carbon	0.37 - 0.44
Silicon	0.17 - 0.37
Manganese	0.50 - 0.80
Nickel	1.45 - 1.95
Chromium	0.7 - 0.9
Molybdenum	0.15 - 0.25
Phosphorus	0.025 max.
Sulphur	0.025 max.

RELATED SPECIFICATIONS

AS 1444-1996	4340
BS EN10083-1-1991	817M40
BS 970-1955	EN 24
JIS G 4103	SNCM 439
SAE & UNS	4340 & G43400
Werkstoff - 1.6565	40NiCrMo6
GB/T 3077-1999	40CrNiMoA

SURFACE TREATMENT:
Will Nitride with a typical surface hardness up to HRC 60.
Will Flame or Induction harden with a typical surface hardness up to HRC 58

MECHANICAL PROPERTY REQUIREMENTS IN CONDITION “U” – to AS 1444-1996

Section mm	0.2% Proof Stress Mpa	Tensile Strength Mpa	Elongation on 5.65√So %	Impact		Hardness HB
Section mm	0.2% Proof Stress Mpa	Tensile Strength Mpa	Elongation on 5.65√So %	Lzod J	Charpy J	Hardness HB
*up to 63	755 min	930 - 1080	9 min	/	/	269 - 331
up to 100	740 min	930 - 1080	12 min	47 min	42 min	269 - 331

*Applies only to bars bright drawn after hardening and tempering

TYPICAL MECHANICAL PROPERTIES – Hardened and tempered in section size listed

Section mm	Yield Strength Mpa	Tensile Strength Mpa	Elongation %	Impact Izod J	Hardness HB
50	880	1000	17	85	295
100	850	980	17	80	290
200	730	930	17	75	275

WELDING:
Readily welded in the annealed condition but avoid when possible if hardened and tempered due to the effect on the mechanical properties. Welding in the nitrided, flame or induction hardened condition is not recommended.

HEAT TREATMENT:
Forging:

Heat to 1150°C Hold till uniform Minimum forging temperature 850°C Cool slowly in ashes or sand etc
Annealing:

Heat to 830°C – 850°C Cool in furnace
Stress Relieving:
Annealed: Heat to 600°C – 650°C
Hardened: Heat to 500°C – 550°C
Cool in still air
Hardening:
Heat to 830°C – 880°C
Cool in Oil or Polymer
Tempering:
Heat to 450°C – 660°C cool in still air
NB. Tempering within the range 250°C – 450°C will result in temper brittleness and should be avoided.

Welding procedure:
Low hydrogen electrodes are recommended. Pre-heat at 200°C – 300°C and maintain during welding. Cool slowly in ashes or sand etc and stress relieve if this is possible. Welding details for guidance only

Flame and Induction Hardening:
Heat quickly to the required case depth at 850°C – 870°C and quench immediately in water or oil. Tempering at 150°C – 200°C will reduce stresses in the case with minimal effect on its hardness. All de-carburised surface material must first be removed to ensure best results

Nitriding:
Heat to 500°C – 530°C and hold for sufficient time to develop the depth of case required Parts should be pre-hardened and tempered as required and also pre-machined leaving a small grinding allowance only. Heat treatment details for guidance only

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