SAE AISI 4340 Steel (UNS G43400)

What is 4340 Steel?

AISI 4340 steel (UNS G43400) is an ultra-high strength medium carbon low alloy steel, which combines deep hardenability, high ductility, toughness and strength, and has high fatigue resistance and creep resistance. It is not particularly affected by tempering and embrittlement, and exhibits good strength retention at high temperatures and is not easily softened. In thin sections, this steel is air-hardened. In practice, it is usually oil quenched.

4340 Alloy Steel Datasheet

The following tables and lists give 4340 alloy steel datasheet and specification including chemical composition, physical properties and mechanical properties, heat treatment, welding, etc.

Chemical Composition

AISI 4340 steel material chemical composition is listed in the following table based on cast analysis.

4340 Chemical Composition, %
ASTM	Steel Grade (UNS)	C	Si	Mn	P (≤)	S (≤)	Ni	Cr	Mo	Notes
ASTM A29/A29M	4340 alloy steel (UNS G43400)	0.38-0.43	0.15-0.35	0.60-0.80	0.035	0.04	1.65-2.00	0.70-0.90	0.20-0.30	Steel Bars, Carbon and Alloy, Hot-Wrought
ASTM A322										Steel Bars, Alloy, Standard Grades
ASTM A519/A519M										Seamless Carbon and Alloy Steel Mechanical Tubing
ASTM A646/A646M										Premium Quality Alloy Steel Blooms and Billets for Aircraft and Aerospace Forgings

AISI 4340 Steel Properties

The tables below list AISI 4340 steel properties, including physical and mechanical properties.

Physical Properties

4340 alloy steel physical properties are given in the following lists, including density, thermal expansion, elastic modulus, thermal conductivity, specific heat capacity and electrical resistance.

Notes:

• 10^-6·K^-1 = 10^-6/K
• 1 Ω·mm²/m = 1 μΩ·m
• 1 g/cm3 = 1 kg/dm3 = 1000 kg/m3
• 1 GPa = 1 kN/mm2
• 1 MPa = 1 N/mm2

Physical Properties
Density, g/cm3 (lb/in.3)	7.85 (0.284)	Conditions
Melting point, °C (°F)	1505 (2740)	–
Specific heat capacity, J/kg·K (Btu/lb ·°F)	475 (0.114) at 20℃	–
Modulus of Elasticity, GPa (ksi)	205 (29700)	–
Bulk Modulus, GPa (ksi)	140 (20300)	–
Poisson’s Ratio	0.29	–
Shear Modulus, GPa (ksi)	80 (11600)	–
Thermal conductivity, W/m·K (Btu/ft · h ·°F)	44.5 (25.73)	–
Coefficient of thermal expansion, 10-6/K (μin./in. ·°F)	12.3 at 20-100 ℃ (68-212 °F)	Oil hardened, tempered 600 °C (1110 °F)
	12.7 at 20-200 ℃ (68-392 °F)
	13.7 at 20-400 ℃ (68-752 °F)
	14.5 at 20-600 ℃ (68-1112 °F)
	11.2 at -100 to 20 °C (-148 to 68 °F)	Oil hardened, tempered 630 °C (1170 °F)
	10.4 from -150 to 20 °C (-238 to 68 °F).
	12.4 at 20-200 ℃ (68-392 °F)
	13.6 at 20-400 ℃ (68-752 °F)
	14.3 at 20-600 ℃ (68-1112 °F)

Mechanical Properties

4340 steel mechanical properties are listed in the following tables.

AISI 4340 Mechanical Properties
Steel	Condition	Tensile strength, MPa (ksi), ≥	Yield strength, MPa (ksi), ≥	Elongation in 50 mm (2 in.), ≥	Reduction in area, %, ≥	Hardness, HB, ≤
4340	Normalized at 870 °C (1600 °F)	1282 (186)	862 (125)	12.2	36.3	363
	Annealed at 810 °C (1490 °F)	745 (108)	470 (68)	22.0	50.0	217
	Oil quenched from 800 °C (1475 °F) and tempered at 540 °C (1000 °F)	1207 (175)	1145 (166)	14.2	45.9	352

Effects of mass on the mechanical properties of 4340 steel
Oil quenched and tempered: Austenitized at 845 °C (1550 °F); tempered at 425 °C (800 °F).
Section diameter	Tensile strength, ≥	Yield strength, ≥	Elongation in 50 mm (2 in.), ≥	Reduction in area, ≥	Hardness, ≤
mm (in.)	MPa (ksi)	MPa (ksi)	%	%	HB
13 (0.5)	1460 (212)	1380 (200)	13	51
38 (1.5)	1450 (210)	1365 (198)	11	45
75 (3)	1420 (206)	1325 (192)	10	38
Water quenched and tempered: 75 mm (3 in.) diam bar austenitized at 800 °C (1475 °F); 100 and 150 mm (4 and 6 in.) diam bars austenitized at 815 °C (1500 °F). All sizes tempered at 650 °C (1200 °F). Test specimens taken at midradius.
Section diameter	Tensile strength, ≥	Yield strength, ≥	Elongation in 50 mm (2 in.), ≥	Reduction in area, ≥	Hardness, ≤
mm (in.)	MPa (ksi)	MPa (ksi)	%	%	HB
75 (3)	1055 (153)	930 (135)	18	52	340
100 (4)	1035 (150)	895 (130)	17	50	330
150 (6)	1000 (145)	850 (123)	16	44	322

Typical mechanical properties of 4340 steel
Oil quenched from 845 °C (1550 °F) and tempered at different temperatures
Tempering temperature	Tensile strength, ≥	Yield strength, ≥	Elongation in 50 mm (2 in.), ≥	Reduction in area, ≥	Hardness, ≤	Hardness	Izod impact energy
°C (°F)	MPa (ksi)	MPa (ksi)	%	%	HB	HRC	J (ft · lbf)
205 (400)	1980 (287)	1860 (270)	11	39	520	53	20 (15)
315 (600)	1760 (255)	1620 (235)	12	44	490	49.5	14 (10)
425 (800)	1500 (217)	1365 (198)	14	48	440	46	16 (12)
540 (1000)	1240 (180)	1160 (168)	17	53	360	39	47 (35)
650 (1200)	1020 (148)	860 (125)	20	60	290	31	100 (74)
705 (1300)	860 (125)	740 (108)	23	63	250	24	102 (75)

Transverse tensile properties of air-melted and vacuum arc remelted 4340 alloy steel, billet size and amount of hot reduction were not available.
Tempering temperature	Tensile strength, ≥	Yield strength, ≥	Elongation in 50 mm (2 in.), ≥	Reduction in area, ≥
°C (°F)	MPa (ksi)	MPa (ksi)	%, ≥	%
Air melted
230 (450)	1945 (282)	1585 (230)	6.0	14
480 (900)	1380 (200)	1190 (173)	8.0	16
540 (1000)	1240 (180)	1125 (163)	10.0	22
Vacuum arc remelted
230 (450)	1930 (280)	1635 (237)	6.5	17
480 (900)	1380 (200)	1210 (175)	9.0	20
540 (1000)	1240 (180)	1100 (160)	10.5	24

Longitudinal mechanical properties of bar stock made from remelted 4340 steel
Melting method	Tensile strength, MPa (ksi), ≥	Yield strength, MPa (ksi), ≥	Elongation in 4D, %, ≥	Reduction in area, %, ≥	Charpy V-notch impact energy at -12 °C (10 °F), J (ft · lbf)	Hardness, HRC
Vacuum arc remelted	1210 (175)	1120 (163)	16.4	61.2	65 (48)	37
Bars were normalized at 900 °C (1650 °F), oil quenched from 845 °C (1550 °F), and tempered 2 h at 541 °C (1005 °F). All specimens taken from midradius.

Cyclic and monotonic properties of as-received and heat-treated 4340 alloy steel
SAE steel		Condition	Ultimate tensile strength	Reduction in area, ≥	Modulus of elasticity	Yield strength	Cyclic strain hardening exponent
Grade	Brinell hardness, HB		MPa (ksi)	%	Gpa (106 psi)	MPa (ksi)
4340	242	As-received	825 (120)	43	192 (27.8)	467 (67.7)	0.17
	409	Quenched + Tempered	1467 (213)	38	200 (29)	876 (127)	0.13

Relative gouging abrasion resistance in the ASTM G 81 jaw crusher test
Steel	Heat Treatment	Laboratory A		Laboratory B
		Wear ratio	Hardness, HB	Wear ratio	Hardness, HB
4340 steel	Oil Quenched and Tempered (650 °C, or 1200 °F)	0.788	321	0.716	340
	Oil Quenched and Tempered (205 °C, or 400 °F)	0.262	555	0.232	520
The ratio of the weight loss of the sample to the weight loss of the standard material martensitic T-1 steel plate. High values indicate poor abrasion resistance.

4340 Steel Heat Treatment

Alloy steel 4340 heat treatment including: normalizing, annealing, hardening, tempering, spheroidization, stress relief, etc. (4340 heat treat)

• Normalizing: Heat to 845 to 900 °C (1550 to 1650 °F) and hold for a period of time, which depends on the thickness of the section; air cooling.
• Annealing: Heating to 830 to 860 °C (1525 to 1575 °F) and maintaining it for a period of time, which depends on the thickness of the section or furnace load; furnace cooling.
• Spheroidization: The preferred schedule is to preheat to 690 °C (1275 ° F) for 2 h, increase the temperature to 745 °C (1375 °F) for 2 h, and cool to 650 °C (1200 °F) ) And hold for 6 hours, cool the furnace to about 600 °C (1100 °F), and finally air-cool to room temperature. Another arrangement is to heat the temperature to 730 to 745 °C (1350 to 1375 °F), hold it for several hours, and then cool the furnace to room temperature.
• Hardening: Heat to 800 to 845 °C (1475 to 1550 °F) for 15 minutes (minimum 15 minutes) per 25 mm (1 inch) thickness; oil quench to below 65 °C (150 °F), or quench in fused salt at 200 to 210 °C (390 to 410 °F), hold for 10 minutes, and then air-cool to below 65 °C (150 °F).
• Tempering: Hold at 200 to 650 °C (400 to 1200 °F) for at least 1/2 hour; air cooling. The temperature and the time at the temperature mainly depend on the required final hardness.
• Stress Relief: After straightening, forming or processing, the stress of the part can be released at a temperature of 650 to 675 °C (1200 to 1250 °F).
• Baking: To avoid hydrogen embrittlement, the plated parts must be baked at least 8h at a temperature of 185 to 195 °C (365 to 385 °F) as soon as possible after plating.
• Forging: 4340 steel is usually forged at a temperature of 1065 to 1230 °C (1950 to 2250 °F); after forging, the parts can be air-cooled in a dry place, or preferably with a furnace.

Welding of AISI 4340 Steel

AISI 4340 steel has good weldability. It can be easily gas or arc welded, but electrodes of the same composition should be used. Since 4340 alloy steel is air hardened, the welded parts should be either annealed or normalized and tempered shortly after welding.

The high hardness of 4340 alloy steel requires that the material be welded in the annealed or tempered state and then heat treated to resist martensite formation and cold cracking. However, as in motor shaft applications, under quenching and tempering conditions, 4340 steel typically use high preheating in low hydrogen processes. Preheating or interpass heating of weld metal and heat affected zones is recommended. Hydrogen control is also essential to prevent cracks in the weld. Extremely clean vacuum smelted steel is the first choice for welding.

Preheating and interpass temperature °C (°F) range for indicate section thickness
Steel	≤13 mm (0.5 in.)	13-25 mm (0.5-1 in.)	25-50 mm (1-2 in.)
4340	290-345 (550-650)	315-370 (600-700)	315-370 (600-700)
Data are for low-hydrogen welding processes and low-hydrogen filler metals.

Typical transverse tensile properties of selected low alloy steel quenched and tempered ARC welded joints
Steel	Welding Process	Thickness, mm (in.)	Filter Metal	Tempering temperature, °C (°F)	Welded joint		Elongation in 50mm (2 in.), %	Approximate base metal tensile strength, MPa (ksi)
					Tensile strength, MPa (ksi)	Yield strength, MPa (ksi)
4340	Gas Metal Arc Welding (GMAW)	25.4 (1)	4340	510 (950)	1307 (189.5)	1251 (181.5)	11	1310 (190)

Machinability and Machining

Hardness and machinability ratings (cold-drawn steel)
Steel (UNS)	Machinability rating	Condition	Range of typical hardness, HB	Microstructure type
4340 (UNS G43400)	50	Annealed and cold drawn	187/241	B, A
E4340 (UNS G43406)
Based on cutting with high-speed tool steels and a machinability rating of 100% for 1212 steel. Type A: predominantly lamellar pearlite and ferrite; Type B: predominantly spheroidized.

Nominal speeds and feeds for turning a variety of steels and cast irons with high-speed steel (HSS) single-point and box tools
Material	Hardness, HB	Condition	Depth of cut, mm (in)	High-speed steel tool				Tool material
				Speed		Feed
				m/min	sfm	mm/rev	in./rev	ISO	AISI
4340, 1340, 1345, 4042, 4047, 4140, 4142, 4145, 4147, 50B40, 50B44, 5046, 50B46, 5140, 5145, 5147, 81B45, 8640, 8642, 8645, 86B45, 8740, 8742	175-225	Hot rolled, annealed, or cold drawn	1 (0.04)	41	135	0.18	0.007	S4, S5	M2, M3
			4 (0.15)	32	105	0.4	0.015
			8 (0.30)	24	80	0.5	0.02
			16 (0.625)	20	65	0.75	0.03
High-strength wrought steels: 4340, 300M, 4330V, 4340Si, 98BV40, D6ac, H11, H13	225-300	Annealed	1 (0.04)	26	85	0.18	0.007	S4, S5	M2, M3
			4 (0.15)	20	65	0.4	0.015
			8 (0.30)	15	50	0.5	0.02
			16 (0.625)	12	40	0.75	0.03

Nominal speeds and feeds for turning a variety of steels and cast irons with carbide-tipped single-point and box tools
Material	Hardness, HB	Condition	Carbide tool
			Uncoated								Coated
			Speed				Feed		Tool material grade		Speed		Feed		Tool material grade
			Brazed		Indexable
			m/min	sfm	m/min	sfm	mm/rev	in./rev	ISO	C	m/min	sfm	mm/rev	in./rev	ISO	C
Medium carbons: 4340, 1340, 1345, 4042, 4047, 4140, 4142, 4145, 4147, 50B40, 50B44, 5046, 50B46, 5140, 5145, 5147, 81B45, 8640, 8642, 8645, 86B45, 8740, 8742	175-225	Hot rolled, annealed, or cold drawn	115	375	150	500	0.18	0.007	P10	C-7	200	650	0.18	0.007	CP10	CC-7
			90	300	120	400	0.50	0.020	P20	C-6	160	525	0.40	0.015	CP20	CC-6
			73	240	95	315	0.75	0.030	P30	C-6	120	400	0.50	0.020	CP30	CC-6
			58	190	76	250	1.00	0.040	–	–	–	–	–	–	–	–
High-strength wrought steels: 4340, 300M, 4330V, 4340Si, 98BV40, D6ac, H11, H13	225-300	Annealed	105	350	135	450	0.18	0.007	P10	C-7	185	600	0.18	0.007	CP10	CC-7
			84	275	105	350	0.40	0.015	P20	C-6	135	450	0.40	0.015	CP20	CC-6
			66	215	84	275	0.50	0.020	P30	C-6	105	350	0.50	0.020	CP30	CC-6
			52	170	69	225	0.75	0.030	P40	C-6	–	–	–	–	–	–

Nominal speeds and feeds for turning a variety of steels and cast irons with ceramic tools
Material	Hardness, HB	Condition	Depth of cut, mm (in)	Speed		Feed		Type of ceramic
				m/min	sfm	mm/rev	in./rev
4340, 1340, 1345, 4042, 4047, 4140, 4142, 4145, 4147, 50B40, 50B44, 5046, 50B46, 5140, 5145, 5147, 81B45, 8640, 8642, 8645, 86B45, 8740, 8742	175-225	Hot rolled, annealed, or cold drawn	1 (0.040)	520	1700	0.13	0.005	Cold-pressed alumina
			4 (0.150)	350	1150	0.25	0.010	Cold-pressed alumina
			8 (0.300)	260	850	0.40	0.015	Hot-pressed cermet
High-strength wrought steels: 4340, 300M, 4330V, 4340Si, 98BV40, D6ac, H11, H13	225-300	Annealed	1 (0.040)	440	1450	0.13	0.005	Hot-pressed cermet
			4 (0.150)	265	875	0.25	0.010	Hot-pressed cermet
			8 (0.300)	205	675	0.40	0.015	Hot-pressed cermet

Nominal speeds and feeds for turning a variety of steels and cast irons with high-speed steel and carbide cutoff and form tools
Material	Hardness, HB	Condition	Speed		Feed, mm/rev (in./rev)								Tool material grade
					Cutoff tool width			Form tool width
			m/min	sfm	1.5 mm (0.062 in.)	3 mm (0.125 in.)	6 mm (0.250 in.)	12 mm (0.500 in.)	18 mm (0.750 in.)	25 mm (1.00 in.)	35 mm (1.50 in.)	50 mm (2.00 in.)	ISO	AISI or C
Medium carbon steel 4340, 1340, 1345, 4042, 4047, 4140, 4142, 4145, 4147, 50B40, 50B44, 5046, 50B46, 5140, 5145, 5147, 81B45, 8640, 8642, 8645, 86B45, 8740, 8742	175-225	Hot rolled, annealed, or cold drawn	29	95	0.038 (0.0015)	0.046 (0.0018)	0.056 (0.0022)	0.046 (0.0018)	0.041 (0.0016)	0.038 (0.0015)	0.033 (0.0013)	0.028 (0.0011)	S4, S5, P40, M40	M2, M3, C-6
			95	305
4340, 300M, 4330V, 4340Si, 98BV40, D6ac, H11, H13	225-300	Annealed	18	60	0.036 (0.0014)	0.043 (0.0017)	0.053 (0.0021)	0.043 (0.0017)	0.038 (0.0015)	0.036 (0.0014)	0.030 (0.0012)	0.025 (0.001)	S4, S5, P40, M40	M2, M3, C-6
			58	190

Speeds and feeds for the deep-hole trepanning of various steels with high-speed tool steels and carbide tools
Material	Hardness, HB	Condition	Speed		Feed		Tool material grade
			m/min	sfm	mm/rev	in./rev	ISO	AISI or C
Medium carbon steel 4340, 1340, 1345, 4042, 4047, 4140, 4142, 4145, 4147, 50B40, 50B44, 5046, 50B46, 5140, 5145, 5147, 81B45, 8640, 8642, 8645, 86B45, 8740, 8742	175-225	Hot rolled, annealed, or cold drawn	18	60	0.15	0.006	S4, S5	M2, M3
			115	375	0.15	0.006	P30	C-6
	325-375	Normalized or quenched and tempered	9	30	0.10	0.004	S9, S11	T15, M42
			90	300	0.13	0.005	P30	C-6

Feeds and speeds for broaching various steels with high-speed tool steels and carbide tools
Material	Hardness, HB	Condition	Speed, m/min (sfm)	Chip load, mm/tooth (in./tooth)	Tool material grade, ISO (AISI or C)
Medium carbon steels: 4340, 1330, 1335, 1340, 1345, 4027, 4028, 4032, 4037, 4042, 5155, 5160, 51B60, 6150, 81B45, 8625, 4047, 4130, 4135, 4137, 4140, 4142, 4145, 4147, 4150, 8627, 8630, 8637, 8640, 8642, 8645, 4161, 4427, 4626, 50B40, 50B44, 5046, 50B46, 50B50, 86B45, 8650, 8655, 8660, 8740, 8742, 5060, 50B60, 5130, 5132, 5135, 5140, 5145, 5147, 5150, 9254, 9255, 9260, 94B30; Low carbon steels: 4012, 4023, 4024, 4118, 4320, 4419, 4422, 4615, 4617, 4620, 4621, 4718, 4720, 4815, 4817, 4820, 5015, 5115, 5120, 6118, 8115, 8617, 8620, 8622, 8822, 9310, 94B15, 94B17; High carbon steels: 50100, 51100, 52100, M-50	125-175	Hot rolled, annealed, or cold drawn	7.5 (25)	0.075 (0.003)	S4, S2 (M2, M7)
	325-375	Normalized, or quenched and tempered	3 (10)	0.05 (0.002)	S9, S11 (T15, M42)
	175-225	Hot rolled, annealed, or cold drawn	6 (20)	0.10 (0.004)	S4, S2 (M2, M7)
	325-375	Normalized, or quenched and tempered	3 (10)	0.05 (0.002)	S9, S11 (T15, M42)
	175-225	Hot rolled, annealed, or cold drawn	6 (20)	0.10 (0.004)	S4, S2 (M2, M7)
	325-375	Normalized, or quenched and tempered	3 (10)	0.05 (0.002)	S9, S11 (T15, M42)

Applications

SAE AISI 4340 steel is usually used in places where severe conditions exist and heavy parts requiring high strength, and can be widely used as billet, bar, bar, forging, sheet, pipe and welding wire. AISI 4340 steel can also be produced as light plates and castings. Typical applications include bolts, screws and other fasteners. Gears, pinions, shafts and similar mechanical components; crankshafts and piston rods of engines; and landing gear and other key structural components of aircraft.

Equivalent

ASTM AISI 4340 steel equivalent to SAE, European (German DIN, British BSI, France NF), Japanese JIS and Chinese GB standard (for reference).

AISI 4340 equivalent
US				European Union		China		Japan		ISO
Standard	Grade (UNS)	Standard	Grade	Standard	Steel name (Steel number)	Standard	Grade	Standard	Grade	Standard	Grade
AISI SAE; ASTM A29/A29M; ASTM A322; ASTM A519/A519M; ASTM A646/A646M	4340 (UNS G43400)	SAE	AMS6414			GB/T 3077	40CrNi2Mo	JIS G 4053	SNCM439