SAE AISI 4340 Steel Properties, Heat Treatment, Equivalent, Hardness Chart, Density, Machinability

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SAE AISI 4340 Steel (UNS G43400)

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, %
ASTMSteel Grade (UNS)CSiMnP (≤)S (≤)NiCrMoNotes
ASTM A29/A29M4340 alloy steel (UNS G43400)0.38-0.430.15-0.350.60-0.800.0350.041.65-2.000.70-0.900.20-0.30Steel Bars, Carbon and Alloy, Hot-Wrought
ASTM A322Steel Bars, Alloy, Standard Grades
ASTM A519/A519MSeamless Carbon and Alloy Steel Mechanical Tubing
ASTM A646/A646MPremium 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 Ratio0.29
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
SteelConditionTensile strength, MPa (ksi), ≥Yield strength, MPa (ksi), ≥Elongation in 50 mm (2 in.), ≥Reduction in area, %, ≥Hardness, HB, ≤
4340Normalized at 870 °C (1600 °F)1282 (186)862 (125)12.236.3363
Annealed at 810 °C (1490 °F)745 (108)470 (68)22.050.0217
Oil quenched from 800 °C (1475 °F) and tempered at 540 °C (1000 °F)1207 (175)1145 (166)14.245.9352
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 diameterTensile 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)1351
38 (1.5)1450 (210)1365 (198)1145
75 (3)1420 (206)1325 (192)1038
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 diameterTensile 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)1852340
100 (4)1035 (150)895 (130)1750330
150 (6)1000 (145)850 (123)1644322
Typical mechanical properties of 4340 steel
Oil quenched from 845 °C (1550 °F) and tempered at different temperatures
Tempering temperatureTensile strength, ≥Yield strength, ≥Elongation in 50 mm (2 in.), ≥Reduction in area, ≥Hardness, ≤HardnessIzod impact energy
°C (°F)MPa (ksi)MPa (ksi)%%HBHRCJ (ft · lbf)
205 (400)1980 (287)1860 (270)11395205320 (15)
315 (600)1760 (255)1620 (235)124449049.514 (10)
425 (800)1500 (217)1365 (198)14484404616 (12)
540 (1000)1240 (180)1160 (168)17533603947 (35)
650 (1200)1020 (148)860 (125)206029031100 (74)
705 (1300)860 (125)740 (108)236325024102 (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 temperatureTensile 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)6.014
480 (900)1380 (200)1190 (173)8.016
540 (1000)1240 (180)1125 (163)10.022
Vacuum arc remelted
230 (450)1930 (280)1635 (237)6.517
480 (900)1380 (200)1210 (175)9.020
540 (1000)1240 (180)1100 (160)10.524
Longitudinal mechanical properties of bar stock made from remelted 4340 steel
Melting methodTensile 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 remelted1210 (175)1120 (163)16.461.265 (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 steelConditionUltimate tensile strengthReduction in area, ≥Modulus of elasticityYield strengthCyclic strain hardening exponent
GradeBrinell hardness, HBMPa (ksi)%Gpa (106 psi)MPa (ksi)
4340242As-received825 (120)43192 (27.8)467 (67.7)0.17
409Quenched + Tempered1467 (213)38200 (29)876 (127)0.13
Relative gouging abrasion resistance in the ASTM G 81 jaw crusher test
SteelHeat TreatmentLaboratory ALaboratory B
Wear ratioHardness, HBWear ratioHardness, HB
4340 steelOil Quenched and Tempered (650 °C, or 1200 °F)0.7883210.716340
Oil Quenched and Tempered (205 °C, or 400 °F)0.2625550.232520
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.)
4340290-345 (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
SteelWelding ProcessThickness, mm (in.)Filter MetalTempering temperature, °C (°F)Welded jointElongation in 50mm (2 in.), %Approximate base metal tensile strength, MPa (ksi)
Tensile strength, MPa (ksi)Yield strength, MPa (ksi)
4340Gas Metal Arc Welding (GMAW)25.4 (1)4340510 (950)1307 (189.5)1251 (181.5)111310 (190)

Machinability and Machining

Hardness and machinability ratings (cold-drawn steel)
Steel (UNS)Machinability ratingConditionRange of typical hardness, HBMicrostructure type
4340 (UNS G43400)50Annealed and cold drawn187/241B, 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
MaterialHardness, HBConditionDepth of cut, mm (in)High-speed steel toolTool material
SpeedFeed
m/minsfmmm/revin./revISOAISI
4340, 1340, 1345, 4042, 4047, 4140, 4142, 4145, 4147, 50B40, 50B44, 5046, 50B46, 5140, 5145, 5147, 81B45, 8640, 8642, 8645, 86B45, 8740, 8742175-225Hot rolled, annealed, or cold drawn1 (0.04)411350.180.007S4, S5M2, M3
4 (0.15)321050.40.015
8 (0.30)24800.50.02
16 (0.625)20650.750.03
High-strength wrought steels: 4340, 300M, 4330V, 4340Si, 98BV40, D6ac, H11, H13225-300Annealed1 (0.04)26850.180.007S4, S5M2, M3
4 (0.15)20650.40.015
8 (0.30)15500.50.02
16 (0.625)12400.750.03
Nominal speeds and feeds for turning a variety of steels and cast irons with carbide-tipped single-point and box tools
MaterialHardness, HBConditionCarbide tool
UncoatedCoated
SpeedFeedTool material gradeSpeedFeedTool material grade
BrazedIndexable
m/minsfmm/minsfmmm/revin./revISOCm/minsfmmm/revin./revISOC
Medium carbons: 4340, 1340, 1345, 4042, 4047, 4140, 4142, 4145, 4147, 50B40, 50B44, 5046, 50B46, 5140, 5145, 5147, 81B45, 8640, 8642, 8645, 86B45, 8740, 8742175-225Hot rolled, annealed, or cold drawn1153751505000.180.007P10C-72006500.180.007CP10CC-7
903001204000.500.020P20C-61605250.400.015CP20CC-6
73240953150.750.030P30C-61204000.500.020CP30CC-6
58190762501.000.040
High-strength wrought steels: 4340, 300M, 4330V, 4340Si, 98BV40, D6ac, H11, H13225-300Annealed1053501354500.180.007P10C-71856000.180.007CP10CC-7
842751053500.400.015P20C-61354500.400.015CP20CC-6
66215842750.500.020P30C-61053500.500.020CP30CC-6
52170692250.750.030P40C-6
Nominal speeds and feeds for turning a variety of steels and cast irons with ceramic tools
MaterialHardness, HBConditionDepth of cut, mm (in)SpeedFeedType of ceramic
m/minsfmmm/revin./rev
4340, 1340, 1345, 4042, 4047, 4140, 4142, 4145, 4147, 50B40, 50B44, 5046, 50B46, 5140, 5145, 5147, 81B45, 8640, 8642, 8645, 86B45, 8740, 8742175-225Hot rolled, annealed, or cold drawn1 (0.040)52017000.130.005Cold-pressed alumina
4 (0.150)35011500.250.010Cold-pressed alumina
8 (0.300)2608500.400.015Hot-pressed cermet
High-strength wrought steels: 4340, 300M, 4330V, 4340Si, 98BV40, D6ac, H11, H13225-300Annealed1 (0.040)44014500.130.005Hot-pressed cermet
4 (0.150)2658750.250.010Hot-pressed cermet
8 (0.300)2056750.400.015Hot-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
MaterialHardness, HBConditionSpeedFeed, mm/rev (in./rev)Tool material grade
Cutoff tool widthForm tool width
m/minsfm1.5 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.)ISOAISI 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, 8742175-225Hot rolled, annealed, or cold drawn29950.038 (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, M40M2, M3, C-6
95305
4340, 300M, 4330V, 4340Si, 98BV40, D6ac, H11, H13225-300Annealed18600.036 (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, M40M2, M3, C-6
58190
Speeds and feeds for the deep-hole trepanning of various steels with high-speed tool steels and carbide tools
MaterialHardness, HBConditionSpeedFeedTool material grade
m/minsfmmm/revin./revISOAISI 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, 8742175-225Hot rolled, annealed, or cold drawn18600.150.006S4, S5M2, M3
1153750.150.006P30C-6
325-375Normalized or quenched and tempered9300.100.004S9, S11T15, M42
903000.130.005P30C-6
Feeds and speeds for broaching various steels with high-speed tool steels and carbide tools
MaterialHardness, HBConditionSpeed, 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
125-175Hot rolled, annealed, or cold drawn7.5 (25)0.075 (0.003)S4, S2 (M2, M7)
325-375Normalized, or quenched and tempered3 (10)0.05 (0.002)S9, S11 (T15, M42)
175-225Hot rolled, annealed, or cold drawn6 (20)0.10 (0.004)S4, S2 (M2, M7)
325-375Normalized, or quenched and tempered3 (10)0.05 (0.002)S9, S11 (T15, M42)
175-225Hot rolled, annealed, or cold drawn6 (20)0.10 (0.004)S4, S2 (M2, M7)
325-375Normalized, or quenched and tempered3 (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
USEuropean UnionChinaJapanISO
StandardGrade (UNS)StandardGradeStandardSteel name (Steel number)StandardGradeStandardGradeStandardGrade
AISI
SAE;
ASTM A29/A29M;
ASTM A322;
ASTM A519/A519M;
ASTM A646/A646M
4340 (UNS G43400)SAEAMS6414GB/T 307740CrNi2MoJIS G 4053SNCM439

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