AISI 4340 Alloy Steel – ASTM A29

WALDUN is a good Chinese AISI 4340 steel Manufacturer and Exporter. You can get supplied with round,square,flat,block,and shaft etc from WALDUN.

AISI 4340 steel is defined as a heat treatable and low alloy steel which has 0.8% Cr, 0.2% Mo and 1.8% Ni as strengthening alloy elements.Compared with AISI 4140,it has higher strength and toughness,also it has very good fatigue resistance, wear resistance and atmospheric corrosion resistance.AISI 4340 steel is generally supplied in  hardened and tempered condition with the tensile range of 930 – 1080 Mpa ,hardness 280-320HB.Pre hardened and tempered 4340 can be further surface hardened by flame or induction hardening and by nitriding.

4340 steel can be used for the requirements of good toughness, high strength, as well as large size of important quenched parts, such as heavy machinery high load shaft, diameter greater than 250mm ware turbine shaft, helicopter rotor shaft, turbojet engine turbine shaft, blade, high load transmission parts, crankshaft fasteners. Gears, etc.; 4340 steel can also be used for operating temperature of more than 400 ℃ rotor shaft and blade, etc.; can also be nitriding treatment, used to manufacture special performance requirements of important parts, after low-temperature tempering or isothermal quenching can be used for ultra-high strength steel.

4340 Steel Supply Form & Size & Tolerance

4340 steel is a high strength alloy that is frequently used in the aerospace industry. It offers excellent toughness and strength, making it ideal for applications where high stress levels are a concern. 4340 steel is available in a variety of different forms, sizes, and tolerances. As a result, it can be easily adapted to meet the specific needs of any project. 4340 steel is an excellent choice for any application where strength and durability are a priority.

Supply Form	Size(mm)	Process	Tolerance
Round	Φ6-Φ100	Cold Drawn	Bright/Black	Best H11
	Φ16-Φ350	Hot Rolled	Black	-0/+1mm
			Peeled/ground	Best H11
	Φ90-Φ1000	Hot Forged	Black	-0/+5mm
			Rough Turned	-0/+3mm
Flat/Square/Block	Thickness :120-800	Hot Forged	Black	-0/+8mm
	Width:120-1500		Rough Machined	-0/+3mm

Remark:Tolerance can be customized as per requests

4340 Steel Chemical Composition

4340 steel is a chromium-molybdenum alloy steel that offers an excellent balance of strength, toughness, and wear resistance. The name 4340 comes from the fact that it has 4340 steel chemical composition. 4340 has a carbon content of 0.38-0.43%, a manganese content of 0.60-0.80%, a chromium content of 0.80-1.10%, a molybdenum content of 0.15-0.25%, a silicon content of 0.15-0.35%, a sulfur content of 0,040%, and a phosphorus content of 0,040%. 4340 also contains trace amounts of other elements including copper, nickel, and aluminum. 4340 steel offers an excellent balance of strength and toughness and is used in a variety of applications, including gears, shafts, bolts, and studs. 4340 is also often used in the aerospace industry for landing gear, turbine blades, and other high-strength applications.

Standard	Grade	C	Si	Mn	P	S	Cr	Ni	Mo
ASTM A29	4340	0.38-0.43	0.15-0.35	0.6-0.8	≤ 0.035	≤ 0.04	0.7-0.9	1.65-2.0	0.2-0.3
EN10250	36CrNiMo4	0.32-0.4	≤ 0.4	0.5-0.8	≤ 0.035	≤ 0.035	0.9-1.2	0.90-1.2	0.15-0.3
	1.6511
BS 970	EN24	0.36-0.44	0.1-0.4	0.45-0.7	≤ 0.035	≤ 0.04	1.0-1.4	1.3-1.7	0.2-0.35
	817M40
JIS G4103	SNCM439	0.36-0.43	0.15-0.35	0.6-0.9	≤ 0.03	≤ 0.03	0.6-1.0	1.6-2.0	0.15-0.3
GB 3077	40CrNiMoA	0.37-0.44	0.17-0.37	0.5-0.8	≤ 0.025	≤ 0.025	0.6-0.9	1.25-1.65	0.15-0.25

4340 Steel Physical Property

4340 steels are medium-carbon nickel-chromium-molybdenum alloy steel. This alloy is forged at a start temperature of around 2250˚F (1230˚C). 4340 steel has excellent shock and impact resistance as well as fatigue strength, toughnes, and ductility. 4340 can gain high strength by heat treatment. And 4340 is known for its ability to withstand heavy loads at elevated temperatures. 4340 also has good machinability and weldability. 4340 alloy steels are used extensively in aircraft Landing Gear because of their ultra-high strength and toughness. 4340 is also frequently used in the production of race cars due to it’s high strengt to weight ratio. 4340 can be nitrided to give a hard surface case with a tough core. 4340 can also be precipitation hardened to achieve a variety of strengths while maintain good toughness and ductility. 4340 finds applications in a wide variety of industries including the automotive, aerospace, and energy sectors. 4340 is available in both standard and processed forms.

Density g/cm3	7.85
Melting point °C	1427
Poisson’s ratio	0.27-0.30
Machinability (AISI 1212 as 100% machinability)	50%
Thermal expansion co-efficient µm/m°C	12.5
Thermal conductivity W/(m.K)	44.5
Modulus of elasticity 10^3 N/mm^2	210
Electric resistivity Ohm.mm2 /m	0.19
Specific heat capacity J/(kg.K)	460
Modulus of elasticity 10^3 N/mm2	100 ℃	200 ℃	300 ℃	400 ℃	500 ℃
	205	195	185	175	165
Thermal expansion 10^6 m/(m.K)	100 ℃	200 ℃	300 ℃	400 ℃	500 ℃
	11.1	12.1	12.9	13.5	13.9

4340 Steel Mechanical Property

4340 steel is a chromium-molybdenum alloy steel that provides optimum combination of strength, toughness, wear resistance, and corrosion resistance. Properties that make 4340 steel an excellent choice for structural applications include good ductility, weldability, and machinability. 4340 steel’s high thermal conductivity is also important for aerospace applications. 4340 alloy steel is heat treated to high strength levels and is frequently used in aircraft and industrial gas turbine engines. 4340 alloy steels can be ordered with a wide variety of heat treatments including normalized, annealed, prehardened, quenched, and tempered. 4340 steel can also be nitrided for wear and surface hardness properties. Other important applications for 4340 alloy steel include forgings for aircraft parts and power train components; seamless rolled rings; shafts; coli; hydraulics; gears; sprockets; valve stems; tool holders; bushings; plunger rods; spindles; ball screws; lead screws; pump shafts and gear seats. 4340 alloy steels are available in many standard sizes and stock form such as round bars, flats, squares, strip and plate.

Mechanical Condition	T	U	V	W	X	Y	Z
Ruling Section (mm)	150	100	63	30	30	30	30
Tensile Strength Mpa	850-1000	930-1080	1000-1150	1080-1230	1150-1300	1230-1380	>1550
Yield Strength,Mpa	≥665	≥740	≥835	≥925	≥1005	≥1080	≥1125
Elongation %	≥13	≥12	≥12	≥11	≥10	≥10	≥5
Izod Impact J	≥54	≥47	≥47	≥41	≥34	≥24	≥10
Charpy Impact J	≥50	≥42	≥42	≥35	≥28	≥20	≥9
Brinell Hardness HB	248-302	269-331	293-352	311-375	341-401	363-429	>444

4340 Steel High Temperature Strength

For quenched and tempered heavy forgings
Diameter mm	Yield strength MPa
	20 ℃	100 ℃	200 ℃	250 ℃	300 ℃	350℃	400℃
≤250	590	549	510	481	441	412	371
250-500	540	505	471	451	412	383	353
500-750	490	466	441	422	392	363	343

4340 Steel Forging

Forging temperature should be carried out between 1150℃-1200℃,The lower the forging-ending temperature ,the finer the grain size .hold suitable time for the steel to be thoroughly heated before forge, but don’t forge below minimum forging temperature 850°C. AISI 4340 has good forging characteristics,but crack is easily occured when improper cooling way after forged,so it  should be cooled as slowly as possible in still air or in sand after forged.

4340 Steel Normalizing

Normalizing is used to refine the structure of forgings that might have cooled non-uniformly after forged,and considered as a conditioning treatment before final heat treatment.Normalizing temperature for AISI 4340 steel should be carried out between 850℃-880℃. hold suitable time for the steel to be thoroughly heated to complete the ferrite to austenite transformation.Cool in still air.

4340 Steel Annealing

Full annealing is recommended  for AISI 4340 before machining, AISI 4340 should be carried our at a nominal temperature of 830℃-850℃,hold suitable time for the steel to be thoroughly heated, then furnace cooling to 610℃ at a rate of 11℃ per hour, finally air cooling.

4340 Steel Hardening

This heat treatment will obtain martensite structure after quenched.It will  increase the surface hardness and strength.AISI 4340 should be carried out between 830℃-865℃, hold suitable time for the steel to be thoroughly heated, soak for 10-15 minutes per 25 mm section, oil quench is recommended.Tempering should be followed  immediately after quenched.

4340 Steel Tempering

AISI 4340 alloy steel should be in the heat treated or normalized and heat treated condition before tempering.Tempering is usually carried out to relieve stresses from the hardening process, but primarily to obtain the required  hardness and mechanical properties. The actual tempering temperature will be chosen to meet the required properties.it is usually carried out at 450℃- 660℃,hold until temperature is uniform throughout the section, soak for 1 hour per 25 mm of section, and cool in still air.Tempering between 250℃-450℃ is not avoided as tempering within this range will seriously reduce the impact value,result in temper brittleness.

4340 Steel Application

AISI 4340 is often used in preference to AISI 4140 at the higher strength levels because of its better hardenability and improved CVN impact toughness.

Typical applications include:Heavy-duty axles, shafts, heavy-duty gears,spindles, pins, studs, collets, bolts, couplings,sprockets, pinions, torsion bars, connecting rods,crow bars, conveyor parts,forged hydraulic,forged steel crankshafts etc.