Yong Kim Steel Sdn Bhd
9, Jalan TPP 5/15,
Taman Perindustrian Puchong,
47100 Puchong,
Selangor Darul Ehsan, Malaysia.
+603-8063 1633
+603-8063 3984
+603-8063 1848

Machinery Steel 4340

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Machinery Steel 4340 Machinery Steel Machinery Steel 4340 Machinery Steel


AISI 4340 steel Manufacturer and Exporter, supplied with round, square, flat, block, and shaft etc. AISI 4340 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 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.

1. Supply Form & Size & Tolerance

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

2. Chemical Composition

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

3. Physical Property

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 íŠ 200 íŠ 300 íŠ 400 íŠ 500 íŠ
205 195 185 175 165
Thermal expansion 10^6 m/(m.K) 100 íŠ 200 íŠ 300 íŠ 400 íŠ 500 íŠ
11.1 12.1 12.9 13.5 13.9

4. Mechanical Property

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

5. High Temperature Strength

For quenched and tempered heavy forgings
Diameter mm Yield strength MPa
20 íŠ 100 íŠ 200 íŠ 250 íŠ 300 íŠ 350íŠ 400íŠ
≤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

6. Forging

Forging temperature should be carried out between 1150íŠ-1200íŠ,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.

7. 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 850íŠ-880íŠ. hold suitable time for the steel to be thoroughly heated to complete the ferrite to austenite transformation.Cool in still air.

8. Annealing

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

9. 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 830íŠ-865íŠ, 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.

10. 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 450íŠ- 660íŠ,hold until temperature is uniform throughout the section, soak for 1 hour per 25 mm of section, and cool in still air.Tempering between 250íŠ-450íŠ is not avoided as tempering within this range will seriously reduce the impact value,result in temper brittleness.

11. 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.

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