AISI 4340 Alloy Structural Steel Round Bar, Square Steel, Flat Steel
AISI 4340 Steel Catalog
Introduction
Chemical Composition
Mechanical Properties
Heat Treatment
Surface Treatment
Application
Test
Introduction
AISI 4340 alloy structural steel is a medium carbon nickel-chromium-molybdenum steel alloy, very similar to 4130 steel, but AISI 4340 alloy steel has high white spot sensitivity and temper brittleness, and is widely used in large-sized important quenched and tempered parts, shafts , transmission parts of heavy chemical machinery, etc., and AISI 4340 steel is a wear-resistant material with particularly good wear resistance, impact resistance and impact resistance, as well as excellent atmospheric corrosion resistance, and because the material is usually in Annealed condition, it also has the advantages of excellent hardenability, stability against overheating and short construction period. Our AISI 4340 alloy steel can be not only heat treated but also fusion and resistance welding.
Chemical Composition
The chemical composition of Song Shun AISI 4340 alloy structural steel.
C:0.37-0.44 Si:0.17-0.37 S:≤0.035 P:≤0.035
Mn:0.50-0.80 Cr:0.60-0.90 Mo:0.15-0.25 Ni:1.25-1.65
Mechanical Properties
The mechanical properties of AISI 4340 alloy structural steel
Tensile strength σb (MPa): ≥980(100)
Yield strength σs (MPa): ≥835(85)
Elongation δ5 (%): ≥12
Area shrinkage ψ (%): ≥55
Impact energy Akv (J): ≥78
Elongation δ5 (%): ≥12
Area shrinkage ψ (%): ≥55
Impact energy Akv (J): ≥78
Impact toughness value αkv (J/cm2): ≥98(10)
Sample size: sample blank size is 25mm
Heat Treatment
1.Forging of 4340 alloy steel
4340 steel is first preheated up to 1150°C – 1200°C for forging until uniform temperature throughout the section.Do not forge below 850 °C, 4340 has good forging characteristics, but care must be taken when cooling as the steel can easily crack. After the forging operation, the workpiece should be cooled as slowly as possible. It is recommended to cool in sand or dry lime etc.
2.SAE 4340 heat treatment
(1)Normalizing: Heat to 870 degrees. air cooling.
(2)Annealing: In order to get the pearlite structure, heat to 830 degrees,rate to 565 degrees; or heat to 830 degrees, rapidly cool to 650 degrees, and set aside for 8 hours. In order to obtain a spheroidized tissue structure, heat to 750 degrees, rapidly cool to 705 degrees, then cool to 650 degrees at a rate not exceeding 3 degrees per hour, and set aside for 12 hours. The spheroidized structure usually facilitates machining and heat treatment.
(3)Quenching: Austenitizing at 845 degrees, then oil quenching. Thin areas of the casting can be air quenched.
(4)Tempering: Like all high hardenability steels, 4340H steel is prone to quench cracks. Before castings reach ambient temperature (38-50 degrees), they should be placed in a tempering furnace. The tempering temperature is most dependent on the desired hardness or overall mechanical properties.
(quenching at 850 degrees; coolant: oil; tempering temperature at 600 degrees; coolant: water, oil);
Brinell hardness HBW less than or equal to 269 in annealed or high temperature tempered supply state;