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;
Surface Treatment
What are our advantages about surface treatment?
For general rough machining, the surface will have obvious machining marks. As shown below:
But our surface treatment can achieve very high quality. In order to improve the quality of our products, we independently developed a new processing equipment. This has led to a particularly noticeable improvement in our processing. See the picture below:
Our materials are superior to those of other suppliers. After polishing, the material is smoother, and as long as there is a defect on the surface, we can find it and remove it, even a very small crack. If it can’t be removed, we won’t ship it to our customers. This further ensures the quality of the materials we provide. There are very few suppliers that can do such a good job on such a large round rod.
Application
It is used as important quenched and tempered parts that require good toughness, high strength and large size, such as heavy machinery and high-load shafts, turbine shafts with a diameter greater than 250mm, helicopter rotor shafts, turbojet engine turbine shafts, blades, high Loaded transmission parts, crankshaft fasteners. Gears, etc.; can also be used for rotor shafts and blades whose operating temperature exceeds 400 °C; can also be used to manufacture important parts with special performance requirements after nitriding treatment, and can be used for ultra-high temperature after low temperature tempering or austempering. Use of strength steel.
Test
We are AISI 4340 Alloy Structural Steel for composition testing using spectrometer.The spectrometer one-time excitation of the sample to analyze its composition method is widely accepted by the public at this stage.Compared with traditional analytical methods, the advantages of spectrometers for the detection of modern steel components are fast, accurate and efficient. This method can directly inject solid samples without chemical digestion, which can reduce the human error caused by the digestion process and the constant volume process; to good quality steel.
