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The Points You Must Know About 4340 Steel

Alloy structural steel 4340 is a material that has gone through multiple rigorous processes. It is also a type of gear steel and has excellent hardenability, stability and strength against overheating, etc. 4340 steel can meet many high-demand application scenarios, but it needs to be noted that it needs to be preheated at high temperature before welding, stress must be eliminated after welding, and it must be quenched and tempered before use.

In Songshun, customers order 4340 steel every month. The market demand is large and it is widely used. This article will give you an in-depth understanding of the AISI 4340 steel we provide, including its steel equivalent, chemical composition analysis, properties, applications, heat treatment specifications, supply, issues and more.

4340 Steel Equivalent

China GB /T 3077 standard: GB 40CrNiMoA, GB 34CrNi3Mo, GB ZG34CrNiMo.
American ASTM A29/A29M standard: AISI/SAE/ASTM 4340.
German EN 10250 standard: DIN EN/DIN 36NiCrMo4 / 34CrNiMo6, W-Nr. 1.6511.
Japanese JIS G 4053 standard: JIS SNCM439.

4340 Steel Chemical Composition

4340 Steel Chemical Composition (%)

The carbon content of AISI 4340 steel is the main element that increases the hardness and strength of the steel. The silicon content of 4340 steel helps to deoxidize the steel. Some customers require Si ≤ 0.10% for this content, which is used for certain cold-formed parts. It also contains more Mn and Cr elements, which can improve its strength, toughness, corrosion resistance and other properties.

SAE 4340 Steel Properties

  • High strength, hardness and toughness
  • Excellent wear resistance, corrosion resistance and hardenability
  • Good weldability, ductility and impact resistance
  • Good machinability and fatigue resistance
  • Good stability against overheating

AISI 4340 Steel Applications

4340 steel is widely used in aerospace, automobile manufacturing, engineering machinery, shipbuilding, oil and gas and other fields. It is often used to manufacture engine parts, bearings, drive shafts, gears, structural parts, high-load shafts for heavy machinery, helicopter rotor shafts, crankshaft fasteners, etc.

4340 Steel Heat Treatment

  • Quenching
    Alloy material 4340 steel is usually quenched at a temperature of 830-870°C, and then quickly oil-cooled to room temperature to achieve hardening.
  • Annealing
    4340 steel adopts a spheroidizing annealing process with a temperature of 840-870°C. After cooling to a certain temperature in the furnace, it can be air-cooled.
  • Tempering
    The tempering temperature of AISI 4340 steel depends on the required strength level and is usually maintained at strength levels in the range of 260 – 280 ksi at a tempering temperature of 150-250°C; in the strength range of 125 – 200 ksi at a tempering temperature of 480-540°C. Due to temper brittleness, tempering in the 250 °C – 450 °C range should be avoided if possible.

Specific heat treatment specifications will vary based on different standards and application requirements.

AISI/ASTM 4340 Steel Supply

Shape types: round bar, steel plate, tube, round steel, flat steel, thin plate, forging, forged pipe, forged plate, bar, square steel, plate, seamless tube, coil, thick plate, steel coil, etc.

Specifications: Complete specifications, can be cut to the size you need.

Surface treatment: black, rough machined, turned or as per given requirement.

Delivery status: Usually delivered in the state of hot rolling, finishing, cold rolling, forging, quenching or heat treatment, or after annealing + other processing methods (peeling, light drawing, grinding or polishing, etc.).

Frequently Asked Questions About 4340 Steel

1.How hard can 4340 steel reach?
The Brinell hardness HBW of AISI 4340 steel in the supply state of annealed or high-temperature tempering is less than or equal to 269; the hardness after quenching is about 30-52 HRC; the hardness after quenching and tempering is about 28-40 HRC.

2.How is SAE 4340 material usually cut and processed?
Gas cutting or plasma cutting should be used when cutting 4340 steel, and the cutting surface should be smooth and free of burrs and welding slag.

3. Is alloy structural steel 4340 likely to cause hydrogen embrittlement?
Possible. It may produce hydrogen embrittlement during heat treatment, resulting in reduced part quality. Therefore, the hydrogen content needs to be controlled during heat treatment to avoid hydrogen embrittlement.

Through the above comprehensive understanding of the 4340 steel provided by Songshun, you can better choose the appropriate materials and processing techniques to meet your different needs. We specialize in providing 4340 materials. We have a deep understanding and experience of 4340 wide application fields, performance, production processes, etc., and can provide you with the best 4340 steel.


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