4340 | 36CrNiMo4 | 1.6511 | EN24

1.CHARACTER:

4340 steel is an ultra-high strength steel classified a medium-carbon, low-alloy steel. 4340 steel has high strength, ductility, toughness, creep resistance, and fatigue resistance relative to most other steels. Hardness ranging from 24 to 53 HRC can be achieved, depending on the heat treatment.

2.CHEMICAL COMPOSITION

3.SUPPLY RANGE:

Surface Finish: Black, Peeled, Machined/Turned or as per given requirements.

Forged Round Bar: 20mm - 650mm (Dia)

Rolled Bars: 12mm - 360mm (Dia)

Forged flats: 30-400mm(T)*500-1200mm(W)

Rolled flats: 10-360mm(T)*30-1020mm(W)

Other sizes of O1 material or as per customer’s requirements

4.HEAT TREATMENT：

Stress Relieving

For pre-hardened steel stress relieving is achieved by heating steel 4340 to between 500 to 550°C. Heat to 600 °C – 650 °C, hold until temperature is uniform throughout the section, soak for 1 hour per 25 mm section, and cool in still air.

Annealing

A full anneal may be done at 844°C (1550 F) followed by controlled (furnace) cooling at a rate not faster than 10°C (50 F) per hour down to 315°C (600 F). From 315°C 600 F it may be air cooled.

Tempering

AISI 4340 alloy steel should be in the heat treated or normalized and heat treated condition before tempering. The tempering temperature for depends upon the strength level desired. For strength levels in the 260 – 280 ksi range temper at 232°C (450 F). For strength in the 125 – 200 ksi range temper at 510°C (950 F). And don’t temper the 4340 steels if it is in the 220 – 260 ksi strength range as tempering can result in degradation of impact resistance for this level of strength.

Tempering should be avoided if possible within the range 250 °C – 450 °C due to temper brittleness.

Flame or Induction Hardening

As mentioned above, pre-hardened and tempered 4340 steel bars or plates can be further surface hardened by either the flame or induction hardening methods resulting in a case hardness in excess of Rc 50. AISI 4340 steel parts should be heated as quickly as possible to the austenitic temperature range (830 °C – 860 °C) and required case depth followed by an immediate oil or water quenching, depending upon hardness required, workpiece size/shape and quenching arrangements.

Following quenching to hand warm, tempering at 150°C – 200°C will reduce stresses in the case with minimal effect on its hardness.

Nitriding

Hardened and tempered 4340 alloy steel can also be nitrided, giving a surface hardness of up to Rc 60. Heat to 500°C – 530°C and hold for sufficient time (from 10 to 60 hours) to develop the depth of case. Nitriding should be followed by slow cooling (no quench) reducing the problem of distortion. The nitrided grade 4340 materials can therefore be machined to near final size, leaving a small grinding allowance only. The tensile strength of the 4340 steel material core is usually not affected since the nitriding temperature range is generally below the original tempering temperature employed.

Surface hardness achievable is 600 to 650HV.

5.APPLICATION：

AISI 4340 steel is used in most industry sectors for applications requiring higher tensile/yield strength than 4140 steel can provide.

Some typical applications such as:

-Aircraft Landing Gear

-Automotive,

-Oil and Gas Drilling,

-Forging,

-Warm and Cold Forming,

-Machine Building,

-Transmission systems, such as power transmission gears and shafts.

-General engineering industries and structural use applications, such as: heavy duty shafts, gears, axles, spindles, couplings, pins, chucks, molds etc.