What is the difference between 4340 vs 34CrNiMo6?

34CrNiMo6 alloy steel plate (European EN standard) and 4340 high-quality Chromoly steel (American SAE/AISI standard) are both medium-carbon alloy structural steels, which are widely used in key components with high stress and high fatigue strength. The following is a comparison from multiple dimensions:

Key differences：

Carbon content: 4340 has higher carbon content, better hardenability, but slightly lower toughness.

Nickel content: 4340 has higher nickel content, which improves low-temperature toughness; 34CrNiMo6 has higher chromium content and slightly better corrosion resistance.

Key differences:

Low-temperature toughness: 34CrNiMo6 alloy steel plate has better corrosion resistance and high-temperature strength due to its higher chromium content; 4340 chromium-molybdenum alloy steel has better impact toughness at low temperatures (below -40°C) due to its high nickel content.

Fatigue strength: 4340 is slightly higher and suitable for high-cycle fatigue applications (such as aviation components).

34CrNiMo6 hot-rolled plate:

• Quenching: 850-880℃ oil quenching.
• Tempering: 540-680℃ (adjusted according to strength requirements), air cooling.
• Surface carburizing or nitriding can be performed to enhance wear resistance.

4340 alloy steel plate:

• Quenching: 815-845℃ oil quenching or water quenching (depending on the cross-sectional size).
• Tempering: 425-650℃, air cooling.
• Be aware of temper brittleness (avoid long stays in the 300-400℃ range).

Key differences:
4340 is easier to achieve deep hardening (suitable for large cross-section parts), but the tempering process needs to be strictly controlled.

34CrNiMo6 hot-rolled alloy steel plate:

• Heavy gears, crankshafts, high-load bolts, ship drive shafts.
• European automotive/heavy industry (such as German DIN standard applications).

4340 hot-rolled alloy steel plate:

• Aircraft landing gear, connecting rods, oil drill pipes, military equipment.
• American aviation and military fields (such as Boeing, Lockheed Martin commonly used).

Neither of them is stainless steel, has limited chromium content, and has average corrosion resistance.

34CrNiMo6 hot-rolled plate has slightly better oxidation resistance in humid environments than 4340 due to its higher chromium content.

Corrosion resistance needs to be improved by plating (chrome plating, nickel plating) or painting.

Machinability: Both can be machined in the annealed state, and 4340 has slightly faster tool wear due to its high carbon content.

Weldability:

• Both require preheating (200-300℃) and post-heat treatment to avoid cracks.
• 34CrNiMo6 hot-rolled alloy plate has slightly poorer weldability (higher alloy content leads to greater hardening tendency).

Raw material cost: 4340 is usually 10-15% higher than 34CrNiMo6 due to its high nickel content.

Regional supply: 34CrNiMo6 hot-rolled alloy plate is more popular in Europe, and 4340 is more common in North America and Asia Pacific.

Choose 34CrNiMo6:
– Requires high corrosion resistance or high temperature strength (≤400℃).
– European standard projects or cost-sensitive industrial parts.

Choose 4340:
– Low temperature environment (such as polar equipment) or large cross-section high hardenability requirements.
– Aviation/military fields or projects that follow US standards.

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FAQ

What material is 34CrNiMo6?

34CrNiMo6 is a quenching and tempering steel with high strength, high toughness and good hardenability. Used for large axles, machine components, tools and high strength fasteners. The steel can be induction hardened and it is weldable under certain conditions.

What is equivalent to 34 Crnimo 6?

The primary equivalent for 34CrNiMo6 steel is AISI 4340, though other national standards also exist, including BS 817M40/EN24 (UK), SNCM439 (Japan), and GB3077: 34Cr2Ni2Mo (China). 34CrNiMo6 is a high-strength, high-toughness alloy steel used in industries like aerospace and automotive, with applications ranging from crankshafts to landing gear components.

What is the equivalent of AISI 4030?

2 Alternative Names, Standards, and Equivalents

What is SAE 4340 steel?

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.

What is the composition of SAE 4340?

Carbon C % 0.380 - 0.430 Silicon Si % 0.150 - 0.350 Manganese Mn % 0.650 - 0.850 Phosphorus P % 0.015 max. Sulphur S % 0.008 max. All information in our data sheets and website is indicative only and is not intended to be a substitute for the full specification from which it is extracted.

What is the difference between SAE 4340 and AISI 4340?

While the number 4340 represents the American alloy steel grade 4340. Therefore, there is no obvious difference between SAE 4340, AISI 4340, and ASTM 4340. Some of them are just different statements under different associations, but they all represent the grade 4340.