4140 vs 4340 Steel: The Nickel Difference and How to Choose

📋 4140 / 42CrMo4 Datasheet → · 4340 / 34CrNiMo6 Datasheet → — chemical composition, section-dependent mechanical properties and international equivalents.

What Are 4140 and 4340?

Both are high-strength quenched-and-tempered steels; the defining difference is nickel:

• 4140 (EN 42CrMo4, 1.7225): chrome-molybdenum steel, no nickel. The economical workhorse.
• 4340 (EN 34CrNiMo6, 1.6582): chrome-nickel-molybdenum steel with ~1.5% nickel. Premium, for highly stressed critical parts.

In short: 4140 is economical high strength in medium sections, 4340 offers superior hardenability + toughness in large sections.

Chemical Composition

Element	4140 (%)	4340 (%)
Carbon (C)	0.38–0.43	0.38–0.43
Manganese (Mn)	0.75–1.00	0.60–0.80
Chromium (Cr)	0.80–1.10	0.70–0.90
Molybdenum (Mo)	0.15–0.25	0.20–0.30
Nickel (Ni)	—	1.65–2.00

To compare chemistry across grades, use our Chemical Composition tool.

Mechanical Properties

Property	4140 (Q&T)	4340 (Q&T)
Tensile strength (Rm)	900–1100 MPa	1100–1300 MPa
Yield strength (Re)	min. 650 MPa	min. 1000 MPa
Hardness	260–320 HB	350–400 HB
Toughness (at high strength)	Good	Superior
Hardenability	Medium-high	Very high (deep section)
Fatigue strength	Good	Superior

The Defining Difference: Nickel → Hardenability and Toughness

Nickel deepens hardenability and preserves toughness even at high strength levels:

• 4340, thanks to its nickel, hardens to the core even in very large sections and stays non-brittle even above 1200 MPa. That is why it is standard for aircraft landing gear, heavy drive shafts and highly stressed critical parts.
• 4140, being nickel-free, is more economical and offers an excellent strength/cost balance in medium sections; but the core will not fully harden in very large cross-sections.

To convert hardness values, use our Hardness Converter.

When to Choose Which?

Choose 4140 if:

• The part is medium-section and cost matters (gears, shafts, axles, dies, bolts)
• 900–1100 MPa strength is sufficient
• Wide stock and short lead time are wanted

Choose 4340 if:

• A large section must harden to the core (heavy shafts, large gears)
• High strength AND high toughness together are required (>1200 MPa)
• Fatigue and impact are critical (aerospace, defense, heavy industry)

Application Areas

Sector	4140	4340
Aerospace & defense	General structural parts	Landing gear, critical drivetrain
Energy	Shafts, gears	Turbine/generator main shafts
Heavy machinery	Axles, shafts, dies	Large-section drive shafts
Oil & gas	Valves, fittings	Critical drilling components

For cross-standard equivalents use the Steel Grade Equivalent tool; for the difference from 4140's lower-carbon "sibling" 4130, see our 4130 vs 4140 article.

Supply from Aktif Çelik

At Aktif Çelik we stock 4140/42CrMo4 and 4340/34CrNiMo6 in hot-rolled bar, forged bar and bright bar forms across a wide diameter range. With 3.1 certified, quenched-and-tempered or normalized options we recommend the most suitable grade for your project. Contact our team for technical consultancy and cut-to-length service.