BLOG · JULY 2026

42CrMo vs 40Cr: The Complete Material Comparison for Hot Forging

Two of the most widely used alloy steels in hot forging are 42CrMo and 40Cr. If you are sourcing forged parts from China, you have likely encountered both grades on quotation requests. While they appear similar, the differences in chemistry, mechanical properties, and cost make each suited for different applications. This guide provides a side-by-side comparison to help you choose the right material for your forged components.

Chemical Composition

Element	42CrMo (GB/T 3077)	40Cr (GB/T 3077)	Remarks
Carbon (C)	0.38-0.45%	0.37-0.44%	Similar range
Chromium (Cr)	0.90-1.20%	0.80-1.10%	42CrMo slightly higher Cr
Molybdenum (Mo)	0.15-0.25%	—	Key differentiator
Manganese (Mn)	0.50-0.80%	0.50-0.80%	Identical range
Silicon (Si)	0.17-0.37%	0.17-0.37%	Identical range
Phosphorus (P) max	0.035%	0.035%	Same limit
Sulfur (S) max	0.035%	0.035%	Same limit

The critical difference is molybdenum (Mo) in 42CrMo. Molybdenum improves hardenability, high-temperature strength, and resistance to temper embrittlement. This single element determines most of the performance differences between the two grades.

Mechanical Properties (After Quenching + Tempering)

Property	42CrMo	40Cr	Advantage
Tensile Strength (Rm)	1,080-1,200 MPa	980-1,100 MPa	42CrMo +10-15%
Yield Strength (Re)	930-1,050 MPa	785-900 MPa	42CrMo +15-20%
Elongation (A5)	>10%	>9%	42CrMo slightly better
Impact Toughness (KU2)	>63 J	>47 J	42CrMo +35%
Hardness (HRC)	35-45 HRC	32-42 HRC	42CrMo harder achievable
Fatigue Limit (10^7 cycles)	~480 MPa	~410 MPa	42CrMo +17%

Forgeability Comparison

Both grades forge well in the temperature range of 1,150-1,200°C. Key differences:

Aspect	42CrMo	40Cr
Forging temperature range	1,100-1,200°C	1,150-1,220°C
Flow stress at 1150°C	~95 MPa	~85 MPa
Die wear rate	Higher (higher flow stress)	Moderate
Cracking susceptibility	Lower (Mo refines grain)	Requires careful cooling
Scale formation	Similar	Similar
Post-forge cooling	Can air cool (thin sections)	Must slow cool or anneal

Cost Comparison

Cost Factor	42CrMo	40Cr	Impact
Raw material (per ton)	~$850-1,100	~$650-850	42CrMo +30-35%
Forging cost (per part)	+5-10%	Base	Slightly higher wear
Heat treatment cost	Similar	Similar	—
Total part cost	+15-25%	Base	Premium for higher performance

Application Guide: When to Choose Which

Choose 42CrMo when:

The part requires high fatigue strength (connecting rods, crankshafts, transmission shafts)
Operating temperature exceeds 200°C (engine components, turbocharger parts)
Impact loading is severe (suspension components, steering knuckles)
The part cross-section is large (>50mm) — molybdenum ensures through-hardening
Safety-critical application where failure cost > material premium

Choose 40Cr when:

Budget is the primary constraint and performance requirements are moderate
Part is small to medium section (<50mm) where hardenability difference is minimal
Operating conditions are standard (room temperature, moderate loading)
Application allows more generous design safety factors

FAQ

Q: Can 40Cr be substituted for 42CrMo?

Only in non-critical applications with lower stress requirements. The lack of molybdenum in 40Cr means lower hardenability and reduced high-temperature strength. Expect 10-15% lower fatigue life.

Q: Which grade is easier to machine after forging?

40Cr is slightly easier to machine due to lower hardness. For 42CrMo, use carbide tooling at reduced speeds (10-15% slower) for optimal tool life.

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