4140 vs 42CrMo4 — any difference?

They are equivalents with overlapping windows: 42CrMo4 allows slightly more carbon and chromium at the top end. Mill certificates are normally accepted cross-wise; state both standards when ordering.

Should I buy 4140 annealed or prehardened?

Prehardened (28–32 HRC) skips your heat treatment and machines well — preferred unless the part needs higher final hardness or case hardening.

Grades · Alloy & Engineering Steel · 4140

4140

Data verified

4140 is the most popular Cr-Mo engineering steel in the world: a through-hardening grade for shafts, gears, bolts and hydraulic parts that need strength with machinability. Supplied annealed, normalized or prehardened as round bar.

Hardness28–40 HRC typical

DIN1.7225 (42CrMo4)

AISI4140

JISSCM440

CategoryAlloy & Engineering Steel

Chemical composition

Element	Content (%)
C	0.38–0.43
Si	0.15–0.35
Mn	0.75–1.00
P	≤0.035
S	≤0.040
Cr	0.80–1.10
Mo	0.15–0.25

Weight percent, per the governing standard ranges. Actual values per heat are on the mill certificate.

Properties

Hardness (Q&T)	28–40 HRC typical
Tensile strength	850–1100 MPa (Q&T)
Yield strength	≥650 MPa (Q&T, section dependent)
Density	7.85 g/cm³
Elastic modulus	210 GPa

Heat treatment

Normalize 870 °C; quench 845 °C oil; temper 540–660 °C to required hardness. Also widely used prehardened (28–32 HRC).

Equivalent grades

Standard	Designation
din	1.7225 (42CrMo4)
aisi	4140
jis	SCM440
gb	42CrMo

Compare side by side: 4140 vs 42CrMo4 · 4140 vs SCM440 · 4140 vs 40Cr

Equivalents overlap in chemistry and use but are not always identical — see our equivalents guide before substituting in certified designs.

Applications & Processing

Applications: Shafts, gears, axles, hydraulic shafts and cylinders, high-strength bolts, oil & gas components.

Processing: Machines well annealed or prehardened; weldable with preheat (150–300 °C) and low-hydrogen practice; can be induction hardened or nitrided.

FAQ

4140 vs 42CrMo4 — any difference?: They are equivalents with overlapping windows: 42CrMo4 allows slightly more carbon and chromium at the top end. Mill certificates are normally accepted cross-wise; state both standards when ordering.
Should I buy 4140 annealed or prehardened?: Prehardened (28–32 HRC) skips your heat treatment and machines well — preferred unless the part needs higher final hardness or case hardening.

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Source: SAE J404 / ASTM A29 published ranges · Last updated 2026-11-03. Data is indicative — verify critical values against the governing standard and mill certificate before use.