8640 / 40NiCrMo2-2 / SNCM240 nickel-chromium-molybdenum steel

Names by standard

What it is called in each region

Region	System	Designation	Norme	Match
USA	AISI/SAE	8640	SAE J404; ASTM A29 (bar)	Same material
	UNS	G86400	—	Same material
UK	BS 970	945M38Listed against 8640 by Total Materia (implicit equivalent). Roymech gives it nominal 1.4% manganese, 0.75% nickel, 0.5% chromium and 0.20% molybdenum, so manganese is well above the 8640 range. No closer BS 970 name was confirmed.	BS 970	Closest equivalent
EU	DIN name and Werkstoff number	40NiCrMo2-2 (1.6546)AZoM lists DIN 1.6546 as an 8640 designation. Composition is almost the same as 8640. No standards body or mill sheet was read to confirm the standard it now sits in.	DIN (national); not confirmed in a current EN standard	Closest equivalent
Japan	JIS G 4053	SNCM240Same carbon, nickel and chromium ranges. Kobelco and Misumi list SNCM240 against 8637 and 8640 (ISO 41CrNiMo2).	JIS G 4053	Equivalent

On equivalence

8640 and 40NiCrMo2-2 have almost the same nickel, chromium and molybdenum ranges. 40NiCrMo2-2 allows 0.37–0.44% carbon and 0.15–0.30% molybdenum against 0.38–0.43% and 0.15–0.25% for 8640, and caps sulphur at 0.035%. It is marked "closest" because no standards body or mill sheet was read for it.
SNCM240 is the standard Japanese match. Kobelco's cross-reference lists it against 8637 and 8640 and against ISO 41CrNiMo2, and shows no EN equivalent.
UK: the BS 970 name for 8640 was not confirmed. 945M38 is listed by Total Materia as an implicit equivalent but carries far more manganese. 805M20 (EN362) is the 8620 grade and is not a substitute.
India: IS 1570 (Part 4):1988 has no grade with about 0.40% carbon and 0.5% each of nickel and chromium. 40Ni6Cr4Mo2 carries 1.20–1.60% nickel and 0.90–1.30% chromium, so it is not a like-for-like match. No Indian notation is given.
Silicon: AZoM gives 0.15–0.30%. Check the ASTM A29 value on the order.
8640 is not 8620. 8620 is a 0.18–0.23% carbon carburizing grade; see its page.

Chemical composition

Composition limits, mass %

Element	8640USA · SAE J404 / ASTM A29 (as tabulated by AZoM)	40NiCrMo2-2 (1.6546)EU · DIN (as tabulated by steel-grades.com)	SNCM240Japan · JIS G 4053 (as tabulated by Kobelco)
C	0.38–0.43	0.37–0.44	0.38–0.43
Si	0.15–0.30	0.15–0.40	0.15–0.35
Mn	0.75–1.00	0.70–1.00	0.70–1.00
P	≤0.035	≤0.035	≤0.030
S	≤0.040	≤0.035	≤0.030
Cr	0.40–0.60	0.40–0.60	0.40–0.60
Ni	0.40–0.70	0.40–0.70	0.40–0.70
Mo	0.15–0.25	0.15–0.30	0.15–0.30

Mechanical properties

Strength and hardness

Condition	Tensile strength	Yield strength	Elongation	Hardness
Quenched and tempered (A400 classes P and Q), selection-guide rangeRange from the ASTM A400 bar selection guide as shown by Total Materia, which does not state a condition. A400 says it is not a procurement specification, so these are guide strength levels, not specified minimums; the page does not say which temper gives which valueASTM A400, 8640, via Total Materia	1000–1413 MPa145–205 ksi	862–1275 MPa125–185 ksi	—	293–429 HB

In practice

Behaviour, heat treatment and uses

Characteristics

The nickel, chromium and molybdenum addition makes 8640 an oil-hardening steel (ASM Alloy Digest title: oil-hardening triple alloy steel).
Carbon of 0.38–0.43% matches 4140, but 8640 has less chromium (0.40–0.60%) and adds 0.40–0.70% nickel, with 0.15–0.25% molybdenum.
The ASTM A400 bar guide notes that classes P and Q should reach their properties by liquid quenching and tempering at 800 °F (427 °C) or higher (via Total Materia).
Heat treatment and welding data for 8640 itself were not found in a readable standard or mill sheet. Take them from the supplier's data for the exact grade.

Heat treatment

Oil hardening and tempering is the normal route. A400 guidance: liquid quench from a suitable austenitizing temperature, then temper at 427 °C (800 °F) or higher (via Total Materia).
For SNCM240, Kobelco's JIS table gives tempering at 580–680 °C; Total Materia lists hardening at 820–870 °C in oil and tempering from 560 °C.
Specific normalizing and annealing temperatures for 8640 were not found in a readable source.

Usages types

Crankshafts, screws, axles and pistons (Continental Steel)
Forged hand tools (Continental Steel)
Aircraft landing gear and airframe parts (Continental Steel)

Alloy and case-hardening steels

Similar grades compared

Grade	C %	Mn %	Cr %	Ni %	Tensile, first listed condition
8640 / SNCM240	0.38–0.43	0.75–1.00	0.40–0.60	0.40–0.70	1000–1413 MPa
4130 / 25CrMo4	0.28–0.33	0.40–0.60	0.80–1.10	≤0.25	590–760 MPa
4135 / 34CrMo4	0.33–0.38	0.70–0.90	0.80–1.10	≤0.25	1000–1200 MPa
4140 / 42CrMo4	0.38–0.43	0.75–1.00	0.80–1.10	≤0.25	655 MPa
4145	0.43–0.48	0.75–1.00	0.80–1.10	≤0.25	≥965 MPa
4150 / 50CrMo4	0.48–0.53	0.75–1.00	0.80–1.10	≤0.25	731 MPa
4340 / EN24	0.38–0.43	0.60–0.80	0.70–0.90	1.65–2.00	745 MPa
5140 / 41Cr4	0.38–0.43	0.70–0.90	0.70–0.90	≤0.25	570 MPa
6150 / 51CrV4	0.48–0.53	0.70–0.90	0.80–1.10	≤0.40	670 MPa
16MnCr5	0.13–0.18	0.70–0.90	0.70–0.90	≤0.25	≥1000 MPa

Composition from the US standard where one exists, otherwise the first standard listed on each grade's page. Strength conditions differ between grades; open a grade for its full table.

Questions et réponses

Common questions

What is the equivalent of 8640 steel?

The Japanese equivalent is SNCM240 (JIS G 4053). The nearest European name is 40NiCrMo2-2 (1.6546), which has almost the same limits. The UK and Indian equivalents are not firmly established; check the drawing before substituting.

What is the difference between 8640 and 4140?

Both have about 0.40% carbon. 4140 relies on 0.80–1.10% chromium and 0.15–0.25% molybdenum, while 8640 adds 0.40–0.70% nickel and cuts chromium to 0.40–0.60%, with the same molybdenum.

Is 8640 the same as 8620?

No. 8620 has 0.18–0.23% carbon and is a carburizing steel. 8640 has 0.38–0.43% carbon and is hardened and tempered through the section.

What is SNCM240?

SNCM240 is the JIS G 4053 nickel-chromium-molybdenum steel that Japanese steel makers list against SAE 8640 and 8637. It has 0.38–0.43% carbon, 0.40–0.70% nickel, 0.40–0.60% chromium and 0.15–0.30% molybdenum.

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References

Sources

AZoM, AISI 8640 Alloy Steel (UNS G86400) — Composition and the list of related designations (DIN 1.6546, ASTM A29/A322, SAE J404).
SAE J404: Chemical compositions of SAE alloy steels — Governs the SAE alloy-steel composition limits. Values here are as tabulated by AZoM and the Central Steel & Wire catalog.
Kobelco: wire rod and bar specification tables (JIS G 4053 alloy steels for machine structure, revision of 20 Nov 2008; JIS G 4107 bolting steels) — JIS composition tables and the JIS-to-ISO/AISI cross-reference table.
Misumi: comparison of JIS and related overseas steel standards — Cross-reference of JIS G 4053 and G 4052 grades to ISO, AISI/SAE and EN names.
Total Materia, ASTM A400 8640 — Tensile, yield and hardness ranges and the quenching guidance.
Total Materia, SAE 8640 — SNCM240 and BS 945 M 38 listed as equivalents.
steel-grades.com, DIN 40NiCrMo2-2 — 40NiCrMo2-2 composition limits.
Total Materia, SNCM240 (proprietary entry) — Heat treatment for SNCM240.
Roymech, sample BS 970 steels — Nominal composition of 945M38.
ASM Alloy Digest SA-15: AISI 8640, oil-hardening triple alloy steel — Title only; abstract not read.
Continental Steel, Alloy Steel 8640 — Typical applications.
ASTM A400, Standard Practice for Steel Bars, Selection Guide, Composition, and Mechanical Properties (ASTM store scope) — Scope: a selection guide for bars by section size and properties; classes P and Q are liquid quenched and tempered. States it is not a procurement specification.

Values summarize published limits and typical data. The governing standard and the current edition control; check them before specifying.