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Resources/Materials & grades/4340 / EN24

Materials & grades

4340 / EN24 / 34CrNiMo6 / SNCM439 nickel-chromium-molybdenum steel

AISI 4340 is a medium-carbon nickel-chromium-molybdenum alloy steel, used hardened and tempered where high strength and toughness are needed in large sections. Its usual counterparts are 817M40 (formerly EN24) in the UK, 34CrNiMo6 (1.6582) in Europe, 40Ni6Cr4Mo3 in India and SNCM439 in Japan.

Names by standard

What it is called in each region

RegionSystemDesignationStandardMatch
USAAISI/SAE4340SAE J404; ASTM A29 (bar)Same material
UNSG43400—Same material
UKBS 970-3 (1991)817M40Less nickel and more chromium than 4340. BS 970 alloy grades are superseded by EN 10083-3 but are still ordered by name, often as 817M40T.BS 970-3Closest equivalent
BS 970 (1955 EN series)EN24Superseded 1955 name for 817M40. Still the most-searched UK name; usually supplied hardened and tempered as EN24T.—Closest equivalent
EUEN 10027-1 name34CrNiMo6The EN grade most charts give for EN24 and 4340, but with lower carbon. Same name was used in the superseded DIN 17200.EN 10083-3; EN ISO 683-2Closest equivalent
EN 10027-2 number1.6582EN 10083-3Closest equivalent
EN 10027-1 name36CrNiMo4 (1.6511)Given by some charts. Its name indicates about 1% nickel, so it is a weaker match than 34CrNiMo6.EN 10083-3Closest equivalent
IndiaIS 157040Ni6Cr4Mo3IS 1570 (Part 4):1988Closest equivalent
IS (pre-1974 designation)40Ni2Cr1Mo28Older Indian letter-symbol name still quoted for EN24. Superseded by the IS 1762 designation system used in IS 1570 (Part 4):1988.IS 4368:1967Closest equivalent
JapanJIS G 4053SNCM439JIS G 4053Equivalent
JIS G 4053SNCM447Listed for 4340 in some references; the name indicates a higher-carbon grade of the same family.JIS G 4053Closest equivalent

On equivalence

  • 4340 and EN24 (817M40) are routinely interchanged, but their chemistries differ: 817M40 has less nickel (1.30–1.70% against 1.65–2.00%) and more chromium (1.00–1.40% against 0.70–0.90%). The match is therefore marked closest.
  • 34CrNiMo6 (1.6582) is the EN grade most charts give for both EN24 and 4340, but its carbon range is lower (0.30–0.38%). Saarstahl cross-references 34CrNiMo6 to 817M40 and 816M40 and to SAE 4337 and 4340.
  • Some charts list 36CrNiMo4 (1.6511) for 4340. It contains about 1% nickel and is a weaker match.
  • India: 40Ni6Cr4Mo3 in IS 1570 (Part 4):1988 is the closest listed grade to EN24. Charts also give 40Ni2Cr1Mo28 (pre-1974 name) or 40NiCr4Mo3; 40Ni6Cr4Mo2 is a lower-molybdenum grade (0.10–0.20% Mo). IS 1570 (Part 4) leaves phosphorus and sulphur limits to the product specification.
  • Japan: SNCM439 overlaps 4340 closely. Its limits here come from a supplier listing of JIS G 4053, not the JIS text, and should be checked against the standard. Some references list SNCM447 instead, which is a higher-carbon grade.
  • Compare grades at the same condition and ruling section. The EN 10083-3 minimum yield of 34CrNiMo6 falls from 1000 MPa (diameter ≤16 mm) to 600 MPa (160–250 mm).

Chemical composition

Composition limits, mass %

Element4340USA · AISI/SAE 4340 (bar)817M40 (EN24)UK · BS 970-334CrNiMo6 (1.6582)EU · EN 10083-340Ni6Cr4Mo3India · IS 1570 (Part 4):1988SNCM439Japan · JIS G 4053
C0.38–0.430.36–0.440.30–0.380.35–0.450.36–0.43
Si0.15–0.350.10–0.35≤0.400.10–0.350.15–0.35
Mn0.60–0.800.45–0.700.50–0.800.40–0.700.60–0.90
P≤0.035≤0.035≤0.025—≤0.030
S≤0.040≤0.040≤0.035—≤0.030
Cr0.70–0.901.00–1.401.30–1.700.90–1.300.60–1.00
Ni1.65–2.001.30–1.701.30–1.701.25–1.751.60–2.00
Mo0.20–0.300.20–0.350.15–0.300.20–0.350.15–0.30

Mechanical properties

Strength and hardness

ConditionTensile strengthYield strengthElongationHardness
AnnealedTypical values, not specified minimumsAZoM, AISI 4340 alloy steel (UNS G43400)745 MPa108 ksi470 MPa68.2 ksi22 %217 HB
Hardened and tempered, condition TBS 970 condition T; values depend on ruling sectionSmiths Metal Centres, EN24 technical datasheet850–1000 MPa123–145 ksi≥650 MPa≥94 ksi≥13 %248–302 HB
Hardened and tempered, condition VBS 970 condition V; values depend on ruling sectionSmiths Metal Centres, EN24 technical datasheet1000–1150 MPa145–167 ksi≥850 MPa≥123 ksi≥12 %293–352 HB
Quenched and tempered (+QT)Specified, diameter 16–40 mm (thickness 8–20 mm); yield and elongation are minimumsEN 10083-3, 34CrNiMo6, via Saarstahl datasheet1100–1300 MPa160–189 ksi≥900 MPa≥131 ksi≥10 %—
Quenched and tempered (+QT)Specified, diameter 40–100 mm (thickness 20–60 mm); yield and elongation are minimumsEN 10083-3, 34CrNiMo6, via Saarstahl datasheet1000–1200 MPa145–174 ksi≥800 MPa≥116 ksi≥11 %—
Quenched and tempered (+QT)Specified, diameter 100–160 mm (thickness 60–100 mm); yield and elongation are minimumsEN 10083-3, 34CrNiMo6, via Saarstahl datasheet900–1100 MPa131–160 ksi≥700 MPa≥102 ksi≥12 %—
Oil hardened and temperedSpecified, limiting ruling section 150 mm; hardness for guidance onlyIS 1570 (Part 4):1988, Table 4, 40Ni6Cr4Mo3890–1040 MPa129–151 ksi≥650 MPa≥94 ksi≥15 %255–311 HB
Soft annealed (+A)Maximum hardnessSaarstahl, 34CrNiMo6 datasheet———≤248 HB

In practice

Behaviour, heat treatment and uses

Characteristics

  • Hardenability is very high. Nickel, chromium and molybdenum together let large sections harden through in oil, which is why the grade is chosen for heavy forgings.
  • Toughness is good, including relatively good impact properties at low temperatures, at strengths of 1000 MPa and above.
  • Wear resistance is good in the hardened and tempered condition.
  • Machinability is rated about 50–57% of AISI 1212 in the annealed condition, depending on the reference. EN24 is normally machined in the supplied hardened and tempered condition.
  • Weldability is poor. Welding needs established preheat and post-heat procedures, and the weld zone will not match the base metal unless the part is re-heat-treated.
  • Corrosion resistance is that of ordinary low-alloy steel. Parts are oiled, plated or coated when protection is needed.
  • The steel is magnetic.

Heat treatment

  • Hardening: 830–860 °C, quench in oil (34CrNiMo6 guidance; US practice is about 830 °C, oil quench).
  • Tempering: 540–660 °C for the standard quenched and tempered property ranges; the temperature is chosen to suit the target strength.
  • Normalizing: 850–880 °C, then air cool.
  • Soft annealing: 650–700 °C with slow furnace cooling, giving ≤248 HB.
  • Forging: about 1100–850 °C.

Typical uses

  • Highly stressed shafts, axles and crankshafts
  • Gears and heavy-duty transmission parts
  • Heavy forgings and large components with big hardened sections
  • Automotive, engine and heavy-vehicle parts
  • Drill bushings, retaining rings and tooling parts

Alloy and case-hardening steels

Similar grades compared

GradeC %Mn %Cr %Ni %Tensile, first listed condition
4340 / EN240.38–0.430.60–0.800.70–0.901.65–2.00745 MPa
4130 / 25CrMo40.28–0.330.40–0.600.80–1.10≤0.25590–760 MPa
4135 / 34CrMo40.33–0.380.70–0.900.80–1.10≤0.251000–1200 MPa
4140 / 42CrMo40.38–0.430.75–1.000.80–1.10≤0.25655 MPa
5140 / 41Cr40.38–0.430.70–0.900.70–0.90≤0.25570 MPa
6150 / 51CrV40.48–0.530.70–0.900.80–1.10≤0.40670 MPa
16MnCr50.13–0.180.70–0.900.70–0.90≤0.25≥1000 MPa
20MnCr50.17–0.220.70–0.900.70–0.90≤0.25≥1200 MPa
655M13 / EN36A0.08–0.130.45–0.651.00–1.403.00–3.50700–770 MPa
8620 / 20NiCrMo2-20.18–0.230.70–0.900.40–0.600.40–0.70530 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 answered

Common questions

What is EN24 equivalent to?

EN24 is the old BS 970 name for 817M40. It is usually equated with AISI 4340 in the USA, 34CrNiMo6 (1.6582) in Europe, 40Ni6Cr4Mo3 in India and SNCM439 in Japan. None of these is chemically identical to EN24, so treat them as closest equivalents.

Is EN24 the same as 4340?

No, but they are close and often substituted. EN24 (817M40) has 1.30–1.70% nickel and 1.00–1.40% chromium, while 4340 has 1.65–2.00% nickel and 0.70–0.90% chromium. Both are nickel-chromium-molybdenum steels used hardened and tempered for similar parts.

What is the difference between EN19 and EN24?

EN19 (708M40) is a chromium-molybdenum steel without nickel. EN24 (817M40) adds about 1.5% nickel and more chromium, giving higher hardenability and toughness in large sections. EN24 costs more and is chosen when section size or impact toughness demands it.

What does EN24T mean?

T is the BS 970 heat-treated condition with 850–1000 MPa tensile strength and typically 248–302 HB. Higher letters, such as V at 1000–1150 MPa, denote stronger conditions. The condition that can be reached depends on the ruling section.

Is 34CrNiMo6 the same as 4340?

They are close but not the same. 34CrNiMo6 has lower carbon (0.30–0.38%), less nickel and more chromium than 4340. Both are quenched and tempered nickel-chromium-molybdenum steels for heavily loaded parts.

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4140 / 42CrMo4AISI 4140 is a medium-carbon chromium-molybdenum alloy steel, normally used hardened and tempered for shafts, gears and high-strength bolts.1045 / C451045 is a medium-carbon steel with about 0.45 % carbon, supplied hot rolled, normalized or quenched and tempered for shafts, pins, gears and forgings.Quenching and temperingQuenching and tempering hardens steel by cooling it rapidly from the austenite range to form martensite, then reheats it below Ac1 to trade some hardness for toughness.NormalizingNormalizing heats steel above its upper critical temperature and lets it cool in still air to give a fine, uniform ferrite–pearlite structure.AnnealingAnnealing heats steel to a set temperature, holds it and cools it slowly to make it softer, more ductile and easier to machine or cold form.Bolt property classesMetric bolts in the UK, EU, India and Japan all use the ISO 898-1 property classes (4.6, 8.8, 10.9, 12.9), while US inch bolts use SAE J429 grades and ASTM specifications.SAE / AISI numbersA four-digit SAE/AISI number such as 1045 or 4140 names a carbon or alloy steel by its chemistry: the first two digits identify the steel family and the last two give the nominal carbon content in hundredths of a percent.EN 10027 names and numbersEuropean steels carry two identifiers under EN 10027: a steel name (Part 1) such as S235JR, C45 or 42CrMo4 that describes the steel's use or chemistry, and a material number (Part 2) such as 1.0503 or 1.7225.BS 970 and the EN seriesBS 970 names steels with a six-character code such as 080M40, in which the first three digits give the steel type, the letter says how the steel is specified and the last two digits give the carbon content.IS 1570 and Indian designationsIndian steel names follow the letter-symbol code in IS 1762 (Part 1), which the IS 1570 schedules use: 45C8 means about 0.45% carbon, C for carbon steel and about 0.8% manganese, while alloy names such as 40Cr4Mo3 list each element with a multiplied content figure.JIS steel designationsJapanese JIS steel symbols start with S for steel and add letters for the steel family or its use, but the number means different things in different standards.

References

Sources

  1. Alro Steel, 4340 hot rolled Q&T grade information — AISI 4340 bar composition.
  2. AZoM, AISI 4340 Alloy Steel (UNS G43400) — Typical annealed properties, machinability rating, US heat-treatment practice, welding note.
  3. Total Materia, ASTM A322 4340 — Confirms C, Mn and Cr ranges for 4340.
  4. Smiths Metal Centres, EN24 technical datasheet — 817M40 composition, BS 970 conditions T to Z, related specifications.
  5. Saarstahl, Werkstoff-Datenblatt 34CrNiMo6 (1.6582) — +QT properties by diameter, heat treatment, cross-references to 817M40, 816M40, SAE 4337 and 4340.
  6. MARKS GmbH, Werkstoffblatt 1.6582 34CrNiMo6 — EN 10083-3 analysis limits.
  7. Bureau of Indian Standards, IS 1570 (Part 4):1988 Schedules for wrought steels, alloy steels (Public.Resource.Org copy) — Table 1 composition for 40Ni6Cr4Mo3 and 40Ni6Cr4Mo2; Table 4 hardened and tempered properties.
  8. Total Materia, IS 40Ni2Cr1Mo28 — Legacy Indian designation under IS 4368:1967.
  9. USI Steels, JIS G 4053 SNCM439 — Supplier listing of SNCM439 composition; verify against JIS G 4053.
  10. Wikipedia, 4340 steel — Equivalent-grade list (including SNCM447) and machinability rating.

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