Materials & grades
4320 / SNCM420 / 20Ni7Cr2Mo2 case-hardening steel
SAE 4320 is a nickel-chromium-molybdenum case-hardening steel with 0.17–0.22% carbon and 1.65–2.00% nickel, carburized to give a hard case over a tough core. Its nearest names are SNCM420 in Japan and 20Ni7Cr2Mo2 in India.
Names by standard
What it is called in each region
| Region | System | Designation | Norm | Match |
|---|---|---|---|---|
| USA | AISI/SAE | 4320 | SAE J404; ASTM A29 (bar) | Same material |
| UNS | G43200 | — | Same material | |
| AISI/SAE | 4320HHardenability-band version. Ovako lists 4320H and 4320RH as similar designations to its 20NiCrMo7 bar. | SAE hardenability-band grade | Closest equivalent | |
| EU | Ovako grade name | 20NiCrMo7 (Ovako 157)Ovako's name for a 4320-type case-hardening bar. Ovako lists ASTM 4320, 4320H and 4320RH as similar designations. It is a mill name, not an EN 10084 designation in the sources checked. | Ovako Steel Navigator | Closest equivalent |
| EN 10027-1 name | 17NiCrMo6-4 (1.6566)Nickel is 1.20–1.50% and chromium 0.80–1.10%, against 1.65–2.00% and 0.40–0.60% for 4320. This is the EN grade behind the UK 815M17. | EN 10084 | Closest equivalent | |
| India | IS 1570 / IS 4432 | 20Ni7Cr2Mo2IS 1570 (Part 4) states in a footnote that this grade is equivalent to AISI 4320. Carbon, manganese, nickel, chromium and molybdenum limits are the same as 4320's. | IS 1570 (Part 4):1988; IS 4432:1988 | Equivalent |
| Japan | JIS G 4053 | SNCM420Kobelco and Misumi list SNCM420 against 4320. | JIS G 4053 | Equivalent |
| JIS G 4052 | SNCM420HHardenability-guaranteed version. Misumi lists it against 4320H. | JIS G 4052 | Closest equivalent |
On equivalence
- SNCM420 and 20Ni7Cr2Mo2 are the nearest matches by composition. SNCM420 allows 0.17–0.23% carbon, 0.40–0.70% manganese and 0.15–0.30% molybdenum against 0.17–0.22%, 0.45–0.65% and 0.20–0.30% for 4320.
- IS 1570 (Part 4):1988 footnote 8 states that 20Ni7Cr2Mo2 is equivalent to AISI 4320. IS 4432 also lists 20Ni7Mo2, which has no chromium; do not confuse the two.
- No European standard grade has 4320's nickel and chromium. 17NiCrMo6-4 (1.6566) has less nickel and more chromium. Ovako sells 20NiCrMo7 (157C, D, G) as its 4320-type bar, with tighter phosphorus and sulphur limits than SAE J404.
- UK: no BS 970 grade was confirmed as a direct equivalent of 4320. 815M17 (EN353) and 822M17 (EN355) are Ni-Cr-Mo case-hardening grades with their own limits; see the 815M17 and 18CrNiMo7-6 pages. No UK notation is given.
- Do not confuse 4320 with 4340. 4340 is the 0.38–0.43% carbon through-hardening grade; see its page. 8620 has much less nickel (0.40–0.70%); see its page.
- Silicon: AZoM gives 0.15–0.30%. Check the ASTM A29 value on the order.
Chemical composition
Composition limits, mass %
| Element | 4320USA · SAE J404 / ASTM A29 (as tabulated by AZoM) | 20NiCrMo7 (157C)EU · Ovako Steel Navigator (variant 157C, tighter mill limits) | 17NiCrMo6-4 (1.6566)EU · EN 10084 (as printed by Saarstahl; closest match) | 20Ni7Cr2Mo2India · IS 1570 (Part 4):1988 and IS 4432:1988 | SNCM420Japan · JIS G 4053 (as tabulated by Kobelco) |
|---|---|---|---|---|---|
| C | 0.17–0.22 | 0.17–0.22 | 0.14–0.20 | 0.17–0.22 | 0.17–0.23 |
| Si | 0.15–0.30 | 0.20–0.30 | ≤0.40 | 0.15–0.35 | 0.15–0.35 |
| Mn | 0.45–0.65 | 0.55–0.65 | 0.60–0.90 | 0.45–0.65 | 0.40–0.70 |
| P | ≤0.035 | ≤0.015 | ≤0.035 | — | ≤0.030 |
| S | ≤0.040 | ≤0.005 | ≤0.035 | — | ≤0.030 |
| Cr | 0.40–0.60 | 0.50–0.60 | 0.80–1.10 | 0.40–0.60 | 0.40–0.60 |
| Ni | 1.65–2.00 | 1.65–2.00 | 1.20–1.50 | 1.65–2.00 | 1.60–2.00 |
| Mo | 0.20–0.30 | 0.23–0.28 | 0.15–0.25 | 0.20–0.30 | 0.15–0.30 |
| V | — | ≤0.014 | — | — | — |
Mechanical properties
Strength and hardness
| Condition | Tensile strength | Yield strength | Elongation | Hardness |
|---|---|---|---|---|
| AnnealedTypical values, not specified minimumsAZoM, AISI 4320 alloy steel (UNS G43200) | 580 MPa84.1 ksi | 425 MPa61.6 ksi | 29 % | 163 HB |
| Quenched and tempered (+QT)Ovako 157C/157D, 25 mm round bar; Ovako lists the yield value as a minimum and the tensile and hardness values as typicalOvako Steel Navigator, 20NiCrMo7 | 1300 MPa189 ksi | ≥1200 MPa≥174 ksi | — | 360 HB |
In practice
Behaviour, heat treatment and uses
Characteristics
- Low carbon (0.17–0.22%) with 1.65–2.00% nickel. The steel is carburized, then hardened, so the case is hard and the core stays tough.
- Ovako describes its 157 grade as a high-cleanliness case-hardening steel for bearing and transmission components.
- AZoM rates machinability at 60 (AISI 1212 = 100) for annealed and cold drawn bar. It machines well when annealed and is difficult to machine once hardened.
- AZoM describes good weldability for the low-carbon grade. Ovako gives a carbon equivalent of at most 0.65 and Pcm at most 0.36 for 157C. Welding a carburized or hardened part still changes the case and core.
- Transformation temperatures (Ovako 157C): Ms 400 °C, Ac1 704 °C, Ac3 806 °C.
Heat treatment
- Ovako 157: hot forging 800–1200 °C; normalizing 860–890 °C, air cool; soft annealing 600–670 °C for 2 hours; quench and temper 840–890 °C in oil.
- Hardening of as-carburized components: 780–830 °C in oil, then temper at 160–250 °C (Ovako).
- IS 4432 (20Ni7Cr2Mo2): carburize at 890–940 °C; direct or single hardening 810–840 °C; double hardening, core at 830–870 °C and case at 780–820 °C; quench in oil, thermal bath or polymer.
- US practice (AZoM): normalize at 872 °C; heat to 816 °C, oil quench and temper to the hardness wanted; temper 205–705 °C; anneal at 872 °C with slow furnace cooling; forge at 1038–1205 °C.
Typische toepassingen
- Gears, pinions and other transmission components (Ovako)
- Bearing components (Ovako)
- Case-hardened parts: IS 4432 covers bars, billets, rods and forgings that are carburized or carbonitrided on the surface
Alloy and case-hardening steels
Similar grades compared
| Klasse | C % | Mn % | Cr % | Ni % | Tensile, first listed condition |
|---|---|---|---|---|---|
| 4320 / SNCM420 | 0.17–0.22 | 0.45–0.65 | 0.40–0.60 | 1.65–2.00 | 580 MPa |
| 16MnCr5 | 0.13–0.18 | 0.70–0.90 | 0.70–0.90 | ≤0.25 | ≥1000 MPa |
| 18CrNiMo7-6 | 0.15–0.21 | 0.50–0.90 | 1.50–1.80 | 1.40–1.70 | 1180–1420 MPa |
| 20MnCr5 | 0.17–0.22 | 0.70–0.90 | 0.70–0.90 | ≤0.25 | ≥1200 MPa |
| 655M13 / EN36A | 0.08–0.13 | 0.45–0.65 | 1.00–1.40 | 3.00–3.50 | 700–770 MPa |
| 815M17 / EN353 | 0.14–0.20 | 0.60–0.90 | 0.80–1.20 | 1.20–1.50 | ≥1200 MPa |
| 8620 / 20NiCrMo2-2 | 0.18–0.23 | 0.70–0.90 | 0.40–0.60 | 0.40–0.70 | 530 MPa |
| 9310 | 0.08–0.13 | 0.45–0.65 | 1.00–1.40 | 3.00–3.50 | 1289 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 |
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.
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Common questions
What is the equivalent of 4320 steel?
The nearest standard grades are SNCM420 in Japan and 20Ni7Cr2Mo2 in India. IS 1570 (Part 4) states the Indian grade is equivalent to AISI 4320. In Europe the nearest name is Ovako's 20NiCrMo7, with 17NiCrMo6-4 (1.6566) as a looser match.
What is the difference between 4320 and 8620?
Nickel. 4320 has 1.65–2.00% nickel and 0.45–0.65% manganese, while 8620 has 0.40–0.70% nickel. Both have about 0.20% carbon and are carburized; the extra nickel typically gives 4320 a stronger, tougher core in larger sections.
Is 4320 steel weldable?
AZoM describes the low-carbon grade as having good weldability. Welding after carburizing or hardening changes the case and core, so weld before heat treatment or qualify a procedure for the finished part.
What is 4320H?
4320H is 4320 supplied to a hardenability band, so Jominy end-quench hardness stays within limits. Ovako lists 4320H and 4320RH as similar designations to its 20NiCrMo7 bar.
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Related references
References
Sources
- Ovako Steel Navigator, 20NiCrMo7 (Ovako 157) — Composition of 157C/157D/157G, similar designations (ASTM 4320, 4320H, 4320RH), transformation temperatures, heat treatment, +QT typical values.
- AZoM, AISI 4320 Alloy Steel (UNS G43200) — Composition, annealed properties, machinability, heat treatment.
- 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.
- IS 1570 (Part 4):1988 Schedules for wrought steels, alloy steels (public copy) — Table 1 composition limits and the footnote cross-references to AISI and DIN grades.
- IS 4432:1988 Case hardening steels (public copy) — Table 1 composition, Table 5 case-hardening temperatures.
- Saarstahl, Werkstoff-Datenblatt 17NiCrMo6-4 / 18NiCrMo6-4 / 17NiCrMoS6-4 / 20NiCrMoS6-4 — EN 10084 composition of 17NiCrMo6-4.
Values summarize published limits and typical data. The governing standard and the current edition control; check them before specifying.