8550 steel – 34CrAlNi7-10 (W.Nr. 1.8550)
Cr-Al-Ni-Mo nitriding steel
Cr-Al-Ni-Mo nitriding steel, known in Brazil as "8550" after the German material number 1.8550 (it is not an SAE grade). Aluminum forms very hard nitrides, giving a nitrided surface ≥ 950 HV, and nickel ensures core hardenability and toughness in large sections. Supplied annealed or quenched and tempered, and nitrided after machining.
Designations and equivalents
| System | Designation |
|---|---|
| UNS | No UNS (no equivalent SAE/AISI grade) |
| W.Nr./EN | 1.8550 – 34CrAlNi7-10 (EN ISO 683-5, formerly EN 10085) |
| DIN | 34CrAlNi7 (DIN 17211, old) |
| JIS | ≈ SACM645 (no Ni, approximate) |
| Trade names | Nitrodur 8550, VN 8550 and similar |
| Others | Closest in the USA: Nitralloy 135M / AISI 7140 (41CrAlMo7-10, 1.8509), without Ni |
Standards by product form
| Form | Standard |
|---|---|
| Bar | EN ISO 683-5 (34CrAlNi7-10) |
| Forging | EN ISO 683-5 / EN 10250-3 (open-die forgings) to specification |
| Bar (old) | DIN 17211 |
| Nitriding | Specify surface hardness and depth (e.g. ≥ 950 HV, Nht 0.3–0.6 mm) |
Tolerances and HS codes
- Forged bars (round and square): machining allowance from 2 mm (Ø 6–16 mm) to 24 mm (Ø 400–500 mm) on the diameter. E.g. Ø 100–125 mm finished: +7 mm, tolerance +6 / −0 (length up to 3,500 mm).
- Forged discs: allowance of 4 to 9 mm on the diameter and 3 to 11 mm on the height, plus-only tolerance.
- Cutting and machining: band saw −0 / +5 to +15 mm on length; waterjet +10 % of thickness on the diameter (min. 2 mm); machined parts −0 / +2 to +5 mm on the diameter. See the full tables (INF 002 and INF 003, the same for every alloy).
| Form | NCM (Brazil, 8 digits) | HS (international, 6 digits) | HTS (USA, 10 digits)* | CN (European Union, 8 digits)* |
|---|---|---|---|---|
| Forged bar | 7228.40.00 | 7228.40 | 7228.40.0000 | 7228 40 90 |
| Hot-rolled bar | 7228.30.00 | 7228.30 | 7228.30.8041 | 7228 30 61 |
| Flange and fitting | 7307.91.00 | 7307.91 | 7307.91.5030 | 7307 91 00 |
Tariff class: alloy steel (by chemical composition, under the Chapter 72 Notes and Section XV Note 5).
*: US and EU codes for reference. NCM per current legislation (General Rules of Interpretation, Notes to Chapters 72, 74 and 75 and Section XV Note 5). Confirm the final code with your customs broker according to the item size and finish. HS = first 6 digits of the NCM.
Chemical composition (%)
EN ISO 683-5 / EN 10085
| Element | Range (%) |
|---|---|
| C | 0.30 – 0.37 |
| Si | ≤ 0.40 |
| Mn | 0.40 – 0.70 |
| P | ≤ 0.025 |
| S | ≤ 0.035 |
| Cr | 1.50 – 1.80 |
| Mo | 0.15 – 0.25 |
| Ni | 0.85 – 1.15 |
| Al | 0.80 – 1.20 |
Mechanical properties
Quenched and tempered (+QT), section Ø 40–100 mm – EN ISO 683-5
| Property | Value |
|---|---|
| Yield strength | ≥ 650 MPa |
| Tensile strength | 850 – 1,050 MPa |
| Elongation | ≥ 12% |
| Charpy V (20 °C) | ≥ 30 J |
| Hardness, annealed (+A) | ≤ 248 HB |
| Nitrided surface hardness | ≥ 950 HV |
Typical physical properties
| Property | Value |
|---|---|
| Modulus of elasticity | ≈ 210 GPa (typical) |
| Thermal conductivity (20 °C) | 33.7 W/m·K |
| Thermal expansion (20–100 °C) | 12.1 µm/m·K |
| Thermal expansion (20–400 °C) | 13.7 µm/m·K |
Heat treatment, welding and machining
| Item | Usual practice |
|---|---|
| Service temperature | Up to ≈ 450–500 °C; the nitrided case keeps its hardness up to near the nitriding temperature. |
| Heat treatment | Annealing 650–700 °C, furnace cool. Normalizing 860–900 °C. Quenching 870–930 °C in oil, gas or salt bath; tempering 580–700 °C (always above the nitriding temperature). Gas or plasma nitriding ≈ 500–530 °C; stress relief before finishing to minimize distortion. |
| Welding | Not recommended (high Al and CE, risk of cracking and loss of nitridability). If unavoidable, preheat 300–350 °C, low-H consumable such as AWS E9018-B3 and temper after welding; never weld over a nitrided case. |
| Machining | Good in the annealed condition; in the quenched and tempered condition (≈ 250–320 HB) machinable with carbide; grind before nitriding. |
Filler metal for welding
The wire composition is usually not identical to the material: each page explains why.
Typical applications
- Screws and barrels for plastic injection and extrusion machines
- Piston rods and plungers
- Nitrided shafts and spindles
- Nitrided gears and pinions
- Cams, eccentrics and guides
- Valve and pump components subject to wear
Alternatives: 41CrAlMo7-10 (1.8509, Nitralloy 135M) for smaller sections; 31CrMoV9 (1.8519) for better case toughness; nitrided 4140 when ≈ 550–650 HV is enough; nitrided stainless or bimetallic when corrosion is present.
Frequently asked questions
What is the chemical composition of 8550 steel?
Per EN ISO 683-5 / EN 10085: C 0.30 – 0.37; Si ≤ 0.40; Mn 0.40 – 0.70; P ≤ 0.025; S ≤ 0.035; Cr 1.50 – 1.80.
Which standards cover 8550 steel?
Bar: EN ISO 683-5 (34CrAlNi7-10). Forging: EN ISO 683-5 / EN 10250-3 (open-die forgings) to specification. Bar (old): DIN 17211. Nitriding: Specify surface hardness and depth (e.g. ≥ 950 HV, Nht 0.3–0.6 mm).
Up to what temperature can 8550 steel be used?
Up to ≈ 450–500 °C; the nitrided case keeps its hardness up to near the nitriding temperature.
Which materials can replace 8550 steel?
41CrAlMo7-10 (1.8509, Nitralloy 135M) for smaller sections; 31CrMoV9 (1.8519) for better case toughness; nitrided 4140 when ≈ 550–650 HV is enough; nitrided stainless or bimetallic when corrosion is present.
