C15 steel (1.0401): properties, composition, equivalents
C15 (1.0401) / C15E (1.1141, ex Ck15) is the plain 0.15 % carbon case-hardening steel of EN 10084: carburized surface 55–62 HRC, core 440–590 MPa. Composition, heat treatment, 1015/S15C/15# equivalents.
What is C15?
C15 is the simplest case-hardening steel: 0.12–0.18 % carbon, no alloying, Werkstoff number 1.0401 for the base quality and 1.1141 for C15E (the old Ck15, with lower phosphorus and fine-grain practice) — both in EN 10084. Carburizing puts 0.7–0.9 % carbon into the surface, which quenches to 55–62 HRC over a soft, tough core of about 500–600 MPa. Hardenability is very low, so the hard case is thin and the part must be small: pins, bushes, small gears, rollers, levers and cold-headed fasteners.
C15 also serves outside case hardening as a general low-carbon engineering bar — the European version of AISI 1015/1018 — for machined parts, welded fittings and cold-drawn shafting where a bright, dimensionally accurate bar is needed and strength is not critical. Cold drawing raises its yield to around 450 MPa.
AISI 1015, JIS S15C and GB/GOST 15 are identical in composition; 1018 is the near match most US warehouses supply. For larger case-hardened parts the step up is 16MnCr5.
C15 chemical composition
| Element | Mass % | Note |
|---|---|---|
| C | 0.12 – 0.18 | |
| Si | ≤ 0.4 | |
| Mn | 0.3 – 0.6 | |
| P | ≤ 0.045 | C15E (1.1141): P ≤ 0.035; C15R (1.1140): S 0.020–0.040 |
| S | ≤ 0.045 | |
| Cr | ≤ 0.4 | C15E/C15R: Cr + Mo + Ni ≤ 0.63 |
| Mo | ≤ 0.1 | |
| Ni | ≤ 0.4 |
EN 10084:2008 Table 3 (C15E/C15R) and EN 10083-2 for C15 as a general-use grade. C10E (1.1121, ex Ck10) is the 0.07–0.13 % C sibling; C16E (1.1148) the 0.12–0.18 % fine-grain variant.
C15 mechanical properties
| Thickness / condition | Yield strength ReH / Rp0.2 MPa (ksi) | Tensile strength Rm MPa (ksi) | Elongation A % | Hardness |
|---|---|---|---|---|
| Core after carburize, harden & temper, 11 mm ref. bar (C15E) | ≥ 355 (≥ 51.5) | 590–780 (85.6–113.1) | 12 | — |
| Core, 30 mm ref. bar | ≥ 295 (≥ 42.8) | 490–640 (71.1–92.8) | 14 | — |
| Surface after carburizing | — | — | — | 55–62 HRC |
| +N normalized (typical bar) | ≥ 260 (typ. 280–320) (≥ 37.7 (typ. 40.6–46.4)) | ≥ 430 (typ. 450–520) (≥ 62.4 (typ. 65.3–75.4)) | 27 | ≈ 130–160 HB |
| +A / +AC annealed (delivery) | — | — | — | ≤ 143 HB |
| Cold-drawn +C (typical, ≤ 16 mm) | ≥ 450 (≥ 65.3) | 600–750 (87.0–108.8) | 8 | ≈ 180–220 HB |
Core values from EN 10084 Annex F (informative, blank-hardened reference bars). Normalized and cold-drawn values are typical supplier data; EN 10084 specifies only chemistry and delivery hardness.
C15 equivalent grades
| Grade | System | Match | Why / differences |
|---|---|---|---|
| 1015 | AISI / SAE | Identical | AISI/SAE 1015 (G10150): C 0.13–0.18, Mn 0.30–0.60 — same window as C15. 1016/1018 have higher Mn (0.60–0.90) for slightly better hardenability. |
| 080M15 | BS (superseded British) | Identical | BS 970 080M15: C 0.13–0.18, Mn 0.70–1.00 (Mn higher). |
| 15 | GB/T (China) | Identical | GB/T 699 grade 15 (15#): C 0.12–0.18, Mn 0.35–0.65. |
| 15 / 15kp | GOST (Russia/CIS) | Identical | GOST 1050 Steel 15: C 0.12–0.19, Mn 0.35–0.65. |
| S15C / S15CK | JIS (Japan) | Identical | JIS G4051 S15C: C 0.13–0.18, Mn 0.30–0.60; S15CK is the case-hardening quality (P/S ≤ 0.025). |
| 1018 | AISI / SAE | Near | C 0.15–0.20, Mn 0.60–0.90; the US stock grade most often supplied against a C15 request. |
| C10E | EN (European) | Near | 1.1121 (ex Ck10): C 0.07–0.13 — softer core, better cold-heading. |
| C10 | EN (European) | Near | Next carbon step (0.12–0.18 %) with slightly stronger core. |
| 16MnCr5 | EN (European) | Functional | Alloyed case-hardening steel for larger sections and higher core strength. |
| S235JR | EN (European) | Functional | Structural steel of similar carbon; not a case-hardening quality (no hardenability or cleanliness control). |
Identical = same composition and mechanical limits within rounding. Near = one limit differs (e.g. carbon max or impact temperature). Functional = interchangeable for most uses after an engineering check. Full cross-reference for C15 →
Old and superseded designations
| Old name | Standard | Note |
|---|---|---|
| Ck15 | DIN 17210 (withdrawn) | = C15E (1.1141). The common German workshop name. |
| C15 (1.0401) | DIN 17210 / DIN 17200 | Base quality, unchanged number. |
| Cm15 | DIN 17210 | = C15R (controlled S). |
| 080M15 / 080A15 | BS 970 | |
| XC15 / XC18 | NF A 35-551 |
Product forms and tolerance standards
Product forms: round, square and hexagon bar (hot-rolled, bright), wire rod and cold-heading wire, forgings, seamless tube (EN 10305 as E155/C15), strip (EN 10132-2 as C15S).
Dimensional tolerances: hot-rolled bar: EN 10060; bright bar: EN 10278; wire: EN 10218.
Key property values
C15 core and surface hardness
Carburized case 55–62 HRC at 0.3–1.0 mm case depth; core ≈ 15–25 HRC (590–780 MPa in an 11 mm bar, 490–640 MPa at 30 mm). Delivery hardness (+A) ≤ 143 HB.
C15 yield and tensile strength (uncarburized)
Normalized: yield ≈ 280–320 MPa, tensile 450–520 MPa, elongation ≈ 27 %. Cold-drawn (+C) small bar: yield ≥ 450 MPa, tensile 600–750 MPa, elongation ≈ 8 %.
Heat treatment
Carburize 880–980 °C (pack, gas or salt); direct quench in water (small parts) or oil from 850–880 °C; core-refine 880–920 °C; temper 150–200 °C. Normalize 880–920 °C. Ac1 ≈ 725 °C, Ac3 ≈ 860 °C.
Hardenability
Very low (no Jominy band specified). Case hardness falls off below the surface rapidly; not suitable for parts over ~20 mm needing a deep case — use 16MnCr5 or 20MnCr5.
Physical properties
Density 7.85 g/cm³, E = 210 GPa, conductivity ≈ 50 W/m·K, expansion 11.9 × 10⁻⁶/K.
Weldability
Excellent weldability in the uncarburized state (CEV ≈ 0.20 %): all arc and resistance processes without preheat. Carburized surfaces should not be welded (cracking); mask or machine off the case first.
Machining, forming and heat treatment
Machinability ≈ 65–70 % (gummy in the annealed state; better after cold drawing or normalizing). C15R with controlled sulphur is preferred for automatic lathes. Cold heading, cold extrusion and bending are excellent (this is a classic cold-heading grade as C15E/C10E). Hot forging 1150–900 °C.
Typical applications
- Small case-hardened parts: pins, bushes, rollers, cam followers, small gears and sprockets
- Cold-headed screws, rivets and studs (often as C10E/C15E)
- Bright-drawn shafting and machined general-purpose parts (as 1.0401)
- Levers, links, spacers and washers
- Welded fittings and low-stress tube parts
- Chain components (roller chain bushes and pins after carburizing)
Frequently asked questions
What is the difference between C15 and C15E?
C15E (1.1141, ex Ck15) is the case-hardening quality: P ≤ 0.035 %, fine-grain (Al-treated) practice, guaranteed hardenability response. C15 (1.0401) is the base quality with P/S ≤ 0.045 % for general engineering use.
Is C15 the same as 1018?
Close but not identical: 1018 has C 0.15–0.20 and Mn 0.60–0.90, slightly richer than C15 (C 0.12–0.18, Mn 0.30–0.60). AISI 1015 is the exact match. 1018 is what most US suppliers deliver against a C15 order and it works in practice.
How hard can C15 get?
Only through carburizing: 55–62 HRC on the surface with a shallow case. Without carburizing it cannot be usefully hardened (as-quenched ≈ 35–40 HRC in very thin sections).
What is C15 equivalent to in JIS and GB?
JIS S15C / S15CK and GB/T 699 grade 15 — identical carbon and manganese windows.
Related grades
Verified against EN 10084:2008; EN 10084:2008 Tables 3, 6 and Annex F; EN 10083-2:2006 (C15 as general grade). Last checked: September 2026.