Steel C55
EN C55 · AISI/SAE 1055 · JIS S55C · GB 55
C55 is a higher medium-carbon non-alloy steel (~0.55 % C) to EN 10083 / 1.0535, with equivalents C55E, 1055, S55C and Ck55, and it responds strongly to hardening in thin and medium sections.
Reference datasheet — C55 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the +N condition
C55 tempers and conditions
C55 is supplied in 10 conditions, soft to hard. +N is the default FabDigit quotes; the values on this page are for it.
Compare all 10 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Annealed | Pick for maximum machinability, cold forming or deep drilling before final hardening. | 350 | 640 | 21 | 195 HB | — |
+NDefault Normalized | Standard stock/reference condition (≈820–860 °C air cool): uniform fine pearlitic structure and the property basis of GB/T 699 and EN 10083-2. | 400 | 750 | 16 | 220 HB | — |
Hot rolled | Cheapest stock condition for parts that will be re-heat-treated after machining or roughing. | 420 | 780 | 14 | 225 HB | — |
+QT | Use for larger diameters where hardenability limits the achievable core strength. | 430 | 770 | 17 | 21 HRC | 8.4 % IACS |
Quenched and tempered | General-purpose toughened condition (≈830 °C quench, 550–660 °C temper) for shafts, cams and gears. | 550 | 870 | 15 | 26 HRC | — |
Induction hardened | Best choice for wear surfaces on shafts, rolls and guideways where a tough core is still required. | 550 | 870 | 12 | 57 HRC | 8.4 % IACS |
Cold drawn | Choose for close-tolerance bright bar and higher as-supplied yield strength without heat treatment. | 650 | 830 | 9 | 24 HRC | — |
high-temper toughened condition | Order when the drawing calls out a through-hardness band for machined shafts and gear blanks. | 700 | 960 | 14 | 30 HRC | — |
low-temper wear condition | For cams, wear plates, blades and flat springs needing hardness with some residual toughness. | 1,150 | 1,350 | 9 | 43 HRC | — |
Hardened, as-quenched | Intermediate state only — maximum hardness but brittle; always temper before service. | 1,600 | 2,000 | 1 | 62 HRC | 7.2 % IACS |
Supply forms, finishes and certifications
Ways C55 is supplied — form, process route, surface or paperwork — without a datasheet of their own. The property values above apply.
| Option | What it is | Type |
|---|---|---|
CR-STRIP | Cold rolled strip, hard | Supply form |
HT-STRIP | Hardened & tempered strip | Supply form |
What is C55?
C55 is a higher medium-carbon non-alloy steel (~0.55 % C) to EN 10083 / 1.0535, with equivalents C55E, 1055, S55C and Ck55, and it responds strongly to hardening in thin and medium sections. It is used for tools, flat springs and wear parts that need more strength and hardness than C50, and is supplied as hot-rolled bar, cold-rolled and hardened strip, and forged discs — default values are 400 MPa yield, 750 MPa tensile, 16 % elongation and 220 HB, with service to about 400 °C. Weldability is poor (CE ≈ 0.7), ductility and machinability are the lowest in the C40–C55 range (machinability score 45), and there is no corrosion resistance. C50 is the easier-processing alternative; 51CrV4 suits more demanding spring duty. C55 has a density of 7.84 g/cm³ (0.283 lb/in³), lighter than 78% of steel grades. It melts at 1,420°C (2,588 °F). C55 has a yield strength of 400 MPa (58 ksi) and a tensile strength of 750 MPa (109 ksi) — weaker than 60% of steel grades. Elongation at break is 16% and the elastic modulus is 210 GPa (30.5 Msi).
What is C55 used for?
- hand tools
- flat springs
- wear plates
- agricultural blades
- forged discs
Advantages
- Low embodied carbon — 1.9 kg CO₂/kg, better than 92% of steel grades
Limitations
- Low fracture toughness — 55 MPa·√m (50.1 ksi·√in), worse than 82% of steel grades
C55 properties
Typical room-temperature values for C55-+N; bars are the position among steel grades.
Physical3
C55 has a density of 7.84 g/cm³ (0.283 lb/in³), lighter than 78% of steel grades. It melts at 1,420°C (2,588 °F).
Mechanical16
C55 has a yield strength of 400 MPa (58 ksi) and a tensile strength of 750 MPa (109 ksi) — weaker than 60% of steel grades. Elongation at break is 16% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
C55 is rated for continuous service to 400°C (752 °F). It conducts heat at 47 W/m·K (27.2 BTU/hr·ft·°F), better than 75% of steel grades. Thermal expansion is 11.4 µm/m·K (6.33 µin/in·°F).
Electrical3
C55 conducts electricity at 8.6 % IACS, better than 66% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (10/100), worse than 86% of steel grades.
Sustainability4
Producing a kilogram of C55 takes about 25 MJ of energy and emits 1.9 kg of CO₂ — less than 82% of steel grades. Typical recycled content is 30%.
Manufacturability7
C55's machinability is fair (45/100, worse than 65% of steel grades); weldability poor (30/100); formability poor (30/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. C55 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with C55
Is C55 easy to machine?
Machine in the annealed or normalized state with rigid setups, carbide tooling and 80–150 m/min; above ~35 HRC switch to CBN/ceramic or grind.
Can C55 be welded?
Poor weldability (CE ≈ 0.7) — preheat 250–350 °C, low-hydrogen consumables, interpass control and immediate stress-relief/temper at 600–650 °C to avoid HAZ cracking.
Can C55 be formed, bent or molded?
Cold forming only in the spheroidize-annealed condition with generous bend radii (≥2t); hot forge 1100–850 °C followed by controlled cooling or normalizing.
C55 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| CEN 10083-2 C55 / GB/T 699 55 | 0.52 – 0.6 | 0.55 |
| Si | ≤ 0.4 | 0.25 |
| Mn | 0.6 – 0.9 | 0.75 |
| PC55E ≤0.030 | ≤ 0.05 | |
| SC55E ≤0.035; C55R 0.020–0.040 | ≤ 0.05 | |
| Crresidual | ≤ 0.4 | |
| Niresidual | ≤ 0.4 | |
| Moresidual | ≤ 0.1 | |
| Cr+Mo+Nisum limit, EN 10083-2 | ≤ 0.63 | |
| CuGB/T 699 residual limit | ≤ 0.25 | |
| Fe | balance |
What surface finishes work on C55?
No corrosion resistance — protect with oil, phosphate, black oxide, zinc/nickel plating or paint; grinds and polishes well when hardened.
Surface treatments FabDigit runs on steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Organic Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel C55 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
How much does C55 cost?
C55 is a budget-cost steel ($), cheaper than about 90% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
C55 — frequently asked
What is C55 used for?
C55 is typically used for hand tools, flat springs, wear plates, agricultural blades and forged discs. In short: hardest of the C-series; spring and wear-part steel; poor weldability, high hardness.
What is the yield strength of C55?
C55 has a typical yield strength of 400 MPa (58 ksi) and a tensile strength of 750 MPa (109 ksi) — weaker than 60% of steel grades. Strength varies by condition: see the 10 listed tempers.
Is C55 easy to machine?
Reasonably — machinability is rated fair (45/100, worse than 65% of steel grades). Machine in the annealed or normalized state with rigid setups, carbide tooling and 80–150 m/min; above ~35 HRC switch to CBN/ceramic or grind.
Can C55 be welded?
Not readily — weldability is rated poor (30/100). Poor weldability (CE ≈ 0.7) — preheat 250–350 °C, low-hydrogen consumables, interpass control and immediate stress-relief/temper at 600–650 °C to avoid HAZ cracking.
What surface finishes work on C55?
No corrosion resistance — protect with oil, phosphate, black oxide, zinc/nickel plating or paint; grinds and polishes well when hardened.
Can C55 be formed, bent or molded?
Cold forming only in the spheroidize-annealed condition with generous bend radii (≥2t); hot forge 1100–850 °C followed by controlled cooling or normalizing.
What is the maximum service temperature of C55?
C55 is rated for continuous use to about 400°C (752 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between C55 +N and C55-IH?
+N is the default condition — standard stock/reference condition (≈820–860 °C air cool): uniform fine pearlitic structure and the property basis of GB/T 699 and EN 10083-2. IH: best choice for wear surfaces on shafts, rolls and guideways where a tough core is still required. Yield strength is 400 MPa in +N versus 550 MPa in IH.
How much does C55 cost?
C55 is a budget-cost steel ($), cheaper than about 90% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- EN 10083-2 Steels for quenching and tempering — Non-alloy steels — CEN (2006)
- EN 10132-4 Cold rolled narrow steel strip — spring and hardenable steels — CEN (2000)
- ASTM A29/A29M & SAE J403 (AISI 1055) — ASTM / SAE (2020)
- JIS G 4051 (S55C) — JSA (2016)
- ASM Handbook Vol.1 Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.4 Heat Treating / Vol.16 Machining — ASM International (1991)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.