S55C
High-Carbon Structural Steel
Overview
S55C is a high-carbon structural steel under JIS G 4051 with a carbon content of 0.52–0.58%, placing it at the high-carbon end of the carbon steel series. Compared with the widely used S45C, S55C carries roughly 10% more carbon, enabling higher surface hardness after quenching and greater strength in the normalized or quench-and-tempered condition. This makes S55C the go-to intermediate choice when higher hardness and wear resistance are required beyond S45C — without resorting to the complex heat treatment of alloy steels. Typical uses include springs, blades, forged hand tools, and mechanical parts.
Double Steel stocks S55C hot-rolled round bars as a permanent inventory item, sourced from CSC, Fengxing, and Weizhi mills. Every shipment includes a mill certificate (MTC) with full chemistry traceability to the specification.
Chemical Composition (JIS G 4051)
| Element | Spec Range (%) |
|---|---|
| C (Carbon) | 0.52 – 0.58 |
| Si (Silicon) | 0.15 – 0.35 |
| Mn (Manganese) | 0.60 – 0.90 |
| P (Phosphorus) | ≤ 0.030 |
| S (Sulfur) | ≤ 0.035 |
| Ni (Nickel) | ≤ 0.20 |
| Cr (Chromium) | ≤ 0.20 |
| Cu (Copper) | ≤ 0.30 |
| Ni + Cr | ≤ 0.35 |
Note: Ni and Cr limits are maximum residual values, not intentionally added elements.
Mechanical Properties (Industry Reference Values)
| Condition | Tensile (MPa) | Yield (MPa) | Elongation (%) | Hardness |
|---|---|---|---|---|
| Hot-rolled (as-rolled) | ≈ 650–750 | ≈ 380–450 | ≈ 15–20 | ≈ 180–220 HB |
| Normalizing | ≈ 700–800 | ≈ 420–490 | ≈ 13–18 | ≈ 200–240 HB |
| Q&T (Tempered at 550–600°C) | ≈ 800–950 | ≈ 630–750 | ≈ 12–16 | ≈ 230–280 HB |
| As-quenched (full hardened) | — | — | — | ≈ HRC 60–63 |
JIS G 4051 does not specify mandatory mechanical properties after heat treatment. Values above are industry reference figures; actual results vary with cross-section size and heat treatment parameters.
Heat Treatment Characteristics
Quench Hardening
Recommended austenitizing temperature is 800–840°C, followed by water or oil quench. Water quench achieves higher surface hardness (HRC 60+) but raises cracking risk on large cross-sections; oil quench cools more gradually and suits complex geometries. S55C is a shallow-hardening carbon steel — on larger sections, core hardness drops noticeably. For through-hardened sections, consider switching to alloy steel such as SCM440.
Tempering
Tempering must follow quench immediately to relieve brittleness. Low-temperature tempering at 150–200°C preserves high hardness (HRC 55–60); medium-to-high tempering at 400–600°C trades hardness for toughness (HRC 30–45). The tempering temperature directly determines whether the part fails by wear or fracture in service.
Normalizing
Heating to 840–880°C followed by air cooling refines grain size, relieves forging residuals, and achieves higher strength than annealing. Used as a pre-machining treatment to homogenize the microstructure.
Induction Hardening
S55C is an ideal material for induction hardening. Its high carbon content allows rapid austenitizing under induction heating, forming a hard surface layer while leaving the core tough — achieving hard-outside, tough-inside performance. Widely used for gears, camshafts, and guideways requiring localized wear resistance. S55C is not suitable for carburizing — its carbon content far exceeds carburizing targets.
International Standard Equivalents
| Standard | Equivalent Grade | Correspondence |
|---|---|---|
| JIS (Japan) | S55C (JIS G 4051) | Reference standard |
| AISI/SAE (USA) | 1055 | Full equivalent |
| ISO | C55, C55E4, C55M2 | Full equivalent |
| DIN/EN (Germany/EU) | C55, C55R (EN 10083-1,2) | Full equivalent |
| BS (UK) | 070M55 | Near equivalent |
| GB (China) | 55 (GB/T 699) | Full equivalent |
DIN and EN entries reference the same standard family (EN 10083-1 supersedes the old DIN 17200) and are listed as one row. BS 070M55 has a slightly different Mn upper limit — verify chemistry on a case-by-case basis before substituting.
Typical Applications
Hand Tools & Agricultural Blades
Wrenches, chisels, agricultural blades, and rakes — hand tools demanding hardness and wear resistance — are S55C's most concentrated use case. Forged and then quench-tempered, the surface hardness meets service requirements at lower cost than alloy steel.
Mechanical Components
Guideways, cam plates, slides, and fixture bases requiring localized wear resistance. Induction hardening can selectively strengthen specific zones while the remainder retains good machinability.
Springs & Elastic Elements
Non-standard spring blades and simple disc springs, particularly in cost-sensitive applications with relatively simple geometry. High-performance springs typically use the SUP series instead.
Machine Tool Parts
Guideway reinforcement bars and wear pads — secondary wear parts — can be locally induction-hardened to extend service life.
Hammer-Type Hand Tools: S55C Is the Industry Standard
Taiwan is a major global exporter of hand tools. Hammer-type products — steel-head hammers, engineer hammers, joiner's hammers, flooring hammers, mason's hammers, riveting hammers, magnetic hammers, and rubber-mallet steel heads — are almost universally made from S55C forging stock.
The Impact Load Profile Dictates the Material Choice
A hammer head is subject to impact loading, not static pressure. Each strike concentrates high stress at the hammer face; the eye bears bending moments; glancing blows subject the side to lateral impact. S55C's carbon content of 0.52–0.58% allows the hammer face to reach HRC 55–60 after quenching, then be tempered back to HRC 45–52 while the core retains toughness — both requirements met in one grade. Switching to higher-carbon S58C or SK tool steels raises hardness further but increases fracture risk under repeated impact, which conflicts with hand tool safety standards.
S55C Behavior in the Forging Process
Forging shops in central Taiwan typically produce hammer heads by hot forging. S55C round bars flow well at 1100–1200°C, fill dies better than low-carbon steel, and show pronounced grain refinement after forging. Its forgeability is comparable to S45C, but the hardening potential is substantially higher — the core reason forging shops prefer S55C over S45C. Post-forge normalizing at 840–880°C relieves residual stresses and homogenizes the microstructure, preparing for downstream differential heat treatment.
Heat Treatment Strategies by Hammer Type
| Hammer Type | Typical Heat Treatment | Face Target Hardness | Notes |
|---|---|---|---|
| Engineer Hammer | Q&T + localized induction hardening | HRC 45–52 | Balances strength and impact resistance |
| Mason's Hammer | Q&T or normalizing | HRC 35–45 | Side impact dominant; toughness priority |
| Joiner's Hammer | Q&T | HRC 40–48 | Maximum face hardness not required |
| Ball Peen Hammer | Full quench + temper | HRC 45–55 | Both face and ball end require high hardness |
| Flooring Hammer | Localized induction hardening | HRC 48–55 | Selective contact-surface hardening |
Procurement Note: Chemistry Consistency and Hand Tool Quality
OEM/ODM hand tool exporters typically require forging suppliers to provide a mill certificate (MTC) for every batch to verify carbon content within spec. S55C's carbon range spans only 0.06% (0.52–0.58%) — low-end heats produce under-hardened hammer faces; high-end heats raise fracture risk. Double Steel's S55C is sourced from Fengxing and Weizhi, the primary Taiwanese bar steel mills, with MTCs meeting JIS G 4051 — directly usable for quality traceability documentation.
Supply Specifications
| Item | Details |
|---|---|
| Form | Hot-rolled round bar (black skin), primary stock |
| Size range | Ø13 – Ø100 mm |
| Source | CSC, Fengxing, Weizhi |
| Documentation | Mill certificate (MTC) included with every shipment |
Non-standard sizes outside the above range can be sourced on request. Every shipment includes a mill certificate with full chemistry and heat number traceability.
Material Selection Guide
S55C occupies the "high-carbon, high-hardness, low-cost" position in the carbon steel lineup. Its selection logic is to fill the gap between S45C and alloy steels — harder than S45C without the complex heat treatment overhead of alloy grades. Key limitation: S55C has relatively poor weldability (high carbon equivalent). Preheat before welding, slow-cool after — not recommended for welded structures. On larger cross-sections, water-quench cracking risk rises significantly; confirm hardenability feasibility at the design stage.
S45C
General hardness requirements; machinability or weldability is priority
S45C is more versatile with better weldability and machinability. Maximum hardness after quench is approximately HRC 55–57 — about 5 HRC units below S55C. Choose S55C when higher hardness or improved wear life is explicitly required.
SCM440
Through-hardening across full cross-section or large bar diameter
SCM440's Cr–Mo alloy additions dramatically improve hardenability, making it suitable for large cross-sections requiring uniform through-hardness. S55C offers a clear cost advantage where only surface hardening is needed.
SUP Series (SUP6, SUP9)
High-performance springs or high-cycle fatigue applications
Spring steel specifications impose stricter chemistry uniformity and surface quality requirements. SUP grades contain Si and Mn for spring-specific strengthening. S55C suits simple low-end spring blades; high-end springs should use the SUP series.
For technical consultation, sample quotations, or mill certificate review, contact the Double Steel sales team via the inquiry form below or LINE customer service.