S45C Carbon Steel (JIS G4051): Material Data & Round Bar Supply
S45C is a medium carbon steel for machine structural use under Japan's JIS G 4051, with 0.42–0.48% carbon. It is equivalent to AISI 1045, EN C45 and GB 45 steel. It is usually used quenched and tempered (reference hardness HB 201–269) for shafts, gears and structural parts.
Overview
S45C is a medium carbon structural steel under JIS G 4051 with a carbon content of 0.42–0.48%, striking a balance between strength and machinability — tougher than low-carbon steel, yet easier to machine and weld than high-carbon grades. It is one of the most widely consumed carbon steel grades in the machining industry, found in shafts, gears, and mold bases — wherever quench-and-tempered components are needed.
Double Steel has specialized in bar steel for over 30 years. S45C is a permanent stock item, available immediately in straight bars and coils. Sourced from authorized Fengxing and Weizhi mills, with a mill certificate (MTC) provided for every shipment.
Chemical Composition (JIS G 4051)
| Element | Spec Range (%) |
|---|---|
| C (Carbon) | 0.42 – 0.48 |
| 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 |
Mechanical Properties After Heat Treatment (Reference)
| Condition | Tensile (MPa) | Yield (MPa) | Elongation (%) | Hardness (HB) |
|---|---|---|---|---|
| Annealed (≈ 810°C, furnace cool) | — | — | — | 137–170 |
| Normalized (820–870°C, air cool) | ≥ 570 | ≥ 345 | ≥ 20 | 167–229 |
| Q+T (quench 820–870°C water, temper 550–650°C) | ≥ 690 | ≥ 490 | ≥ 17 | 201–269 |
| After High-Frequency Hardening | — | — | — | HRC 52–58 (surface) |
Values above are the reference figures after heat treatment commonly used by Japanese steel suppliers, not guaranteed values for as-rolled bars. The current JIS G 4051 does not specify mechanical properties after heat treatment; actual results vary with cross-section size and heat treatment parameters. Q+T reference values also include reduction of area ≥ 45% and Charpy impact ≥ 78 J/cm². Hardness conversion (ASTM E140): HB 201 ≈ HRB 93, HB 229 ≈ HRC 20.5, HB 269 ≈ HRC 28. Contact Double Steel to arrange specific mechanical property testing if required.
For Q&T and induction hardness, HRC conversion and the effect of section size, see S45C Mechanical Properties: Strength, Hardness & Heat Treatment Data.
Heat Treatment Characteristics
Quench Hardening
Austenitizing temperature is typically 820–870°C, followed by water or oil quench. Note that plain carbon steels have limited hardenability — with water quenching, only sections up to about Ø25 mm harden through to the core, and on larger cross-sections, insufficient hardness at the core becomes noticeable. This is the key difference versus alloy steels such as SCM440.
Quench & Temper (Q+T)
Q+T (quench + high-temperature temper at 550–650°C) is the most common delivery condition for S45C. The goal is to balance hardness (reference HB 201–269, up to about HRC 28) with toughness, giving the part adequate fatigue strength under dynamic loading. Tempering should follow immediately after quench to avoid cracking — especially important for plain carbon steels.
High-Frequency Surface Hardening
For parts requiring a hard surface with a tough core — shafts, gears — high-frequency heating followed by localized quench can achieve HRC 52–58 at the surface (depending on process parameters) while preserving core toughness; quenching and tempering beforehand gives more uniform hardness and microstructure. This is one of S45C's key advantages in mechanical structural parts.
Normalizing
Normalizing (heat to 820–870°C, air cool) is used to relieve machining stresses and homogenize the microstructure as a pre-treatment before finish machining. Because S45C contains no Cr or Mo, it is not suitable for carburizing — parts requiring a carburized case should use SCM415 or SCM420.
International Standard Equivalents
| Standard | Equivalent Grade | Correspondence |
|---|---|---|
| JIS (Japan) | S45C (G 4051) | Reference standard |
| AISI/SAE (USA) | 1045 | Equivalent |
| DIN (Germany) | C45 / Ck45 | Equivalent |
| EN (Europe) | C45E (1.1191) | Equivalent |
| ISO | C45 (ISO 683-1) | Equivalent |
| GB (China) | #45 (45 Steel) | Equivalent |
| BS (UK) | 080M46 | Near equivalent |
Composition ranges differ slightly between standards: AISI/SAE 1045 is C 0.43–0.50%, Mn 0.60–0.90%, S ≤ 0.050%; EN C45 is C 0.42–0.50%, Si ≤ 0.40%, Mn 0.50–0.80%; GB/T 699 Grade 45 is C 0.42–0.50%, Si 0.17–0.37%, Mn 0.50–0.80%. Each standard also specifies acceptance criteria for mechanical properties differently. JIS G 4051 does not mandate mechanical property testing after heat treatment, whereas ISO 683-1 and EN standards require explicit tensile and impact test results. Contact Double Steel technical support to determine the correct delivery condition and documentation for your specific standard.
Typical Applications
Machine Tool Industry
Spindles, lead screws, worktables, and turret bases — structural parts demanding both rigidity and machining precision — heavily use quench-tempered S45C bar. High-frequency hardened S45C is also widely used for slideway mating surfaces.
Automotive & Motorcycle Parts
Camshafts, rocker arms, and steering knuckle arms under moderate loads use Q+T S45C in non-performance vehicle applications to reduce material cost.
Hand Tools
Wrench and plier handles and link structures use S45C to balance strength with cost.
Mechanical Components
Flanges, couplings, gears (low module, moderate load), piston rods, and mounting blocks — S45C is the default choice across this broad category.
Supply Specifications
| Form | Size Range | Source |
|---|---|---|
| Hot-rolled round bar | Ø 9 – 100 mm | Fengxing |
| Hot-rolled round bar | Ø 14 – 130 mm | CSC / Toufen |
| Hot-rolled round bar | Ø 25 – 250 mm | Import |
| Coil (wire rod) | Ø 13 – 50 mm | Fengxing / CSC |
| Ground bar | Ø 6 – 100 mm | — |
| Flat bar | W 12–205 mm × T 3–28 mm | — |
| Square bar | 9.5 – 52.5 mm | — |
Length 5–12 m; cut-to-length available on request. Non-standard sizes outside the above range can be sourced — please inquire. Every shipment includes a mill certificate (MTC) with full chemistry and heat number traceability.
Material Selection Guide
S45C is the go-to choice for medium-load mechanical structural parts where machinability matters and cost is a consideration. Its excellent machinability, well-established heat treatment process, and stable market supply make it the most common stock steel at Taiwanese machining shops.
SCM440 / SNCM439
Full cross-section uniform hardening and high strength-toughness combination needed
Alloying with Cr, Mo, and Ni dramatically improves hardenability. Q+T strength is significantly better than S45C. Also stocked by Double Steel.
Carburized surface case with tough core required
For heavy-load gears and pins requiring a carburized case, S45C's higher carbon content makes it unsuitable — switch to low-carbon alloy steels.
SS400
Primary process is welding with low strength requirements
SS400 offers better weldability at lower cost; there is no need to select S45C for weld-primary applications.
For technical consultation, sample quotations, or mill certificate review, contact the Double Steel sales team via the inquiry form below or LINE customer service. MOQ, port of loading and Incoterms are agreed case by case — tell us the grade, size, quantity and destination, and we will quote.
Related Grades
For cross-standard composition and mechanical property tables, see the technical reference tables.
FAQ
- What is S45C steel?
- S45C is a medium carbon steel for machine structural use specified in Japan's JIS G 4051, with 0.42–0.48% carbon. It is stronger than low-carbon steel, easier to machine than high-carbon grades, and is usually used in the quenched and tempered condition.
- Is S45C the same as AISI 1045 or C45?
- S45C (JIS G 4051) is generally regarded as equivalent to AISI/SAE 1045, DIN/EN C45 (C45E, 1.1191) and GB 45 steel, but the composition ranges differ slightly: 1045 is C 0.43–0.50%; C45 and GB 45 are C 0.42–0.50% with Mn 0.50–0.80%. Where certification to a specific standard is required, follow the standard named on the drawing.
- What is the chemical composition of S45C?
- JIS G 4051 specifies C 0.42–0.48%, Si 0.15–0.35%, Mn 0.60–0.90%, P ≤ 0.030%, S ≤ 0.035%, with Ni ≤ 0.20%, Cr ≤ 0.20%, Cu ≤ 0.30% and Ni+Cr ≤ 0.35%.
- What is the hardness of S45C (HB / HRC)?
- It depends on heat treatment (reference values): annealed HB 137–170, normalized HB 167–229, quenched and tempered HB 201–269 (up to about HRC 28); induction hardening can reach HRC 52–58 at the surface. Hardness is not guaranteed on as-rolled bars.
- What is the density of S45C?
- The density of S45C is approximately 7.85 g/cm³.
- What does S45C-D mean?
- S45C-D is a JIS G 3123 cold-finished bar designation. D stands for cold drawn; G is ground and T is turned. Heat treatment symbols are N (normalized), Q (quenched and tempered) and A (annealed). The JIS example "S45C-DQG7" means cold drawn, quenched and tempered, then ground to tolerance grade IT7.
- What applications is S45C suitable for?
- Shafts, gears, bolts, and mechanical structural parts. Particularly suited for quench-and-tempered components and high-frequency surface hardening applications.
- Can S45C be carburized?
- Not recommended. S45C's carbon content is too high for carburizing. Select SCM415 or SCM420 for carburized case applications.
- S45C vs SCM440: which should I choose?
- S45C contains no Cr or Mo, giving it limited hardenability and shallow hardening depth after quenching. SCM440, with chromium (0.90–1.20%) and molybdenum (0.15–0.30%), has far superior hardenability — delivering uniform strength and toughness across the full cross-section. Choose SCM440 for larger sections or where full-section hardening is required.
- What S45C sizes does Double Steel supply? Can bars be cut to length?
- Hot-rolled round bar Ø 9–250 mm, coil (wire rod) Ø 13–50 mm and ground bar Ø 6–100 mm, plus flat and square bar. Lengths are 5–12 m and bars can be cut to length; a mill certificate is supplied with every shipment.
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