S45C
Medium Carbon Steel
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) |
|---|---|---|---|---|
| Normalizing | ≈ 700 | ≈ 400 | ≥ 20 | ≈ 200 |
| Q+T (Tempered at 550°C) | ≈ 800–950 | ≈ 650–800 | ≥ 15 | ≈ 230–280 |
| After High-Frequency Hardening | — | — | — | 54–58 HRC (surface) |
Values above are reference figures after heat treatment. Actual results vary with cross-section size and heat treatment parameters. Contact Double Steel to arrange specific mechanical property testing if required.
Heat Treatment Characteristics
Quench Hardening
Austenitizing temperature is typically 820–860°C, followed by water or oil quench. Note that plain carbon steels have limited hardenability — 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 (HB 230–280) 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 54–58 HRC at the surface while preserving core toughness. This is one of S45C's key advantages in mechanical structural parts.
Normalizing
Normalizing (heat to 800–880°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 | Full equivalent |
| DIN (Germany) | C45 / Ck45 | Full equivalent |
| EN (Europe) | C45E (1.1191) | Full equivalent |
| ISO | C45 (ISO 683-1) | Full equivalent |
| GB (China) | #45 (45 Steel) | Full equivalent |
| BS (UK) | 080M46 | Near equivalent |
Each standard 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.
SCM415 / SCM420
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.