JIS S45C is a medium carbon steel defined in JIS G4051, widely used for machine structural parts requiring moderate strength and good machinability. Its nearest equivalent in the US is ASTM/AISI 1045. This article covers the full comparison of international equivalents, chemical composition, mechanical and physical properties, heat treatment conditions, and practical tips for machinists and engineers.
1. Quick Comparison Box
S45C is a medium carbon steel with broad international equivalents. The table below summarizes cross-standard equivalents. Note the distinction between Exact Match and Nearest Equivalent — substituting without checking composition limits can lead to dimensional or strength failures.
| Standard | Region | Designation | Match Type | Notes |
|---|---|---|---|---|
| JIS G4051 | Japan | S45C | — | Base standard |
| ASTM A29 / AISI | USA | 1045 | Nearest Equivalent | C range slightly differs; check Mn upper limit |
| ISO 683-1 | International | C45 | Nearest Equivalent | Very close; ISO C content 0.42–0.50% |
| DIN 17200 | Germany | C45 / Ck45 | Nearest Equivalent | Ck45 has tighter S/P limits for turning |
| EN 10083-2 | Europe | C45 / 1.0503 | Nearest Equivalent | EN C45E (1.1191) has tighter residual limits |
None of the overseas equivalents are an exact chemical match to JIS S45C. The carbon range of AISI 1045 (0.43–0.50%) overlaps but is not identical to S45C (0.42–0.48%). Always verify composition certificates before substituting in safety-critical applications.
2. Chemical Composition
| Element | JIS S45C (%) | AISI 1045 (%) | EN C45 / 1.0503 (%) |
|---|---|---|---|
| C (Carbon) | 0.42 – 0.48 | 0.43 – 0.50 | 0.42 – 0.50 |
| Si (Silicon) | 0.15 – 0.35 | — | ≤ 0.40 |
| Mn (Manganese) | 0.60 – 0.90 | 0.60 – 0.90 | 0.50 – 0.80 |
| P (Phosphorus) | ≤ 0.030 | ≤ 0.040 | ≤ 0.030 |
| S (Sulfur) | ≤ 0.035 | ≤ 0.050 | ≤ 0.035 |
| Cr (Chromium) | ≤ 0.20 | — | ≤ 0.40 |
| Ni (Nickel) | ≤ 0.20 | — | ≤ 0.40 |
| Cu (Copper) | ≤ 0.30 | — | — |
Sources: JIS G4051:2016, ASTM A29/A29M, EN 10083-2:2006
3. Mechanical Properties
3-1. As-Normalized (Standard Heat Treatment)
| Property | S45C (Normalized) | AISI 1045 (Normalized) | Unit |
|---|---|---|---|
| Tensile Strength | ≥ 570 (83 ksi) | ≈ 585 (85 ksi) | MPa (ksi) |
| Yield Point (0.2% proof) | ≥ 370 (54 ksi) | ≈ 450 (65 ksi) | MPa (ksi) |
| Elongation | ≥ 20 | ≈ 16 | % |
| Reduction of Area | ≥ 45 | ≈ 40 | % |
| Hardness (annealed) | 137 – 229 HB | 163 – 235 HB | HB |
3-2. Quenched & Tempered (Q&T) — Representative Values
| Property | Value (Q&T, 25 mm dia.) | Unit |
|---|---|---|
| Tensile Strength | 690 – 900 (100 – 131 ksi) | MPa (ksi) |
| Yield Point | ≥ 490 (71 ksi) | MPa (ksi) |
| Elongation | ≥ 17 | % |
| Reduction of Area | ≥ 45 | % |
| Charpy Impact (V-notch, room temp.) | ≥ 63 J (≥ 46 ft·lbf) | J (ft·lbf) |
| Hardness (Q&T) | 201 – 269 HB / 20 – 28 HRC | HB / HRC |
Source: JIS G4051:2016, representative test bar values. Actual values depend on bar diameter and heat treatment parameters.
4. Physical Properties
| Property | Value | Unit |
|---|---|---|
| Density | 7.85 g/cm³ (0.284 lb/in³) | g/cm³ (lb/in³) |
| Young’s Modulus | 206 GPa (29,900 ksi) | GPa (ksi) |
| Thermal Conductivity | 48 W/(m·K) (333 BTU·in/(hr·ft²·°F)) | W/(m·K) |
| Coefficient of Thermal Expansion | 11.2 × 10⁻⁶ /°C (6.2 × 10⁻⁶ /°F) | 10⁻⁶ /°C (10⁻⁶ /°F) |
| Specific Heat Capacity | 486 J/(kg·K) (0.116 BTU/(lb·°F)) | J/(kg·K) |
| Electrical Resistivity | ≈ 0.17 μΩ·m | μΩ·m |
5. Heat Treatment Conditions
| Process | Temperature | Cooling Method | Purpose |
|---|---|---|---|
| Annealing | 800 – 850°C (1472 – 1562°F) | Furnace cool | Soften, relieve stress, improve machinability |
| Normalizing | 840 – 880°C (1544 – 1616°F) | Air cool | Refine grain, improve uniformity |
| Hardening (Quenching) | 820 – 860°C (1508 – 1580°F) | Water or oil quench | Achieve high hardness (≥ 55 HRC possible) |
| Tempering | 550 – 650°C (1022 – 1202°F) | Air cool | Reduce brittleness, achieve target hardness |
| Induction Hardening (surface) | 850 – 950°C (1562 – 1742°F) | Water spray quench | Surface hardness 55–60 HRC, tough core |
| Stress Relieving | 550 – 650°C (1022 – 1202°F) | Slow cool | Remove residual stress after machining |
6. Practical Advice
6-1. Machinability
S45C in the normalized or annealed condition machines well. Its machinability rating is approximately 65–70% of AISI B1112 (free-machining baseline).
- Use carbide tooling (ISO P20–P30) for turning; coated HSS is acceptable for drilling.
- Annealed condition (≤ 229 HB) gives the best chip control and surface finish.
- After Q&T (200–270 HB), reduce cutting speed by 20–30% compared to normalized stock.
- Avoid heavy interrupted cuts above 55 HRC — use grinding instead.
6-2. Heat Treatment Guide
- For parts requiring uniform through-hardness in sections > 50 mm (2 in), consider upgrading to SCM440 (ASTM 4140) — S45C has limited hardenability.
- Water quenching achieves higher hardness but increases distortion and cracking risk; oil quenching is preferred for complex geometry.
- Temper immediately after quenching to avoid quench cracking.
6-3. Welding Tips
S45C has a carbon equivalent (CE) of approximately 0.55–0.65, which puts it in the “requires preheat” zone. Welding without preheat risks hydrogen-induced cold cracking (HICC).
- Preheat: 150–250°C (302–482°F) for sections > 20 mm (0.79 in).
- Filler: Use low-hydrogen electrodes (E7016 / E7018) or MIG wire ER70S-6.
- Post-weld heat treatment (PWHT): Stress relief at 600–650°C (1112–1202°F) is recommended for structural welds.
- For high-hardness areas (induction-hardened surfaces), avoid welding — the heat-affected zone (HAZ) will soften significantly.
6-4. Common Mistakes
While S45C and AISI 1045 are frequently listed as equivalents, the AISI 1045 has a slightly wider C range (up to 0.50% vs. 0.48% for S45C) and looser P/S limits. For high-precision heat treatment (induction hardening with tight HRC targets), use mill certificates to confirm actual chemistry before switching.
S45C has relatively low hardenability (Jominy end-quench hardness drops sharply beyond 10–15 mm from the quenched end). For shafts or blocks > 50 mm (2 in) diameter requiring uniform strength, SCM440 or S35C may be more appropriate.
Attempting repair welds on induction-hardened S45C shafts without preheat almost always results in HAZ cracking. If repair welding is needed, the component must be annealed first.
6-5. When to Choose S45C
- Choose S45C when: You need moderate strength (≥ 570 MPa normalized, up to 900 MPa Q&T), good machinability, and surface hardenability for wear surfaces such as shafts, gears, keys, and spindles.
- Choose SCM440 instead when: Section size > 50 mm (2 in) or through-hardening uniformity is critical.
- Choose S35C instead when: Welding is a primary requirement (lower CE reduces cracking risk).
- Choose S55C instead when: Higher hardness after induction hardening is needed (up to 58–62 HRC).
7. FAQ
S45C and AISI 1045 are the nearest equivalents, not exact matches. The carbon content of S45C is 0.42–0.48%, while AISI 1045 allows up to 0.50%. Sulfur and phosphorus limits are also slightly tighter in S45C. They can generally be substituted in non-critical applications, but always verify mill certificates for precision or safety-critical uses.
After water quenching from 820–860°C (1508–1580°F), S45C can achieve surface hardness of approximately 55–60 HRC. After induction hardening, the case can reach up to 58–62 HRC with a tough ferritic/pearlitic core. Through-hardness in large sections will be lower due to limited hardenability.
Yes, but with precautions. Preheat to 150–250°C (302–482°F) is required for sections over 20 mm (0.79 in). Use low-hydrogen filler materials and perform stress-relief PWHT at 600–650°C (1112–1202°F). Welding already-hardened S45C components is not recommended without first annealing.
The European EN equivalent is EN C45 (material number 1.0503), defined in EN 10083-2. For tighter residual element control suitable for precision turning, EN C45E (1.1191) is the closer analog. Both are “nearest equivalents” rather than exact matches.
S45C is widely used for machine structural components: shafts, gears, keys, bolts, spindles, crankshafts, and connecting rods. It is especially favored for induction-hardenable journal surfaces in rotating machinery. In the normalized condition it is also commonly used for general-purpose structural parts in jigs and fixtures.
- JIS S45C is a medium carbon machine structural steel (JIS G4051) with C = 0.42–0.48%.
- Nearest equivalents: AISI 1045 (USA), ISO C45, DIN C45/Ck45, EN 1.0503 — none are exact matches.
- Normalized tensile strength ≥ 570 MPa (83 ksi); Q&T up to 900 MPa (131 ksi).
- Excellent for induction hardening: surface hardness up to 60 HRC, tough core.
- Weldable with preheat; avoid welding hardened sections.
- For sections > 50 mm (2 in) or critical hardenability, consider SCM440 instead.
comment