AISI 1045 Medium Carbon Steel: Properties, Equivalents & Heat Treatment
AISI/SAE 1045 · Published: 2026-07-15 · Updated: July 2026
AISI 1045 is a medium-carbon steel containing approximately 0.45% carbon, offering a practical compromise between the weldability and formability of low-carbon steels and the strength/hardenability of higher-carbon grades. In the normalized...
AISI 1045 is a medium-carbon steel containing approximately 0.45% carbon, offering a practical compromise between the weldability and formability of low-carbon steels and the strength/hardenability of higher-carbon grades. In the normalized condition, 1045 provides 310 MPa yield strength and 565 MPa tensile strength — significantly stronger than A36 (250 MPa yield) while remaining machinable and moderately weldable. 1045 is the standard material for shafts, gears, crankshafts, connecting rods, hydraulic cylinder rods, and machine components requiring strength through heat treatment. Unlike low-carbon steels, 1045 responds well to quench-and-temper heat treatment: quenching from 820-860°C in oil or water produces a martensitic structure with hardness of 50-58 HRC, which is then tempered to the desired strength-ductility balance. Typical service hardness: 25-35 HRC for shafts and gears (tempered 400-600°C). Key limitation: through-hardening is limited to approximately 25mm diameter in oil quench; larger sections develop a mixed martensite/pearlite core. For through-hardening larger sections, specify AISI 4140 or 4340 which have alloy additions for superior hardenability.
Quick Facts
| Category | Carbon Steel |
| Standard | AISI/SAE 1045 |
| Density | 7.85 g/cm³ |
| Yield Strength | 310 MPa (45 ksi) normalized |
| Tensile Strength | 565 MPa (82 ksi) normalized |
Detailed Mechanical Properties
| Elongation | 16% (normalized) |
| Hardness | 170-210 HB (normalized), 50-58 HRC (quenched) |
| Charpy V Notch | 24J at 20°C (normalized) |
| Shear Modulus | 79.0 GPa |
Physical Properties
| Melting Point | 1410-1490 °C |
| Thermal Conductivity | 51.9 W/m·K at 20°C |
| Electrical Resistivity | 0.0000164 Ω·cm |
| Specific Heat | 486 J/kg·K |
Global Equivalents & Cross-Reference
| Alternative Standard / Grade | Action |
|---|---|
| C45 (EN/DIN) | Compare |
| S45C (JIS) | Compare |
| CK45 | Compare |
| 080M46 (BS) | Compare |
Heat Treatment & Processing
| Normalizing | 840-870°C, air cool |
| Annealing | 790-870°C, furnace cool to 650°C |
| Quenching | 820-860°C, oil or water quench |
| Tempering | 400-650°C based on desired hardness, air cool |
| Note | Water quenching produces highest hardness but highest cracking risk; oil quench preferred for most applications |
Welding & Fabrication
| Preheat | 150-260°C for thicknesses >3mm; 200-300°C for >12mm |
| Filler Metal | E7018 (SMAW), ER70S-6 (GMAW) for moderate strength; E8018-B2 for matching strength |
| Interpass Temp | Max 315°C |
| Pwht | Stress relieve at 595-650°C recommended; mandatory for dynamic loading |
| Weldability Rating | Fair — preheat required, low-hydrogen process mandatory |
Related Materials
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Frequently Asked Questions
Can AISI 1045 be welded as easily as A36?
No. 1045's 0.45% carbon content significantly reduces weldability compared to A36 (0.25% C). Preheat of 150-260°C is required for thicknesses over 3mm to prevent hydrogen-induced cold cracking in the heat-affected zone. Low-hydrogen electrodes (E7018) are mandatory. Post-weld heat treatment (stress relief at 595-650°C) is recommended for restrained joints and dynamic-loading applications. For heavily welded structures, A36 or A572 Gr 50 are preferred; for moderately welded machine components, 1045 is acceptable with proper preheat and filler metal selection.
What is the maximum section size that 1045 can through-harden?
In oil quench, AISI 1045 through-hardens to approximately 25mm (1 inch) diameter. Water quench extends this to approximately 40mm, but water quenching 1045 carries significant cracking risk for complex geometries. For sections larger than 25mm requiring uniform through-hardness, specify AISI 4140 (oil-quench hardenable to 75mm) or AISI 4340 (to 125mm). Many 1045 shafts are surface-hardened by induction heating instead of through-hardening — this provides a hard, wear-resistant case (50-58 HRC) over a tough, ductile core.
References & International Standards
- ASTM International. Standard Specifications for Steel & Metal Alloys. astm.org
- International Organization for Standardization (ISO). Metallic Materials — Cross-Reference Database. iso.org
- American Iron and Steel Institute (AISI). Steel Grade Designations & Equivalents. steel.org
- European Committee for Standardization (CEN). EN Steel Standards & Numbering System. cencenelec.eu
Specialty Metals — Engineering Reference
Non-ferrous metals — aluminum, copper, titanium, zinc, magnesium — serve applications where steel cannot: electrical conductivity, thermal management, weight reduction, corrosion resistance in specific chemical environments. Each metal family has its own classification system and selection logic.
ASTM B209/B221 (Al), ASTM B152/B187 (Cu), ASTM B265/B348 (Ti), ASTM B86 (Zn), ASTM B90/B91 (Mg)
Electrical wiring and busbars (Cu), aircraft structures and automotive bodies (Al), medical implants and aerospace fasteners (Ti), die-cast consumer products (Zn), lightweight electronic enclosures (Mg)
Galvanic corrosion is the #1 failure mode in multi-metal assemblies. When joining dissimilar metals, consult the galvanic series: the more anodic metal will corrode preferentially. Use isolating washers, protective coatings, or select metals close together on the galvanic series.