SAE 1045 steel
Medium-carbon engineering steel: chemistry identity, condition-specific bar properties, hardenability and surface-treatment limits.
Tags: materials, steel, medium-carbon-steel, sae
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Identity and purchase definition
Atlas's typical 1045 quenched-and-tempered bar table gives proof-stress entries of 430 MPa through 40 mm and 370 MPa above 40 through 100 mm, so 50 mm falls in the 370 MPa row. The table labels the cells “minimum” within typical data. Ordinary supply meets chemistry requirements, with guaranteed properties available by special order. Atlas 1045 supply and property table
SAE 1045 is a medium-carbon steel chemistry designation. Metallus' Practical Data for Metallurgists, 19th edition, lists carbon 0.43–0.50% and manganese 0.60–0.90% by mass for its 1045 reference row, with phosphorus 0.040% maximum and sulfur 0.050% maximum. Keep the source and governing specification with these limits rather than assigning them to every internationally similar product. Metallus, standard carbon steels, page 4
SAE J403 covers chemical compositions, with heat-analysis ranges distinguished from product-analysis allowances. Its public listing identifies J403_202402, stabilized February 23, 2024, technically revised June 2014. The grade number does not establish delivered strength, hardness, straightness or heat treatment. SAE International, J403
Similar designations and supply routes
Ovako lists SAE 1045 among similar designations for its C45 family, but distinguishes variants with narrowed chemistry, inclusion treatment and casting route. It explicitly says its data apply to Ovako material and that another product meeting similar international specifications need not have the same properties. “Similar designation” is therefore a comparison lead, not an approved substitution. Ovako, C45 Steel Navigator
Nucor lists 1045 in cold-finished rounds, squares and hexagons, and in turned/polished and turned/ground/polished offerings. Its dimensional envelopes depend on product grade. These processing descriptions should remain separate: a smooth bright surface does not by itself establish the amount of cold work or the strength of the core. Nucor, cold-finished bar
Record the actual route and inspection document. Where a surface finish, machining allowance or straightness is important, order it explicitly rather than inferring it from chemistry or trade terminology.
Typical properties versus guarantees
Atlas' September 2021 sheet states that ordinary 1045 supply meets specified chemistry only and does not guarantee minimum mechanical properties. Its condition table is explicitly typical, despite individual cells carrying “min” labels. It describes guaranteed bright-bar or normalized-black-bar mechanical properties as special-order options. Atlas Steels, 1045 grade data sheet, supply conditions
The same sheet gives this typical quenched-and-tempered bar comparison:
| Diameter | Tensile range | 0.2% proof-stress entry |
|---|---|---|
| Up to 40 mm inclusive | 650–800 MPa | 430 MPa minimum |
| Over 40–100 mm inclusive | 630–780 MPa | 370 MPa minimum |
| Over 100–250 mm inclusive | 590–740 MPa | 340 MPa minimum |
Retain the table's typical-data qualification; it is not a generic SAE guarantee. Atlas, typical heat-treated properties
For a comparison only, the first two proof-stress entries differ by 430 − 370 = 60 MPa, approximately 60 / 430 × 100 = 14%. A 50 mm bar belongs to the second row, not the first. This arithmetic does not calculate allowable shaft torque or a fatigue limit. Design still needs certified values where required, stress concentrations, loading spectrum, size effects and the governing safety basis.
Hardenability and heat treatment
Interlloy characterizes its 1045 as having low through-hardening capability and generally recommends only sections up to around 60 mm for through hardening and tempering. Geometry, chemistry, quench and required core properties still control applicability. Interlloy, 1045 carbon steel bar
Distinguish hardness, the measured indentation response, from hardenability, the ability to develop a hardened structure through a section under a cooling condition. A hard surface does not prove a hard core. Specify sampling locations or a hardness traverse when the distribution matters; a single surface reading cannot establish it.
Interlloy also qualifies heat-treatment temperatures, rates and soaking/cooling times by workpiece size/shape, furnace, quenching medium and transfer facilities. Use a qualified process for the actual part, not an isolated temperature copied from a catalogue. Interlloy, heat-treatment notes
Retain prior processing, austenitizing/quench/temper sequence, actual section and final inspection with the material record. Review any later thermal cycle or straightening against the required final condition. A treatment temperature is not an approved service-temperature envelope.
Induction and flame hardening
Interlloy describes successful flame or induction hardening of as-rolled/normalized 1045, with surface hardness up to approximately 54–60 HRC depending on setup, section and quench. It warns that a decarburized surface layer must first be removed. These are conditional surface-treatment results, not bulk mechanical properties. Interlloy, surface hardening
For an induction-hardened shaft, specify required surface hardness, effective case-depth definition, core condition, transition zones and final dimensional tolerance. Agree the measuring method and locations. Include grinding allowance and crack inspection where required. Neither a generic “hardened” label nor surface HRC alone demonstrates contact-fatigue life or resistance to bending failure.
Machining, welding and service selection
Atlas states that pre- and post-heating are required in its welding procedure guidance to avoid cracking, including light sections. This is a warning to qualify joining, not a complete welding procedure or universal temperature recipe. Atlas, welding section
Interlloy advises against welding its hardened-and-tempered, flame-hardened or induction-hardened 1045 condition. A repair proposal must therefore address the starting condition and consequences for the heat-affected zone and final properties. Interlloy, welding
Choose tooling for the supplied hardness and leave stock for finish machining after heat treatment where required.
Source editions and acceptance record
Retain the ordered grade/product standards, actual chemistry, form/size, supplied and final conditions, certificate and inspection criteria. Keep typical reference values separate from guaranteed requirements and measured results. Approve alternatives against the complete requirement rather than a cross-reference name.
Atlas' sheet is revised and printed September 10, 2021. Metallus' guide is 19th edition, copyright 2024. Ovako's C45 page gives a January 30, 2025 revision timestamp. No printed revision date was verified for the Interlloy sheet or Nucor page; old standard editions listed as related specifications do not establish current requirements. Confirm contractual editions and current processing guidance separately.
See also grades, tempers and conditions.