1045 Carbon Steel: Properties, Uses and Machinability
1045 is a plain medium-carbon steel with about 0.45% carbon. It is a useful choice for machined shafts, pins and wear surfaces that need a stronger hardening response than low-carbon steel. Its grade name alone does not specify tensile strength, hardness or delivery condition.
Match the property data to the bar size and processing route, then define what the finished part must pass.
Steel bar production. The photograph does not identify the steel grade.
What does 1045 steel mean?
In the SAE designation, “10” identifies a plain-carbon steel family and “45” indicates nominal carbon near 0.45%. You may also see AISI 1045 or UNS G10450. These identifiers describe the material grade; they do not mean that a bar is annealed, cold drawn or already hardened.
Cold drawing and heat treatment can change mechanical properties. Turning, grinding and polishing primarily describe surface or dimensional processing. A polished bar can still have different bulk properties from a cold-drawn bar.
The composition shown is for Atlas 1045 bar. Use the chemistry limits and product requirements named on the order. SAE J403 addresses carbon-steel chemical compositions; a supplier’s published table is not a replacement for the governing specification.
| Element | Published range or maximum |
|---|---|
| Carbon, C | 0.43–0.50% |
| Manganese, Mn | 0.60–0.90% |
| Silicon, Si | 0.10–0.35% |
| Phosphorus, P | 0.040% maximum |
| Sulfur, S | 0.040% maximum |
1045 mechanical properties depend on condition and size
Start with the delivery condition, then locate the applicable diameter range. A cold-drawn bar, a rolled bar and a quenched-and-tempered component should not share one generic “1045 strength” value.
Atlas supplies ordinary 1045 on a chemistry basis and explicitly does not guarantee minimum mechanical properties. Its tabulated figures below are reference values. Guaranteed properties must be agreed separately with the supplier.
| Bar condition | Diameter (mm) | Tensile strength (MPa)* | Yield strength (MPa)* | Elongation (%)† | Hardness (HB)* |
|---|---|---|---|---|---|
| Cold drawn | ≤16 | 690 | 540 | 8 | 207 |
| Cold drawn | >16–38 | 650 | 510 | 8 | 195 |
| Cold drawn | >38–80 | 640 | 500 | 9 | 190 |
| Rolled or turned and polished | ≤260 | 600 | 300 | 14 | 179 |
*The source labels these entries “min,” while stating that its table gives typical properties only. They become acceptance limits only under an agreed property-controlled order. †Elongation uses a 50 mm gauge length. Source: Atlas, page 1. On a narrow screen, scroll the table horizontally.
Example: a 15 mm shaft machined from 20 mm cold-drawn bar. The 20 mm supplied bar falls in the >16–38 mm row. Turning it down to 15 mm does not make it stock from the ≤16 mm cold-drawn category. If the design requires 540 MPa yield strength, that smaller-bar reference figure does not prove compliance. Agree the required property, processing state and test basis with the supplier.
Quenched and tempered is a separate condition
Atlas also gives an illustrative tensile range of 650–800 MPa for quenched-and-tempered bar up to 40 mm diameter. That is a different material condition from the rows above, not a strength upgrade to apply to every 1045 part. The treatment, section and test location must match the requirement.
“Normalized” likewise needs its own data. It is not another name for hot rolled, and neither state establishes a fixed hardness without a specification or test.
Strength, hardness and stiffness answer different questions
Yield strength concerns permanent deformation. Hardness describes resistance to local indentation and helps monitor a heat-treated surface. Elastic stiffness governs how far a loaded part deflects before yielding.
A harder shaft is not automatically much stiffer. If elastic bending is the problem, review diameter, unsupported length and support positions before treating hardness as the solution.
Physical-property estimates need their own source
For preliminary calculations, the following values are published by Ovako for the related C45 family. They are useful context for medium-carbon steel, but are not certified properties for an arbitrary 1045 heat. Use supplier data for the actual grade and temperature in a final model.
| Property | Typical value | Published temperature basis |
|---|---|---|
| Density | 7,800 kg/m³ (7.80 g/cm³) | No temperature stated in the table |
| Young’s modulus | 210 GPa | No temperature stated in the table |
| Thermal conductivity | 40–45 W/(m·K) | Ambient temperature |
| Average thermal expansion | 12 µm/(m·K) | 20–300°C |
| Specific heat capacity | 460–480 J/(kg·K) | 50/100°C, as listed by the supplier |
Source: Ovako C45, “Other properties (typical values).” Do not extend ambient values to welding temperatures or treat this table as evidence of grade equivalence.
How hard can 1045 become?
1045 can develop a hard surface after suitable heating and quenching. For example, voestalpine lists an average surface hardness of about 57 HRC after hardening at 800–830°C and water quenching. This is a supplier treatment example, not a guaranteed final hardness throughout the part or after every tempering cycle.
Hardness is not hardenability. Hardenability describes how deeply a steel can harden under a given cooling condition. A high surface reading does not establish the properties at the center of a thick shaft.
Choose the treatment for the property you need
| Route | Published temperature example | Purpose and verification |
|---|---|---|
| Full annealing | 800–850°C, Atlas | Prepare a softer machining condition. Agree cooling practice and final hardness. |
| Normalizing | 840–880°C, Atlas | Establish a controlled starting structure. Verify the required hardness or mechanical properties. |
| Quench and temper | Harden at 820–860°C; temper at 550–660°C, Atlas | Develop a usable strength–ductility balance. Qualify the quench and confirm properties at the specified section. |
| Induction or flame hardening | 820–860°C, voestalpine | Harden a selected surface. Define hardness, depth, transition zones and the subsequent tempering requirement. |
| Stress relieving | 600–650°C, voestalpine | Reduce residual stress where the material condition permits. Check compatibility with any previous temper and final hardness. |
Sources: Atlas, heat treatment and voestalpine, AISI 1045. These are separate route references, not a complete furnace instruction. Holding time, atmosphere, transfer, quench conditions and final testing remain to be specified.
Specify the depth as well as the surface number. For an induction-hardened pin, agree the hardened zone, effective-depth definition, surface hardness and core requirement. Check the final part after finishing: grinding allowance and local soft zones can matter even when one surface indentation passes.
Tempering and stress relieving can occupy overlapping temperature ranges, but they serve different purposes. In particular, Atlas’s 550–660°C entry is tempering. A later stress-relief cycle must be reviewed against the previous treatment; it can alter the hardness that the part was meant to retain.
A bar supported between centers during lathe turning. Support and workpiece condition affect machining behavior.
Is 1045 easy to machine?
1045 is routinely turned, drilled and milled, but a useful cutting recommendation needs the workpiece condition and hardness. One machinability percentage cannot set a shop’s speed and feed.
Start with the material actually in the chuck
Confirm the delivery condition, measured hardness, scale and any hardened layer. Sandvik Coromant separates unalloyed-steel cutting data by carbon level and heat-treatment condition. Use the toolmaker’s data for the specific insert or drill and the operation being performed.
Resolve setup problems before chasing speed
On a long shaft, check support, overhang and workholding when taper or chatter appears. On an interrupted cut, include the interruption in insert selection. Record wear and chip behavior so the next adjustment responds to an observed problem.
Plan the final surface before hardening
Complete major stock removal in a suitable machinable state, and agree any allowance for treatment distortion and finishing. A journal that will be hardened and ground needs a different route from a pin machined entirely in its delivery condition.
Can 1045 steel be welded?
Yes, with an appropriate procedure, but it deserves more preparation than a routine low-carbon-steel weld. The thermal cycle can create a hard heat-affected zone, and cracking risk depends on the material, hydrogen and joint stresses.
TWI’s hydrogen-cracking guidance explains how preheat slows cooling and helps hydrogen escape. The required temperature depends on composition, thickness, restraint, consumables and heat input. A universal preheat number for every 1045 joint would hide those differences.
If welding and cold forming dominate a new design, compare the 1018 route against the strength and wear requirements before committing to 1045.
What should a 1045 welding trial establish?
- Material and geometry: heat chemistry, starting hardness, joint dimensions, restraint and any existing surface treatment.
- Procedure: filler where used, preparation, hydrogen control, preheat/interpass limits, heat input and the cooling or post-treatment route.
- Acceptance: required penetration, weld and HAZ hardness, crack examination at the specified time, and relevant mechanical tests.
For laser welding, apply these checks to a sample made with the intended joint and process. A narrow or smooth bead alone does not demonstrate suitable hardness, penetration or crack resistance. Existing hardened zones also need evaluation for local property changes.
A crankshaft with journals and section changes. Geometry and loading must be considered separately from the steel grade.
Where does 1045 make sense?
Common uses include shafts, axles, pins, piston rods and gear racks. These are starting applications, not evidence that every part with that name should use 1045.
For a wear-loaded pin, a surface-hardening route may meet the need while preserving a different core condition. For a highly loaded shaft, the controlling issue may instead be core strength, impact resistance or fatigue at a shoulder.
Check the entire part: a keyway, abrupt diameter change or damaged journal can govern performance even when a material certificate meets the stated tensile requirement.
Compare complete material and manufacturing routes. The cheapest bar quote can lose its advantage if it adds straightening, tool wear, heat-treatment rework or extra inspection.
1045 vs 1018 and 4140: what should drive the choice?
Use the requirement that the proposed 1045 route cannot meet as the reason to change grade. A larger number in the grade name is not a performance ranking.
| Grade to consider | When it is useful | What must be confirmed |
|---|---|---|
| 1018 mild steel | Welding, forming and general machined parts where the required core properties allow a low-carbon grade. | Finished strength and whether a separate carburizing route is needed for the wear surface. |
| 1045 carbon steel | Machined parts needing a medium-carbon hardening response, including selected induction-hardened surfaces. | Supply condition, property distribution, hardened depth and the actual section response. |
| 4140 alloy steel | A Cr–Mo alloy route when deeper hardening or a required core-property combination cannot be achieved reliably with 1045. | Properties at the relevant depth after the specified treatment. Fatigue and toughness still need their own evidence. |
Compare the same product form, section and final condition. A surface-hardened 1045 part and an annealed 4140 bar answer different requirements.
Specify the material beyond “1045”
Are C45 and S45C equivalent to 1045?
C45, C45E, C45R and S45C are common sourcing comparisons. Ovako lists them as similar designations, but also shows composition differences between its C45 variants. Similar names do not authorize a substitution.
Compare the applicable chemistry limits, product form, delivery condition, size-dependent properties and test requirements. If a drawing requires SAE 1045, have the responsible purchaser or design authority approve a different standard before ordering it.
What belongs on the purchase order?
Give the supplier enough information to quote the required condition and inspection. Separate incoming-stock acceptance from tests required after the component is machined or heat treated.
- Grade and product form
- Name the governing specification and revision basis, grade, bar or forging form, quantity and dimensions. A bar specification should not be assumed to cover plate or a finished forging.
- Delivery condition
- State rolled, cold drawn, normalized, annealed or quenched and tempered as applicable. Add diameter tolerance, straightness and surface-finish requirements.
- Required properties
- Define the tensile, yield, hardness or toughness values the design actually needs. For a hardened surface, add the zone, depth definition and core requirement.
- Tests and traceability
- Agree test location, orientation, method, sampling frequency and material condition at testing. Require results traceable to the supplied heat or lot.
- Surface and finishing
- Address scale, surface defects, decarburization, machining allowance and corrosion protection where they affect the finished part or subsequent processing.
Two more questions about 1045 steel
Will 1045 rust outdoors?
Yes. 1045 is carbon steel, not stainless steel. Select storage protection, coating or another corrosion-control method for the exposure and working surface. For sliding or sealed surfaces, also check whether the protection changes dimensions, friction or compatibility with seals.
Can handheld XRF confirm that a bar is 1045?
It cannot confirm the carbon content needed to identify 1045. Evident explains the carbon limitation of XRF. Use traceable material documentation and, when chemical verification is required, a suitable carbon-capable method such as calibrated spark optical emission spectroscopy (OES). Hitachi describes OES analysis of carbon and other steel elements. Chemistry verification still does not establish hardness or mechanical properties.
Planning a laser process for a 1045 part?
Share the drawing, material condition and acceptance requirements with Oceanplayer Laser. A representative sample helps establish whether the proposed process meets the part’s requirements.
Include with your inquiry
Part drawing and thickness, material certificate or heat chemistry, delivery hardness, existing treatments, intended laser operation and required inspection results.
Technical sources
- Atlas Steels — 1045 bar data sheet. Composition, conditional mechanical data and heat treatment. Revised 10 September 2021.
- voestalpine — AISI 1045. Applications and treatment examples, including surface hardness.
- Ovako Steel Navigator — C45. Related grade variants and explicitly labeled C45 physical-property data.
- SAE J403 — carbon-steel chemical compositions. Public scope; full specification governs an order that names it.
- Sandvik Coromant — workpiece materials. Machining classification by material and condition.
- TWI — preventing hydrogen cracks in steels. Preheat, hydrogen control and welding procedure considerations.
- Evident — XRF questions and limitations. Why handheld XRF does not determine carbon.
- Hitachi High-Tech — metals analysis for QA/QC. Carbon-capable OES analysis.