What Is 1018 Mild Steel? 1018 vs 1045
SAE 1018 is a low-carbon steel grade valued for formability, weldability, machinability and case-hardening potential. The important catch: “1018” identifies chemistry—not surface finish, bar tolerance, strength, heat treatment or product form.
Hero image: Fornax / Wikimedia Commons, CC BY-SA 3.0.
A chemistry grade
It does not automatically mean cold rolled, cold drawn, polished, annealed or mechanically certified.
General-purpose bar parts
Shafts, pins, fixtures, spacers, brackets and case-hardened components with moderate core demands.
1045 for higher strength
More carbon provides a stronger heat-treatment response, but reduces welding and forming margin.
Specify condition and form
Product standard, size, finish, tolerance, straightness and required properties belong on the purchase order.
1018 is the “easy to make” choice; 1045 is the “more strength and hardening” choice.
Choose 1018 when the job rewards cold forming, welding, a clean cold-finished bar surface, reasonable machinability or a hard case over a ductile core. Choose 1045 when the component needs more core strength, wear resistance or a meaningful quench-and-temper or induction-hardening response.
Neither choice is complete until you define the product form and delivery condition. A cold-drawn 1018 round bar and a hot-wrought 1018 bar can share chemistry while differing substantially in surface finish, dimensional accuracy, residual stress and tensile properties.
What is 1018 mild steel?
SAE 1018 is an unalloyed, low-carbon steel identified primarily by its chemical composition. In the four-digit SAE designation, the first two digits—“10”—identify a plain carbon steel family, while the final two digits indicate a nominal carbon level near 0.18%. The actual permitted carbon range is broader than the nominal number.
The term mild steel is an informal family description, not a complete procurement specification. It usually refers to low-carbon steels that are comparatively ductile, formable and weldable. Saying “mild steel” does not establish an exact grade, minimum yield strength, surface condition, dimensional tolerance or testing requirement.
Likewise, saying “1018” does not tell a supplier whether you need hot-wrought bar, cold-drawn bar, turned-and-polished shafting, stress-relieved stock, ground bar or plate. In North American practice, cold-finished carbon and alloy steel bars are commonly ordered under ASTM A108, while hot-wrought special-quality carbon steel bars are covered by ASTM A576 together with the general requirements of ASTM A29/A29M.
SAE 1018 answers “what chemistry family is this?” ASTM A108 or A576 answers “what bar-product route and requirements apply?” A drawing or purchase order normally needs both kinds of information, plus the actual finish, tolerance and property requirements.
Is 1018 the same as cold-rolled steel?
No. Cold-rolled sheet and cold-finished bar are not interchangeable descriptions. 1018 is frequently sold as cold-drawn bar because that route produces useful size control and surface finish, but the same grade may also be supplied hot wrought. Sheet products are governed by different product standards and grade systems. If a design needs sheet, do not assume that a bar-grade designation automatically maps to the available sheet product.
1018 steel chemical composition.
The commonly published heat-analysis range below aligns with SAE 1018 data used for carbon steel bars. Always use the governing standard revision and material certificate for acceptance.
| Element | Common 1018 range | Why it matters | Procurement note |
|---|---|---|---|
| Carbon (C) | 0.15–0.20% | Controls strength, hardening response, weldability and formability. | The “18” is nominal; it is not an exact 0.18% requirement. |
| Manganese (Mn) | 0.60–0.90% | Contributes to strength, deoxidation and hardenability. | Confirm the heat analysis when chemistry traceability matters. |
| Phosphorus (P) | 0.040% max | Excess phosphorus can reduce ductility and toughness. | Maximum values are acceptance limits, not target additions. |
| Sulfur (S) | 0.050% max | Sulfur affects inclusions, ductility and machining behavior. | 1018 is not a resulfurized free-machining grade. |
| Iron (Fe) | Balance | Base metal matrix. | Residual elements may also be reported when required. |
SAE J403 notes that product form and section size can require composition flexibility. Treat a website table as orientation; use the applicable standard and mill test report for conformance.
Mostly ferrite, with enough pearlite to add strength.
In a slowly cooled low-carbon steel, the microstructure is commonly dominated by soft, ductile ferrite with a smaller fraction of pearlite. That balance helps explain why 1018 bends and welds readily yet does not develop the deep, high hardness expected from medium-carbon or alloy steels.
Cold drawing can raise strength and hardness through strain hardening without changing the nominal chemistry. Heat treatment, section size and cooling rate can also change the microstructure. This is why chemistry alone cannot predict the finished part’s mechanical properties.
Supports ductility, forming and comparatively forgiving welding behavior.
Restricts through-hardening potential but works well for a carbon-enriched case.
Cold work and thermal history can change strength more than the grade name suggests.
1018 steel properties depend on size and delivery condition.
A single internet value such as “440 MPa tensile strength” is not a universal design value. Cold work, bar diameter, stress relief, annealing and testing direction all change the result.
Better finish and dimensional control
Drawing produces a smoother surface and closer size control while increasing strength through cold work. It can also introduce residual stress that matters when long, asymmetric or heavily machined parts are produced.
- Common for pins, shafts, spacers and precision bar parts
- Strength varies with bar size and processing
- Stock removal can release residual stress
More economical starting stock
Hot-wrought bar generally has looser dimensional control and a scaled surface. It may be preferable where the part will be heavily machined, forged or fabricated and a cold-finished surface adds little value.
- Useful for forgings and general machined parts
- Do not assume cold-drawn minimum properties
- Allow for scale and machining allowance
Different balance of stability and strength
Thermal treatment can reduce cold-work effects and improve dimensional stability or formability, but it also changes mechanical properties. The treatment and acceptance criteria must be stated.
- Useful when distortion risk is significant
- Not implied by “1018” alone
- Verify hardness and final dimensions after treatment
| Property question | Responsible answer | What to request |
|---|---|---|
| Tensile and yield strength | Cold-drawn supplier data can span roughly 55–70 ksi tensile and 45–60 ksi yield across common 5/8–3 in bar sizes; another size or condition can differ. | Required minimums, size range, test direction and governing product specification. |
| Hardness | Often in a relatively soft bar range before case hardening; cold work and size change the value. | Hardness range and test method if it controls machining or forming. |
| Elastic modulus | Approximately 200 GPa (29,000 ksi), similar to other carbon steels; 1045 is not meaningfully “stiffer.” | Use the design code and verified material data for calculation. |
| Density | Approximately 7.87 g/cm³ (0.284 lb/in³), similar to plain carbon steels. | Use actual dimensions and agreed density for weight estimates. |
| Fatigue performance | Not defined by grade name; surface finish, stress concentration, size, residual stress and loading dominate. | Part-specific fatigue design and process control. |
One table may describe a small cold-drawn bar, another a generic cold-drawn condition, and another hot-rolled stock. Differences do not automatically mean one source is wrong. They often describe different sizes, test bases or processing histories.
Which steel route should you investigate first?
Choose the closest product situation. The recommendation updates instantly and points to a starting route—not a final material approval.
Start with cold-finished 1018
For a precision pin, spacer or small shaft where finish and tolerance lead the decision, cold-finished 1018 is a practical starting point.
Screening only. Final selection requires the drawing, load case, section size, manufacturing route, service environment and applicable code.
1018 vs 1045—and where A36, 1020 and 12L14 fit.
The most useful comparison is not “which steel is best?” It is “which specification and product condition best fit this part?”
| Material route | What it identifies | Primary advantage | Main limitation | Good starting applications |
|---|---|---|---|---|
| SAE 1018 | Low-carbon chemistry grade, often supplied as cold-finished or hot-wrought bar. | Balanced weldability, forming, machining and case-hardening potential. | Limited core hardness and strength compared with 1045. | Pins, spacers, fixtures, small shafts, studs and carburized parts. |
| SAE 1020 | Nearby low-carbon chemistry grade with overlapping practical use depending on product and supplier. | General fabrication, machining and forming flexibility. | Do not assume it is identical to 1018 in chemistry, availability or properties. | General bar parts, forgings, tubes and fabricated components. |
| SAE 1045 | Medium-carbon chemistry grade, commonly supplied in multiple bar and heat-treated conditions. | Higher strength and better induction/quench hardening response. | Less forgiving welding and forming; hardenability still depends on section size. | Loaded shafts, pins, axles, gears, rolls and wear surfaces. |
| ASTM A36 | Structural carbon-steel specification for shapes, plate and bars—not a direct SAE chemistry equivalent. | Availability and structural fabrication route. | Does not provide the same tight chemistry identity or cold-finished bar expectation as 1018. | Frames, base plates, brackets and general structural construction. |
| 12L14 | Leaded, resulfurized free-machining carbon steel, commonly used for high-rate bar machining. | Excellent chip control and machining productivity. | Poor choice where welding, high ductility or lead restrictions matter. | Fittings, fasteners and complex screw-machine parts in suitable service. |
Manufacturing simplicity leads.
- The part needs welding or substantial cold forming.
- Cold-finished bar tolerance and surface finish reduce machining.
- A hard wear-resistant case over a relatively ductile core is useful.
- Loads do not require the higher core strength of 1045 or 4140.
- Material traceability and product condition can be clearly specified.
Strength and hardening lead.
- The shaft, pin or journal carries higher load or contact stress.
- Induction hardening or quench-and-temper response is required.
- Wear resistance must extend beyond a thin carburized case.
- The welding procedure can address higher carbon and restraint.
- Section-size hardenability and final property testing are understood.
1045 can be stronger and harder, but both are carbon steels with an elastic modulus near 200 GPa. Replacing 1018 with 1045 usually does not reduce elastic deflection unless the geometry or load changes. Strength and stiffness are different design properties.
1018 machines readily—but “free machining” is not the same thing.
1018 is widely machined because it is relatively soft, available in convenient bar forms and compatible with common tooling. However, its ductility can produce long or stringy chips. Resulfurized or leaded grades such as 12L14 are designed for much higher machining productivity and chip control, but they trade away weldability, ductility and—in the case of leaded stock—compatibility with some environmental or product requirements.
Cold-finished 1018 can reduce stock removal because the starting size and surface are controlled more closely. The tradeoff is residual stress. Removing a large amount of material from one side, cutting a long keyway or creating a slender shaft can release that stress and move the part.
Speed and feed depend on tool grade, coating, rigidity, coolant, operation and actual hardness.
For distortion-sensitive parts, rough-machine symmetrically, allow relaxation and finish later.
Chip control, tolerance, welding and material restrictions may matter more than a catalog rating.
Is 1018 steel weldable?
Yes. Its low carbon level generally gives 1018 good weldability with common arc, resistance and laser-welding processes when the material condition, joint design, restraint and service requirements are appropriate. That does not mean every 1018 part can be welded without procedure qualification or thermal control.
Preheat decisions should not be reduced to a single thickness rule. The appropriate procedure depends on actual chemistry or carbon equivalent, combined thickness, restraint, ambient temperature, hydrogen control, heat input, filler, prior case hardening and the required properties. A small clean bracket and a highly restrained thick assembly do not present the same cracking risk.
Do not weld through oil, scale, zinc coating, carburized layers or unknown surface treatments without evaluating the process hazards and metallurgical effects. For laser welding, fit-up, focus, travel speed, shielding, reflectivity, penetration and access to Class 4 laser controls also matter. If the part will be case hardened after welding, coordinate the welding and heat-treatment sequence to avoid distortion and brittle local conditions.
1018 is a case-hardening steel—not a deep through-hardening shortcut.
The low bulk carbon level limits the amount of martensitic hardness that can be developed through the full section. The practical route is often to enrich or transform the surface while preserving a lower-carbon core.
Define the wear depth
Specify case depth, surface hardness, core properties and the location where they must be measured.
Select the process
Carburizing or carbonitriding may suit a hard case; induction hardening is limited by the available carbon and section response.
Control distortion
Machining allowance, part geometry, heating uniformity, quench severity and fixturing influence final size.
Verify the result
Use hardness traverse, effective case depth, microstructure and dimensional inspection as required.
Can 1018 be through hardened?
Thin sections may show some hardening after aggressive quenching, but 1018 does not normally provide the deep, high, uniform core hardness expected from 1045 or alloy steels. If the design needs a strong hardened core, choose a grade and heat-treatment route developed for that requirement rather than trying to force 1018 into the role.
When is carburized 1018 a good choice?
It can be effective for pins, bushings, small gears, pawls, guides and other parts that benefit from a wear-resistant surface over a comparatively ductile core. The correct case depth is application-specific. A shallow case may wear through; an excessive or poorly controlled case can increase distortion, grinding stock and brittleness risk.
Start with the product form the drawing actually needs.
Cold-finished 1018 is attractive when the starting bar’s accuracy and appearance reduce machining. Hot-wrought material can be more economical when scale will be removed, the part will be forged, or generous machining allowance already exists.
| Decision | Cold-finished bar | Hot-wrought bar |
|---|---|---|
| Surface | Smoother, cleaner starting finish | Scale and more surface variation |
| Size control | Closer, specification-defined tolerances | Looser hot-wrought tolerances |
| Strength | Often raised by cold work | Depends on hot-wrought condition and requirements |
| Residual stress | Can be significant | Usually less cold-work stress |
| Best value | Near-net bar parts | Heavy machining, forging or general fabrication |
Common 1018 steel applications.
1018 works best where manufacturing flexibility and moderate mechanical demands are more valuable than maximum strength.
Pins, dowels & spacers
Cold-finished stock can reduce initial turning and support repeatable diameters when the tolerance is specified.
Light-duty shafts
Suitable where load, fatigue, keyway stress and surface wear remain within the verified condition’s capability.
Brackets & fixtures
Good welding and forming behavior supports jigs, mounts and general manufactured components.
Pins, pawls & small gears
A hard surface over a lower-carbon core can provide economical wear performance in suitable designs.
Studs, bolts & threaded parts
Useful for non-high-strength applications when the fastener specification and proof requirements are met.
Cold-headed & bent components
Low carbon supports forming, but actual product cleanliness, geometry and reduction still control cracking risk.
A grade commonly used for shafts is not automatically suitable for every shaft. Torque, fatigue, diameter, keyways, surface finish, corrosion, impact, heat treatment and safety factor determine the final choice.
How to specify 1018 steel correctly.
A robust order separates chemistry, product requirements and finished-part requirements. Avoid asking a supplier simply for “1018 cold rolled.”
State SAE 1018 / UNS G10180 and the applicable chemistry standard or agreed limits.
For example, ASTM A108 for cold-finished bar or ASTM A576 with A29/A29M requirements for hot-wrought bar.
Round, square, hex or flat; nominal size; length; cut condition; and quantity.
Cold drawn, turned and polished, ground, hot wrought, annealed or stress relieved—as actually required.
Use the product standard or state tighter values, including out-of-round and straightness where critical.
Add tensile, yield, elongation or hardness requirements only with an applicable test basis and size range.
Define defect limits, machining allowance or supplementary requirements when the surface enters the finished part.
Request the material test report, heat number, test reports and marking method needed by the quality plan.
Related steel and fabrication resources.
Need to weld, clean or mark a 1018 or 1045 steel part?
Send the grade, product condition, dimensions, drawing, surface state and required result. Oceanplayer can help screen a laser process route and plan representative sample testing before equipment selection.
1018 mild steel FAQ.
Is 1018 steel considered mild steel?
Yes. 1018 is commonly described as mild or low-carbon steel because its carbon range is about 0.15–0.20%. “Mild steel” remains a broad informal category, so use the actual grade and product specification for procurement.
What is the difference between 1018 and 1045 steel?
1018 contains less carbon and generally offers better welding and forming margin. 1045 contains about 0.45% nominal carbon, supporting higher strength and a stronger hardening response. Section size and delivery condition still control actual properties.
Is 1018 stronger than A36?
That question is incomplete without condition and product form. Cold-finished 1018 bar may show higher strength than common A36 structural products, but A36 is a structural specification and 1018 is a chemistry grade. Compare certified products, not labels.
Is 1018 cold rolled or hot rolled?
Neither is automatic. 1018 can be supplied as cold-finished bar or hot-wrought bar. “Cold rolled” more commonly describes sheet or strip, while “cold drawn” or “cold finished” is typical bar terminology.
Can 1018 steel be hardened?
Its low carbon content limits deep through hardening. Surface-hardening routes such as carburizing can create a hard case over a lower-carbon core. The case depth, hardness, distortion and core requirements must be specified and verified.
What hardness is 1018 steel?
There is no single hardness for all 1018. Cold drawing, bar size, annealing, stress relief and case hardening change the value. Use the supplier certificate or specify a hardness range and test method when it matters.
Is 1018 steel easy to weld?
It is generally considered readily weldable because of its low carbon level. Actual procedure requirements still depend on chemistry, thickness, restraint, hydrogen control, ambient temperature, coating and service requirements.
Is 1018 steel easy to machine?
It is commonly and successfully machined, but ductility can create stringy chips. 12L14 usually offers faster machining and better chip control, while 1018 offers better welding and forming compatibility.
Will 1018 steel rust?
Yes. It is plain carbon steel with limited atmospheric corrosion resistance. Select oil, paint, plating, black oxide, conversion coating or a corrosion-resistant alloy according to the actual environment.
Is 1018 good for shafts?
It can be a good choice for light- to moderate-duty shafts, especially in cold-finished form. Higher loads, fatigue, wear, large sections or hardened journals may justify 1045 or an alloy steel such as 4140.
Does 1045 make a shaft stiffer than 1018?
Not to a meaningful degree. Both have a similar elastic modulus near 200 GPa, so geometry controls elastic deflection. 1045 can support higher stress or hardness, but it is not substantially stiffer.
What should a 1018 steel purchase order include?
Include the grade, governing product standard, shape, size, length, finish, delivery condition, tolerance, straightness, surface-quality requirements, required mechanical properties, certification and traceability.
Standards and supporting sources.
This guide distinguishes mandatory standard requirements from representative supplier data and explanatory material.
Editorially reviewed and updated July 26, 2026. Use the latest applicable standard revision, engineering drawing and material certificate for purchasing or safety-critical design.