5140 Steel: Chemical Composition, Properties, Hardness, Heat Treatment and Applications
📑 Table of Contents
When engineers and purchasing teams search for 5140 steel, they are usually looking for a practical combination of strength, toughness, hardenability and cost. The grade belongs to the AISI/SAE 5100 chromium alloy steel family and is widely considered for shafts, axles, pins, gears, machine parts and other components that need more performance than plain carbon steel can provide.
However, the grade designation alone does not define the final performance. Annealed 5140 behaves very differently from normalized or quenched-and-tempered material. Section size also affects the cooling rate and therefore the hardness and strength that the steel can achieve through the section.
For international buyers, another important point is grade comparison. 5140 is frequently compared with 41Cr4 / 1.7035, but the two designations should not automatically be treated as chemically identical. The applicable standard, chemistry, delivery condition and mechanical-property requirements should always be checked before substitution.
This article examines 5140 from both an engineering and purchasing perspective, including chemical composition, mechanical properties, heat treatment, hardness, equivalent grades, applications, machining, welding and supplier selection.
🔍 1. What Is 5140 Steel?
5140 is a medium-carbon chromium alloy steel commonly specified under the AISI/SAE system. Its UNS designation is G51400, and the material is also associated with specifications such as ASTM A322, ASTM A331, ASTM A505 and ASTM A519 depending on the product form and application.
The grade contains roughly 0.40% carbon and around 0.80% chromium. This combination gives it greater hardenability than a comparable plain carbon steel while keeping the alloy system relatively economical.
In production, 5140 can be supplied in annealed, normalized or quenched-and-tempered conditions. Buyers should therefore include the required delivery condition in the purchase specification instead of requesting only “5140 steel.”
| Item | 5140 Steel Information |
|---|---|
| AISI/SAE designation | 5140 |
| UNS | G51400 |
| Steel family | Medium-carbon chromium alloy steel |
| Main alloying element | Chromium |
| Common conditions | Annealed, normalized, quenched and tempered |
| Typical role | General-purpose strength-oriented engineering steel |
In simple terms, 5140 is a medium-carbon chromium steel selected when a component needs a useful balance of strength, toughness and hardenability. It is not stainless steel, despite containing chromium, because its chromium content remains far below the level required for stainless behavior.
🧪 2. 5140 Steel Chemical Composition
The chemical composition of 5140 explains why the grade performs differently from ordinary medium-carbon steel. Carbon provides the basic hardening potential, while chromium improves hardenability. Manganese also contributes to strength and hardening response.
| Element | Typical AISI 5140 Range / Limit (%) | Main Contribution |
|---|---|---|
| C | 0.38–0.43 | Hardness and strength after heat treatment |
| Si | 0.15–0.30 | Deoxidation and strengthening |
| Mn | 0.70–0.90 | Strength and hardenability |
| Cr | 0.70–0.90 | Hardenability and wear resistance contribution |
| P | Max. 0.035 | Controlled residual element |
| S | Max. 0.040 | Residual element affecting machinability and toughness |
The chemistry makes 5140 particularly useful for heat-treated components. Its carbon level is high enough to develop substantial hardness, while chromium improves the ability to harden beyond the immediate surface.
For procurement, the actual mill test certificate remains more important than a generic composition table. A professional buyer should verify the heat number, chemical analysis, applicable material standard and delivery condition before accepting the material.
It is also worth separating 5140 from nearby grades. For example, 5140 is not the same chemical grade as 4140. AISI 4140 contains molybdenum and a higher chromium range, while 5140 relies primarily on chromium and manganese for its alloying effect. That difference becomes important when engineers compare hardenability, strength and heat-treatment response.
⚙️ 3. 5140 Steel Mechanical Properties
The mechanical properties of 5140 depend strongly on its metallurgical condition. This point matters because data for annealed, normalized and quenched-and-tempered material can differ substantially.
For example, MatWeb reports annealed 5140 at approximately 570 MPa ultimate tensile strength, 295 MPa yield strength and 167 HB under its stated annealing condition. A normalized 25 mm round example reaches approximately 793 MPa tensile strength and 470 MPa yield strength. These values demonstrate why the delivery condition must accompany a material quotation.
| Condition / Example | Ultimate Tensile Strength | Yield Strength | Hardness |
|---|---|---|---|
| Annealed reference | About 570 MPa | About 295 MPa | About 167 HB |
| Normalized, 25 mm round | About 793 MPa | About 470 MPa | About 229 HB |
| Normalized, 100 mm round | About 765 MPa | About 415 MPa | About 217 HB |
| QT reference, 25 mm round | About 972 MPa | About 841 MPa | About 293 HB |
The QT values above come from a specific 25 mm round condition using oil quenching from 845°C followed by tempering at 540°C. They should therefore be treated as a reference condition rather than a universal specification for every 5140 product.
For engineering calculations, designers should use the mechanical values specified for the actual product standard and section size. Do not use a generic 5140 tensile-strength value without checking the delivery condition and dimensions.
🔥 4. 5140 Steel Heat Treatment
Heat treatment allows manufacturers to adjust the strength and hardness of 5140 for different component requirements. The most common route is quenching followed by tempering, although annealing and normalizing also play important roles during manufacturing.
| Treatment | Reference Temperature / Condition | Purpose |
|---|---|---|
| Annealing | Example reference: 830°C, furnace cooling | Reduce hardness and improve machinability |
| Normalizing | Example: 870°C, air cooling | Refine structure and establish a more uniform condition |
| Hardening | Example QT condition: 845°C | Austenitize before quenching |
| Quenching | Oil used in the reference QT example | Develop martensitic hardness |
| Tempering | Example: 540°C | Balance strength, hardness and toughness |
The 845°C hardening and 540°C tempering values above come from a specific published 25 mm round test condition. Actual production parameters should account for section size, furnace loading, quenching equipment and required final properties.
For larger sections, the center cools more slowly than the surface. Consequently, the final hardness can vary through the cross-section. This is one reason why a supplier should not promise a single HRC value without knowing the product dimensions and heat-treatment condition.
The practical sequence is define the required mechanical properties → select the hardening condition → control the holding period → quench correctly → temper → verify hardness and test results.
📏 5. 5140 Steel Hardness
Hardness is one of the most frequently searched properties when buyers look for 5140. However, there is no single hardness value that applies to every 5140 steel product.
Annealed 5140 can be around 167 HB in a published reference condition, while normalized 25 mm material reaches approximately 229 HB. A specific quenched-and-tempered 25 mm example reaches about 293 HB after oil quenching from 845°C and tempering at 540°C.
| Condition | Reference Hardness | Typical Purpose |
|---|---|---|
| Annealed | About 167 HB | Machining and manufacturing preparation |
| Normalized, 25 mm | About 229 HB | General engineering condition |
| QT, 25 mm reference | About 293 HB / 31 HRC | Higher strength and toughness balance |
| Oil-quenched surface, reference | About 53 HRC before tempering in the cited example | High as-quenched surface hardness |
In the cited 25 mm round QT example, the hardness after quenching was approximately 53 HRC at the surface, 48 HRC at half-radius and 45 HRC at the center. This illustrates the influence of section position on hardening response.
For purchasing, always specify the required hardness together with the delivery condition. A request such as “5140 steel, 30 HRC” is far more useful to a supplier than simply requesting 5140 without a final property requirement.
🔄 6. 5140 Steel Equivalent Grades
Equivalent-grade searches are common in international steel purchasing because customers may design a component under one national standard while sourcing from another country.
5140 is commonly compared with 41Cr4, 1.7035 and several other chromium alloy steel designations. Nevertheless, the comparison should focus on chemistry and specification rather than the name alone.
| Grade / Designation | System / Region | Relationship to 5140 |
|---|---|---|
| AISI/SAE 5140 | USA | Reference grade |
| UNS G51400 | UNS | UNS designation associated with 5140 |
| 41Cr4 | EN / Europe | Commonly compared / close equivalent; verify chemistry |
| 1.7035 | European Werkstoff number | Material number associated with 41Cr4 |
| SCr440 / SCr440H | Japan | Comparable chromium alloy steel family |
| 42C4 / 40Cr4 family | European / historical designations | May appear in cross-reference data |
The important distinction is between a commercially comparable grade and a strict standard equivalent. 5140 and 41Cr4 are frequently grouped together, but their chromium ranges are not identical. AISI 5140 is commonly listed around 0.70–0.90% Cr, whereas EN 41Cr4 is commonly specified around 0.90–1.20% Cr.
For this reason, a replacement should follow the sequence compare chemistry → compare standard → compare mechanical properties → confirm heat treatment → approve the substitute.
🏭 7. 5140 Steel Applications
5140 is widely considered for mechanical components that experience moderate to high loads and benefit from heat treatment. Its combination of medium carbon and chromium makes it suitable for components where strength and toughness matter more than corrosion resistance.
| Application | Reason for Considering 5140 | Key Engineering Check |
|---|---|---|
| Shafts | Good strength after heat treatment | Torsion, fatigue and diameter |
| Axles | Useful strength/toughness balance | Impact and fatigue loading |
| Pins | Can be hardened for wear resistance | Contact stress and surface hardness |
| Gears | Suitable for selected surface-hardening processes | Hardness profile and tooth fatigue |
| Machine parts | Balanced alloy-steel performance | Machining condition and final hardness |
| Automotive components | Useful for strength-oriented parts | Load, fatigue and heat-treatment specification |
For example, shafts and pins can benefit from the strength developed after quenching and tempering, while wear-prone surfaces may receive induction hardening. Meanwhile, less demanding parts can use normalized or annealed stock before machining.
5140 can also be considered when the customer wants a cost-conscious chromium alloy steel without moving to a more heavily alloyed grade. However, the final decision should always reflect the component’s actual load, size and required service life.
🛠️ 8. Machining, Welding and Surface Hardening
Machining performance depends on the supplied condition. Annealed 5140 is generally easier to machine than hardened material, making it a practical choice when the customer needs to remove substantial material before final heat treatment.
When a component requires close dimensional control, buyers can also consider rough machining before heat treatment followed by finish machining or grinding. This approach helps manage distortion when the heat-treatment specification is demanding.
Welding requires more care because the carbon content allows the heat-affected zone to harden during cooling. Preheating, controlled heat input and appropriate post-weld treatment may be necessary depending on thickness, joint design and service requirements.
For critical welded parts, the welding procedure should be developed and qualified for the actual grade and thickness. A supplier should not simply treat 5140 like a low-carbon structural steel.
Surface hardening offers another useful route. Induction hardening can produce a hard outer layer while retaining a tougher interior. In one published 25 mm reference condition, oil-quenched 5140 showed approximately 53 HRC at the surface, 48 HRC at half-radius and 45 HRC at the center before the cited tempering condition.
For an actual production order, the specification should state surface hardness + effective hardened depth + inspection method rather than simply saying “hardened 5140.”
📦 9. Buying 5140 Steel: Specifications and Supplier Checks
When buyers search for a 5140 steel supplier, the lowest quoted price is rarely the only factor that matters. Grade verification, stock availability, dimensional accuracy, processing capability and inspection documents can directly affect the total project cost.
A good purchase inquiry should define the product form and final use. For example, “5140 steel plate” does not tell the supplier the required thickness, width, length, delivery condition or inspection level.
| Purchase Requirement | Information to Confirm |
|---|---|
| Grade | AISI/SAE 5140 and applicable standard |
| Product form | Plate, round bar, flat bar, forged product or other form |
| Dimensions | Thickness/diameter, width and length |
| Condition | Annealed, normalized, QT or specified condition |
| Mechanical requirements | Tensile strength, yield strength, elongation or hardness |
| Inspection | MTC, UT, dimensional inspection or third-party inspection |
| Processing | Saw cutting, CNC machining, grinding or heat treatment |
| Packaging | Anti-rust protection, steel strapping or wooden cases |
Stock availability can shorten the purchasing cycle when the required dimensions already exist in inventory. This is especially useful for prototype orders, maintenance projects and customers who need several different sizes rather than one mill-production dimension.
For an international quotation, the most effective inquiry format is 5140 + standard + product form + dimensions + quantity + delivery condition + inspection + processing requirements. With these details, a supplier can check stock and provide a more accurate quotation.
🏢 10. Why Buy 5140 Steel from Otai?
Otai Special Steel supplies alloy steels and tool steels to international industrial customers. For buyers looking for a reliable 5140 steel stockist, distributor or exporter, the practical value comes from combining inventory with cutting, machining, inspection and export support.
- 5140 steel plate stock: 4–300 mm thickness available from stock, subject to current inventory confirmation.
- 10,000+ tons of total steel stock: Large inventory supports faster material selection and shipment planning.
- 20 saw cutting machines: Saw cutting allows customers to purchase material closer to the required dimensions.
- CNC machining and grinding: Additional processing can reduce downstream preparation work.
- Custom size and tolerance: Cutting and machining can be coordinated according to customer drawings and technical requirements.
- One-stop service: Cutting, machining, heat treatment, inspection and export packaging can be arranged through one supplier.
- Inspection support: Material certificates, ultrasonic testing and third-party inspection support are available according to project requirements.
- International export experience: Otai has exported steel to customers in 54+ countries since 1999.
- Export packaging: Anti-rust packaging, steel strapping and wooden box packaging can be arranged according to shipment requirements.
- B2B technical support: Buyers can confirm grade, dimensions, delivery condition and processing requirements before shipment.
For buyers comparing a 5140 steel manufacturer with other international suppliers, the most useful question is whether the supplier can consistently match the requested specification, size, inspection level and delivery schedule. Those factors can have a greater impact on the final purchasing result than the nominal material price alone.
❓ FAQ
1. What is 5140 steel?
5140 is a medium-carbon chromium alloy steel in the AISI/SAE system. It contains approximately 0.38–0.43% carbon and 0.70–0.90% chromium and is commonly used for shafts, axles, pins, gears and other mechanical components requiring heat-treated strength.
2. Is 5140 the same as 41Cr4?
5140 and 41Cr4 are commonly compared and often treated as close equivalent grades in international steel sourcing. However, they do not have identical chemistry: 5140 is commonly specified with about 0.70–0.90% Cr, while EN 41Cr4 is commonly specified with about 0.90–1.20% Cr. Always verify the applicable standard before substitution.
3. What is the hardness of 5140 steel?
The hardness depends on the condition. A published annealed reference is about 167 HB, while a normalized 25 mm round example is about 229 HB. A specific quenched-and-tempered 25 mm example reaches about 293 HB or 31 HRC.
4. What temperature is used for 5140 heat treatment?
A published QT example uses 845°C oil quenching followed by 540°C tempering for a 25 mm round. Actual production temperatures and holding times should be selected according to section size, furnace practice and the required final properties.
5. Is 5140 suitable for induction hardening?
Yes. Its medium-carbon chromium chemistry makes 5140 suitable for surface-hardening applications. The exact result depends on induction parameters, section geometry and prior condition, so buyers should specify the required surface hardness and effective hardened depth.