4140 Steel Square Bar: A Versatile Choice for Strength and Machinability
When it comes to combining strength, toughness, and excellent machinability in one compact shape, the 4140 steel square bar stands out as a top-tier choice. Whether you’re designing components for automotive, oil & gas, or heavy machinery, this bar stock offers exactly what engineers need: reliable performance under pressure.
Let’s dive into the technical details, practical uses, and why this steel grade is such a staple in modern manufacturing.
🔎 What Is a 4140 Steel Square Bar?
A 4140 steel square bar is a hot-rolled or forged bar with equal width and height, commonly used in precision parts, gears, dies, and shafts. Made from chromium-molybdenum alloy steel, it is known for its high tensile strength, impact resistance, and uniform hardness across sections.
This shape is ideal when strength and symmetry are key to the project—plus, it’s easy to handle in CNC machines, lathes, and mills.
📐 Chemical Composition of 4140 Steel
Here’s a breakdown of the typical chemical content:
| Element | Content (%) |
|---|---|
| Carbon (C) | 0.38 – 0.43 |
| Manganese (Mn) | 0.75 – 1.00 |
| Chromium (Cr) | 0.80 – 1.10 |
| Molybdenum (Mo) | 0.15 – 0.25 |
| Silicon (Si) | 0.15 – 0.35 |
| Phosphorus (P) | ≤ 0.035 |
| Sulfur (S) | ≤ 0.040 |
This composition makes 4140 suitable for high-strength square bar stock applications, such as heat-treated tool holders and torsion-resistant parts.
⚙️ Mechanical Properties: How Strong Is It?
Whether it’s hot rolled or heat treated, 4140 square bar shows excellent strength and resilience:
| Condition | Tensile Strength (MPa) | Yield Strength (MPa) | Elongation (%) | Hardness (HRC) |
|---|---|---|---|---|
| Annealed | 655 – 850 | 415 – 655 | ~25 | 15 – 22 |
| Quenched & Tempered | 850 – 1100 | 700 – 950 | ~18 | 28 – 32 |
| Hardened & Tempered | Up to 1300 | Up to 1100 | ~14 | 35 – 45 |
These figures make it perfect for high-load square bar uses in everything from tool shanks to press frames.
🛠️ Applications of 4140 Steel Square Bars
Thanks to its machinability and toughness, the square form of 4140 is widely used in:
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Mold bases and die blocks
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Hydraulic cylinder rods
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Drive shafts and axles
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Crankshafts and spindles
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Bolts and fasteners for high-stress assemblies
Its clean geometry helps with precision fitting and strength distribution, especially in parts requiring tight tolerances.
🔩 Why Choose 4140 Square Bar Over Round or Flat?
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✅ Symmetry: Ideal for applications requiring equal stress distribution
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✅ Ease of Fixturing: Clamps and mounts better in jigs or machines
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✅ Minimal Material Waste: Cuts cleanly with fewer offcuts
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✅ Superior Dimensional Stability: Less warping during heat treatment
This is especially important in CNC-machined 4140 bar stock where tolerances below ±0.01 mm are crucial.
🧪 Heat Treatment Compatibility
One of the biggest advantages of 4140 square bars is how well they respond to various heat treatments:
| Process | Effect |
|---|---|
| Normalizing | Improves toughness and grain structure |
| Quenching & Tempering | Maximizes strength and wear resistance |
| Stress Relieving | Reduces internal stresses after machining |
| Flame/Induction Hardening | Targets hardness on specific surfaces |
This makes the square bar ideal for wear-prone tooling components and impact-resistant fixtures.
🧲 Machinability & Weldability
4140 steel is easily machinable in the annealed condition and moderately weldable with preheat and post-weld heat treatment.
Recommended cutting tools: Carbide inserts or coated HSS
Typical cutting speed: 25–35 m/min for turning and milling (with coolant)
Preheat for welding: 150–260°C
Post-weld treatment: Tempering to avoid cracking
This makes it suitable for custom-machined 4140 square bar products in both small-batch and large-scale production.
📏 Standard Sizes and Tolerances
| Common Sizes (mm) | Typical Lengths (mm) | Tolerance (as rolled) |
|---|---|---|
| 20 × 20 to 200 × 200 | 3000 / 6000 | ±1.0 mm |
Need something custom? Most suppliers offer cut-to-length square bar in 4140.
🏭 Otai Special Steel: Your Trusted 4140 Steel Supplier
At Otai Special Steel, we offer premium 4140 alloy in round bars, flat bars, and plates with full heat treatment services—including normalizing, annealing, quenching, and stress relieving.
We maintain a large inventory (6mm–300mm thickness, over 10,000 tons), ready for cutting, packaging, and export worldwide. Our clients include major corporations in automotive, oil & gas, and tool-making industries.
We also offer:
- ✅ Ultrasonic testing (UT)
- ✅ Full chemical composition reports
- ✅ Third-party inspection (SGS, BV)
- ✅ Custom mechanical property adjustment based on your specs
Need a quote for your next project? 📩 Contact us now and get expert advice tailored to your application!
📧 Contact us: jack@otaisteel.com
📱 WhatsApp: +8676923190193
❓ FAQ: Frequently Asked Questions
Q1: Is 4140 square bar available in both hot rolled and cold drawn forms?
A: Yes. Hot rolled is more common and economical; cold drawn offers better surface finish and tighter tolerances.
Q2: Can I use 4140 square bar for heat-treated tools?
A: Absolutely. It responds well to quenching, tempering, and surface hardening.
Q3: What’s the minimum order quantity at Otai?
A: We serve both small custom orders and bulk shipments—starting from just 1 piece.
Q4: Is 4140 steel square bar corrosion-resistant?
A: It has moderate corrosion resistance. Surface treatments like black oxide or plating are recommended for humid environments.
Q5: Do you offer export packaging?
A: Yes, we offer fumigation-free wooden cases, steel pallets, and rust-proof paper for sea shipment.
