+86-13928348837
China Steel CNC Machining Service: Reliable Parts from Leading Suppliers and Factory Experts
Major Steel Categories and Typical Grades
Steel is an alloy primarily composed of iron and carbon. Its properties are precisely controlled by adjusting the carbon content, adding other alloying elements (such as chromium, nickel, molybdenum, vanadium), and through heat treatment processes.
The steel family is vast, mainly categorized into carbon steel, alloy steel, stainless steel, and tool steel. This covers a full spectrum of choices ranging from high ductility to ultra-high strength, and from general weather resistance to extreme corrosion resistance. Modern CNC technology can efficiently machine various steels, achieving a perfect combination of complex geometries and high dimensional accuracy.
1. Carbon Steel
Low Carbon Steel e.g. 1018, 1045
Characteristics: Carbon content typically below 0.25%. Lower strength but excellent toughness, ductility, and weldability. Easy to cold form and machine.
Typical Applications: Mechanical structural parts, shafts, bolts, gears, frames, welded structures.
Medium Carbon Steel e.g. 1045, 4140
Characteristics: Carbon content ~0.25%–0.60%. After heat treatment, achieves a good balance of strength, hardness, and wear resistance. Most commonly used quenched and tempered structural steel.
Typical Applications: Crankshafts, connecting rods, high-strength bolts, mold bases, gears, hydraulic cylinder tubes.
High Carbon Steel e.g. 1095, C45
Characteristics: Carbon content above 0.60%. Achieves very high hardness and wear resistance, but brittleness increases and weldability is poor.
Typical Applications: Cutlery, springs, saw blades, bearing parts, high-strength wire.
📊 AISI 1045 (Medium Carbon Steel) Typical Properties — Normalized Condition
| Property | Value | Notes |
|---|---|---|
| Tensile Strength (MPa) | 570 – 700 | |
| Yield Strength (MPa) | ≥ 310 | |
| Elongation at Break (%) | ≥ 16 | Good overall mechanical properties |
| Hardness (Brinell) | ~ 170 | |
| Density (g/cm³) | 7.85 | |
| ⚠️ Note: Properties can be significantly improved after heat treatment. | ||
2. Alloy Steel
Alloy steel contains elements such as molybdenum, chromium, and nickel added to carbon steel to enhance strength, toughness, hardenability, or heat resistance.
AISI/SAE 4140 Cr-Mo Steel
Characteristics: A versatile medium-carbon alloy steel. Molybdenum and chromium additions deliver excellent hardenability, strength, and toughness, allowing uniform properties across larger cross-sections.
Typical Applications: High-strength shafts, gears, connecting rods, oil drilling equipment, molds.
AISI/SAE 4340 Ni-Cr-Mo Steel
Characteristics: The representative of ultra-high-strength alloy steel. Nickel additions allow it to maintain excellent toughness and fatigue resistance even at very high strength levels, for parts under extreme loads.
Typical Applications: Aircraft landing gear, heavy vehicle drive shafts, high-strength fasteners, critical military equipment parts.
3. Stainless Steel
Stainless steel uses chromium (≥10.5%) as the main alloying element to form a passive film, thereby providing superior corrosion resistance.
Austenitic Stainless Steel 304 / 316
Characteristics: Non-magnetic, excellent corrosion resistance, and superb formability and weldability. Due to molybdenum addition, 316 offers better pitting and chemical resistance (especially to chlorides) than 304.
Typical Applications: Food and medical equipment, chemical containers, marine fittings, architectural decoration, consumer goods.
Martensitic Stainless Steel 410 / 440C
Characteristics: Can be heat-treated to achieve high hardness and strength. Offers certain corrosion and wear resistance, but toughness and weldability are relatively poor.
Typical Applications: Cutlery, surgical instruments, bearings, valve parts, pump shafts.
Precipitation Hardening SS 17-4 PH
Characteristics: Through precipitation hardening, it achieves mechanical properties close to high-strength alloy steel while maintaining good corrosion resistance. Low tendency for work hardening.
Typical Applications: Aerospace structural parts, high-speed centrifuge components, nuclear industry parts, high-end molds.
📊 AISI 304 Stainless Steel Typical Properties — Solution Annealed Condition
| Property | Value | Notes |
|---|---|---|
| Tensile Strength (MPa) | ≥ 515 | |
| Yield Strength (0.2% Offset, MPa) | ≥ 205 | |
| Elongation at Break (%) | ≥ 40 | Excellent plasticity and toughness |
| Hardness (Brinell) | ≤ 201 | |
| Density (g/cm³) | 8.00 |
4. Tool Steel
Tool steel is specifically developed for manufacturing tools (such as molds and cutlery), pursuing extreme hardness, wear resistance, red hardness, and dimensional stability.
🔩 D2 — High Carbon, High Chromium Cold Work Steel
High wear resistance with moderate toughness, used for high-life cold stamping dies and fine blanking dies.
🔥 H13 — Hot Work Die Steel
Maintains high strength and wear resistance at high temperatures with good resistance to thermal fatigue. Used for die-casting molds and hot forging dies.
⚒️ S7 — Impact Resisting Tool Steel
Renowned for its excellent toughness. Used for chisels, punches, and shear blades subjected to high impact loads.
Frequently Asked Questions
What is the difference between carbon steel and alloy steel?
Carbon steel is primarily composed of iron and carbon, while alloy steel incorporates additional elements such as chromium, nickel, molybdenum, or vanadium. These additions enhance specific properties like hardenability, toughness, heat resistance, or corrosion resistance beyond what carbon alone can achieve.
Why is AISI 4140 one of the most widely used alloy steels in CNC machining?
AISI 4140 offers an excellent combination of strength, toughness, hardenability, and machinability. It responds well to heat treatment and maintains consistent mechanical properties across larger cross-sections, making it highly versatile for shafts, gears, molds, and structural components.
What is the key difference between 304 and 316 stainless steel?
The primary difference is that 316 stainless steel contains molybdenum (approximately 2–3%), which significantly improves its resistance to pitting corrosion and chemical attack — especially in chloride-rich environments such as marine or chemical processing applications. 304 is more cost-effective for general-purpose use.
When should I choose tool steel over standard alloy steel?
Tool steel should be selected when the application demands extreme hardness, superior wear resistance, dimensional stability under stress, or the ability to retain hardness at elevated temperatures (red hardness). Typical use cases include cutting tools, stamping dies, injection molds, and high-impact tooling components.
Can stainless steel be used for high-strength structural applications?
Yes — particularly precipitation hardening grades such as 17-4 PH, which can achieve mechanical properties approaching high-strength alloy steel through specialized heat treatment, while still maintaining good corrosion resistance. Martensitic grades like 440C also offer high hardness suitable for demanding structural and wear applications.
How does heat treatment affect the properties of carbon and alloy steels?
Heat treatment processes such as quenching, tempering, annealing, and normalizing can dramatically alter the mechanical properties of steel. For example, AISI 1045 in its normalized condition has a tensile strength of 570–700 MPa, but after quenching and tempering, its strength and hardness can increase substantially — making heat treatment a critical step in optimizing steel performance for specific applications.
Finishes and Post-Processing Options
The zinc alloy substrate is highly suitable for various surface treatments to enhance decoration, protection, or functionality:
Electroplating: Such as chrome, nickel, gold, or silver plating, providing a highly decorative appearance, excellent wear and corrosion resistance. This is the most common choice.
-
Passivation or Chromate Conversion Coating:
-
Powder Coating:
-
Painting:
-
Physical Vapor Deposition (PVD):
Design and Machining Considerations
-
Process Selection:
-
Design Considerations:
-
Material Selection:
Zamak 3 and 5 are suitable for the vast majority of general-purpose parts requiring good appearance and strength; ZA-8 is better for wear and bearing applications; for making rapid tooling, choose specialized alloys like Kirksite.
Ready to Start Your CNC Project?
Send us your drawings to receive professional manufacturing solutions.