+86-13928348837
China Steel CNC Machining Service - Reliable Factory Suppliers for Precision Parts and Industrial Solutions
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.
Carbon Steel
● Low Carbon Steel (e.g., AISI/SAE 1018, 1045)
Characteristics: Carbon content is typically below 0.25%. It has lower strength but excellent toughness, ductility, and weldability. It is easy to perform cold forming and machining.
Typical Applications: Mechanical structural parts, shafts, bolts, gears, frames, welded structures.
● Medium Carbon Steel (e.g., AISI/SAE 1045, 4140)
Characteristics: Carbon content is approximately 0.25%–0.60%. After heat treatment (quenching and tempering), it achieves a good balance of strength, hardness, and wear resistance. It is the 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., AISI/SAE 1095, C45)
Characteristics: Carbon content is higher than 0.60%. It can achieve very high hardness and wear resistance, but brittleness increases and weldability is poor. It is typically used for making tools and parts requiring extremely high surface hardness.
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. | ||
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 (Chromium-Molybdenum Steel)
Characteristics: A versatile medium-carbon alloy steel. The addition of molybdenum and chromium gives it excellent hardenability, strength, and toughness, allowing uniform properties to be obtained across larger cross-sections.
Typical Applications: High-strength shafts, gears, connecting rods, oil drilling equipment, molds.
● AISI/SAE 4340 (Nickel-Chromium-Molybdenum Steel)
Characteristics: The representative of ultra-high-strength alloy steel. The addition of nickel allows it to maintain excellent toughness and fatigue resistance even at very high strength levels, making it suitable for parts subjected to extreme loads.
Typical Applications: Aircraft landing gear, heavy vehicle drive shafts, high-strength fasteners, critical military equipment parts.
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 (e.g., 304, 316)
Characteristics: Non-magnetic, excellent corrosion resistance, and superb formability and weldability. Due to the addition of molybdenum, 316 has better pitting corrosion resistance 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 (e.g., 410, 440C)
Characteristics: Can be heat-treated to achieve high hardness and strength. It has certain corrosion resistance and wear resistance, but its toughness and weldability are relatively poor.
Typical Applications: Cutlery, surgical instruments, bearings, valve parts, pump shafts.
● Precipitation Hardening Stainless Steel (e.g., 17-4 PH)
Characteristics: Through special heat treatment (precipitation hardening), it achieves mechanical properties close to high-strength alloy steel while maintaining good corrosion resistance. It has a 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 |
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
Q
What is the difference between carbon steel and alloy steel?
Carbon steel contains iron and carbon as its primary elements, with minimal other alloying additions. Alloy steel, by contrast, intentionally incorporates elements such as chromium, molybdenum, nickel, or vanadium to enhance specific properties like hardenability, toughness, corrosion resistance, or high-temperature performance beyond what carbon alone can achieve.
Q
When should I choose 316 stainless steel over 304?
316 stainless steel should be selected when the application involves exposure to chlorides, saltwater, or harsh chemicals — such as marine environments, chemical processing equipment, or medical implants. The molybdenum content in 316 significantly improves pitting and crevice corrosion resistance compared to 304, though 304 remains the more cost-effective choice for general-purpose applications.
Q
Can all steel grades be CNC machined?
Most steel grades can be CNC machined, but machinability varies significantly. Low carbon steels like 1018 are very easy to machine, while high-carbon steels and hardened tool steels require more specialized tooling, slower cutting speeds, and careful parameter selection. Austenitic stainless steels tend to work-harden during machining, requiring sharp tooling and appropriate cutting strategies.
Q
What is precipitation hardening in stainless steel (e.g., 17-4 PH)?
Precipitation hardening is a heat treatment process in which fine particles (precipitates) are formed within the steel's microstructure, significantly increasing its strength and hardness. In 17-4 PH stainless steel, this process achieves mechanical properties approaching those of high-strength alloy steels, while still maintaining good corrosion resistance — making it ideal for aerospace, defense, and high-performance industrial applications.
Q
What makes tool steels like D2, H13, and S7 different from structural steels?
Tool steels are specifically engineered to withstand the extreme demands of cutting, forming, and impact operations. They are formulated for exceptional hardness, wear resistance, dimensional stability, and in some cases, red hardness (retention of hardness at elevated temperatures). Structural steels, on the other hand, prioritize a balance of strength, ductility, and weldability for load-bearing applications rather than surface durability under abrasive or impact conditions.
Q
How does heat treatment affect the mechanical properties of steel?
Heat treatment can dramatically alter a steel's mechanical properties. Processes such as quenching and tempering increase hardness and tensile strength while controlling brittleness. Annealing softens steel to improve machinability or ductility. Normalizing refines the grain structure for more uniform properties. For example, AISI 1045 in its normalized condition has a tensile strength of 570–700 MPa, but after quenching and tempering, this can be significantly increased — making heat treatment a critical step in tailoring 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.