A Guide to Special Steel CNC Machining: Types, Properties, and Applications
Last updated : 2026/8/19
Key Takeaways
Special steels use alloying elements to provide superior strength, durability, corrosion resistance, and heat resistance compared to ordinary steel.
Different grades are engineered for specific applications, including structural components, tools, bearings, springs, and high-temperature environments.
Heat treatment and proper machining techniques are essential to achieve the desired performance and precision of special steel parts.
Overview
Special steel is an alloy created by adding elements such as nickel, chromium, or molybdenum to iron. These additions enhance strength, corrosion resistance, toughness, heat resistance, and workability, making it suitable for demanding applications where ordinary steel is insufficient.
Properties of Special Steel
By adjusting alloying elements, special steel can achieve properties that ordinary steel cannot, enhancing product performance and safety. Key benefits include:
Increased Hardness: Used as tool steel for cutting and mold materials
Enhanced Durability: Improves resistance to breakage from metal fatigue in moving parts.
Improved Toughness: Strengthens ductility and impact resistance, ideal for springs.
Improved Corrosion Resistance: Protects against water and seawater, useful for marine components.
Increased Heat Resistance: Maintains strength at elevated temperatures, ideal for engines and similar components.
Enhanced Wear Resistance: Reduces friction damage in sliding or rotating parts.
Improved Workability: Allows machining of high-precision parts.
Alloying Elements and Their Effects
Materials | Description |
|---|---|
Nickel (Ni) | Improves toughness, strength, and heat resistance. |
Chromium (Cr) | Enhances corrosion and wear resistance. |
Molybdenum (Mo) | Increases toughness and strength at high temperatures. |
Copper (Cu) | Improves corrosion resistance. |
Cobalt (Co) | Improves strength at high temperatures. |
Titanium (Ti) | Enhances toughness, corrosion resistance, and rust resistance. |
Manganese (Mn) | Increases strength. |
Tungsten (W) | Improves heat and wear resistance. |
Vanadium (V) | Increases strength and wear resistance. |
Types of Special Steel
Special steel is primarily classified into structural steel, tool steel, and other special-purpose steels. The other special-purpose steels include stainless steel, heat-resistant steel, superalloys, spring steel, bearing steel, and free-cutting steel.
Types | Description |
|---|---|
Available in many varieties and used across numerous industries. Adjusted for structural applications, it is a high-strength steel. | |
Tool Steel (SK, SKD) | Further classified into carbon tool steel, alloy tool steel, and high-speed tool steel. U sed for molds and cutting tools, it is strong, hard, and highly wear-resistant. |
Contains at least 11% chromium (Cr) with rust-resistant properties. Its surface is covered by a passive film, giving it excellent corrosion resistance. | |
Heat-Resistant Steel (SUH) | Maintains strength and oxidation resistance at high temperatures. Some stainless steels are also classified as heat-resistant steel due to their high-temperature performance. |
Superalloys | Special steel that maintains oxidation resistance, corrosion resistance, and strength in high-temperature environments. |
Spring Steel (SUJ) | Adjusted for spring components with enhanced impact and fatigue resistance. |
Bearing Steel (SUJ) | High-carbon chromium steel used in sliding parts and ball bearings; multi-step heat treatment required, making production time-consuming. |
Free-Cutting Steel (SUM) | Contains sulfur for easier machining than ordinary steel, suitable for precision parts. |
Heat Treatment of Special Steel
Heat treatment is used to enhance desired properties, most commonly to increase hardness. Processes include the following.
Quenching
Heating steel to 850–950°C and rapidly cooling in water or oil to harden it, increasing strength. This process requires tempering afterward due to brittleness. Methods include through-hardening, vacuum quenching, carburizing quenching, and induction hardening.
Tempering
After quenching, the steel is reheated to a suitable temperature for each type of special steel and then cooled. This stabilizes the brittle microstructure and improves toughness.
Annealing
Steel is heated to 700 to 900°C (1292 to 1652°F) and cooled slowly to remove internal stresses.
Normalizing
Steel is heated to around 850 to 950°C (1562 to 1742°F) and air-cooled to refine and homogenize the microstructure.
Nitriding
A surface hardening process that introduces nitrogen to the surface to create a hard layer, improving wear resistance, heat resistance, and corrosion resistance. Unlike quenching, deformation is minimal, making it suitable for precision parts.
Machining of Special Steel
Special steels are often more difficult to machine than ordinary steel, except for free-cutting steel. Due to the variety of materials, cutting tools must match the characteristics of each type. Machining conditions such as feed rate and spindle speed must be carefully controlled to maintain product quality.
Special Steel CNC Machining at Yumoto Electric
Yumoto Electric delivers high-quality components fast, worldwide. We provide precision machining for a wide range of metals using milling, turning, and specialized metal processing. We have experience with over 200 materials including aluminum alloys, stainless steel, molybdenum, and titanium.
If you’re unsure about material selection or machining methods, we offer complimentary consultations to help optimize your design and production. For any questions, please feel free to contact us.
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